2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
6 <refentry id=
"systemd.exec" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
8 <title>systemd.exec
</title>
9 <productname>systemd
</productname>
13 <refentrytitle>systemd.exec
</refentrytitle>
14 <manvolnum>5</manvolnum>
18 <refname>systemd.exec
</refname>
19 <refpurpose>Execution environment configuration
</refpurpose>
23 <para><filename><replaceable>service
</replaceable>.service
</filename>,
24 <filename><replaceable>socket
</replaceable>.socket
</filename>,
25 <filename><replaceable>mount
</replaceable>.mount
</filename>,
26 <filename><replaceable>swap
</replaceable>.swap
</filename></para>
30 <title>Description
</title>
32 <para>Unit configuration files for services, sockets, mount points, and swap devices share a subset of
33 configuration options which define the execution environment of spawned processes.
</para>
35 <para>This man page lists the configuration options shared by these four unit types. See
36 <citerefentry><refentrytitle>systemd.unit
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for the common
37 options of all unit configuration files, and
38 <citerefentry><refentrytitle>systemd.service
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
39 <citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
40 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and
41 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
42 information on the specific unit configuration files. The execution specific configuration options are configured
43 in the [Service], [Socket], [Mount], or [Swap] sections, depending on the unit type.
</para>
45 <para>In addition, options which control resources through Linux Control Groups (cgroups) are listed in
46 <citerefentry><refentrytitle>systemd.resource-control
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
47 Those options complement options listed here.
</para>
51 <title>Implicit Dependencies
</title>
53 <para>A few execution parameters result in additional, automatic dependencies to be added:
</para>
56 <listitem><para>Units with
<varname>WorkingDirectory=
</varname>,
<varname>RootDirectory=
</varname>,
57 <varname>RootImage=
</varname>,
<varname>RuntimeDirectory=
</varname>,
<varname>StateDirectory=
</varname>,
58 <varname>CacheDirectory=
</varname>,
<varname>LogsDirectory=
</varname> or
59 <varname>ConfigurationDirectory=
</varname> set automatically gain dependencies of type
60 <varname>Requires=
</varname> and
<varname>After=
</varname> on all mount units required to access the specified
61 paths. This is equivalent to having them listed explicitly in
62 <varname>RequiresMountsFor=
</varname>.
</para></listitem>
64 <listitem><para>Similar, units with
<varname>PrivateTmp=
</varname> enabled automatically get mount unit
65 dependencies for all mounts required to access
<filename>/tmp
</filename> and
<filename>/var/tmp
</filename>. They
66 will also gain an automatic
<varname>After=
</varname> dependency on
67 <citerefentry><refentrytitle>systemd-tmpfiles-setup.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para></listitem>
69 <listitem><para>Units whose standard output or error output is connected to
<option>journal
</option>,
70 <option>syslog
</option> or
<option>kmsg
</option> (or their combinations with console output, see below)
71 automatically acquire dependencies of type
<varname>After=
</varname> on
72 <filename>systemd-journald.socket
</filename>.
</para></listitem>
76 <!-- We don't have any default dependency here. -->
81 <para>The following settings may be used to change a service's view of the filesystem. Please note that the paths
82 must be absolute and must not contain a
<literal>..
</literal> path component.
</para>
84 <variablelist class='unit-directives'
>
87 <term><varname>WorkingDirectory=
</varname></term>
89 <listitem><para>Takes a directory path relative to the service's root directory specified by
90 <varname>RootDirectory=
</varname>, or the special value
<literal>~
</literal>. Sets the working directory for
91 executed processes. If set to
<literal>~
</literal>, the home directory of the user specified in
92 <varname>User=
</varname> is used. If not set, defaults to the root directory when systemd is running as a
93 system instance and the respective user's home directory if run as user. If the setting is prefixed with the
94 <literal>-
</literal> character, a missing working directory is not considered fatal. If
95 <varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname> is not set, then
96 <varname>WorkingDirectory=
</varname> is relative to the root of the system running the service manager. Note
97 that setting this parameter might result in additional dependencies to be added to the unit (see
98 above).
</para></listitem>
102 <term><varname>RootDirectory=
</varname></term>
104 <listitem><para>Takes a directory path relative to the host's root directory (i.e. the root of the system
105 running the service manager). Sets the root directory for executed processes, with the
<citerefentry
106 project='man-pages'
><refentrytitle>chroot
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
107 call. If this is used, it must be ensured that the process binary and all its auxiliary files are available in
108 the
<function>chroot()
</function> jail. Note that setting this parameter might result in additional
109 dependencies to be added to the unit (see above).
</para>
111 <para>The
<varname>MountAPIVFS=
</varname> and
<varname>PrivateUsers=
</varname> settings are particularly useful
112 in conjunction with
<varname>RootDirectory=
</varname>. For details, see below.
</para>
114 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
118 <term><varname>RootImage=
</varname></term>
120 <listitem><para>Takes a path to a block device node or regular file as argument. This call is similar to
121 <varname>RootDirectory=
</varname> however mounts a file system hierarchy from a block device node or loopback
122 file instead of a directory. The device node or file system image file needs to contain a file system without a
123 partition table, or a file system within an MBR/MS-DOS or GPT partition table with only a single
124 Linux-compatible partition, or a set of file systems within a GPT partition table that follows the
<ulink
125 url=
"https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Discoverable Partitions
126 Specification
</ulink>.
</para>
128 <para>When
<varname>DevicePolicy=
</varname> is set to
<literal>closed
</literal> or
129 <literal>strict
</literal>, or set to
<literal>auto
</literal> and
<varname>DeviceAllow=
</varname> is
130 set, then this setting adds
<filename>/dev/loop-control
</filename> with
<constant>rw
</constant> mode,
131 <literal>block-loop
</literal> and
<literal>block-blkext
</literal> with
<constant>rwm
</constant> mode
132 to
<varname>DeviceAllow=
</varname>. See
133 <citerefentry><refentrytitle>systemd.resource-control
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
134 for the details about
<varname>DevicePolicy=
</varname> or
<varname>DeviceAllow=
</varname>. Also, see
135 <varname>PrivateDevices=
</varname> below, as it may change the setting of
136 <varname>DevicePolicy=
</varname>.
</para>
138 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
142 <term><varname>MountAPIVFS=
</varname></term>
144 <listitem><para>Takes a boolean argument. If on, a private mount namespace for the unit's processes is created
145 and the API file systems
<filename>/proc
</filename>,
<filename>/sys
</filename>, and
<filename>/dev
</filename>
146 are mounted inside of it, unless they are already mounted. Note that this option has no effect unless used in
147 conjunction with
<varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname> as these three mounts are
148 generally mounted in the host anyway, and unless the root directory is changed, the private mount namespace
149 will be a
1:
1 copy of the host's, and include these three mounts. Note that the
<filename>/dev
</filename> file
150 system of the host is bind mounted if this option is used without
<varname>PrivateDevices=
</varname>. To run
151 the service with a private, minimal version of
<filename>/dev/
</filename>, combine this option with
152 <varname>PrivateDevices=
</varname>.
</para>
154 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
158 <term><varname>BindPaths=
</varname></term>
159 <term><varname>BindReadOnlyPaths=
</varname></term>
161 <listitem><para>Configures unit-specific bind mounts. A bind mount makes a particular file or directory
162 available at an additional place in the unit's view of the file system. Any bind mounts created with this
163 option are specific to the unit, and are not visible in the host's mount table. This option expects a
164 whitespace separated list of bind mount definitions. Each definition consists of a colon-separated triple of
165 source path, destination path and option string, where the latter two are optional. If only a source path is
166 specified the source and destination is taken to be the same. The option string may be either
167 <literal>rbind
</literal> or
<literal>norbind
</literal> for configuring a recursive or non-recursive bind
168 mount. If the destination path is omitted, the option string must be omitted too.
169 Each bind mount definition may be prefixed with
<literal>-
</literal>, in which case it will be ignored
170 when its source path does not exist.
</para>
172 <para><varname>BindPaths=
</varname> creates regular writable bind mounts (unless the source file system mount
173 is already marked read-only), while
<varname>BindReadOnlyPaths=
</varname> creates read-only bind mounts. These
174 settings may be used more than once, each usage appends to the unit's list of bind mounts. If the empty string
175 is assigned to either of these two options the entire list of bind mounts defined prior to this is reset. Note
176 that in this case both read-only and regular bind mounts are reset, regardless which of the two settings is
179 <para>This option is particularly useful when
<varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname>
180 is used. In this case the source path refers to a path on the host file system, while the destination path
181 refers to a path below the root directory of the unit.
</para>
183 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
190 <title>Credentials
</title>
192 <xi:include href=
"system-only.xml" xpointer=
"plural"/>
194 <variablelist class='unit-directives'
>
197 <term><varname>User=
</varname></term>
198 <term><varname>Group=
</varname></term>
200 <listitem><para>Set the UNIX user or group that the processes are executed as, respectively. Takes a single
201 user or group name, or a numeric ID as argument. For system services (services run by the system service
202 manager, i.e. managed by PID
1) and for user services of the root user (services managed by root's instance of
203 <command>systemd --user
</command>), the default is
<literal>root
</literal>, but
<varname>User=
</varname> may be
204 used to specify a different user. For user services of any other user, switching user identity is not
205 permitted, hence the only valid setting is the same user the user's service manager is running as. If no group
206 is set, the default group of the user is used. This setting does not affect commands whose command line is
207 prefixed with
<literal>+
</literal>.
</para>
209 <para>Note that restrictions on the user/group name syntax are enforced: the specified name must consist only
210 of the characters a-z, A-Z,
0-
9,
<literal>_
</literal> and
<literal>-
</literal>, except for the first character
211 which must be one of a-z, A-Z or
<literal>_
</literal> (i.e. numbers and
<literal>-
</literal> are not permitted
212 as first character). The user/group name must have at least one character, and at most
31. These restrictions
213 are enforced in order to avoid ambiguities and to ensure user/group names and unit files remain portable among
214 Linux systems.
</para>
216 <para>When used in conjunction with
<varname>DynamicUser=
</varname> the user/group name specified is
217 dynamically allocated at the time the service is started, and released at the time the service is stopped —
218 unless it is already allocated statically (see below). If
<varname>DynamicUser=
</varname> is not used the
219 specified user and group must have been created statically in the user database no later than the moment the
220 service is started, for example using the
221 <citerefentry><refentrytitle>sysusers.d
</refentrytitle><manvolnum>5</manvolnum></citerefentry> facility, which
222 is applied at boot or package install time.
</para></listitem>
226 <term><varname>DynamicUser=
</varname></term>
228 <listitem><para>Takes a boolean parameter. If set, a UNIX user and group pair is allocated
229 dynamically when the unit is started, and released as soon as it is stopped. The user and group will
230 not be added to
<filename>/etc/passwd
</filename> or
<filename>/etc/group
</filename>, but are managed
231 transiently during runtime. The
232 <citerefentry><refentrytitle>nss-systemd
</refentrytitle><manvolnum>8</manvolnum></citerefentry> glibc
233 NSS module provides integration of these dynamic users/groups into the system's user and group
234 databases. The user and group name to use may be configured via
<varname>User=
</varname> and
235 <varname>Group=
</varname> (see above). If these options are not used and dynamic user/group
236 allocation is enabled for a unit, the name of the dynamic user/group is implicitly derived from the
237 unit name. If the unit name without the type suffix qualifies as valid user name it is used directly,
238 otherwise a name incorporating a hash of it is used. If a statically allocated user or group of the
239 configured name already exists, it is used and no dynamic user/group is allocated. Note that if
240 <varname>User=
</varname> is specified and the static group with the name exists, then it is required
241 that the static user with the name already exists. Similarly, if
<varname>Group=
</varname> is
242 specified and the static user with the name exists, then it is required that the static group with
243 the name already exists. Dynamic users/groups are allocated from the UID/GID range
61184…
65519. It is
244 recommended to avoid this range for regular system or login users. At any point in time each UID/GID
245 from this range is only assigned to zero or one dynamically allocated users/groups in use. However,
246 UID/GIDs are recycled after a unit is terminated. Care should be taken that any processes running as
247 part of a unit for which dynamic users/groups are enabled do not leave files or directories owned by
248 these users/groups around, as a different unit might get the same UID/GID assigned later on, and thus
249 gain access to these files or directories. If
<varname>DynamicUser=
</varname> is enabled,
250 <varname>RemoveIPC=
</varname>,
<varname>PrivateTmp=
</varname> are implied. This ensures that the
251 lifetime of IPC objects and temporary files created by the executed processes is bound to the runtime
252 of the service, and hence the lifetime of the dynamic user/group. Since
<filename>/tmp
</filename> and
253 <filename>/var/tmp
</filename> are usually the only world-writable directories on a system this
254 ensures that a unit making use of dynamic user/group allocation cannot leave files around after unit
255 termination. Furthermore
<varname>NoNewPrivileges=
</varname> and
<varname>RestrictSUIDSGID=
</varname>
256 are implicitly enabled to ensure that processes invoked cannot take benefit or create SUID/SGID files
257 or directories. Moreover
<varname>ProtectSystem=strict
</varname> and
258 <varname>ProtectHome=read-only
</varname> are implied, thus prohibiting the service to write to
259 arbitrary file system locations. In order to allow the service to write to certain directories, they
260 have to be whitelisted using
<varname>ReadWritePaths=
</varname>, but care must be taken so that
261 UID/GID recycling doesn't create security issues involving files created by the service. Use
262 <varname>RuntimeDirectory=
</varname> (see below) in order to assign a writable runtime directory to a
263 service, owned by the dynamic user/group and removed automatically when the unit is terminated. Use
264 <varname>StateDirectory=
</varname>,
<varname>CacheDirectory=
</varname> and
265 <varname>LogsDirectory=
</varname> in order to assign a set of writable directories for specific
266 purposes to the service in a way that they are protected from vulnerabilities due to UID reuse (see
267 below). If this option is enabled, care should be taken that the unit's processes do not get access
268 to directories outside of these explicitly configured and managed ones. Specifically, do not use
269 <varname>BindPaths=
</varname> and be careful with
<constant>AF_UNIX
</constant> file descriptor
270 passing for directory file descriptors, as this would permit processes to create files or directories
271 owned by the dynamic user/group that are not subject to the lifecycle and access guarantees of the
272 service. Defaults to off.
</para></listitem>
276 <term><varname>SupplementaryGroups=
</varname></term>
278 <listitem><para>Sets the supplementary Unix groups the processes are executed as. This takes a space-separated
279 list of group names or IDs. This option may be specified more than once, in which case all listed groups are
280 set as supplementary groups. When the empty string is assigned, the list of supplementary groups is reset, and
281 all assignments prior to this one will have no effect. In any way, this option does not override, but extends
282 the list of supplementary groups configured in the system group database for the user. This does not affect
283 commands prefixed with
<literal>+
</literal>.
</para></listitem>
287 <term><varname>PAMName=
</varname></term>
289 <listitem><para>Sets the PAM service name to set up a session as. If set, the executed process will be
290 registered as a PAM session under the specified service name. This is only useful in conjunction with the
291 <varname>User=
</varname> setting, and is otherwise ignored. If not set, no PAM session will be opened for the
292 executed processes. See
<citerefentry
293 project='man-pages'
><refentrytitle>pam
</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
296 <para>Note that for each unit making use of this option a PAM session handler process will be maintained as
297 part of the unit and stays around as long as the unit is active, to ensure that appropriate actions can be
298 taken when the unit and hence the PAM session terminates. This process is named
<literal>(sd-pam)
</literal> and
299 is an immediate child process of the unit's main process.
</para>
301 <para>Note that when this option is used for a unit it is very likely (depending on PAM configuration) that the
302 main unit process will be migrated to its own session scope unit when it is activated. This process will hence
303 be associated with two units: the unit it was originally started from (and for which
304 <varname>PAMName=
</varname> was configured), and the session scope unit. Any child processes of that process
305 will however be associated with the session scope unit only. This has implications when used in combination
306 with
<varname>NotifyAccess=
</varname><option>all
</option>, as these child processes will not be able to affect
307 changes in the original unit through notification messages. These messages will be considered belonging to the
308 session scope unit and not the original unit. It is hence not recommended to use
<varname>PAMName=
</varname> in
309 combination with
<varname>NotifyAccess=
</varname><option>all
</option>.
</para>
317 <title>Capabilities
</title>
319 <xi:include href=
"system-only.xml" xpointer=
"plural"/>
321 <variablelist class='unit-directives'
>
324 <term><varname>CapabilityBoundingSet=
</varname></term>
326 <listitem><para>Controls which capabilities to include in the capability bounding set for the executed
327 process. See
<citerefentry
328 project='man-pages'
><refentrytitle>capabilities
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
329 details. Takes a whitespace-separated list of capability names, e.g.
<constant>CAP_SYS_ADMIN
</constant>,
330 <constant>CAP_DAC_OVERRIDE
</constant>,
<constant>CAP_SYS_PTRACE
</constant>. Capabilities listed will be
331 included in the bounding set, all others are removed. If the list of capabilities is prefixed with
332 <literal>~
</literal>, all but the listed capabilities will be included, the effect of the assignment
333 inverted. Note that this option also affects the respective capabilities in the effective, permitted and
334 inheritable capability sets. If this option is not used, the capability bounding set is not modified on process
335 execution, hence no limits on the capabilities of the process are enforced. This option may appear more than
336 once, in which case the bounding sets are merged by
<constant>OR
</constant>, or by
<constant>AND
</constant> if
337 the lines are prefixed with
<literal>~
</literal> (see below). If the empty string is assigned to this option,
338 the bounding set is reset to the empty capability set, and all prior settings have no effect. If set to
339 <literal>~
</literal> (without any further argument), the bounding set is reset to the full set of available
340 capabilities, also undoing any previous settings. This does not affect commands prefixed with
341 <literal>+
</literal>.
</para>
343 <para>Example: if a unit has the following,
344 <programlisting>CapabilityBoundingSet=CAP_A CAP_B
345 CapabilityBoundingSet=CAP_B CAP_C
</programlisting>
346 then
<constant>CAP_A
</constant>,
<constant>CAP_B
</constant>, and
<constant>CAP_C
</constant> are set.
347 If the second line is prefixed with
<literal>~
</literal>, e.g.,
348 <programlisting>CapabilityBoundingSet=CAP_A CAP_B
349 CapabilityBoundingSet=~CAP_B CAP_C
</programlisting>
350 then, only
<constant>CAP_A
</constant> is set.
