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1 | <!-- |
2 | ||
3 | lxc: linux Container library | |
4 | ||
5 | (C) Copyright IBM Corp. 2007, 2008 | |
6 | ||
7 | Authors: | |
9afe19d6 | 8 | Daniel Lezcano <daniel.lezcano at free.fr> |
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9 | |
10 | This library is free software; you can redistribute it and/or | |
11 | modify it under the terms of the GNU Lesser General Public | |
12 | License as published by the Free Software Foundation; either | |
13 | version 2.1 of the License, or (at your option) any later version. | |
14 | ||
15 | This library is distributed in the hope that it will be useful, | |
16 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public | |
21 | License along with this library; if not, write to the Free Software | |
250b1eec | 22 | Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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23 | |
24 | --> | |
25 | ||
7f951458 | 26 | <!DOCTYPE refentry PUBLIC @docdtd@ [ |
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27 | |
28 | <!ENTITY commonoptions SYSTEM "@builddir@/common_options.sgml"> | |
29 | <!ENTITY seealso SYSTEM "@builddir@/see_also.sgml"> | |
30 | ]> | |
31 | ||
32 | <refentry> | |
33 | ||
34 | <docinfo><date>@LXC_GENERATE_DATE@</date></docinfo> | |
35 | ||
36 | <refmeta> | |
37 | <refentrytitle>lxc-attach</refentrytitle> | |
38 | <manvolnum>1</manvolnum> | |
39 | </refmeta> | |
40 | ||
41 | <refnamediv> | |
42 | <refname>lxc-attach</refname> | |
43 | ||
44 | <refpurpose> | |
45 | start a process inside a running container. | |
46 | </refpurpose> | |
47 | </refnamediv> | |
48 | ||
49 | <refsynopsisdiv> | |
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50 | <cmdsynopsis> |
51 | <command>lxc-attach</command> | |
52 | <arg choice="req">-n <replaceable>name</replaceable></arg> | |
53 | <arg choice="opt">-a <replaceable>arch</replaceable></arg> | |
54 | <arg choice="opt">-e</arg> | |
e13eeea2 | 55 | <arg choice="opt">-s <replaceable>namespaces</replaceable></arg> |
7a0b0b56 | 56 | <arg choice="opt">-R</arg> |
799f96fd CS |
57 | <arg choice="opt">--keep-env</arg> |
58 | <arg choice="opt">--clear-env</arg> | |
b4578c5b DE |
59 | <arg choice="opt">-- <replaceable>command</replaceable></arg> |
60 | </cmdsynopsis> | |
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61 | </refsynopsisdiv> |
62 | ||
63 | <refsect1> | |
64 | <title>Description</title> | |
65 | ||
66 | <para> | |
67 | <command>lxc-attach</command> runs the specified | |
68 | <replaceable>command</replaceable> inside the container | |
69 | specified by <replaceable>name</replaceable>. The container | |
70 | has to be running already. | |
71 | </para> | |
72 | <para> | |
73 | If no <replaceable>command</replaceable> is specified, the | |
74 | current default shell of the user running | |
75 | <command>lxc-attach</command> will be looked up inside the | |
76 | container and executed. This will fail if no such user exists | |
77 | inside the container or the container does not have a working | |
78 | nsswitch mechanism. | |
79 | </para> | |
80 | ||
81 | </refsect1> | |
82 | ||
83 | <refsect1> | |
84 | ||
85 | <title>Options</title> | |
86 | ||
87 | <variablelist> | |
88 | ||
89 | <varlistentry> | |
90 | <term> | |
91 | <option>-a, --arch <replaceable>arch</replaceable></option> | |
92 | </term> | |
93 | <listitem> | |
94 | <para> | |
95 | Specify the architecture which the kernel should appear to be | |
96 | running as to the command executed. This option will accept the | |
97 | same settings as the <option>lxc.arch</option> option in | |
98 | container configuration files, see | |
99 | <citerefentry> | |
100 | <refentrytitle><filename>lxc.conf</filename></refentrytitle> | |
101 | <manvolnum>5</manvolnum> | |
102 | </citerefentry>. By default, the current archictecture of the | |
103 | running container will be used. | |
104 | </para> | |
105 | </listitem> | |
106 | </varlistentry> | |
107 | ||
108 | <varlistentry> | |
109 | <term> | |
110 | <option>-e, --elevated-privileges</option> | |
111 | </term> | |
112 | <listitem> | |
113 | <para> | |
114 | Do not drop privileges when running | |
115 | <replaceable>command</replaceable> inside the container. If | |
116 | this option is specified, the new process will | |
117 | <emphasis>not</emphasis> be added to the container's cgroup(s) | |
118 | and it will not drop its capabilities before executing. | |
119 | </para> | |
120 | <para> | |
121 | <emphasis>Warning:</emphasis> This may leak privileges into the | |
122 | container if the command starts subprocesses that remain active | |
123 | after the main process that was attached is terminated. The | |
124 | (re-)starting of daemons inside the container is problematic, | |
