pct: improve configuration section
[pve-docs.git] / pct.adoc
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1ifdef::manvolnum[]
2PVE({manvolnum})
3================
38fd0958 4include::attributes.txt[]
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5
6NAME
7----
8
9pct - Tool to manage Linux Containers (LXC) on Proxmox VE
10
11
12SYNOPSYS
13--------
14
15include::pct.1-synopsis.adoc[]
16
17DESCRIPTION
18-----------
19endif::manvolnum[]
20
21ifndef::manvolnum[]
22Proxmox Container Toolkit
23=========================
38fd0958 24include::attributes.txt[]
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25endif::manvolnum[]
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27
28Containers are a lightweight alternative to fully virtualized
29VMs. Instead of emulating a complete Operating System (OS), containers
30simply use the OS of the host they run on. This implies that all
31containers use the same kernel, and that they can access resources
32from the host directly.
33
34This is great because containers do not waste CPU power nor memory due
35to kernel emulation. Container run-time costs are close to zero and
36usually negligible. But there are also some drawbacks you need to
37consider:
38
39* You can only run Linux based OS inside containers, i.e. it is not
40 possible to run Free BSD or MS Windows inside.
41
42* For security reasons, access to host resources need to be
43 restricted. This is done with AppArmor, SecComp filters and other
44 kernel feature. Be prepared that some syscalls are not allowed
45 inside containers.
46
47{pve} uses https://linuxcontainers.org/[LXC] as underlying container
48technology. We consider LXC as low-level library, which provides
49countless options. It would be to difficult to use those tools
50directly. Instead, we provide a small wrapper called `pct`, the
51"Proxmox Container Toolkit".
52
53The toolkit it tightly coupled with {pve}. That means that it is aware
54of the cluster setup, and it can use the same network and storage
55resources as fully virtualized VMs. You can even use the {pve}
56firewall, or manage containers using the HA framework.
57
58Our primary goal is to offer an environment as one would get from a
59VM, but without the additional overhead. We call this "System
60Containers".
61
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62NOTE: If you want to run micro-containers (with docker, rct, ...), it
63is best to run them inside a VM.
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64
65
66Security Considerations
67-----------------------
68
69Containers use the same kernel as the host, so there is a big attack
70surface for malicious users. You should consider this fact if you
71provide containers to totally untrusted people. In general, fully
72virtualized VM provides better isolation.
73
74The good news is that LXC uses many kernel security features like
75AppArmor, CGroups and PID and user namespaces, which makes containers
76usage quite secure. We distinguish two types of containers:
77
78Privileged containers
79~~~~~~~~~~~~~~~~~~~~~
80
81Security is done by dropping capabilities, using mandatory access
82control (AppArmor), SecComp filters and namespaces. The LXC team
83considers this kind of container as unsafe, and they will not consider
84new container escape exploits to be security issues worthy of a CVE
85and quick fix. So you should use this kind of containers only inside a
86trusted environment, or when no untrusted task is running as root in
87the container.
88
89Unprivileged containers
90~~~~~~~~~~~~~~~~~~~~~~~
91
92This kind of containers use a new kernel feature, called user
93namespaces. The root uid 0 inside the container is mapped to an
94unprivileged user outside the container. This means that most security
95issues (container escape, resource abuse, ...) in those containers
96will affect a random unprivileged user, and so would be a generic
97kernel security bug rather than a LXC issue. LXC people think
98unprivileged containers are safe by design.
99
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100
101Configuration
102-------------
103
104The '/etc/pve/lxc/<CTID>.conf' files stores container configuration,
105where '<CTID>' is the numeric ID of the given container. Note that
106CTIDs < 100 are reserved for internal purposes. CTIDs need to be
107unique - cluster wide. Files are stored inside '/etc/pve/', so they get
108automatically replicated to all other cluster nodes.
109
110Those configuration files are simple text files, and you can edit them
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111using a normal text editor ('vi', 'nano', ...). This is sometimes
112useful to do small corrections, but keep in mind that you need to
113restart the container to apply such changes.
114
115For that reason, it is usually better to use the 'pct' command to
116generate and modify those files, or do the whole thing using the GUI.