</para></listitem>
354 <term><varname>AmbientCapabilities=
</varname></term>
356 <listitem><para>Controls which capabilities to include in the ambient capability set for the executed
357 process. Takes a whitespace-separated list of capability names, e.g.
<constant>CAP_SYS_ADMIN
</constant>,
358 <constant>CAP_DAC_OVERRIDE
</constant>,
<constant>CAP_SYS_PTRACE
</constant>. This option may appear more than
359 once in which case the ambient capability sets are merged (see the above examples in
360 <varname>CapabilityBoundingSet=
</varname>). If the list of capabilities is prefixed with
<literal>~
</literal>,
361 all but the listed capabilities will be included, the effect of the assignment inverted. If the empty string is
362 assigned to this option, the ambient capability set is reset to the empty capability set, and all prior
363 settings have no effect. If set to
<literal>~
</literal> (without any further argument), the ambient capability
364 set is reset to the full set of available capabilities, also undoing any previous settings. Note that adding
365 capabilities to ambient capability set adds them to the process's inherited capability set.
</para><para>
366 Ambient capability sets are useful if you want to execute a process as a non-privileged user but still want to
367 give it some capabilities. Note that in this case option
<constant>keep-caps
</constant> is automatically added
368 to
<varname>SecureBits=
</varname> to retain the capabilities over the user
369 change.
<varname>AmbientCapabilities=
</varname> does not affect commands prefixed with
370 <literal>+
</literal>.
</para></listitem>
377 <title>Security
</title>
379 <variablelist class='unit-directives'
>
382 <term><varname>NoNewPrivileges=
</varname></term>
384 <listitem><para>Takes a boolean argument. If true, ensures that the service process and all its
385 children can never gain new privileges through
<function>execve()
</function> (e.g. via setuid or
386 setgid bits, or filesystem capabilities). This is the simplest and most effective way to ensure that
387 a process and its children can never elevate privileges again. Defaults to false, but certain
388 settings override this and ignore the value of this setting. This is the case when
389 <varname>SystemCallFilter=
</varname>,
<varname>SystemCallArchitectures=
</varname>,
390 <varname>RestrictAddressFamilies=
</varname>,
<varname>RestrictNamespaces=
</varname>,
391 <varname>PrivateDevices=
</varname>,
<varname>ProtectKernelTunables=
</varname>,
392 <varname>ProtectKernelModules=
</varname>,
<varname>MemoryDenyWriteExecute=
</varname>,
393 <varname>RestrictRealtime=
</varname>,
<varname>RestrictSUIDSGID=
</varname>,
394 <varname>DynamicUser=
</varname> or
<varname>LockPersonality=
</varname> are specified. Note that even
395 if this setting is overridden by them,
<command>systemctl show
</command> shows the original value of
396 this setting. Also see
<ulink
397 url=
"https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
398 Flag
</ulink>.
</para></listitem>
402 <term><varname>SecureBits=
</varname></term>
404 <listitem><para>Controls the secure bits set for the executed process. Takes a space-separated combination of
405 options from the following list:
<option>keep-caps
</option>,
<option>keep-caps-locked
</option>,
406 <option>no-setuid-fixup
</option>,
<option>no-setuid-fixup-locked
</option>,
<option>noroot
</option>, and
407 <option>noroot-locked
</option>. This option may appear more than once, in which case the secure bits are
408 ORed. If the empty string is assigned to this option, the bits are reset to
0. This does not affect commands
409 prefixed with
<literal>+
</literal>. See
<citerefentry
410 project='man-pages'
><refentrytitle>capabilities
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
411 details.
</para></listitem>
418 <title>Mandatory Access Control
</title>
420 <xi:include href=
"system-only.xml" xpointer=
"plural"/>
422 <variablelist class='unit-directives'
>
425 <term><varname>SELinuxContext=
</varname></term>
427 <listitem><para>Set the SELinux security context of the executed process. If set, this will override the
428 automated domain transition. However, the policy still needs to authorize the transition. This directive is
429 ignored if SELinux is disabled. If prefixed by
<literal>-
</literal>, all errors will be ignored. This does not
430 affect commands prefixed with
<literal>+
</literal>. See
<citerefentry
431 project='die-net'
><refentrytitle>setexeccon
</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
432 details.
</para></listitem>
436 <term><varname>AppArmorProfile=
</varname></term>
438 <listitem><para>Takes a profile name as argument. The process executed by the unit will switch to this profile
439 when started. Profiles must already be loaded in the kernel, or the unit will fail. This result in a non
440 operation if AppArmor is not enabled. If prefixed by
<literal>-
</literal>, all errors will be ignored. This
441 does not affect commands prefixed with
<literal>+
</literal>.
</para></listitem>
445 <term><varname>SmackProcessLabel=
</varname></term>
447 <listitem><para>Takes a
<option>SMACK64
</option> security label as argument. The process executed by the unit
448 will be started under this label and SMACK will decide whether the process is allowed to run or not, based on
449 it. The process will continue to run under the label specified here unless the executable has its own
450 <option>SMACK64EXEC
</option> label, in which case the process will transition to run under that label. When not
451 specified, the label that systemd is running under is used. This directive is ignored if SMACK is
454 <para>The value may be prefixed by
<literal>-
</literal>, in which case all errors will be ignored. An empty
455 value may be specified to unset previous assignments. This does not affect commands prefixed with
456 <literal>+
</literal>.
</para></listitem>
463 <title>Process Properties
</title>
465 <variablelist class='unit-directives'
>
468 <term><varname>LimitCPU=
</varname></term>
469 <term><varname>LimitFSIZE=
</varname></term>
470 <term><varname>LimitDATA=
</varname></term>
471 <term><varname>LimitSTACK=
</varname></term>
472 <term><varname>LimitCORE=
</varname></term>
473 <term><varname>LimitRSS=
</varname></term>
474 <term><varname>LimitNOFILE=
</varname></term>
475 <term><varname>LimitAS=
</varname></term>
476 <term><varname>LimitNPROC=
</varname></term>
477 <term><varname>LimitMEMLOCK=
</varname></term>
478 <term><varname>LimitLOCKS=
</varname></term>
479 <term><varname>LimitSIGPENDING=
</varname></term>
480 <term><varname>LimitMSGQUEUE=
</varname></term>
481 <term><varname>LimitNICE=
</varname></term>
482 <term><varname>LimitRTPRIO=
</varname></term>
483 <term><varname>LimitRTTIME=
</varname></term>
485 <listitem><para>Set soft and hard limits on various resources for executed processes. See
486 <citerefentry><refentrytitle>setrlimit
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details on
487 the resource limit concept. Resource limits may be specified in two formats: either as single value to set a
488 specific soft and hard limit to the same value, or as colon-separated pair
<option>soft:hard
</option> to set
489 both limits individually (e.g.
<literal>LimitAS=
4G:
16G
</literal>). Use the string
<option>infinity
</option> to
490 configure no limit on a specific resource. The multiplicative suffixes K, M, G, T, P and E (to the base
1024)
491 may be used for resource limits measured in bytes (e.g. LimitAS=
16G). For the limits referring to time values,
492 the usual time units ms, s, min, h and so on may be used (see
493 <citerefentry><refentrytitle>systemd.time
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
494 details). Note that if no time unit is specified for
<varname>LimitCPU=
</varname> the default unit of seconds
495 is implied, while for
<varname>LimitRTTIME=
</varname> the default unit of microseconds is implied. Also, note
496 that the effective granularity of the limits might influence their enforcement. For example, time limits
497 specified for
<varname>LimitCPU=
</varname> will be rounded up implicitly to multiples of
1s. For
498 <varname>LimitNICE=
</varname> the value may be specified in two syntaxes: if prefixed with
<literal>+
</literal>
499 or
<literal>-
</literal>, the value is understood as regular Linux nice value in the range -
20.
.19. If not
500 prefixed like this the value is understood as raw resource limit parameter in the range
0.
.40 (with
0 being
501 equivalent to
1).
</para>
503 <para>Note that most process resource limits configured with these options are per-process, and processes may
504 fork in order to acquire a new set of resources that are accounted independently of the original process, and
505 may thus escape limits set. Also note that
<varname>LimitRSS=
</varname> is not implemented on Linux, and
506 setting it has no effect. Often it is advisable to prefer the resource controls listed in
507 <citerefentry><refentrytitle>systemd.resource-control
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
508 over these per-process limits, as they apply to services as a whole, may be altered dynamically at runtime, and
509 are generally more expressive. For example,
<varname>MemoryLimit=
</varname> is a more powerful (and working)
510 replacement for
<varname>LimitRSS=
</varname>.
</para>
512 <para>For system units these resource limits may be chosen freely. For user units however (i.e. units run by a
514 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>), these limits are
515 bound by (possibly more restrictive) per-user limits enforced by the OS.
</para>
517 <para>Resource limits not configured explicitly for a unit default to the value configured in the various
518 <varname>DefaultLimitCPU=
</varname>,
<varname>DefaultLimitFSIZE=
</varname>, … options available in
519 <citerefentry><refentrytitle>systemd-system.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and –
520 if not configured there – the kernel or per-user defaults, as defined by the OS (the latter only for user
521 services, see above).
</para>
524 <title>Resource limit directives, their equivalent
<command>ulimit
</command> shell commands and the unit used
</title>
527 <colspec colname='directive'
/>
528 <colspec colname='equivalent'
/>
529 <colspec colname='unit'
/>
532 <entry>Directive
</entry>
533 <entry><command>ulimit
</command> equivalent
</entry>
539 <entry>LimitCPU=
</entry>
540 <entry>ulimit -t
</entry>
541 <entry>Seconds
</entry>
544 <entry>LimitFSIZE=
</entry>
545 <entry>ulimit -f
</entry>
549 <entry>LimitDATA=
</entry>
550 <entry>ulimit -d
</entry>
554 <entry>LimitSTACK=
</entry>
555 <entry>ulimit -s
</entry>
559 <entry>LimitCORE=
</entry>
560 <entry>ulimit -c
</entry>
564 <entry>LimitRSS=
</entry>
565 <entry>ulimit -m
</entry>
569 <entry>LimitNOFILE=
</entry>
570 <entry>ulimit -n
</entry>
571 <entry>Number of File Descriptors
</entry>
574 <entry>LimitAS=
</entry>
575 <entry>ulimit -v
</entry>
579 <entry>LimitNPROC=
</entry>
580 <entry>ulimit -u
</entry>
581 <entry>Number of Processes
</entry>
584 <entry>LimitMEMLOCK=
</entry>
585 <entry>ulimit -l
</entry>
589 <entry>LimitLOCKS=
</entry>
590 <entry>ulimit -x
</entry>
591 <entry>Number of Locks
</entry>
594 <entry>LimitSIGPENDING=
</entry>
595 <entry>ulimit -i
</entry>
596 <entry>Number of Queued Signals
</entry>
599 <entry>LimitMSGQUEUE=
</entry>
600 <entry>ulimit -q
</entry>
604 <entry>LimitNICE=
</entry>
605 <entry>ulimit -e
</entry>
606 <entry>Nice Level
</entry>
609 <entry>LimitRTPRIO=
</entry>
610 <entry>ulimit -r
</entry>
611 <entry>Realtime Priority
</entry>
614 <entry>LimitRTTIME=
</entry>
615 <entry>No equivalent
</entry>
616 <entry>Microseconds
</entry>
624 <term><varname>UMask=
</varname></term>
626 <listitem><para>Controls the file mode creation mask. Takes an access mode in octal notation. See
627 <citerefentry><refentrytitle>umask
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details. Defaults
628 to
0022.
</para></listitem>
632 <term><varname>KeyringMode=
</varname></term>
634 <listitem><para>Controls how the kernel session keyring is set up for the service (see
<citerefentry
635 project='man-pages'
><refentrytitle>session-keyring
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
636 details on the session keyring). Takes one of
<option>inherit
</option>,
<option>private
</option>,
637 <option>shared
</option>. If set to
<option>inherit
</option> no special keyring setup is done, and the kernel's
638 default behaviour is applied. If
<option>private
</option> is used a new session keyring is allocated when a
639 service process is invoked, and it is not linked up with any user keyring. This is the recommended setting for
640 system services, as this ensures that multiple services running under the same system user ID (in particular
641 the root user) do not share their key material among each other. If
<option>shared
</option> is used a new
642 session keyring is allocated as for
<option>private
</option>, but the user keyring of the user configured with
643 <varname>User=
</varname> is linked into it, so that keys assigned to the user may be requested by the unit's
644 processes. In this modes multiple units running processes under the same user ID may share key material. Unless
645 <option>inherit
</option> is selected the unique invocation ID for the unit (see below) is added as a protected
646 key by the name
<literal>invocation_id
</literal> to the newly created session keyring. Defaults to
647 <option>private
</option> for services of the system service manager and to
<option>inherit
</option> for
648 non-service units and for services of the user service manager.
</para></listitem>
652 <term><varname>OOMScoreAdjust=
</varname></term>
654 <listitem><para>Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes an integer
655 between -
1000 (to disable OOM killing for this process) and
1000 (to make killing of this process under memory
656 pressure very likely). See
<ulink
657 url=
"https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt
</ulink> for
658 details.
</para></listitem>
662 <term><varname>TimerSlackNSec=
</varname></term>
663 <listitem><para>Sets the timer slack in nanoseconds for the executed processes. The timer slack controls the
664 accuracy of wake-ups triggered by timers. See
665 <citerefentry><refentrytitle>prctl
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for more
666 information. Note that in contrast to most other time span definitions this parameter takes an integer value in
667 nano-seconds if no unit is specified. The usual time units are understood too.
</para></listitem>
671 <term><varname>Personality=
</varname></term>
673 <listitem><para>Controls which kernel architecture
<citerefentry
674 project='man-pages'
><refentrytitle>uname
</refentrytitle><manvolnum>2</manvolnum></citerefentry> shall report,
675 when invoked by unit processes. Takes one of the architecture identifiers
<constant>x86
</constant>,
676 <constant>x86-
64</constant>,
<constant>ppc
</constant>,
<constant>ppc-le
</constant>,
<constant>ppc64
</constant>,
677 <constant>ppc64-le
</constant>,
<constant>s390
</constant> or
<constant>s390x
</constant>. Which personality
678 architectures are supported depends on the system architecture. Usually the
64bit versions of the various
679 system architectures support their immediate
32bit personality architecture counterpart, but no others. For
680 example,
<constant>x86-
64</constant> systems support the
<constant>x86-
64</constant> and
681 <constant>x86
</constant> personalities but no others. The personality feature is useful when running
32-bit
682 services on a
64-bit host system. If not specified, the personality is left unmodified and thus reflects the
683 personality of the host system's kernel.
</para></listitem>
687 <term><varname>IgnoreSIGPIPE=
</varname></term>
689 <listitem><para>Takes a boolean argument. If true, causes
<constant>SIGPIPE
</constant> to be ignored in the
690 executed process. Defaults to true because
<constant>SIGPIPE
</constant> generally is useful only in shell
691 pipelines.
</para></listitem>
698 <title>Scheduling
</title>
700 <variablelist class='unit-directives'
>
703 <term><varname>Nice=
</varname></term>
705 <listitem><para>Sets the default nice level (scheduling priority) for executed processes. Takes an integer
706 between -
20 (highest priority) and
19 (lowest priority). See
707 <citerefentry><refentrytitle>setpriority
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
708 details.
</para></listitem>
712 <term><varname>CPUSchedulingPolicy=
</varname></term>
714 <listitem><para>Sets the CPU scheduling policy for executed processes. Takes one of
<option>other
</option>,
715 <option>batch
</option>,
<option>idle
</option>,
<option>fifo
</option> or
<option>rr
</option>. See
716 <citerefentry><refentrytitle>sched_setscheduler
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
717 details.
</para></listitem>
721 <term><varname>CPUSchedulingPriority=
</varname></term>
723 <listitem><para>Sets the CPU scheduling priority for executed processes. The available priority range depends
724 on the selected CPU scheduling policy (see above). For real-time scheduling policies an integer between
1
725 (lowest priority) and
99 (highest priority) can be used. See
726 <citerefentry><refentrytitle>sched_setscheduler
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
727 details.
</para></listitem>
731 <term><varname>CPUSchedulingResetOnFork=
</varname></term>
733 <listitem><para>Takes a boolean argument. If true, elevated CPU scheduling priorities and policies will be
734 reset when the executed processes fork, and can hence not leak into child processes. See
735 <citerefentry><refentrytitle>sched_setscheduler
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
736 details. Defaults to false.
</para></listitem>
740 <term><varname>CPUAffinity=
</varname></term>
742 <listitem><para>Controls the CPU affinity of the executed processes. Takes a list of CPU indices or ranges
743 separated by either whitespace or commas. CPU ranges are specified by the lower and upper CPU indices separated
744 by a dash. This option may be specified more than once, in which case the specified CPU affinity masks are
745 merged. If the empty string is assigned, the mask is reset, all assignments prior to this will have no
747 <citerefentry><refentrytitle>sched_setaffinity
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
748 details.
</para></listitem>
752 <term><varname>IOSchedulingClass=
</varname></term>
754 <listitem><para>Sets the I/O scheduling class for executed processes. Takes an integer between
0 and
3 or one
755 of the strings
<option>none
</option>,
<option>realtime
</option>,
<option>best-effort
</option> or
756 <option>idle
</option>. If the empty string is assigned to this option, all prior assignments to both
757 <varname>IOSchedulingClass=
</varname> and
<varname>IOSchedulingPriority=
</varname> have no effect. See
758 <citerefentry><refentrytitle>ioprio_set
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
759 details.
</para></listitem>
763 <term><varname>IOSchedulingPriority=
</varname></term>
765 <listitem><para>Sets the I/O scheduling priority for executed processes. Takes an integer between
0 (highest
766 priority) and
7 (lowest priority). The available priorities depend on the selected I/O scheduling class (see
767 above). If the empty string is assigned to this option, all prior assignments to both
768 <varname>IOSchedulingClass=
</varname> and
<varname>IOSchedulingPriority=
</varname> have no effect.
769 See
<citerefentry><refentrytitle>ioprio_set
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
770 details.