125 | especially if the daemon starts a lot of subprocesses such as | |
126 | <command>cron</command> or <command>sshd</command>. | |
127 | <emphasis>Use with great care.</emphasis> | |
128 | </para> | |
129 | </listitem> | |
130 | </varlistentry> | |
131 | ||
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132 | <varlistentry> |
133 | <term> | |
134 | <option>-s, --namespaces <replaceable>namespaces</replaceable></option> | |
135 | </term> | |
136 | <listitem> | |
137 | <para> | |
037ba55c | 138 | Specify the namespaces to attach to, as a pipe-separated list, |
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139 | e.g. <replaceable>NETWORK|IPC</replaceable>. Allowed values are |
140 | <replaceable>MOUNT</replaceable>, <replaceable>PID</replaceable>, | |
141 | <replaceable>UTSNAME</replaceable>, <replaceable>IPC</replaceable>, | |
142 | <replaceable>USER </replaceable> and | |
143 | <replaceable>NETWORK</replaceable>. This allows one to change | |
144 | the context of the process to e.g. the network namespace of the | |
145 | container while retaining the other namespaces as those of the | |
146 | host. | |
147 | </para> | |
148 | <para> | |
149 | <emphasis>Important:</emphasis> This option implies | |
150 | <option>-e</option>. | |
151 | </para> | |
152 | </listitem> | |
153 | </varlistentry> | |
154 | ||
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155 | <varlistentry> |
156 | <term> | |
157 | <option>-R, --remount-sys-proc</option> | |
158 | </term> | |
159 | <listitem> | |
160 | <para> | |
161 | When using <option>-s</option> and the mount namespace is not | |
162 | included, this flag will cause <command>lxc-attach</command> | |
163 | to remount <replaceable>/proc</replaceable> and | |
164 | <replaceable>/sys</replaceable> to reflect the current other | |
165 | namespace contexts. | |
166 | </para> | |
167 | <para> | |
168 | Please see the <emphasis>Notes</emphasis> section for more | |
169 | details. | |
170 | </para> | |
171 | <para> | |
172 | This option will be ignored if one tries to attach to the | |
173 | mount namespace anyway. | |
174 | </para> | |
175 | </listitem> | |
176 | </varlistentry> | |
177 | ||
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178 | <varlistentry> |
179 | <term> | |
180 | <option>--keep-env</option> | |
181 | </term> | |
182 | <listitem> | |
183 | <para> | |
184 | Keep the current environment for attached programs. This is | |
185 | the current default behaviour (as of version 0.9), but is | |
186 | is likely to change in the future, since this may leak | |
187 | undesirable information into the container. If you rely on | |
188 | the environment being available for the attached program, | |
189 | please use this option to be future-proof. In addition to | |
190 | current environment variables, container=lxc will be set. | |
191 | </para> | |
192 | </listitem> | |
193 | </varlistentry> | |
194 | ||
195 | <varlistentry> | |
196 | <term> | |
197 | <option>--clear-env</option> | |
198 | </term> | |
199 | <listitem> | |
200 | <para> | |
201 | Clear the environment before attaching, so no undesired | |
202 | environment variables leak into the container. The variable | |
203 | container=lxc will be the only environment with which the | |
204 | attached program starts. | |
205 | </para> | |
206 | </listitem> | |
207 | </varlistentry> | |
208 | ||
7a0b0b56 | 209 | </variablelist> |
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210 | |
211 | </refsect1> | |
212 | ||
213 | &commonoptions; | |
214 | ||
215 | <refsect1> | |
216 | <title>Examples</title> | |
217 | <para> | |
218 | To spawn a new shell running inside an existing container, use | |
219 | <programlisting> | |
220 | lxc-attach -n container | |
221 | </programlisting> | |
222 | </para> | |
223 | <para> | |
224 | To restart the cron service of a running Debian container, use | |
225 | <programlisting> | |
226 | lxc-attach -n container -- /etc/init.d/cron restart | |
227 | </programlisting> | |
228 | </para> | |
229 | <para> | |
230 | To deactivate the network link eth1 of a running container that | |
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231 | does not have the NET_ADMIN capability, use either the |
232 | <option>-e</option> option to use increased capabilities, | |
233 | assuming the <command>ip</command> tool is installed: | |
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234 | <programlisting> |
235 | lxc-attach -n container -e -- /sbin/ip link delete eth1 | |
236 | </programlisting> | |
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237 | Or, alternatively, use the <option>-s</option> to use the |
238 | tools installed on the host outside the container: | |
239 | <programlisting> | |