117Our toolkit is smart enough to instantaneously apply most changes to
118running containers (hot plug).
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119
120
121File Format
122~~~~~~~~~~~
123
124Container configuration files use a simple colon separated key/value
125format. Each line has the following format:
126
127 # this is a comment
128 OPTION: value
129
130Blank lines in those files are ignored, and lines starting with a '#'
131character are treated as comments and are also ignored.
132
133It is possible to add low-level, LXC style configuration directly, for
134example:
135
136 lxc.init_cmd: /sbin/my_own_init
137
138or
139
140 lxc.init_cmd = /sbin/my_own_init
141
142Those settings are directly passed to the LXC low-level tools.
143
144
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145Container Storage
146-----------------
147
148Traditional containers use a very simple storage model, only allowing
149a single mount point, the root file system. This was further
150restricted to specific file system types like 'ext4' and 'nfs'.
151Additional mounts are often done by user provided scripts. This turend
152out to be complex and error prone, so we trie to avoid that now.
153
154Our new LXC based container model is more flexible regarding
155storage. First, you can have more than a single mount point. This
156allows you to choose a suitable storage for each application. For
157example, you can use a relatively slow (and thus cheap) storage for
158the container root file system. Then you can use a second mount point
159to mount a very fast, distributed storage for your database
160application.
161
162The second big improvement is that you can use any storage type
163supported by the {pve} storage library. That means that you can store
164your containers on local 'lvmthin' or 'zfs', shared 'iSCSI' storage,
165or even on distributed storage systems like 'ceph'. And it enables us
166to use advanced storage features like snapshots and clones. 'vzdump'
167can also use the snapshots feature to provide consistent container
168backups.
169
170Last but not least, you can also mount local devices directly, or
171mount local directories using bind mounts. That way you can access
172local storage inside containers with zero overhead. Such bind mounts
173also provides an easy way to share data between different containers.
174
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175
176Managing Containers with 'pct'
177------------------------------
178
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179'pct' is the tool to manage Linux Containers on {pve}. You can create
180and destroy containers, and control execution (start, stop, migrate,
181...). You can use pct to set parameters in the associated config file,
182like network configuration or memory.
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183
184CLI Usage Examples
185------------------
186
187Create a container based on a Debian template (provided you downloaded
188the template via the webgui before)
189
190 pct create 100 /var/lib/vz/template/cache/debian-8.0-standard_8.0-1_amd64.tar.gz
191
192Start container 100
193
194 pct start 100
195
196Start a login session via getty
197
198 pct console 100
199
200Enter the LXC namespace and run a shell as root user
201
202 pct enter 100
203
204Display the configuration
205
206 pct config 100
207
208Add a network interface called eth0, bridged to the host bridge vmbr0,
209set the address and gateway, while it's running
210
211 pct set 100 -net0 name=eth0,bridge=vmbr0,ip=192.168.15.147/24,gw=192.168.15.1
212
213Reduce the memory of the container to 512MB
214
215 pct set -memory 512 100
216
217Files
218------
219
9dfe82f1 220'/etc/pve/lxc/<CTID>.conf'::
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9dfe82f1 222Configuration file for the container '<CTID>'.
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223
224
225Container Advantages
226--------------------
227
228- Simple, and fully integrated into {pve}. Setup looks similar to a normal
229 VM setup.
230
231 * Storage (ZFS, LVM, NFS, Ceph, ...)
232
233 * Network
234
235 * Authentification
236
237 * Cluster
238
239- Fast: minimal overhead, as fast as bare metal
240
241- High density (perfect for idle workloads)
242
243- REST API
244
245- Direct hardware access
246
247
248Technology Overview
249-------------------
250
251- Integrated into {pve} graphical user interface (GUI)
252
253- LXC (https://linuxcontainers.org/)
254
255- cgmanager for cgroup management
256
257- lxcfs to provive containerized /proc file system
258
259- apparmor
260
261- CRIU: for live migration (planned)
262
263- We use latest available kernels (4.2.X)
264
265- image based deployment (templates)
266
267- Container setup from host (Network, DNS, Storage, ...)
268
269
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271include::pve-copyright.adoc[]
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