</para></listitem>
777 <title>Sandboxing
</title>
779 <para>The following sandboxing options are an effective way to limit the exposure of the system towards the unit's
780 processes. It is recommended to turn on as many of these options for each unit as is possible without negatively
781 affecting the process' ability to operate. Note that many of these sandboxing features are gracefully turned off on
782 systems where the underlying security mechanism is not available. For example,
<varname>ProtectSystem=
</varname>
783 has no effect if the kernel is built without file system namespacing or if the service manager runs in a container
784 manager that makes file system namespacing unavailable to its payload. Similar,
785 <varname>RestrictRealtime=
</varname> has no effect on systems that lack support for SECCOMP system call filtering,
786 or in containers where support for this is turned off.
</para>
788 <para>Also note that some sandboxing functionality is generally not available in user services (i.e. services run
789 by the per-user service manager). Specifically, the various settings requiring file system namespacing support
790 (such as
<varname>ProtectSystem=
</varname>) are not available, as the underlying kernel functionality is only
791 accessible to privileged processes.
</para>
793 <variablelist class='unit-directives'
>
796 <term><varname>ProtectSystem=
</varname></term>
798 <listitem><para>Takes a boolean argument or the special values
<literal>full
</literal> or
799 <literal>strict
</literal>. If true, mounts the
<filename>/usr
</filename> and
<filename>/boot
</filename>
800 directories read-only for processes invoked by this unit. If set to
<literal>full
</literal>, the
801 <filename>/etc
</filename> directory is mounted read-only, too. If set to
<literal>strict
</literal> the entire
802 file system hierarchy is mounted read-only, except for the API file system subtrees
<filename>/dev
</filename>,
803 <filename>/proc
</filename> and
<filename>/sys
</filename> (protect these directories using
804 <varname>PrivateDevices=
</varname>,
<varname>ProtectKernelTunables=
</varname>,
805 <varname>ProtectControlGroups=
</varname>). This setting ensures that any modification of the vendor-supplied
806 operating system (and optionally its configuration, and local mounts) is prohibited for the service. It is
807 recommended to enable this setting for all long-running services, unless they are involved with system updates
808 or need to modify the operating system in other ways. If this option is used,
809 <varname>ReadWritePaths=
</varname> may be used to exclude specific directories from being made read-only. This
810 setting is implied if
<varname>DynamicUser=
</varname> is set. This setting cannot ensure protection in all
811 cases. In general it has the same limitations as
<varname>ReadOnlyPaths=
</varname>, see below. Defaults to
812 off.
</para></listitem>
816 <term><varname>ProtectHome=
</varname></term>
818 <listitem><para>Takes a boolean argument or the special values
<literal>read-only
</literal> or
819 <literal>tmpfs
</literal>. If true, the directories
<filename>/home
</filename>,
<filename>/root
</filename> and
820 <filename>/run/user
</filename> are made inaccessible and empty for processes invoked by this unit. If set to
821 <literal>read-only
</literal>, the three directories are made read-only instead. If set to
<literal>tmpfs
</literal>,
822 temporary file systems are mounted on the three directories in read-only mode. The value
<literal>tmpfs
</literal>
823 is useful to hide home directories not relevant to the processes invoked by the unit, while necessary directories
824 are still visible by combining with
<varname>BindPaths=
</varname> or
<varname>BindReadOnlyPaths=
</varname>.
</para>
826 <para>Setting this to
<literal>yes
</literal> is mostly equivalent to set the three directories in
827 <varname>InaccessiblePaths=
</varname>. Similarly,
<literal>read-only
</literal> is mostly equivalent to
828 <varname>ReadOnlyPaths=
</varname>, and
<literal>tmpfs
</literal> is mostly equivalent to
829 <varname>TemporaryFileSystem=
</varname>.
</para>
831 <para> It is recommended to enable this setting for all long-running services (in particular network-facing
832 ones), to ensure they cannot get access to private user data, unless the services actually require access to
833 the user's private data. This setting is implied if
<varname>DynamicUser=
</varname> is set. This setting cannot
834 ensure protection in all cases. In general it has the same limitations as
<varname>ReadOnlyPaths=
</varname>,
837 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
841 <term><varname>RuntimeDirectory=
</varname></term>
842 <term><varname>StateDirectory=
</varname></term>
843 <term><varname>CacheDirectory=
</varname></term>
844 <term><varname>LogsDirectory=
</varname></term>
845 <term><varname>ConfigurationDirectory=
</varname></term>
847 <listitem><para>These options take a whitespace-separated list of directory names. The specified directory
848 names must be relative, and may not include
<literal>..
</literal>. If set, one or more
849 directories by the specified names will be created (including their parents) below the locations
850 defined in the following table, when the unit is started. Also, the corresponding environment variable
851 is defined with the full path of directories. If multiple directories are set, then in the environment variable
852 the paths are concatenated with colon (
<literal>:
</literal>).
</para>
854 <title>Automatic directory creation and environment variables
</title>
858 <entry>Directory
</entry>
859 <entry>Below path for system units
</entry>
860 <entry>Below path for user units
</entry>
861 <entry>Environment variable set
</entry>
866 <entry><varname>RuntimeDirectory=
</varname></entry>
867 <entry><filename>/run/
</filename></entry>
868 <entry><varname>$XDG_RUNTIME_DIR
</varname></entry>
869 <entry><varname>$RUNTIME_DIRECTORY
</varname></entry>
872 <entry><varname>StateDirectory=
</varname></entry>
873 <entry><filename>/var/lib/
</filename></entry>
874 <entry><varname>$XDG_CONFIG_HOME
</varname></entry>
875 <entry><varname>$STATE_DIRECTORY
</varname></entry>
878 <entry><varname>CacheDirectory=
</varname></entry>
879 <entry><filename>/var/cache/
</filename></entry>
880 <entry><varname>$XDG_CACHE_HOME
</varname></entry>
881 <entry><varname>$CACHE_DIRECTORY
</varname></entry>
884 <entry><varname>LogsDirectory=
</varname></entry>
885 <entry><filename>/var/log/
</filename></entry>
886 <entry><varname>$XDG_CONFIG_HOME
</varname><filename>/log/
</filename></entry>
887 <entry><varname>$LOGS_DIRECTORY
</varname></entry>
890 <entry><varname>ConfigurationDirectory=
</varname></entry>
891 <entry><filename>/etc/
</filename></entry>
892 <entry><varname>$XDG_CONFIG_HOME
</varname></entry>
893 <entry><varname>$CONFIGURATION_DIRECTORY
</varname></entry>
899 <para>In case of
<varname>RuntimeDirectory=
</varname> the innermost subdirectories are removed when
900 the unit is stopped. It is possible to preserve the specified directories in this case if
901 <varname>RuntimeDirectoryPreserve=
</varname> is configured to
<option>restart
</option> or
902 <option>yes
</option> (see below). The directories specified with
<varname>StateDirectory=
</varname>,
903 <varname>CacheDirectory=
</varname>,
<varname>LogsDirectory=
</varname>,
904 <varname>ConfigurationDirectory=
</varname> are not removed when the unit is stopped.
</para>
906 <para>Except in case of
<varname>ConfigurationDirectory=
</varname>, the innermost specified directories will be
907 owned by the user and group specified in
<varname>User=
</varname> and
<varname>Group=
</varname>. If the
908 specified directories already exist and their owning user or group do not match the configured ones, all files
909 and directories below the specified directories as well as the directories themselves will have their file
910 ownership recursively changed to match what is configured. As an optimization, if the specified directories are
911 already owned by the right user and group, files and directories below of them are left as-is, even if they do
912 not match what is requested. The innermost specified directories will have their access mode adjusted to the
913 what is specified in
<varname>RuntimeDirectoryMode=
</varname>,
<varname>StateDirectoryMode=
</varname>,
914 <varname>CacheDirectoryMode=
</varname>,
<varname>LogsDirectoryMode=
</varname> and
915 <varname>ConfigurationDirectoryMode=
</varname>.
</para>
917 <para>These options imply
<varname>BindPaths=
</varname> for the specified paths. When combined with
918 <varname>RootDirectory=
</varname> or
<varname>RootImage=
</varname> these paths always reside on the host and
919 are mounted from there into the unit's file system namespace.
</para>
921 <para>If
<varname>DynamicUser=
</varname> is used in conjunction with
<varname>StateDirectory=
</varname>,
922 <varname>CacheDirectory=
</varname> and
<varname>LogsDirectory=
</varname> is slightly altered: the directories
923 are created below
<filename>/var/lib/private
</filename>,
<filename>/var/cache/private
</filename> and
924 <filename>/var/log/private
</filename>, respectively, which are host directories made inaccessible to
925 unprivileged users, which ensures that access to these directories cannot be gained through dynamic user ID
926 recycling. Symbolic links are created to hide this difference in behaviour. Both from perspective of the host
927 and from inside the unit, the relevant directories hence always appear directly below
928 <filename>/var/lib
</filename>,
<filename>/var/cache
</filename> and
<filename>/var/log
</filename>.
</para>
930 <para>Use
<varname>RuntimeDirectory=
</varname> to manage one or more runtime directories for the unit and bind
931 their lifetime to the daemon runtime. This is particularly useful for unprivileged daemons that cannot create
932 runtime directories in
<filename>/run
</filename> due to lack of privileges, and to make sure the runtime
933 directory is cleaned up automatically after use. For runtime directories that require more complex or different
934 configuration or lifetime guarantees, please consider using
935 <citerefentry><refentrytitle>tmpfiles.d
</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
937 <para>Example: if a system service unit has the following,
938 <programlisting>RuntimeDirectory=foo/bar baz
</programlisting>
939 the service manager creates
<filename>/run/foo
</filename> (if it does not exist),
940 <filename>/run/foo/bar
</filename>, and
<filename>/run/baz
</filename>. The directories
941 <filename>/run/foo/bar
</filename> and
<filename>/run/baz
</filename> except
<filename>/run/foo
</filename> are
942 owned by the user and group specified in
<varname>User=
</varname> and
<varname>Group=
</varname>, and removed
943 when the service is stopped.
</para>
945 <para>Example: if a system service unit has the following,
946 <programlisting>RuntimeDirectory=foo/bar
947 StateDirectory=aaa/bbb ccc
</programlisting>
948 then the environment variable
<literal>RUNTIME_DIRECTORY
</literal> is set with
<literal>/run/foo/bar
</literal>, and
949 <literal>STATE_DIRECTORY
</literal> is set with
<literal>/var/lib/aaa/bbb:/var/lib/ccc
</literal>.
</para></listitem>
953 <term><varname>RuntimeDirectoryMode=
</varname></term>
954 <term><varname>StateDirectoryMode=
</varname></term>
955 <term><varname>CacheDirectoryMode=
</varname></term>
956 <term><varname>LogsDirectoryMode=
</varname></term>
957 <term><varname>ConfigurationDirectoryMode=
</varname></term>
959 <listitem><para>Specifies the access mode of the directories specified in
<varname>RuntimeDirectory=
</varname>,
960 <varname>StateDirectory=
</varname>,
<varname>CacheDirectory=
</varname>,
<varname>LogsDirectory=
</varname>, or
961 <varname>ConfigurationDirectory=
</varname>, respectively, as an octal number. Defaults to
962 <constant>0755</constant>. See
"Permissions" in
<citerefentry
963 project='man-pages'
><refentrytitle>path_resolution
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for a
964 discussion of the meaning of permission bits.
</para></listitem>
968 <term><varname>RuntimeDirectoryPreserve=
</varname></term>
970 <listitem><para>Takes a boolean argument or
<option>restart
</option>. If set to
<option>no
</option> (the
971 default), the directories specified in
<varname>RuntimeDirectory=
</varname> are always removed when the service
972 stops. If set to
<option>restart
</option> the directories are preserved when the service is both automatically
973 and manually restarted. Here, the automatic restart means the operation specified in
974 <varname>Restart=
</varname>, and manual restart means the one triggered by
<command>systemctl restart
975 foo.service
</command>. If set to
<option>yes
</option>, then the directories are not removed when the service is
976 stopped. Note that since the runtime directory
<filename>/run
</filename> is a mount point of
977 <literal>tmpfs
</literal>, then for system services the directories specified in
978 <varname>RuntimeDirectory=
</varname> are removed when the system is rebooted.
</para></listitem>
982 <term><varname>ReadWritePaths=
</varname></term>
983 <term><varname>ReadOnlyPaths=
</varname></term>
984 <term><varname>InaccessiblePaths=
</varname></term>
986 <listitem><para>Sets up a new file system namespace for executed processes. These options may be used to limit
987 access a process might have to the file system hierarchy. Each setting takes a space-separated list of paths
988 relative to the host's root directory (i.e. the system running the service manager). Note that if paths
989 contain symlinks, they are resolved relative to the root directory set with
990 <varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname>.
</para>
992 <para>Paths listed in
<varname>ReadWritePaths=
</varname> are accessible from within the namespace with the same
993 access modes as from outside of it. Paths listed in
<varname>ReadOnlyPaths=
</varname> are accessible for
994 reading only, writing will be refused even if the usual file access controls would permit this. Nest
995 <varname>ReadWritePaths=
</varname> inside of
<varname>ReadOnlyPaths=
</varname> in order to provide writable
996 subdirectories within read-only directories. Use
<varname>ReadWritePaths=
</varname> in order to whitelist
997 specific paths for write access if
<varname>ProtectSystem=strict
</varname> is used.
</para>
999 <para>Paths listed in
<varname>InaccessiblePaths=
</varname> will be made inaccessible for processes inside
1000 the namespace along with everything below them in the file system hierarchy. This may be more restrictive than
1001 desired, because it is not possible to nest
<varname>ReadWritePaths=
</varname>,
<varname>ReadOnlyPaths=
</varname>,
1002 <varname>BindPaths=
</varname>, or
<varname>BindReadOnlyPaths=
</varname> inside it. For a more flexible option,
1003 see
<varname>TemporaryFileSystem=
</varname>.
</para>
1005 <para>Non-directory paths may be specified as well. These options may be specified more than once,
1006 in which case all paths listed will have limited access from within the namespace. If the empty string is
1007 assigned to this option, the specific list is reset, and all prior assignments have no effect.
</para>
1009 <para>Paths in
<varname>ReadWritePaths=
</varname>,
<varname>ReadOnlyPaths=
</varname> and
1010 <varname>InaccessiblePaths=
</varname> may be prefixed with
<literal>-
</literal>, in which case they will be
1011 ignored when they do not exist. If prefixed with
<literal>+
</literal> the paths are taken relative to the root
1012 directory of the unit, as configured with
<varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname>,
1013 instead of relative to the root directory of the host (see above). When combining
<literal>-
</literal> and
1014 <literal>+
</literal> on the same path make sure to specify
<literal>-
</literal> first, and
<literal>+
</literal>
1017 <para>Note that these settings will disconnect propagation of mounts from the unit's processes to the
1018 host. This means that this setting may not be used for services which shall be able to install mount points in
1019 the main mount namespace. For
<varname>ReadWritePaths=
</varname> and
<varname>ReadOnlyPaths=
</varname>
1020 propagation in the other direction is not affected, i.e. mounts created on the host generally appear in the
1021 unit processes' namespace, and mounts removed on the host also disappear there too. In particular, note that
1022 mount propagation from host to unit will result in unmodified mounts to be created in the unit's namespace,
1023 i.e. writable mounts appearing on the host will be writable in the unit's namespace too, even when propagated
1024 below a path marked with
<varname>ReadOnlyPaths=
</varname>! Restricting access with these options hence does
1025 not extend to submounts of a directory that are created later on. This means the lock-down offered by that
1026 setting is not complete, and does not offer full protection.
</para>
1028 <para>Note that the effect of these settings may be undone by privileged processes. In order to set up an
1029 effective sandboxed environment for a unit it is thus recommended to combine these settings with either
1030 <varname>CapabilityBoundingSet=~CAP_SYS_ADMIN
</varname> or
1031 <varname>SystemCallFilter=~@mount
</varname>.
</para>
1033 <xi:include href=
"system-only.xml" xpointer=
"plural"/></listitem>
1037 <term><varname>TemporaryFileSystem=
</varname></term>
1039 <listitem><para>Takes a space-separated list of mount points for temporary file systems (tmpfs). If set, a new file
1040 system namespace is set up for executed processes, and a temporary file system is mounted on each mount point.
1041 This option may be specified more than once, in which case temporary file systems are mounted on all listed mount
1042 points. If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
1043 Each mount point may optionally be suffixed with a colon (
<literal>:
</literal>) and mount options such as
1044 <literal>size=
10%
</literal> or
<literal>ro
</literal>. By default, each temporary file system is mounted
1045 with
<literal>nodev,strictatime,mode=
0755</literal>. These can be disabled by explicitly specifying the corresponding
1046 mount options, e.g.,
<literal>dev
</literal> or
<literal>nostrictatime
</literal>.
</para>
1048 <para>This is useful to hide files or directories not relevant to the processes invoked by the unit, while necessary
1049 files or directories can be still accessed by combining with
<varname>BindPaths=
</varname> or
1050 <varname>BindReadOnlyPaths=
</varname>. See the example below.
</para>
1052 <para>Example: if a unit has the following,
1053 <programlisting>TemporaryFileSystem=/var:ro
1054 BindReadOnlyPaths=/var/lib/systemd
</programlisting>
1055 then the invoked processes by the unit cannot see any files or directories under
<filename>/var
</filename> except for
1056 <filename>/var/lib/systemd
</filename> or its contents.