240 | lxc-attach -n container -s NETWORK -- /sbin/ip link delete eth1 | |
241 | </programlisting> | |
49ee6cdc | 242 | </para> |
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243 | </refsect1> |
244 | ||
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245 | <refsect1> |
246 | <title>Compatibility</title> | |
247 | <para> | |
248 | Attaching completely (including the pid and mount namespaces) to a | |
249 | container requires a patched kernel, please see the lxc website for | |
250 | details. <command>lxc-attach</command> will fail in that case if | |
251 | used with an unpatched kernel. | |
252 | </para> | |
253 | <para> | |
254 | Nevertheless, it will succeed on an unpatched kernel of version 3.0 | |
255 | or higher if the <option>-s</option> option is used to restrict the | |
aa8d013e | 256 | namespaces that the process is to be attached to to one or more of |
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257 | <replaceable>NETWORK</replaceable>, <replaceable>IPC</replaceable> |
258 | and <replaceable>UTSNAME</replaceable>. | |
259 | </para> | |
260 | <para> | |
261 | Attaching to user namespaces is currently completely unsupported | |
262 | by the kernel. <command>lxc-attach</command> should however be able | |
263 | to do this once once future kernel versions implement this. | |
264 | </para> | |
265 | </refsect1> | |
266 | ||
267 | <refsect1> | |
268 | <title>Notes</title> | |
269 | <para> | |
270 | The Linux <replaceable>/proc</replaceable> and | |
271 | <replaceable>/sys</replaceable> filesystems contain information | |
272 | about some quantities that are affected by namespaces, such as | |
273 | the directories named after process ids in | |
274 | <replaceable>/proc</replaceable> or the network interface infromation | |
275 | in <replaceable>/sys/class/net</replaceable>. The namespace of the | |
276 | process mounting the pseudo-filesystems determines what information | |
277 | is shown, <emphasis>not</emphasis> the namespace of the process | |
278 | accessing <replaceable>/proc</replaceable> or | |
279 | <replaceable>/sys</replaceable>. | |
280 | </para> | |
281 | <para> | |
282 | If one uses the <option>-s</option> option to only attach to | |
283 | the pid namespace of a container, but not its mount namespace | |
284 | (which will contain the <replaceable>/proc</replaceable> of the | |
285 | container and not the host), the contents of <option>/proc</option> | |
286 | will reflect that of the host and not the container. Analogously, | |
287 | the same issue occurs when reading the contents of | |
288 | <replaceable>/sys/class/net</replaceable> and attaching to just | |
289 | the network namespace. | |
290 | </para> | |
291 | <para> | |
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292 | To work around this problem, the <option>-R</option> flag provides |
293 | the option to remount <replaceable>/proc</replaceable> and | |
294 | <replaceable>/sys</replaceable> in order for them to reflect the | |
295 | network/pid namespace context of the attached process. In order | |
296 | not to interfere with the host's actual filesystem, the mount | |
297 | namespace will be unshared (like <command>lxc-unshare</command> | |
298 | does) before this is done, esentially giving the process a new | |
299 | mount namespace, which is identical to the hosts's mount namespace | |
300 | except for the <replaceable>/proc</replaceable> and | |
301 | <replaceable>/sys</replaceable> filesystems. | |
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302 | </para> |
303 | </refsect1> | |
304 | ||
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305 | <refsect1> |
306 | <title>Security</title> | |
307 | <para> | |
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308 | The <option>-e</option> and <option>-s</option> options should |
309 | be used with care, as it may break the isolation of the containers | |
310 | if used improperly. | |
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311 | </para> |
312 | </refsect1> | |
313 | ||
314 | &seealso; | |
315 | ||
316 | <refsect1> | |
317 | <title>Author</title> | |
318 | <para>Daniel Lezcano <email>daniel.lezcano@free.fr</email></para> | |
319 | </refsect1> | |
320 | ||
321 | </refentry> | |
322 | ||
323 | <!-- Keep this comment at the end of the file | |
324 | Local variables: | |
325 | mode: sgml | |
326 | sgml-omittag:t | |
327 | sgml-shorttag:t | |
328 | sgml-minimize-attributes:nil | |
329 | sgml-always-quote-attributes:t | |
330 | sgml-indent-step:2 | |
331 | sgml-indent-data:t | |
332 | sgml-parent-document:nil | |
333 | sgml-default-dtd-file:nil | |
334 | sgml-exposed-tags:nil | |
335 | sgml-local-catalogs:nil | |
336 | sgml-local-ecat-files:nil | |
337 | End: | |
338 | --> |