</para>
1058 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1062 <term><varname>PrivateTmp=
</varname></term>
1064 <listitem><para>Takes a boolean argument. If true, sets up a new file system namespace for the executed
1065 processes and mounts private
<filename>/tmp
</filename> and
<filename>/var/tmp
</filename> directories inside it
1066 that is not shared by processes outside of the namespace. This is useful to secure access to temporary files of
1067 the process, but makes sharing between processes via
<filename>/tmp
</filename> or
<filename>/var/tmp
</filename>
1068 impossible. If this is enabled, all temporary files created by a service in these directories will be removed
1069 after the service is stopped. Defaults to false. It is possible to run two or more units within the same
1070 private
<filename>/tmp
</filename> and
<filename>/var/tmp
</filename> namespace by using the
1071 <varname>JoinsNamespaceOf=
</varname> directive, see
1072 <citerefentry><refentrytitle>systemd.unit
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
1073 details. This setting is implied if
<varname>DynamicUser=
</varname> is set. For this setting the same
1074 restrictions regarding mount propagation and privileges apply as for
<varname>ReadOnlyPaths=
</varname> and
1075 related calls, see above. Enabling this setting has the side effect of adding
<varname>Requires=
</varname> and
1076 <varname>After=
</varname> dependencies on all mount units necessary to access
<filename>/tmp
</filename> and
1077 <filename>/var/tmp
</filename>. Moreover an implicitly
<varname>After=
</varname> ordering on
1078 <citerefentry><refentrytitle>systemd-tmpfiles-setup.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1081 <para>Note that the implementation of this setting might be impossible (for example if mount namespaces are not
1082 available), and the unit should be written in a way that does not solely rely on this setting for
1085 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1089 <term><varname>PrivateDevices=
</varname></term>
1091 <listitem><para>Takes a boolean argument. If true, sets up a new
<filename>/dev
</filename> mount for the
1092 executed processes and only adds API pseudo devices such as
<filename>/dev/null
</filename>,
1093 <filename>/dev/zero
</filename> or
<filename>/dev/random
</filename> (as well as the pseudo TTY subsystem) to it,
1094 but no physical devices such as
<filename>/dev/sda
</filename>, system memory
<filename>/dev/mem
</filename>,
1095 system ports
<filename>/dev/port
</filename> and others. This is useful to securely turn off physical device
1096 access by the executed process. Defaults to false. Enabling this option will install a system call filter to
1097 block low-level I/O system calls that are grouped in the
<varname>@raw-io
</varname> set, will also remove
1098 <constant>CAP_MKNOD
</constant> and
<constant>CAP_SYS_RAWIO
</constant> from the capability bounding set for the
1099 unit (see above), and set
<varname>DevicePolicy=closed
</varname> (see
1100 <citerefentry><refentrytitle>systemd.resource-control
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1101 for details). Note that using this setting will disconnect propagation of mounts from the service to the host
1102 (propagation in the opposite direction continues to work). This means that this setting may not be used for
1103 services which shall be able to install mount points in the main mount namespace. The new
1104 <filename>/dev
</filename> will be mounted read-only and 'noexec'. The latter may break old programs which try
1105 to set up executable memory by using
1106 <citerefentry><refentrytitle>mmap
</refentrytitle><manvolnum>2</manvolnum></citerefentry> of
1107 <filename>/dev/zero
</filename> instead of using
<constant>MAP_ANON
</constant>. For this setting the same
1108 restrictions regarding mount propagation and privileges apply as for
<varname>ReadOnlyPaths=
</varname> and
1109 related calls, see above. If turned on and if running in user mode, or in system mode, but without the
1110 <constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
<varname>User=
</varname>),
1111 <varname>NoNewPrivileges=yes
</varname> is implied.
</para>
1113 <para>Note that the implementation of this setting might be impossible (for example if mount namespaces are not
1114 available), and the unit should be written in a way that does not solely rely on this setting for
1117 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1121 <term><varname>PrivateNetwork=
</varname></term>
1123 <listitem><para>Takes a boolean argument. If true, sets up a new network namespace for the executed processes
1124 and configures only the loopback network device
<literal>lo
</literal> inside it. No other network devices will
1125 be available to the executed process. This is useful to turn off network access by the executed process.
1126 Defaults to false. It is possible to run two or more units within the same private network namespace by using
1127 the
<varname>JoinsNamespaceOf=
</varname> directive, see
1128 <citerefentry><refentrytitle>systemd.unit
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
1129 details. Note that this option will disconnect all socket families from the host, including
1130 <constant>AF_NETLINK
</constant> and
<constant>AF_UNIX
</constant>. Effectively, for
1131 <constant>AF_NETLINK
</constant> this means that device configuration events received from
1132 <citerefentry><refentrytitle>systemd-udevd.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry> are
1133 not delivered to the unit's processes. And for
<constant>AF_UNIX
</constant> this has the effect that
1134 <constant>AF_UNIX
</constant> sockets in the abstract socket namespace of the host will become unavailable to
1135 the unit's processes (however, those located in the file system will continue to be accessible).
</para>
1137 <para>Note that the implementation of this setting might be impossible (for example if network namespaces are
1138 not available), and the unit should be written in a way that does not solely rely on this setting for
1141 <para>When this option is used on a socket unit any sockets bound on behalf of this unit will be
1142 bound within a private network namespace. This may be combined with
1143 <varname>JoinsNamespaceOf=
</varname> to listen on sockets inside of network namespaces of other
1146 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1150 <term><varname>NetworkNamespacePath=
</varname></term>
1152 <listitem><para>Takes an absolute file system path refererring to a Linux network namespace
1153 pseudo-file (i.e. a file like
<filename>/proc/$PID/ns/net
</filename> or a bind mount or symlink to
1154 one). When set the invoked processes are added to the network namespace referenced by that path. The
1155 path has to point to a valid namespace file at the moment the processes are forked off. If this
1156 option is used
<varname>PrivateNetwork=
</varname> has no effect. If this option is used together with
1157 <varname>JoinsNamespaceOf=
</varname> then it only has an effect if this unit is started before any of
1158 the listed units that have
<varname>PrivateNetwork=
</varname> or
1159 <varname>NetworkNamespacePath=
</varname> configured, as otherwise the network namespace of those
1160 units is reused.
</para>
1162 <para>When this option is used on a socket unit any sockets bound on behalf of this unit will be
1163 bound within the specified network namespace.
</para>
1165 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1169 <term><varname>PrivateUsers=
</varname></term>
1171 <listitem><para>Takes a boolean argument. If true, sets up a new user namespace for the executed processes and
1172 configures a minimal user and group mapping, that maps the
<literal>root
</literal> user and group as well as
1173 the unit's own user and group to themselves and everything else to the
<literal>nobody
</literal> user and
1174 group. This is useful to securely detach the user and group databases used by the unit from the rest of the
1175 system, and thus to create an effective sandbox environment. All files, directories, processes, IPC objects and
1176 other resources owned by users/groups not equaling
<literal>root
</literal> or the unit's own will stay visible
1177 from within the unit but appear owned by the
<literal>nobody
</literal> user and group. If this mode is enabled,
1178 all unit processes are run without privileges in the host user namespace (regardless if the unit's own
1179 user/group is
<literal>root
</literal> or not). Specifically this means that the process will have zero process
1180 capabilities on the host's user namespace, but full capabilities within the service's user namespace. Settings
1181 such as
<varname>CapabilityBoundingSet=
</varname> will affect only the latter, and there's no way to acquire
1182 additional capabilities in the host's user namespace. Defaults to off.
</para>
1184 <para>This setting is particularly useful in conjunction with
1185 <varname>RootDirectory=
</varname>/
<varname>RootImage=
</varname>, as the need to synchronize the user and group
1186 databases in the root directory and on the host is reduced, as the only users and groups who need to be matched
1187 are
<literal>root
</literal>,
<literal>nobody
</literal> and the unit's own user and group.
</para>
1189 <para>Note that the implementation of this setting might be impossible (for example if user namespaces are not
1190 available), and the unit should be written in a way that does not solely rely on this setting for
1193 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1197 <term><varname>ProtectHostname=
</varname></term>
1199 <listitem><para>Takes a boolean argument. When set, sets up a new UTS namespace for the executed
1200 processes. In addition, changing hostname or domainname is prevented. Defaults to off.
</para>
1202 <para>Note that the implementation of this setting might be impossible (for example if UTS namespaces
1203 are not available), and the unit should be written in a way that does not solely rely on this setting
1204 for security.
</para>
1206 <para>Note that when this option is enabled for a service hostname changes no longer propagate from
1207 the system into the service, it is hence not suitable for services that need to take notice of system
1208 hostname changes dynamically.
</para>
1210 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1214 <term><varname>ProtectKernelTunables=
</varname></term>
1216 <listitem><para>Takes a boolean argument. If true, kernel variables accessible through
1217 <filename>/proc/sys
</filename>,
<filename>/sys
</filename>,
<filename>/proc/sysrq-trigger
</filename>,
1218 <filename>/proc/latency_stats
</filename>,
<filename>/proc/acpi
</filename>,
1219 <filename>/proc/timer_stats
</filename>,
<filename>/proc/fs
</filename> and
<filename>/proc/irq
</filename> will
1220 be made read-only to all processes of the unit. Usually, tunable kernel variables should be initialized only at
1221 boot-time, for example with the
1222 <citerefentry><refentrytitle>sysctl.d
</refentrytitle><manvolnum>5</manvolnum></citerefentry> mechanism. Few
1223 services need to write to these at runtime; it is hence recommended to turn this on for most services. For this
1224 setting the same restrictions regarding mount propagation and privileges apply as for
1225 <varname>ReadOnlyPaths=
</varname> and related calls, see above. Defaults to off. If turned on and if running
1226 in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. services
1227 for which
<varname>User=
</varname> is set),
<varname>NoNewPrivileges=yes
</varname> is implied. Note that this
1228 option does not prevent indirect changes to kernel tunables effected by IPC calls to other processes. However,
1229 <varname>InaccessiblePaths=
</varname> may be used to make relevant IPC file system objects inaccessible. If
1230 <varname>ProtectKernelTunables=
</varname> is set,
<varname>MountAPIVFS=yes
</varname> is
1233 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1237 <term><varname>ProtectKernelModules=
</varname></term>
1239 <listitem><para>Takes a boolean argument. If true, explicit module loading will be denied. This allows
1240 module load and unload operations to be turned off on modular kernels. It is recommended to turn this on for most services
1241 that do not need special file systems or extra kernel modules to work. Defaults to off. Enabling this option
1242 removes
<constant>CAP_SYS_MODULE
</constant> from the capability bounding set for the unit, and installs a
1243 system call filter to block module system calls, also
<filename>/usr/lib/modules
</filename> is made
1244 inaccessible. For this setting the same restrictions regarding mount propagation and privileges apply as for
1245 <varname>ReadOnlyPaths=
</varname> and related calls, see above. Note that limited automatic module loading due
1246 to user configuration or kernel mapping tables might still happen as side effect of requested user operations,
1247 both privileged and unprivileged. To disable module auto-load feature please see
1248 <citerefentry><refentrytitle>sysctl.d
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1249 <constant>kernel.modules_disabled
</constant> mechanism and
1250 <filename>/proc/sys/kernel/modules_disabled
</filename> documentation. If turned on and if running in user
1251 mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
1252 <varname>User=
</varname>),
<varname>NoNewPrivileges=yes
</varname> is implied.
</para>
1254 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1258 <term><varname>ProtectControlGroups=
</varname></term>
1260 <listitem><para>Takes a boolean argument. If true, the Linux Control Groups (
<citerefentry
1261 project='man-pages'
><refentrytitle>cgroups
</refentrytitle><manvolnum>7</manvolnum></citerefentry>) hierarchies
1262 accessible through
<filename>/sys/fs/cgroup
</filename> will be made read-only to all processes of the
1263 unit. Except for container managers no services should require write access to the control groups hierarchies;
1264 it is hence recommended to turn this on for most services. For this setting the same restrictions regarding
1265 mount propagation and privileges apply as for
<varname>ReadOnlyPaths=
</varname> and related calls, see
1266 above. Defaults to off. If
<varname>ProtectControlGroups=
</varname> is set,
<varname>MountAPIVFS=yes
</varname>
1269 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1273 <term><varname>RestrictAddressFamilies=
</varname></term>
1275 <listitem><para>Restricts the set of socket address families accessible to the processes of this unit. Takes a
1276 space-separated list of address family names to whitelist, such as
<constant>AF_UNIX
</constant>,
1277 <constant>AF_INET
</constant> or
<constant>AF_INET6
</constant>. When prefixed with
<constant>~
</constant> the
1278 listed address families will be applied as blacklist, otherwise as whitelist. Note that this restricts access
1279 to the
<citerefentry
1280 project='man-pages'
><refentrytitle>socket
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call
1281 only. Sockets passed into the process by other means (for example, by using socket activation with socket
1282 units, see
<citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
1283 are unaffected. Also, sockets created with
<function>socketpair()
</function> (which creates connected AF_UNIX
1284 sockets only) are unaffected. Note that this option has no effect on
32-bit x86, s390, s390x, mips, mips-le,
1285 ppc, ppc-le, pcc64, ppc64-le and is ignored (but works correctly on other ABIs, including x86-
64). Note that on
1286 systems supporting multiple ABIs (such as x86/x86-
64) it is recommended to turn off alternative ABIs for
1287 services, so that they cannot be used to circumvent the restrictions of this option. Specifically, it is
1288 recommended to combine this option with
<varname>SystemCallArchitectures=native
</varname> or similar. If
1289 running in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN
</constant> capability
1290 (e.g. setting
<varname>User=nobody
</varname>),
<varname>NoNewPrivileges=yes
</varname> is implied. By default,
1291 no restrictions apply, all address families are accessible to processes. If assigned the empty string, any
1292 previous address familiy restriction changes are undone. This setting does not affect commands prefixed with
1293 <literal>+
</literal>.
</para>
1295 <para>Use this option to limit exposure of processes to remote access, in particular via exotic and sensitive
1296 network protocols, such as
<constant>AF_PACKET
</constant>. Note that in most cases, the local
1297 <constant>AF_UNIX
</constant> address family should be included in the configured whitelist as it is frequently
1298 used for local communication, including for
1299 <citerefentry><refentrytitle>syslog
</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1300 logging.
</para></listitem>
1304 <term><varname>RestrictNamespaces=
</varname></term>
1306 <listitem><para>Restricts access to Linux namespace functionality for the processes of this unit. For details
1307 about Linux namespaces, see
<citerefentry
1308 project='man-pages'
><refentrytitle>namespaces
</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Either
1309 takes a boolean argument, or a space-separated list of namespace type identifiers. If false (the default), no
1310 restrictions on namespace creation and switching are made. If true, access to any kind of namespacing is
1311 prohibited. Otherwise, a space-separated list of namespace type identifiers must be specified, consisting of
1312 any combination of:
<constant>cgroup
</constant>,
<constant>ipc
</constant>,
<constant>net
</constant>,
1313 <constant>mnt
</constant>,
<constant>pid
</constant>,
<constant>user
</constant> and
<constant>uts
</constant>. Any
1314 namespace type listed is made accessible to the unit's processes, access to namespace types not listed is
1315 prohibited (whitelisting). By prepending the list with a single tilde character (
<literal>~
</literal>) the
1316 effect may be inverted: only the listed namespace types will be made inaccessible, all unlisted ones are
1317 permitted (blacklisting). If the empty string is assigned, the default namespace restrictions are applied,
1318 which is equivalent to false. This option may appear more than once, in which case the namespace types are
1319 merged by
<constant>OR
</constant>, or by
<constant>AND
</constant> if the lines are prefixed with
1320 <literal>~
</literal> (see examples below). Internally, this setting limits access to the
1321 <citerefentry><refentrytitle>unshare
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
1322 <citerefentry><refentrytitle>clone
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
1323 <citerefentry><refentrytitle>setns
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls, taking
1324 the specified flags parameters into account. Note that — if this option is used — in addition to restricting
1325 creation and switching of the specified types of namespaces (or all of them, if true) access to the
1326 <function>setns()
</function> system call with a zero flags parameter is prohibited. This setting is only
1327 supported on x86, x86-
64, mips, mips-le, mips64, mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390
1328 and s390x, and enforces no restrictions on other architectures. If running in user mode, or in system mode, but
1329 without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
<varname>User=
</varname>),
1330 <varname>NoNewPrivileges=yes
</varname> is implied.
</para>
1332 <para>Example: if a unit has the following,
1333 <programlisting>RestrictNamespaces=cgroup ipc
1334 RestrictNamespaces=cgroup net
</programlisting>
1335 then
<constant>cgroup
</constant>,
<constant>ipc
</constant>, and
<constant>net
</constant> are set.
1336 If the second line is prefixed with
<literal>~
</literal>, e.g.,
1337 <programlisting>RestrictNamespaces=cgroup ipc
1338 RestrictNamespaces=~cgroup net
</programlisting>
1339 then, only
<constant>ipc
</constant> is set.
</para></listitem>
1343 <term><varname>LockPersonality=
</varname></term>
1345 <listitem><para>Takes a boolean argument. If set, locks down the
<citerefentry
1346 project='man-pages'
><refentrytitle>personality
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
1347 call so that the kernel execution domain may not be changed from the default or the personality selected with
1348 <varname>Personality=
</varname> directive. This may be useful to improve security, because odd personality
1349 emulations may be poorly tested and source of vulnerabilities. If running in user mode, or in system mode, but
1350 without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
<varname>User=
</varname>),
1351 <varname>NoNewPrivileges=yes
</varname> is implied.
</para></listitem>
1355 <term><varname>MemoryDenyWriteExecute=
</varname></term>
1357 <listitem><para>Takes a boolean argument. If set, attempts to create memory mappings that are writable and
1358 executable at the same time, or to change existing memory mappings to become executable, or mapping shared
1359 memory segments as executable are prohibited. Specifically, a system call filter is added that rejects
1360 <citerefentry><refentrytitle>mmap
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls with both
1361 <constant>PROT_EXEC
</constant> and
<constant>PROT_WRITE
</constant> set,
1362 <citerefentry><refentrytitle>mprotect
</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
1363 <citerefentry><refentrytitle>pkey_mprotect
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls
1364 with
<constant>PROT_EXEC
</constant> set and
1365 <citerefentry><refentrytitle>shmat
</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls with
1366 <constant>SHM_EXEC
</constant> set. Note that this option is incompatible with programs and libraries that
1367 generate program code dynamically at runtime, including JIT execution engines, executable stacks, and code
1368 "trampoline" feature of various C compilers. This option improves service security, as it makes harder for
1369 software exploits to change running code dynamically. However, the protection can be circumvented, if
1370 the service can write to a filesystem, which is not mounted with
<constant>noexec
</constant> (such as
1371 <filename>/dev/shm
</filename>), or it can use
<function>memfd_create()
</function>. This can be
1372 prevented by making such file systems inaccessible to the service
1373 (e.g.
<varname>InaccessiblePaths=/dev/shm
</varname>) and installing further system call filters
1374 (
<varname>SystemCallFilter=~memfd_create
</varname>). Note that this feature is fully available on
1375 x86-
64, and partially on x86. Specifically, the
<function>shmat()
</function> protection is not
1376 available on x86. Note that on systems supporting multiple ABIs (such as x86/x86-
64) it is
1377 recommended to turn off alternative ABIs for services, so that they cannot be used to circumvent the
1378 restrictions of this option. Specifically, it is recommended to combine this option with
1379 <varname>SystemCallArchitectures=native
</varname> or similar. If running in user mode, or in system
1380 mode, but without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
1381 <varname>User=
</varname>),
<varname>NoNewPrivileges=yes
</varname> is implied.
</para></listitem>
1385 <term><varname>RestrictRealtime=
</varname></term>
1387 <listitem><para>Takes a boolean argument. If set, any attempts to enable realtime scheduling in a process of
1388 the unit are refused. This restricts access to realtime task scheduling policies such as
1389 <constant>SCHED_FIFO
</constant>,
<constant>SCHED_RR
</constant> or
<constant>SCHED_DEADLINE
</constant>. See
1390 <citerefentry project='man-pages'
><refentrytitle>sched
</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1391 for details about these scheduling policies. If running in user mode, or in system mode, but without the
1392 <constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
<varname>User=
</varname>),
1393 <varname>NoNewPrivileges=yes
</varname> is implied. Realtime scheduling policies may be used to monopolize CPU
1394 time for longer periods of time, and may hence be used to lock up or otherwise trigger Denial-of-Service
1395 situations on the system. It is hence recommended to restrict access to realtime scheduling to the few programs
1396 that actually require them. Defaults to off.
</para></listitem>
1400 <term><varname>RestrictSUIDSGID=
</varname></term>
1402 <listitem><para>Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
1403 set-group-ID (SGID) bits on files or directories will be denied (for details on these bits see
1405 project='man-pages'
><refentrytitle>inode
</refentrytitle><manvolnum>7</manvolnum></citerefentry>). If
1406 running in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN
</constant>
1407 capability (e.g. setting
<varname>User=
</varname>),
<varname>NoNewPrivileges=yes
</varname> is
1408 implied. As the SUID/SGID bits are mechanisms to elevate privileges, and allows users to acquire the
1409 identity of other users, it is recommended to restrict creation of SUID/SGID files to the few
1410 programs that actually require them. Note that this restricts marking of any type of file system
1411 object with these bits, including both regular files and directories (where the SGID is a different
1412 meaning than for files, see documentation). This option is implied if
<varname>DynamicUser=
</varname>
1413 is enabled. Defaults to off.
</para></listitem>
1417 <term><varname>RemoveIPC=
</varname></term>
1419 <listitem><para>Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user and
1420 group the processes of this unit are run as are removed when the unit is stopped. This setting only has an
1421 effect if at least one of
<varname>User=
</varname>,
<varname>Group=
</varname> and
1422 <varname>DynamicUser=
</varname> are used. It has no effect on IPC objects owned by the root user. Specifically,
1423 this removes System V semaphores, as well as System V and POSIX shared memory segments and message queues. If
1424 multiple units use the same user or group the IPC objects are removed when the last of these units is
1425 stopped. This setting is implied if
<varname>DynamicUser=
</varname> is set.
</para>
1427 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1431 <term><varname>PrivateMounts=
</varname></term>
1433 <listitem><para>Takes a boolean parameter. If set, the processes of this unit will be run in their own private
1434 file system (mount) namespace with all mount propagation from the processes towards the host's main file system
1435 namespace turned off. This means any file system mount points established or removed by the unit's processes
1436 will be private to them and not be visible to the host. However, file system mount points established or
1437 removed on the host will be propagated to the unit's processes. See
<citerefentry
1438 project='man-pages'
><refentrytitle>mount_namespaces
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
1439 details on file system namespaces. Defaults to off.
</para>
1441 <para>When turned on, this executes three operations for each invoked process: a new
1442 <constant>CLONE_NEWNS
</constant> namespace is created, after which all existing mounts are remounted to
1443 <constant>MS_SLAVE
</constant> to disable propagation from the unit's processes to the host (but leaving
1444 propagation in the opposite direction in effect). Finally, the mounts are remounted again to the propagation
1445 mode configured with
<varname>MountFlags=
</varname>, see below.
</para>
1447 <para>File system namespaces are set up individually for each process forked off by the service manager. Mounts
1448 established in the namespace of the process created by
<varname>ExecStartPre=
</varname> will hence be cleaned
1449 up automatically as soon as that process exits and will not be available to subsequent processes forked off for
1450 <varname>ExecStart=
</varname> (and similar applies to the various other commands configured for
1451 units). Similarly,
<varname>JoinsNamespaceOf=
</varname> does not permit sharing kernel mount namespaces between
1452 units, it only enables sharing of the
<filename>/tmp/
</filename> and
<filename>/var/tmp/
</filename>
1455 <para>Other file system namespace unit settings —
<varname>PrivateMounts=
</varname>,
1456 <varname>PrivateTmp=
</varname>,
<varname>PrivateDevices=
</varname>,
<varname>ProtectSystem=
</varname>,
1457 <varname>ProtectHome=
</varname>,
<varname>ReadOnlyPaths=
</varname>,
<varname>InaccessiblePaths=
</varname>,
1458 <varname>ReadWritePaths=
</varname>, … — also enable file system namespacing in a fashion equivalent to this
1459 option. Hence it is primarily useful to explicitly request this behaviour if none of the other settings are
1462 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1466 <term><varname>MountFlags=
</varname></term>
1468 <listitem><para>Takes a mount propagation setting:
<option>shared
</option>,
<option>slave
</option> or
1469 <option>private
</option>, which controls whether file system mount points in the file system namespaces set up
1470 for this unit's processes will receive or propagate mounts and unmounts from other file system namespaces. See
1471 <citerefentry project='man-pages'
><refentrytitle>mount
</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1472 for details on mount propagation, and the three propagation flags in particular.
</para>
1474 <para>This setting only controls the
<emphasis>final
</emphasis> propagation setting in effect on all mount
1475 points of the file system namespace created for each process of this unit. Other file system namespacing unit
1476 settings (see the discussion in
<varname>PrivateMounts=
</varname> above) will implicitly disable mount and
1477 unmount propagation from the unit's processes towards the host by changing the propagation setting of all mount
1478 points in the unit's file system namepace to
<option>slave
</option> first. Setting this option to
1479 <option>shared
</option> does not reestablish propagation in that case.
</para>
1481 <para>If not set – but file system namespaces are enabled through another file system namespace unit setting –
1482 <option>shared
</option> mount propagation is used, but — as mentioned — as
<option>slave
</option> is applied
1483 first, propagation from the unit's processes to the host is still turned off.
</para>
1485 <para>It is not recommended to to use
<option>private
</option> mount propagation for units, as this means
1486 temporary mounts (such as removable media) of the host will stay mounted and thus indefinitely busy in forked
1487 off processes, as unmount propagation events won't be received by the file system namespace of the unit.
</para>
1489 <para>Usually, it is best to leave this setting unmodified, and use higher level file system namespacing
1490 options instead, in particular
<varname>PrivateMounts=
</varname>, see above.
</para>
1492 <xi:include href=
"system-only.xml" xpointer=
"singular"/></listitem>
1499 <title>System Call Filtering
</title>
1500 <variablelist class='unit-directives'
>
1503 <term><varname>SystemCallFilter=
</varname></term>
1505 <listitem><para>Takes a space-separated list of system call names. If this setting is used, all system calls
1506 executed by the unit processes except for the listed ones will result in immediate process termination with the
1507 <constant>SIGSYS
</constant> signal (whitelisting). If the first character of the list is
<literal>~
</literal>,
1508 the effect is inverted: only the listed system calls will result in immediate process termination
1509 (blacklisting). Blacklisted system calls and system call groups may optionally be suffixed with a colon
1510 (
<literal>:
</literal>) and
<literal>errno
</literal> error number (between
0 and
4095) or errno name such as
1511 <constant>EPERM
</constant>,
<constant>EACCES
</constant> or
<constant>EUCLEAN
</constant>. This value will be
1512 returned when a blacklisted system call is triggered, instead of terminating the processes immediately. This
1513 value takes precedence over the one given in
<varname>SystemCallErrorNumber=
</varname>. If running in user
1514 mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
1515 <varname>User=nobody
</varname>),
<varname>NoNewPrivileges=yes
</varname> is implied. This feature makes use of
1516 the Secure Computing Mode
2 interfaces of the kernel ('seccomp filtering') and is useful for enforcing a
1517 minimal sandboxing environment. Note that the
<function>execve
</function>,
<function>exit
</function>,
1518 <function>exit_group
</function>,
<function>getrlimit
</function>,
<function>rt_sigreturn
</function>,
1519 <function>sigreturn
</function> system calls and the system calls for querying time and sleeping are implicitly
1520 whitelisted and do not need to be listed explicitly. This option may be specified more than once, in which case
1521 the filter masks are merged. If the empty string is assigned, the filter is reset, all prior assignments will
1522 have no effect. This does not affect commands prefixed with
<literal>+
</literal>.
</para>
1524 <para>Note that on systems supporting multiple ABIs (such as x86/x86-
64) it is recommended to turn off
1525 alternative ABIs for services, so that they cannot be used to circumvent the restrictions of this
1526 option. Specifically, it is recommended to combine this option with
1527 <varname>SystemCallArchitectures=native
</varname> or similar.
</para>
1529 <para>Note that strict system call filters may impact execution and error handling code paths of the service
1530 invocation. Specifically, access to the
<function>execve
</function> system call is required for the execution
1531 of the service binary — if it is blocked service invocation will necessarily fail. Also, if execution of the
1532 service binary fails for some reason (for example: missing service executable), the error handling logic might
1533 require access to an additional set of system calls in order to process and log this failure correctly. It
1534 might be necessary to temporarily disable system call filters in order to simplify debugging of such
1537 <para>If you specify both types of this option (i.e. whitelisting and blacklisting), the first encountered
1538 will take precedence and will dictate the default action (termination or approval of a system call). Then the
1539 next occurrences of this option will add or delete the listed system calls from the set of the filtered system
1540 calls, depending of its type and the default action. (For example, if you have started with a whitelisting of
1541 <function>read
</function> and
<function>write
</function>, and right after it add a blacklisting of
1542 <function>write
</function>, then
<function>write
</function> will be removed from the set.)
</para>
1544 <para>As the number of possible system calls is large, predefined sets of system calls are provided. A set
1545 starts with
<literal>@
</literal> character, followed by name of the set.
1548 <title>Currently predefined system call sets
</title>
1551 <colspec colname='set'
/>
1552 <colspec colname='description'
/>
1556 <entry>Description
</entry>
1562 <entry>Asynchronous I/O (
<citerefentry project='man-pages'
><refentrytitle>io_setup
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>io_submit
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1565 <entry>@basic-io
</entry>
1566 <entry>System calls for basic I/O: reading, writing, seeking, file descriptor duplication and closing (
<citerefentry project='man-pages'
><refentrytitle>read
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>write
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1569 <entry>@chown
</entry>
1570 <entry>Changing file ownership (
<citerefentry project='man-pages'
><refentrytitle>chown
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>fchownat
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1573 <entry>@clock
</entry>
1574 <entry>System calls for changing the system clock (
<citerefentry project='man-pages'
><refentrytitle>adjtimex
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>settimeofday
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1577 <entry>@cpu-emulation
</entry>
1578 <entry>System calls for CPU emulation functionality (
<citerefentry project='man-pages'
><refentrytitle>vm86
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1581 <entry>@debug
</entry>
1582 <entry>Debugging, performance monitoring and tracing functionality (
<citerefentry project='man-pages'
><refentrytitle>ptrace
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>perf_event_open
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1585 <entry>@file-system
</entry>
1586 <entry>File system operations: opening, creating files and directories for read and write, renaming and removing them, reading file properties, or creating hard and symbolic links.
</entry>
1589 <entry>@io-event
</entry>
1590 <entry>Event loop system calls (
<citerefentry project='man-pages'
><refentrytitle>poll
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>select
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>epoll
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>eventfd
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1594 <entry>Pipes, SysV IPC, POSIX Message Queues and other IPC (
<citerefentry project='man-pages'
><refentrytitle>mq_overview
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>svipc
</refentrytitle><manvolnum>7</manvolnum></citerefentry>)
</entry>
1597 <entry>@keyring
</entry>
1598 <entry>Kernel keyring access (
<citerefentry project='man-pages'
><refentrytitle>keyctl
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1601 <entry>@memlock
</entry>
1602 <entry>Locking of memory into RAM (
<citerefentry project='man-pages'
><refentrytitle>mlock
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>mlockall
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1605 <entry>@module
</entry>
1606 <entry>Loading and unloading of kernel modules (
<citerefentry project='man-pages'
><refentrytitle>init_module
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>delete_module
</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)
</entry>
1609 <entry>@mount
</entry>
1610 <entry>Mounting and unmounting of file systems (
<citerefentry project='man-pages'
><refentrytitle>mount
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>chroot
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1613 <entry>@network-io
</entry>
1614 <entry>Socket I/O (including local AF_UNIX):
<citerefentry project='man-pages'
><refentrytitle>socket
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>unix
</refentrytitle><manvolnum>7</manvolnum></citerefentry></entry>
1617 <entry>@obsolete
</entry>
1618 <entry>Unusual, obsolete or unimplemented (
<citerefentry project='man-pages'
><refentrytitle>create_module
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>gtty
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)
</entry>
1621 <entry>@privileged
</entry>
1622 <entry>All system calls which need super-user capabilities (
<citerefentry project='man-pages'
><refentrytitle>capabilities
</refentrytitle><manvolnum>7</manvolnum></citerefentry>)
</entry>
1625 <entry>@process
</entry>
1626 <entry>Process control, execution, namespaceing operations (
<citerefentry project='man-pages'
><refentrytitle>clone
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>kill
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>namespaces
</refentrytitle><manvolnum>7</manvolnum></citerefentry>, …
</entry>
1629 <entry>@raw-io
</entry>
1630 <entry>Raw I/O port access (
<citerefentry project='man-pages'
><refentrytitle>ioperm
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>iopl
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<function>pciconfig_read()
</function>, …)
</entry>
1633 <entry>@reboot
</entry>
1634 <entry>System calls for rebooting and reboot preparation (
<citerefentry project='man-pages'
><refentrytitle>reboot
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<function>kexec()
</function>, …)
</entry>
1637 <entry>@resources
</entry>
1638 <entry>System calls for changing resource limits, memory and scheduling parameters (
<citerefentry project='man-pages'
><refentrytitle>setrlimit
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>setpriority
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)
</entry>
1641 <entry>@setuid
</entry>
1642 <entry>System calls for changing user ID and group ID credentials, (
<citerefentry project='man-pages'
><refentrytitle>setuid
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>setgid
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>setresuid
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)
</entry>
1645 <entry>@signal
</entry>
1646 <entry>System calls for manipulating and handling process signals (
<citerefentry project='man-pages'
><refentrytitle>signal
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>sigprocmask
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)
</entry>
1649 <entry>@swap
</entry>
1650 <entry>System calls for enabling/disabling swap devices (
<citerefentry project='man-pages'
><refentrytitle>swapon
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>swapoff
</refentrytitle><manvolnum>2</manvolnum></citerefentry>)
</entry>
1653 <entry>@sync
</entry>
1654 <entry>Synchronizing files and memory to disk: (
<citerefentry project='man-pages'
><refentrytitle>fsync
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>msync
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)
</entry>
1657 <entry>@system-service
</entry>
1658 <entry>A reasonable set of system calls used by common system services, excluding any special purpose calls. This is the recommended starting point for whitelisting system calls for system services, as it contains what is typically needed by system services, but excludes overly specific interfaces. For example, the following APIs are excluded:
<literal>@clock
</literal>,
<literal>@mount
</literal>,
<literal>@swap
</literal>,
<literal>@reboot
</literal>.
</entry>
1661 <entry>@timer
</entry>
1662 <entry>System calls for scheduling operations by time (
<citerefentry project='man-pages'
><refentrytitle>alarm
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry project='man-pages'
><refentrytitle>timer_create
</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)
</entry>
1668 Note, that as new system calls are added to the kernel, additional system calls might be added to the groups
1669 above. Contents of the sets may also change between systemd versions. In addition, the list of system calls
1670 depends on the kernel version and architecture for which systemd was compiled. Use
1671 <command>systemd-analyze syscall-filter
</command> to list the actual list of system calls in each
1674 <para>Generally, whitelisting system calls (rather than blacklisting) is the safer mode of operation. It is
1675 recommended to enforce system call whitelists for all long-running system services. Specifically, the
1676 following lines are a relatively safe basic choice for the majority of system services:
</para>
1678 <programlisting>[Service]
1679 SystemCallFilter=@system-service
1680 SystemCallErrorNumber=EPERM
</programlisting>
1682 <para>It is recommended to combine the file system namespacing related options with
1683 <varname>SystemCallFilter=~@mount
</varname>, in order to prohibit the unit's processes to undo the
1684 mappings. Specifically these are the options
<varname>PrivateTmp=
</varname>,
1685 <varname>PrivateDevices=
</varname>,
<varname>ProtectSystem=
</varname>,
<varname>ProtectHome=
</varname>,
1686 <varname>ProtectKernelTunables=
</varname>,
<varname>ProtectControlGroups=
</varname>,
1687 <varname>ReadOnlyPaths=
</varname>,
<varname>InaccessiblePaths=
</varname> and
1688 <varname>ReadWritePaths=
</varname>.
</para></listitem>
1692 <term><varname>SystemCallErrorNumber=
</varname></term>
1694 <listitem><para>Takes an
<literal>errno
</literal> error number (between
1 and
4095) or errno name such as
1695 <constant>EPERM
</constant>,
<constant>EACCES
</constant> or
<constant>EUCLEAN
</constant>, to return when the
1696 system call filter configured with
<varname>SystemCallFilter=
</varname> is triggered, instead of terminating
1697 the process immediately. When this setting is not used, or when the empty string is assigned, the process will
1698 be terminated immediately when the filter is triggered.
</para></listitem>
1702 <term><varname>SystemCallArchitectures=
</varname></term>
1704 <listitem><para>Takes a space-separated list of architecture identifiers to include in the system call
1705 filter. The known architecture identifiers are the same as for
<varname>ConditionArchitecture=
</varname>
1706 described in
<citerefentry><refentrytitle>systemd.unit
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1707 as well as
<constant>x32
</constant>,
<constant>mips64-n32
</constant>,
<constant>mips64-le-n32
</constant>, and
1708 the special identifier
<constant>native
</constant>. The special identifier
<constant>native
</constant>
1709 implicitly maps to the native architecture of the system (or more precisely: to the architecture the system
1710 manager is compiled for). If running in user mode, or in system mode, but without the
1711 <constant>CAP_SYS_ADMIN
</constant> capability (e.g. setting
<varname>User=nobody
</varname>),
1712 <varname>NoNewPrivileges=yes
</varname> is implied. By default, this option is set to the empty list, i.e. no
1713 system call architecture filtering is applied.
</para>
1715 <para>If this setting is used, processes of this unit will only be permitted to call native system calls, and
1716 system calls of the specified architectures. For the purposes of this option, the x32 architecture is treated
1717 as including x86-
64 system calls. However, this setting still fulfills its purpose, as explained below, on
1720 <para>System call filtering is not equally effective on all architectures. For example, on x86
1721 filtering of network socket-related calls is not possible, due to ABI limitations — a limitation that x86-
64
1722 does not have, however. On systems supporting multiple ABIs at the same time — such as x86/x86-
64 — it is hence
1723 recommended to limit the set of permitted system call architectures so that secondary ABIs may not be used to
1724 circumvent the restrictions applied to the native ABI of the system. In particular, setting
1725 <varname>SystemCallArchitectures=native
</varname> is a good choice for disabling non-native ABIs.
</para>
1727 <para>System call architectures may also be restricted system-wide via the
1728 <varname>SystemCallArchitectures=
</varname> option in the global configuration. See
1729 <citerefentry><refentrytitle>systemd-system.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
1730 details.
</para></listitem>
1737 <title>Environment
</title>
1739 <variablelist class='unit-directives'
>
1742 <term><varname>Environment=
</varname></term>
1744 <listitem><para>Sets environment variables for executed processes. Takes a space-separated list of variable
1745 assignments. This option may be specified more than once, in which case all listed variables will be set. If
1746 the same variable is set twice, the later setting will override the earlier setting. If the empty string is
1747 assigned to this option, the list of environment variables is reset, all prior assignments have no
1748 effect. Variable expansion is not performed inside the strings, however, specifier expansion is possible. The $
1749 character has no special meaning. If you need to assign a value containing spaces or the equals sign to a
1750 variable, use double quotes (
") for the assignment.</para>
1753 <programlisting>Environment="VAR1=word1 word2
" VAR2=word3 "VAR3=$word
5 6"</programlisting>
1754 gives three variables <literal>VAR1</literal>,
1755 <literal>VAR2</literal>, <literal>VAR3</literal>
1756 with the values <literal>word1 word2</literal>,
1757 <literal>word3</literal>, <literal>$word 5 6</literal>.
1762 project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
1763 about environment variables.</para>
1765 <para>Note that environment variables are not suitable for passing secrets (such as passwords, key material, …)
1766 to service processes. Environment variables set for a unit are exposed to unprivileged clients via D-Bus IPC,
1767 and generally not understood as being data that requires protection. Moreover, environment variables are
1768 propagated down the process tree, including across security boundaries (such as setuid/setgid executables), and
1769 hence might leak to processes that should not have access to the secret data.</para></listitem>
1773 <term><varname>EnvironmentFile=</varname></term>
1775 <listitem><para>Similar to <varname>Environment=</varname> but reads the environment variables from a text
1776 file. The text file should contain new-line-separated variable assignments. Empty lines, lines without an
1777 <literal>=</literal> separator, or lines starting with ; or # will be ignored, which may be used for
1778 commenting. A line ending with a backslash will be concatenated with the following one, allowing multiline
1779 variable definitions. The parser strips leading and trailing whitespace from the values of assignments, unless
1780 you use double quotes (").
</para>
1782 <para>The argument passed should be an absolute filename or wildcard expression, optionally prefixed with
1783 <literal>-
</literal>, which indicates that if the file does not exist, it will not be read and no error or
1784 warning message is logged. This option may be specified more than once in which case all specified files are
1785 read. If the empty string is assigned to this option, the list of file to read is reset, all prior assignments
1786 have no effect.
</para>
1788 <para>The files listed with this directive will be read shortly before the process is executed (more
1789 specifically, after all processes from a previous unit state terminated. This means you can generate these
1790 files in one unit state, and read it with this option in the next).
</para>
1792 <para>Settings from these files override settings made with
<varname>Environment=
</varname>. If the same
1793 variable is set twice from these files, the files will be read in the order they are specified and the later
1794 setting will override the earlier setting.
</para></listitem>
1798 <term><varname>PassEnvironment=
</varname></term>
1800 <listitem><para>Pass environment variables set for the system service manager to executed processes. Takes a
1801 space-separated list of variable names. This option may be specified more than once, in which case all listed
1802 variables will be passed. If the empty string is assigned to this option, the list of environment variables to
1803 pass is reset, all prior assignments have no effect. Variables specified that are not set for the system
1804 manager will not be passed and will be silently ignored. Note that this option is only relevant for the system
1805 service manager, as system services by default do not automatically inherit any environment variables set for
1806 the service manager itself. However, in case of the user service manager all environment variables are passed
1807 to the executed processes anyway, hence this option is without effect for the user service manager.
</para>
1809 <para>Variables set for invoked processes due to this setting are subject to being overridden by those
1810 configured with
<varname>Environment=
</varname> or
<varname>EnvironmentFile=
</varname>.
</para>
1813 <programlisting>PassEnvironment=VAR1 VAR2 VAR3
</programlisting>
1814 passes three variables
<literal>VAR1
</literal>,
1815 <literal>VAR2
</literal>,
<literal>VAR3
</literal>
1816 with the values set for those variables in PID1.
</para>
1820 project='man-pages'
><refentrytitle>environ
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
1821 about environment variables.
</para></listitem>
1825 <term><varname>UnsetEnvironment=
</varname></term>
1827 <listitem><para>Explicitly unset environment variable assignments that would normally be passed from the
1828 service manager to invoked processes of this unit. Takes a space-separated list of variable names or variable
1829 assignments. This option may be specified more than once, in which case all listed variables/assignments will
1830 be unset. If the empty string is assigned to this option, the list of environment variables/assignments to
1831 unset is reset. If a variable assignment is specified (that is: a variable name, followed by
1832 <literal>=
</literal>, followed by its value), then any environment variable matching this precise assignment is
1833 removed. If a variable name is specified (that is a variable name without any following
<literal>=
</literal> or
1834 value), then any assignment matching the variable name, regardless of its value is removed. Note that the
1835 effect of
<varname>UnsetEnvironment=
</varname> is applied as final step when the environment list passed to
1836 executed processes is compiled. That means it may undo assignments from any configuration source, including
1837 assignments made through
<varname>Environment=
</varname> or
<varname>EnvironmentFile=
</varname>, inherited from
1838 the system manager's global set of environment variables, inherited via
<varname>PassEnvironment=
</varname>,
1839 set by the service manager itself (such as
<varname>$NOTIFY_SOCKET
</varname> and such), or set by a PAM module
1840 (in case
<varname>PAMName=
</varname> is used).
</para>
1844 project='man-pages'
><refentrytitle>environ
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
1845 about environment variables.
</para></listitem>
1852 <title>Logging and Standard Input/Output
</title>
1854 <variablelist class='unit-directives'
>
1857 <term><varname>StandardInput=
</varname></term>
1859 <listitem><para>Controls where file descriptor
0 (STDIN) of the executed processes is connected to. Takes one
1860 of
<option>null
</option>,
<option>tty
</option>,
<option>tty-force
</option>,
<option>tty-fail
</option>,
1861 <option>data
</option>,
<option>file:
<replaceable>path
</replaceable></option>,
<option>socket
</option> or
1862 <option>fd:
<replaceable>name
</replaceable></option>.
</para>
1864 <para>If
<option>null
</option> is selected, standard input will be connected to
<filename>/dev/null
</filename>,
1865 i.e. all read attempts by the process will result in immediate EOF.
</para>
1867 <para>If
<option>tty
</option> is selected, standard input is connected to a TTY (as configured by
1868 <varname>TTYPath=
</varname>, see below) and the executed process becomes the controlling process of the
1869 terminal. If the terminal is already being controlled by another process, the executed process waits until the
1870 current controlling process releases the terminal.
</para>
1872 <para><option>tty-force
</option> is similar to
<option>tty
</option>, but the executed process is forcefully and
1873 immediately made the controlling process of the terminal, potentially removing previous controlling processes
1874 from the terminal.
</para>
1876 <para><option>tty-fail
</option> is similar to
<option>tty
</option>, but if the terminal already has a
1877 controlling process start-up of the executed process fails.
</para>
1879 <para>The
<option>data
</option> option may be used to configure arbitrary textual or binary data to pass via
1880 standard input to the executed process. The data to pass is configured via
1881 <varname>StandardInputText=
</varname>/
<varname>StandardInputData=
</varname> (see below). Note that the actual
1882 file descriptor type passed (memory file, regular file, UNIX pipe, …) might depend on the kernel and available
1883 privileges. In any case, the file descriptor is read-only, and when read returns the specified data followed by
1886 <para>The
<option>file:
<replaceable>path
</replaceable></option> option may be used to connect a specific file
1887 system object to standard input. An absolute path following the
<literal>:
</literal> character is expected,
1888 which may refer to a regular file, a FIFO or special file. If an
<constant>AF_UNIX
</constant> socket in the
1889 file system is specified, a stream socket is connected to it. The latter is useful for connecting standard
1890 input of processes to arbitrary system services.
</para>
1892 <para>The
<option>socket
</option> option is valid in socket-activated services only, and requires the relevant
1893 socket unit file (see
1894 <citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details)
1895 to have
<varname>Accept=yes
</varname> set, or to specify a single socket only. If this option is set, standard
1896 input will be connected to the socket the service was activated from, which is primarily useful for
1897 compatibility with daemons designed for use with the traditional
<citerefentry
1898 project='freebsd'
><refentrytitle>inetd
</refentrytitle><manvolnum>8</manvolnum></citerefentry> socket activation
1901 <para>The
<option>fd:
<replaceable>name
</replaceable></option> option connects standard input to a specific,
1902 named file descriptor provided by a socket unit. The name may be specified as part of this option, following a
1903 <literal>:
</literal> character (e.g.
<literal>fd:foobar
</literal>). If no name is specified, the name
1904 <literal>stdin
</literal> is implied (i.e.
<literal>fd
</literal> is equivalent to
<literal>fd:stdin
</literal>).
1905 At least one socket unit defining the specified name must be provided via the
<varname>Sockets=
</varname>
1906 option, and the file descriptor name may differ from the name of its containing socket unit. If multiple
1907 matches are found, the first one will be used. See
<varname>FileDescriptorName=
</varname> in
1908 <citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
1909 details about named file descriptors and their ordering.
</para>
1911 <para>This setting defaults to
<option>null
</option>.
</para>
1913 <para>Note that services which specify
<option>DefaultDependencies=no
</option> and use
1914 <varname>StandardInput=
</varname> or
<varname>StandardOutput=
</varname> with
1915 <option>tty
</option>/
<option>tty-force
</option>/
<option>tty-fail
</option>, should specify
1916 <option>After=systemd-vconsole-setup.service
</option>, to make sure that the tty intialization is
1917 finished before they start.
</para></listitem>
1921 <term><varname>StandardOutput=
</varname></term>
1923 <listitem><para>Controls where file descriptor
1 (STDOUT) of the executed processes is connected to. Takes one
1924 of
<option>inherit
</option>,
<option>null
</option>,
<option>tty
</option>,
<option>journal
</option>,
1925 <option>syslog
</option>,
<option>kmsg
</option>,
<option>journal+console
</option>,
1926 <option>syslog+console
</option>,
<option>kmsg+console
</option>,
1927 <option>file:
<replaceable>path
</replaceable></option>,
<option>append:
<replaceable>path
</replaceable></option>,
1928 <option>socket
</option> or
<option>fd:
<replaceable>name
</replaceable></option>.
</para>
1930 <para><option>inherit
</option> duplicates the file descriptor of standard input for standard output.
</para>
1932 <para><option>null
</option> connects standard output to
<filename>/dev/null
</filename>, i.e. everything written
1933 to it will be lost.
</para>
1935 <para><option>tty
</option> connects standard output to a tty (as configured via
<varname>TTYPath=
</varname>,
1936 see below). If the TTY is used for output only, the executed process will not become the controlling process of
1937 the terminal, and will not fail or wait for other processes to release the terminal.
</para>
1939 <para><option>journal
</option> connects standard output with the journal which is accessible via
1940 <citerefentry><refentrytitle>journalctl
</refentrytitle><manvolnum>1</manvolnum></citerefentry>. Note that
1941 everything that is written to syslog or kmsg (see below) is implicitly stored in the journal as well, the
1942 specific two options listed below are hence supersets of this one.
</para>
1944 <para><option>syslog
</option> connects standard output to the
<citerefentry
1945 project='man-pages'
><refentrytitle>syslog
</refentrytitle><manvolnum>3</manvolnum></citerefentry> system syslog
1946 service, in addition to the journal. Note that the journal daemon is usually configured to forward everything
1947 it receives to syslog anyway, in which case this option is no different from
<option>journal
</option>.
</para>
1949 <para><option>kmsg
</option> connects standard output with the kernel log buffer which is accessible via
1950 <citerefentry project='man-pages'
><refentrytitle>dmesg
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1951 in addition to the journal. The journal daemon might be configured to send all logs to kmsg anyway, in which
1952 case this option is no different from
<option>journal
</option>.
</para>
1954 <para><option>journal+console
</option>,
<option>syslog+console
</option> and
<option>kmsg+console
</option> work
1955 in a similar way as the three options above but copy the output to the system console as well.
</para>
1957 <para>The
<option>file:
<replaceable>path
</replaceable></option> option may be used to connect a specific file
1958 system object to standard output. The semantics are similar to the same option of
1959 <varname>StandardInput=
</varname>, see above. If
<replaceable>path
</replaceable> refers to a regular file
1960 on the filesystem, it is opened (created if it doesn't exist yet) for writing at the beginning of the file,
1961 but without truncating it.
1962 If standard input and output are directed to the same file path, it is opened only once, for reading as well
1963 as writing and duplicated. This is particularly useful when the specified path refers to an
1964 <constant>AF_UNIX
</constant> socket in the file system, as in that case only a
1965 single stream connection is created for both input and output.
</para>
1967 <para><option>append:
<replaceable>path
</replaceable></option> is similar to
<option>file:
<replaceable>path
1968 </replaceable></option> above, but it opens the file in append mode.
</para>
1970 <para><option>socket
</option> connects standard output to a socket acquired via socket activation. The
1971 semantics are similar to the same option of
<varname>StandardInput=
</varname>, see above.
</para>
1973 <para>The
<option>fd:
<replaceable>name
</replaceable></option> option connects standard output to a specific,
1974 named file descriptor provided by a socket unit. A name may be specified as part of this option, following a
1975 <literal>:
</literal> character (e.g.
<literal>fd:foobar
</literal>). If no name is specified, the name
1976 <literal>stdout
</literal> is implied (i.e.
<literal>fd
</literal> is equivalent to
1977 <literal>fd:stdout
</literal>). At least one socket unit defining the specified name must be provided via the
1978 <varname>Sockets=
</varname> option, and the file descriptor name may differ from the name of its containing
1979 socket unit. If multiple matches are found, the first one will be used. See
1980 <varname>FileDescriptorName=
</varname> in
1981 <citerefentry><refentrytitle>systemd.socket
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
1982 details about named descriptors and their ordering.
</para>
1984 <para>If the standard output (or error output, see below) of a unit is connected to the journal, syslog or the
1985 kernel log buffer, the unit will implicitly gain a dependency of type
<varname>After=
</varname> on
1986 <filename>systemd-journald.socket
</filename> (also see the
"Implicit Dependencies" section above). Also note
1987 that in this case stdout (or stderr, see below) will be an
<constant>AF_UNIX
</constant> stream socket, and not
1988 a pipe or FIFO that can be re-opened. This means when executing shell scripts the construct
<command>echo
1989 "hello" > /dev/stderr
</command> for writing text to stderr will not work. To mitigate this use the construct
1990 <command>echo
"hello" >&2</command> instead, which is mostly equivalent and avoids this pitfall.
</para>
1992 <para>This setting defaults to the value set with
<varname>DefaultStandardOutput=
</varname> in
1993 <citerefentry><refentrytitle>systemd-system.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry>, which
1994 defaults to
<option>journal
</option>. Note that setting this parameter might result in additional dependencies
1995 to be added to the unit (see above).
</para></listitem>
1999 <term><varname>StandardError=
</varname></term>
2001 <listitem><para>Controls where file descriptor
2 (STDERR) of the executed processes is connected to. The
2002 available options are identical to those of
<varname>StandardOutput=
</varname>, with some exceptions: if set to
2003 <option>inherit
</option> the file descriptor used for standard output is duplicated for standard error, while
2004 <option>fd:
<replaceable>name
</replaceable></option> will use a default file descriptor name of
2005 <literal>stderr
</literal>.
</para>
2007 <para>This setting defaults to the value set with
<varname>DefaultStandardError=
</varname> in
2008 <citerefentry><refentrytitle>systemd-system.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry>, which
2009 defaults to
<option>inherit
</option>. Note that setting this parameter might result in additional dependencies
2010 to be added to the unit (see above).
</para></listitem>
2014 <term><varname>StandardInputText=
</varname></term>
2015 <term><varname>StandardInputData=
</varname></term>
2017 <listitem><para>Configures arbitrary textual or binary data to pass via file descriptor
0 (STDIN) to the
2018 executed processes. These settings have no effect unless
<varname>StandardInput=
</varname> is set to
2019 <option>data
</option>. Use this option to embed process input data directly in the unit file.
</para>
2021 <para><varname>StandardInputText=
</varname> accepts arbitrary textual data. C-style escapes for special
2022 characters as well as the usual
<literal>%
</literal>-specifiers are resolved. Each time this setting is used
2023 the specified text is appended to the per-unit data buffer, followed by a newline character (thus every use
2024 appends a new line to the end of the buffer). Note that leading and trailing whitespace of lines configured
2025 with this option is removed. If an empty line is specified the buffer is cleared (hence, in order to insert an
2026 empty line, add an additional
<literal>\n
</literal> to the end or beginning of a line).
</para>
2028 <para><varname>StandardInputData=
</varname> accepts arbitrary binary data, encoded in
<ulink
2029 url=
"https://tools.ietf.org/html/rfc2045#section-6.8">Base64
</ulink>. No escape sequences or specifiers are
2030 resolved. Any whitespace in the encoded version is ignored during decoding.
</para>
2032 <para>Note that
<varname>StandardInputText=
</varname> and
<varname>StandardInputData=
</varname> operate on the
2033 same data buffer, and may be mixed in order to configure both binary and textual data for the same input
2034 stream. The textual or binary data is joined strictly in the order the settings appear in the unit
2035 file. Assigning an empty string to either will reset the data buffer.
</para>
2037 <para>Please keep in mind that in order to maintain readability long unit file settings may be split into
2038 multiple lines, by suffixing each line (except for the last) with a
<literal>\
</literal> character (see
2039 <citerefentry><refentrytitle>systemd.unit
</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
2040 details). This is particularly useful for large data configured with these two options. Example:
</para>
2044 StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy4KSWNrIGtpZWtl \
2045 LCBzdGF1bmUsIHd1bmRyZSBtaXIsCnVmZiBlZW1hbCBqZWh0IHNlIHVmZiBkaWUgVMO8ci4KTmFu \
2046 dSwgZGVuayBpY2ssIGljayBkZW5rIG5hbnUhCkpldHogaXNzZSB1ZmYsIGVyc2NodCB3YXIgc2Ug \
2047 enUhCkljayBqZWhlIHJhdXMgdW5kIGJsaWNrZSDigJQKdW5kIHdlciBzdGVodCBkcmF1w59lbj8g \
2049 …
</programlisting></listitem>
2053 <term><varname>LogLevelMax=
</varname></term>
2055 <listitem><para>Configures filtering by log level of log messages generated by this unit. Takes a
2056 <command>syslog
</command> log level, one of
<option>emerg
</option> (lowest log level, only highest priority
2057 messages),
<option>alert
</option>,
<option>crit
</option>,
<option>err
</option>,
<option>warning
</option>,
2058 <option>notice
</option>,
<option>info
</option>,
<option>debug
</option> (highest log level, also lowest priority
2059 messages). See
<citerefentry
2060 project='man-pages'
><refentrytitle>syslog
</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
2061 details. By default no filtering is applied (i.e. the default maximum log level is
<option>debug
</option>). Use
2062 this option to configure the logging system to drop log messages of a specific service above the specified
2063 level. For example, set
<varname>LogLevelMax=
</varname><option>info
</option> in order to turn off debug logging
2064 of a particularly chatty unit. Note that the configured level is applied to any log messages written by any
2065 of the processes belonging to this unit, sent via any supported logging protocol. The filtering is applied
2066 early in the logging pipeline, before any kind of further processing is done. Moreover, messages which pass
2067 through this filter successfully might still be dropped by filters applied at a later stage in the logging
2068 subsystem. For example,
<varname>MaxLevelStore=
</varname> configured in
2069 <citerefentry><refentrytitle>journald.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry> might
2070 prohibit messages of higher log levels to be stored on disk, even though the per-unit
2071 <varname>LogLevelMax=
</varname> permitted it to be processed.
</para></listitem>
2075 <term><varname>LogExtraFields=
</varname></term>
2077 <listitem><para>Configures additional log metadata fields to include in all log records generated by processes
2078 associated with this unit. This setting takes one or more journal field assignments in the format
2079 <literal>FIELD=VALUE
</literal> separated by whitespace. See
2080 <citerefentry><refentrytitle>systemd.journal-fields
</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
2081 details on the journal field concept. Even though the underlying journal implementation permits binary field
2082 values, this setting accepts only valid UTF-
8 values. To include space characters in a journal field value,
2083 enclose the assignment in double quotes (
"). The usual specifiers are expanded in all assignments (see
2084 below). Note that this setting is not only useful for attaching additional metadata to log records of a unit,
2085 but given that all fields and values are indexed may also be used to implement cross-unit log record
2086 matching. Assign an empty string to reset the list.</para></listitem>
2090 <term><varname>LogRateLimitIntervalSec=</varname></term>
2091 <term><varname>LogRateLimitBurst=</varname></term>
2093 <listitem><para>Configures the rate limiting that is applied to messages generated by this unit. If, in the
2094 time interval defined by <varname>LogRateLimitIntervalSec=</varname>, more messages than specified in
2095 <varname>LogRateLimitBurst=</varname> are logged by a service, all further messages within the interval are
2096 dropped until the interval is over. A message about the number of dropped messages is generated. The time
2097 specification for <varname>LogRateLimitIntervalSec=</varname> may be specified in the following units: "s
",
2098 "min
", "h
", "ms
", "us
" (see
2099 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details).
2100 The default settings are set by <varname>RateLimitIntervalSec=</varname> and <varname>RateLimitBurst=</varname>
2101 configured in <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
2106 <term><varname>SyslogIdentifier=</varname></term>
2108 <listitem><para>Sets the process name ("<command>syslog
</command> tag
") to prefix log lines sent to the logging
2109 system or the kernel log buffer with. If not set, defaults to the process name of the executed process. This
2110 option is only useful when <varname>StandardOutput=</varname> or <varname>StandardError=</varname> are set to
2111 <option>journal</option>, <option>syslog</option> or <option>kmsg</option> (or to the same settings in
2112 combination with <option>+console</option>) and only applies to log messages written to stdout or
2113 stderr.</para></listitem>
2117 <term><varname>SyslogFacility=</varname></term>
2119 <listitem><para>Sets the <command>syslog</command> facility identifier to use when logging. One of
2120 <option>kern</option>, <option>user</option>, <option>mail</option>, <option>daemon</option>,
2121 <option>auth</option>, <option>syslog</option>, <option>lpr</option>, <option>news</option>,
2122 <option>uucp</option>, <option>cron</option>, <option>authpriv</option>, <option>ftp</option>,
2123 <option>local0</option>, <option>local1</option>, <option>local2</option>, <option>local3</option>,
2124 <option>local4</option>, <option>local5</option>, <option>local6</option> or <option>local7</option>. See
2125 <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
2126 for details. This option is only useful when <varname>StandardOutput=</varname> or
2127 <varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
2128 <option>kmsg</option> (or to the same settings in combination with <option>+console</option>), and only applies
2129 to log messages written to stdout or stderr. Defaults to <option>daemon</option>.</para></listitem>
2133 <term><varname>SyslogLevel=</varname></term>
2135 <listitem><para>The default <command>syslog</command> log level to use when logging to the logging system or
2136 the kernel log buffer. One of <option>emerg</option>, <option>alert</option>, <option>crit</option>,
2137 <option>err</option>, <option>warning</option>, <option>notice</option>, <option>info</option>,
2138 <option>debug</option>. See <citerefentry
2139 project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
2140 details. This option is only useful when <varname>StandardOutput=</varname> or
2141 <varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
2142 <option>kmsg</option> (or to the same settings in combination with <option>+console</option>), and only applies
2143 to log messages written to stdout or stderr. Note that individual lines output by executed processes may be
2144 prefixed with a different log level which can be used to override the default log level specified here. The
2145 interpretation of these prefixes may be disabled with <varname>SyslogLevelPrefix=</varname>, see below. For
2146 details, see <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
2147 Defaults to <option>info</option>.</para></listitem>
2151 <term><varname>SyslogLevelPrefix=</varname></term>
2153 <listitem><para>Takes a boolean argument. If true and <varname>StandardOutput=</varname> or
2154 <varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
2155 <option>kmsg</option> (or to the same settings in combination with <option>+console</option>), log lines
2156 written by the executed process that are prefixed with a log level will be processed with this log level set
2157 but the prefix removed. If set to false, the interpretation of these prefixes is disabled and the logged lines
2158 are passed on as-is. This only applies to log messages written to stdout or stderr. For details about this
2159 prefixing see <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
2160 Defaults to true.</para></listitem>
2164 <term><varname>TTYPath=</varname></term>
2166 <listitem><para>Sets the terminal device node to use if standard input, output, or error are connected to a TTY
2167 (see above). Defaults to <filename>/dev/console</filename>.</para></listitem>
2171 <term><varname>TTYReset=</varname></term>
2173 <listitem><para>Reset the terminal device specified with <varname>TTYPath=</varname> before and after
2174 execution. Defaults to <literal>no</literal>.</para></listitem>
2178 <term><varname>TTYVHangup=</varname></term>
2180 <listitem><para>Disconnect all clients which have opened the terminal device specified with
2181 <varname>TTYPath=</varname> before and after execution. Defaults to <literal>no</literal>.</para></listitem>
2185 <term><varname>TTYVTDisallocate=</varname></term>
2187 <listitem><para>If the terminal device specified with <varname>TTYPath=</varname> is a virtual console
2188 terminal, try to deallocate the TTY before and after execution. This ensures that the screen and scrollback
2189 buffer is cleared. Defaults to <literal>no</literal>.</para></listitem>
2195 <title>System V Compatibility</title>
2196 <variablelist class='unit-directives'>
2199 <term><varname>UtmpIdentifier=</varname></term>
2201 <listitem><para>Takes a four character identifier string for an <citerefentry
2202 project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry> and wtmp entry
2203 for this service. This should only be set for services such as <command>getty</command> implementations (such
2205 project='die-net'><refentrytitle>agetty</refentrytitle><manvolnum>8</manvolnum></citerefentry>) where utmp/wtmp
2206 entries must be created and cleared before and after execution, or for services that shall be executed as if
2207 they were run by a <command>getty</command> process (see below). If the configured string is longer than four
2208 characters, it is truncated and the terminal four characters are used. This setting interprets %I style string
2209 replacements. This setting is unset by default, i.e. no utmp/wtmp entries are created or cleaned up for this
2210 service.</para></listitem>
2214 <term><varname>UtmpMode=</varname></term>
2216 <listitem><para>Takes one of <literal>init</literal>, <literal>login</literal> or <literal>user</literal>. If
2217 <varname>UtmpIdentifier=</varname> is set, controls which type of <citerefentry
2218 project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>/wtmp entries
2219 for this service are generated. This setting has no effect unless <varname>UtmpIdentifier=</varname> is set
2220 too. If <literal>init</literal> is set, only an <constant>INIT_PROCESS</constant> entry is generated and the
2221 invoked process must implement a <command>getty</command>-compatible utmp/wtmp logic. If
2222 <literal>login</literal> is set, first an <constant>INIT_PROCESS</constant> entry, followed by a
2223 <constant>LOGIN_PROCESS</constant> entry is generated. In this case, the invoked process must implement a
2225 project='die-net'><refentrytitle>login</refentrytitle><manvolnum>1</manvolnum></citerefentry>-compatible
2226 utmp/wtmp logic. If <literal>user</literal> is set, first an <constant>INIT_PROCESS</constant> entry, then a
2227 <constant>LOGIN_PROCESS</constant> entry and finally a <constant>USER_PROCESS</constant> entry is
2228 generated. In this case, the invoked process may be any process that is suitable to be run as session
2229 leader. Defaults to <literal>init</literal>.</para></listitem>
2236 <title>Environment variables in spawned processes</title>
2238 <para>Processes started by the service manager are executed with an environment variable block assembled from
2239 multiple sources. Processes started by the system service manager generally do not inherit environment variables
2240 set for the service manager itself (but this may be altered via <varname>PassEnvironment=</varname>), but processes
2241 started by the user service manager instances generally do inherit all environment variables set for the service
2242 manager itself.</para>
2244 <para>For each invoked process the list of environment variables set is compiled from the following sources:</para>
2247 <listitem><para>Variables globally configured for the service manager, using the
2248 <varname>DefaultEnvironment=</varname> setting in
2249 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, the kernel command line option <varname>systemd.setenv=</varname> (see
2250 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or via
2251 <command>systemctl set-environment</command> (see <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).</para></listitem>
2253 <listitem><para>Variables defined by the service manager itself (see the list below)</para></listitem>
2255 <listitem><para>Variables set in the service manager's own environment variable block (subject to <varname>PassEnvironment=</varname> for the system service manager)</para></listitem>
2257 <listitem><para>Variables set via <varname>Environment=</varname> in the unit file</para></listitem>
2259 <listitem><para>Variables read from files specified via <varname>EnvironmentFile=</varname> in the unit file</para></listitem>
2261 <listitem><para>Variables set by any PAM modules in case <varname>PAMName=</varname> is in effect,
2263 project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry></para></listitem>
2266 <para>If the same environment variables are set by multiple of these sources, the later source — according to the
2267 order of the list above — wins. Note that as final step all variables listed in
2268 <varname>UnsetEnvironment=</varname> are removed again from the compiled environment variable list, immediately
2269 before it is passed to the executed process.</para>
2271 <para>The following select environment variables are set or propagated by the service manager for each invoked
2274 <variablelist class='environment-variables'>
2276 <term><varname>$PATH</varname></term>
2278 <listitem><para>Colon-separated list of directories to use
2279 when launching executables. systemd uses a fixed value of
2280 <filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename>:<filename>/sbin</filename>:<filename>/bin</filename>.
2285 <term><varname>$LANG</varname></term>
2287 <listitem><para>Locale. Can be set in
2288 <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
2289 or on the kernel command line (see
2290 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
2292 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
2297 <term><varname>$USER</varname></term>
2298 <term><varname>$LOGNAME</varname></term>
2299 <term><varname>$HOME</varname></term>
2300 <term><varname>$SHELL</varname></term>
2302 <listitem><para>User name (twice), home directory, and the
2303 login shell. The variables are set for the units that have
2304 <varname>User=</varname> set, which includes user
2305 <command>systemd</command> instances. See
2306 <citerefentry project='die-net'><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
2311 <term><varname>$INVOCATION_ID</varname></term>
2313 <listitem><para>Contains a randomized, unique 128bit ID identifying each runtime cycle of the unit, formatted
2314 as 32 character hexadecimal string. A new ID is assigned each time the unit changes from an inactive state into
2315 an activating or active state, and may be used to identify this specific runtime cycle, in particular in data
2316 stored offline, such as the journal. The same ID is passed to all processes run as part of the
2317 unit.</para></listitem>
2321 <term><varname>$XDG_RUNTIME_DIR</varname></term>
2323 <listitem><para>The directory to use for runtime objects (such as IPC objects) and volatile state. Set for all
2324 services run by the user <command>systemd</command> instance, as well as any system services that use
2325 <varname>PAMName=</varname> with a PAM stack that includes <command>pam_systemd</command>. See below and
2326 <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry> for more
2327 information.</para></listitem>
2331 <term><varname>$MAINPID</varname></term>
2333 <listitem><para>The PID of the unit's main process if it is
2334 known. This is only set for control processes as invoked by
2335 <varname>ExecReload=</varname> and similar. </para></listitem>
2339 <term><varname>$MANAGERPID</varname></term>
2341 <listitem><para>The PID of the user <command>systemd</command>
2342 instance, set for processes spawned by it. </para></listitem>
2346 <term><varname>$LISTEN_FDS</varname></term>
2347 <term><varname>$LISTEN_PID</varname></term>
2348 <term><varname>$LISTEN_FDNAMES</varname></term>
2350 <listitem><para>Information about file descriptors passed to a
2351 service for socket activation. See
2352 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
2357 <term><varname>$NOTIFY_SOCKET</varname></term>
2359 <listitem><para>The socket
2360 <function>sd_notify()</function> talks to. See
2361 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
2366 <term><varname>$WATCHDOG_PID</varname></term>
2367 <term><varname>$WATCHDOG_USEC</varname></term>
2369 <listitem><para>Information about watchdog keep-alive notifications. See
2370 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
2375 <term><varname>$TERM</varname></term>
2377 <listitem><para>Terminal type, set only for units connected to
2378 a terminal (<varname>StandardInput=tty</varname>,
2379 <varname>StandardOutput=tty</varname>, or
2380 <varname>StandardError=tty</varname>). See
2381 <citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
2386 <term><varname>$JOURNAL_STREAM</varname></term>
2388 <listitem><para>If the standard output or standard error output of the executed processes are connected to the
2389 journal (for example, by setting <varname>StandardError=journal</varname>) <varname>$JOURNAL_STREAM</varname>
2390 contains the device and inode numbers of the connection file descriptor, formatted in decimal, separated by a
2391 colon (<literal>:</literal>). This permits invoked processes to safely detect whether their standard output or
2392 standard error output are connected to the journal. The device and inode numbers of the file descriptors should
2393 be compared with the values set in the environment variable to determine whether the process output is still
2394 connected to the journal. Note that it is generally not sufficient to only check whether
2395 <varname>$JOURNAL_STREAM</varname> is set at all as services might invoke external processes replacing their
2396 standard output or standard error output, without unsetting the environment variable.</para>
2398 <para>If both standard output and standard error of the executed processes are connected to the journal via a
2399 stream socket, this environment variable will contain information about the standard error stream, as that's
2400 usually the preferred destination for log data. (Note that typically the same stream is used for both standard
2401 output and standard error, hence very likely the environment variable contains device and inode information
2402 matching both stream file descriptors.)</para>
2404 <para>This environment variable is primarily useful to allow services to optionally upgrade their used log
2405 protocol to the native journal protocol (using
2406 <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> and other
2407 functions) if their standard output or standard error output is connected to the journal anyway, thus enabling
2408 delivery of structured metadata along with logged messages.</para></listitem>
2412 <term><varname>$SERVICE_RESULT</varname></term>
2414 <listitem><para>Only defined for the service unit type, this environment variable is passed to all
2415 <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname> processes, and encodes the service
2416 "result
". Currently, the following values are defined:</para>
2419 <title>Defined <varname>$SERVICE_RESULT</varname> values</title>
2421 <colspec colname='result'/>
2422 <colspec colname='meaning'/>
2425 <entry>Value</entry>
2426 <entry>Meaning</entry>
2432 <entry><literal>success</literal></entry>
2433 <entry>The service ran successfully and exited cleanly.</entry>
2436 <entry><literal>protocol</literal></entry>
2437 <entry>A protocol violation occurred: the service did not take the steps required by its unit configuration (specifically what is configured in its <varname>Type=</varname> setting).</entry>
2440 <entry><literal>timeout</literal></entry>
2441 <entry>One of the steps timed out.</entry>
2444 <entry><literal>exit-code</literal></entry>
2445 <entry>Service process exited with a non-zero exit code; see <varname>$EXIT_CODE</varname> below for the actual exit code returned.</entry>
2448 <entry><literal>signal</literal></entry>
2449 <entry>A service process was terminated abnormally by a signal, without dumping core. See <varname>$EXIT_CODE</varname> below for the actual signal causing the termination.</entry>
2452 <entry><literal>core-dump</literal></entry>
2453 <entry>A service process terminated abnormally with a signal and dumped core. See <varname>$EXIT_CODE</varname> below for the signal causing the termination.</entry>
2456 <entry><literal>watchdog</literal></entry>
2457 <entry>Watchdog keep-alive ping was enabled for the service, but the deadline was missed.</entry>
2460 <entry><literal>start-limit-hit</literal></entry>
2461 <entry>A start limit was defined for the unit and it was hit, causing the unit to fail to start. See <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s <varname>StartLimitIntervalSec=</varname> and <varname>StartLimitBurst=</varname> for details.</entry>
2464 <entry><literal>resources</literal></entry>
2465 <entry>A catch-all condition in case a system operation failed.</entry>
2471 <para>This environment variable is useful to monitor failure or successful termination of a service. Even
2472 though this variable is available in both <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname>, it
2473 is usually a better choice to place monitoring tools in the latter, as the former is only invoked for services
2474 that managed to start up correctly, and the latter covers both services that failed during their start-up and
2475 those which failed during their runtime.</para></listitem>
2479 <term><varname>$EXIT_CODE</varname></term>
2480 <term><varname>$EXIT_STATUS</varname></term>
2482 <listitem><para>Only defined for the service unit type, these environment variables are passed to all
2483 <varname>ExecStop=</varname>, <varname>ExecStopPost=</varname> processes and contain exit status/code
2484 information of the main process of the service. For the precise definition of the exit code and status, see
2485 <citerefentry><refentrytitle>wait</refentrytitle><manvolnum>2</manvolnum></citerefentry>. <varname>$EXIT_CODE</varname>
2486 is one of <literal>exited</literal>, <literal>killed</literal>,
2487 <literal>dumped</literal>. <varname>$EXIT_STATUS</varname> contains the numeric exit code formatted as string
2488 if <varname>$EXIT_CODE</varname> is <literal>exited</literal>, and the signal name in all other cases. Note
2489 that these environment variables are only set if the service manager succeeded to start and identify the main
2490 process of the service.</para>
2493 <title>Summary of possible service result variable values</title>
2495 <colspec colname='result' />
2496 <colspec colname='code' />
2497 <colspec colname='status' />
2500 <entry><varname>$SERVICE_RESULT</varname></entry>
2501 <entry><varname>$EXIT_CODE</varname></entry>
2502 <entry><varname>$EXIT_STATUS</varname></entry>
2508 <entry valign="top
"><literal>success</literal></entry>
2509 <entry valign="top
"><literal>exited</literal></entry>
2510 <entry><literal>0</literal></entry>
2513 <entry morerows="1" valign="top
"><literal>protocol</literal></entry>
2514 <entry valign="top
">not set</entry>
2515 <entry>not set</entry>
2518 <entry><literal>exited</literal></entry>
2519 <entry><literal>0</literal></entry>
2522 <entry morerows="1" valign="top
"><literal>timeout</literal></entry>
2523 <entry valign="top
"><literal>killed</literal></entry>
2524 <entry><literal>TERM</literal>, <literal>KILL</literal></entry>
2527 <entry valign="top
"><literal>exited</literal></entry>
2528 <entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
2529 >3</literal>, …, <literal>255</literal></entry>
2532 <entry valign="top
"><literal>exit-code</literal></entry>
2533 <entry valign="top
"><literal>exited</literal></entry>
2534 <entry><literal>1</literal>, <literal>2</literal>, <literal
2535 >3</literal>, …, <literal>255</literal></entry>
2538 <entry valign="top
"><literal>signal</literal></entry>
2539 <entry valign="top
"><literal>killed</literal></entry>
2540 <entry><literal>HUP</literal>, <literal>INT</literal>, <literal>KILL</literal>, …</entry>
2543 <entry valign="top
"><literal>core-dump</literal></entry>
2544 <entry valign="top
"><literal>dumped</literal></entry>
2545 <entry><literal>ABRT</literal>, <literal>SEGV</literal>, <literal>QUIT</literal>, …</entry>
2548 <entry morerows="2" valign="top
"><literal>watchdog</literal></entry>
2549 <entry><literal>dumped</literal></entry>
2550 <entry><literal>ABRT</literal></entry>
2553 <entry><literal>killed</literal></entry>
2554 <entry><literal>TERM</literal>, <literal>KILL</literal></entry>
2557 <entry><literal>exited</literal></entry>
2558 <entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
2559 >3</literal>, …, <literal>255</literal></entry>
2562 <entry><literal>start-limit-hit</literal></entry>
2563 <entry>not set</entry>
2564 <entry>not set</entry>
2567 <entry><literal>resources</literal></entry>
2568 <entry>any of the above</entry>
2569 <entry>any of the above</entry>
2572 <entry namest="results
" nameend="status
">Note: the process may be also terminated by a signal not sent by systemd. In particular the process may send an arbitrary signal to itself in a handler for any of the non-maskable signals. Nevertheless, in the <literal>timeout</literal> and <literal>watchdog</literal> rows above only the signals that systemd sends have been included. Moreover, using <varname>SuccessExitStatus=</varname> additional exit statuses may be declared to indicate clean termination, which is not reflected by this table.</entry>
2582 <term><varname>$PIDFILE</varname></term>
2584 <listitem><para>The path to the configured PID file, in case the process is forked off on behalf of a
2585 service that uses the <varname>PIDFile=</varname> setting, see
2586 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
2587 for details. Service code may use this environment variable to automatically generate a PID file at
2588 the location configured in the unit file. This field is set to an absolute path in the file
2589 system.</para></listitem>
2594 <para>For system services, when <varname>PAMName=</varname> is enabled and <command>pam_systemd</command> is part
2595 of the selected PAM stack, additional environment variables defined by systemd may be set for
2596 services. Specifically, these are <varname>$XDG_SEAT</varname>, <varname>$XDG_VTNR</varname>, see
2597 <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry> for details.</para>
2601 <title>Process exit codes</title>
2603 <para>When invoking a unit process the service manager possibly fails to apply the execution parameters configured
2604 with the settings above. In that case the already created service process will exit with a non-zero exit code
2605 before the configured command line is executed. (Or in other words, the child process possibly exits with these
2606 error codes, after having been created by the <citerefentry
2607 project='man-pages'><refentrytitle>fork</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call, but
2608 before the matching <citerefentry
2609 project='man-pages'><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call is
2610 called.) Specifically, exit codes defined by the C library, by the LSB specification and by the systemd service
2611 manager itself are used.</para>
2613 <para>The following basic service exit codes are defined by the C library.</para>
2616 <title>Basic C library exit codes</title>
2620 <entry>Exit Code</entry>
2621 <entry>Symbolic Name</entry>
2622 <entry>Description</entry>
2628 <entry><constant>EXIT_SUCCESS</constant></entry>
2629 <entry>Generic success code.</entry>
2633 <entry><constant>EXIT_FAILURE</constant></entry>
2634 <entry>Generic failure or unspecified error.</entry>
2640 <para>The following service exit codes are defined by the <ulink
2641 url="https://refspecs.linuxbase.org/LSB_5.0
.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
">LSB specification
2646 <title>LSB service exit codes</title>
2650 <entry>Exit Code</entry>
2651 <entry>Symbolic Name</entry>
2652 <entry>Description</entry>
2658 <entry><constant>EXIT_INVALIDARGUMENT</constant></entry>
2659 <entry>Invalid or excess arguments.</entry>
2663 <entry><constant>EXIT_NOTIMPLEMENTED</constant></entry>
2664 <entry>Unimplemented feature.</entry>
2668 <entry><constant>EXIT_NOPERMISSION</constant></entry>
2669 <entry>The user has insufficient privileges.</entry>
2673 <entry><constant>EXIT_NOTINSTALLED</constant></entry>
2674 <entry>The program is not installed.</entry>
2678 <entry><constant>EXIT_NOTCONFIGURED</constant></entry>
2679 <entry>The program is not configured.</entry>
2683 <entry><constant>EXIT_NOTRUNNING</constant></entry>
2684 <entry>The program is not running.</entry>
2691 The LSB specification suggests that error codes 200 and above are reserved for implementations. Some of them are
2692 used by the service manager to indicate problems during process invocation:
2695 <title>systemd-specific exit codes</title>
2699 <entry>Exit Code</entry>
2700 <entry>Symbolic Name</entry>
2701 <entry>Description</entry>
2707 <entry><constant>EXIT_CHDIR</constant></entry>
2708 <entry>Changing to the requested working directory failed. See <varname>WorkingDirectory=</varname> above.</entry>
2712 <entry><constant>EXIT_NICE</constant></entry>
2713 <entry>Failed to set up process scheduling priority (nice level). See <varname>Nice=</varname> above.</entry>
2717 <entry><constant>EXIT_FDS</constant></entry>
2718 <entry>Failed to close unwanted file descriptors, or to adjust passed file descriptors.</entry>
2722 <entry><constant>EXIT_EXEC</constant></entry>
2723 <entry>The actual process execution failed (specifically, the <citerefentry project='man-pages'><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call). Most likely this is caused by a missing or non-accessible executable file.</entry>
2727 <entry><constant>EXIT_MEMORY</constant></entry>
2728 <entry>Failed to perform an action due to memory shortage.</entry>
2732 <entry><constant>EXIT_LIMITS</constant></entry>
2733 <entry>Failed to adjust resource limits. See <varname>LimitCPU=</varname> and related settings above.</entry>
2737 <entry><constant>EXIT_OOM_ADJUST</constant></entry>
2738 <entry>Failed to adjust the OOM setting. See <varname>OOMScoreAdjust=</varname> above.</entry>
2742 <entry><constant>EXIT_SIGNAL_MASK</constant></entry>
2743 <entry>Failed to set process signal mask.</entry>
2747 <entry><constant>EXIT_STDIN</constant></entry>
2748 <entry>Failed to set up standard input. See <varname>StandardInput=</varname> above.</entry>
2752 <entry><constant>EXIT_STDOUT</constant></entry>
2753 <entry>Failed to set up standard output. See <varname>StandardOutput=</varname> above.</entry>
2757 <entry><constant>EXIT_CHROOT</constant></entry>
2758 <entry>Failed to change root directory (<citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>). See <varname>RootDirectory=</varname>/<varname>RootImage=</varname> above.</entry>
2762 <entry><constant>EXIT_IOPRIO</constant></entry>
2763 <entry>Failed to set up IO scheduling priority. See <varname>IOSchedulingClass=</varname>/<varname>IOSchedulingPriority=</varname> above.</entry>
2767 <entry><constant>EXIT_TIMERSLACK</constant></entry>
2768 <entry>Failed to set up timer slack. See <varname>TimerSlackNSec=</varname> above.</entry>
2772 <entry><constant>EXIT_SECUREBITS</constant></entry>
2773 <entry>Failed to set process secure bits. See <varname>SecureBits=</varname> above.</entry>
2777 <entry><constant>EXIT_SETSCHEDULER</constant></entry>
2778 <entry>Failed to set up CPU scheduling. See <varname>CPUSchedulingPolicy=</varname>/<varname>CPUSchedulingPriority=</varname> above.</entry>
2782 <entry><constant>EXIT_CPUAFFINITY</constant></entry>
2783 <entry>Failed to set up CPU affinity. See <varname>CPUAffinity=</varname> above.</entry>
2787 <entry><constant>EXIT_GROUP</constant></entry>
2788 <entry>Failed to determine or change group credentials. See <varname>Group=</varname>/<varname>SupplementaryGroups=</varname> above.</entry>
2792 <entry><constant>EXIT_USER</constant></entry>
2793 <entry>Failed to determine or change user credentials, or to set up user namespacing. See <varname>User=</varname>/<varname>PrivateUsers=</varname> above.</entry>
2797 <entry><constant>EXIT_CAPABILITIES</constant></entry>
2798 <entry>Failed to drop capabilities, or apply ambient capabilities. See <varname>CapabilityBoundingSet=</varname>/<varname>AmbientCapabilities=</varname> above.</entry>
2802 <entry><constant>EXIT_CGROUP</constant></entry>
2803 <entry>Setting up the service control group failed.</entry>
2807 <entry><constant>EXIT_SETSID</constant></entry>
2808 <entry>Failed to create new process session.</entry>
2812 <entry><constant>EXIT_CONFIRM</constant></entry>
2813 <entry>Execution has been cancelled by the user. See the <varname>systemd.confirm_spawn=</varname> kernel command line setting on <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details.</entry>
2817 <entry><constant>EXIT_STDERR</constant></entry>
2818 <entry>Failed to set up standard error output. See <varname>StandardError=</varname> above.</entry>
2822 <entry><constant>EXIT_PAM</constant></entry>
2823 <entry>Failed to set up PAM session. See <varname>PAMName=</varname> above.</entry>
2827 <entry><constant>EXIT_NETWORK</constant></entry>
2828 <entry>Failed to set up network namespacing. See <varname>PrivateNetwork=</varname> above.</entry>
2832 <entry><constant>EXIT_NAMESPACE</constant></entry>
2833 <entry>Failed to set up mount namespacing. See <varname>ReadOnlyPaths=</varname> and related settings above.</entry>
2837 <entry><constant>EXIT_NO_NEW_PRIVILEGES</constant></entry>
2838 <entry>Failed to disable new privileges. See <varname>NoNewPrivileges=yes</varname> above.</entry>
2842 <entry><constant>EXIT_SECCOMP</constant></entry>
2843 <entry>Failed to apply system call filters. See <varname>SystemCallFilter=</varname> and related settings above.</entry>
2847 <entry><constant>EXIT_SELINUX_CONTEXT</constant></entry>
2848 <entry>Determining or changing SELinux context failed. See <varname>SELinuxContext=</varname> above.</entry>
2852 <entry><constant>EXIT_PERSONALITY</constant></entry>
2853 <entry>Failed to set up an execution domain (personality). See <varname>Personality=</varname> above.</entry>
2857 <entry><constant>EXIT_APPARMOR_PROFILE</constant></entry>
2858 <entry>Failed to prepare changing AppArmor profile. See <varname>AppArmorProfile=</varname> above.</entry>
2862 <entry><constant>EXIT_ADDRESS_FAMILIES</constant></entry>
2863 <entry>Failed to restrict address families. See <varname>RestrictAddressFamilies=</varname> above.</entry>
2867 <entry><constant>EXIT_RUNTIME_DIRECTORY</constant></entry>
2868 <entry>Setting up runtime directory failed. See <varname>RuntimeDirectory=</varname> and related settings above.</entry>
2872 <entry><constant>EXIT_CHOWN</constant></entry>
2873 <entry>Failed to adjust socket ownership. Used for socket units only.</entry>
2877 <entry><constant>EXIT_SMACK_PROCESS_LABEL</constant></entry>
2878 <entry>Failed to set SMACK label. See <varname>SmackProcessLabel=</varname> above.</entry>
2882 <entry><constant>EXIT_KEYRING</constant></entry>
2883 <entry>Failed to set up kernel keyring.</entry>
2887 <entry><constant>EXIT_STATE_DIRECTORY</constant></entry>
2888 <entry>Failed to set up unit's state directory. See <varname>StateDirectory=</varname> above.</entry>
2892 <entry><constant>EXIT_CACHE_DIRECTORY</constant></entry>
2893 <entry>Failed to set up unit's cache directory. See <varname>CacheDirectory=</varname> above.</entry>
2897 <entry><constant>EXIT_LOGS_DIRECTORY</constant></entry>
2898 <entry>Failed to set up unit's logging directory. See <varname>LogsDirectory=</varname> above.</entry>
2902 <entry><constant>EXIT_CONFIGURATION_DIRECTORY</constant></entry>
2903 <entry>Failed to set up unit's configuration directory. See <varname>ConfigurationDirectory=</varname> above.</entry>
2909 <para>Finally, the BSD operating systems define a set of exit codes, typically defined on Linux systems too:</para>
2912 <title>BSD exit codes</title>
2916 <entry>Exit Code</entry>
2917 <entry>Symbolic Name</entry>
2918 <entry>Description</entry>
2924 <entry><constant>EX_USAGE</constant></entry>
2925 <entry>Command line usage error</entry>
2929 <entry><constant>EX_DATAERR</constant></entry>
2930 <entry>Data format error</entry>
2934 <entry><constant>EX_NOINPUT</constant></entry>
2935 <entry>Cannot open input</entry>
2939 <entry><constant>EX_NOUSER</constant></entry>
2940 <entry>Addressee unknown</entry>
2944 <entry><constant>EX_NOHOST</constant></entry>
2945 <entry>Host name unknown</entry>
2949 <entry><constant>EX_UNAVAILABLE</constant></entry>
2950 <entry>Service unavailable</entry>
2954 <entry><constant>EX_SOFTWARE</constant></entry>
2955 <entry>internal software error</entry>
2959 <entry><constant>EX_OSERR</constant></entry>
2960 <entry>System error (e.g., can't fork)</entry>
2964 <entry><constant>EX_OSFILE</constant></entry>
2965 <entry>Critical OS file missing</entry>
2969 <entry><constant>EX_CANTCREAT</constant></entry>
2970 <entry>Can't create (user) output file</entry>
2974 <entry><constant>EX_IOERR</constant></entry>
2975 <entry>Input/output error</entry>
2979 <entry><constant>EX_TEMPFAIL</constant></entry>
2980 <entry>Temporary failure; user is invited to retry</entry>
2984 <entry><constant>EX_PROTOCOL</constant></entry>
2985 <entry>Remote error in protocol</entry>
2989 <entry><constant>EX_NOPERM</constant></entry>
2990 <entry>Permission denied</entry>
2994 <entry><constant>EX_CONFIG</constant></entry>
2995 <entry>Configuration error</entry>
3003 <title>See Also</title>
3005 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
3006 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
3007 <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
3008 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
3009 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3010 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3011 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3012 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3013 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3014 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3015 <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3016 <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3017 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
3018 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
3019 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
3020 <citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
projects / systemd.git / blob