pct: move "security considerations" below CT settings

[pve-docs.git] / pct.adoc

[[chapter_pct]]
ifdef::manvolnum[]
pct(1)
======
:pve-toplevel:

NAME
----

pct - Tool to manage Linux Containers (LXC) on Proxmox VE


SYNOPSIS
--------

include::pct.1-synopsis.adoc[]

DESCRIPTION
-----------
endif::manvolnum[]

ifndef::manvolnum[]
Proxmox Container Toolkit
=========================
:pve-toplevel:
endif::manvolnum[]
ifdef::wiki[]
:title: Linux Container
endif::wiki[]

Containers are a lightweight alternative to fully virtualized machines (VMs).
They use the kernel of the host system that they run on, instead of emulating a
full operating system (OS). This means that containers can access resources on
the host system directly.

The runtime costs for containers is low, usually negligible. However, there are
some drawbacks that need be considered:

* Only Linux distributions can be run in containers.It is not possible to run
  other Operating Systems like, for example, FreeBSD or Microsoft Windows
  inside a container.

* For security reasons, access to host resources needs to be restricted.
  Containers run in their own separate namespaces. Additionally some syscalls
  are not allowed within containers.

{pve} uses https://linuxcontainers.org/[Linux Containers (LXC)] as underlying
container technology. The ``Proxmox Container Toolkit'' (`pct`) simplifies the
usage and management of LXC containers.

Containers are tightly integrated with {pve}. This means that they are aware of
the cluster setup, and they can use the same network and storage resources as
virtual machines. You can also use the {pve} firewall, or manage containers
using the HA framework.

Our primary goal is to offer an environment as one would get from a VM, but
without the additional overhead. We call this ``System Containers''.

NOTE: If you want to run micro-containers, for example, 'Docker' or 'rkt', it
is best to run them inside a VM.


Technology Overview
-------------------

* LXC (https://linuxcontainers.org/)

* Integrated into {pve} graphical web user interface (GUI)

* Easy to use command line tool `pct`

* Access via {pve} REST API

* 'lxcfs' to provide containerized /proc file system

* Control groups ('cgroups') for resource isolation and limitation

* 'AppArmor' and 'seccomp' to improve security

* Modern Linux kernels

* Image based deployment (templates)

* Uses {pve} xref:chapter_storage[storage library]

* Container setup from host (network, DNS, storage, etc.)


[[pct_container_images]]
Container Images
----------------

Container images, sometimes also referred to as ``templates'' or
``appliances'', are `tar` archives which contain everything to run a container.
`pct` uses them to create a new container, for example:

----
# pct create 999 local:vztmpl/debian-10.0-standard_10.0-1_amd64.tar.gz
----

{pve} itself provides a variety of basic templates for the most common Linux
distributions. They can be downloaded using the GUI or the `pveam` (short for
{pve} Appliance Manager) command line utility.
Additionally, https://www.turnkeylinux.org/[TurnKey Linux] container templates
are also available to download.

The list of available templates is updated daily via cron. To trigger it
manually:

----
# pveam update
----

To view the list of available images run:

----
# pveam available
----

You can restrict this large list by specifying the `section` you are
interested in, for example basic `system` images:

.List available system images
----
# pveam available --section system
system          alpine-3.10-default_20190626_amd64.tar.xz
system          alpine-3.9-default_20190224_amd64.tar.xz
system          archlinux-base_20190924-1_amd64.tar.gz
system          centos-6-default_20191016_amd64.tar.xz
system          centos-7-default_20190926_amd64.tar.xz
system          centos-8-default_20191016_amd64.tar.xz
system          debian-10.0-standard_10.0-1_amd64.tar.gz
system          debian-8.0-standard_8.11-1_amd64.tar.gz
system          debian-9.0-standard_9.7-1_amd64.tar.gz
system          fedora-30-default_20190718_amd64.tar.xz
system          fedora-31-default_20191029_amd64.tar.xz
system          gentoo-current-default_20190718_amd64.tar.xz
system          opensuse-15.0-default_20180907_amd64.tar.xz
system          opensuse-15.1-default_20190719_amd64.tar.xz
system          ubuntu-16.04-standard_16.04.5-1_amd64.tar.gz
system          ubuntu-18.04-standard_18.04.1-1_amd64.tar.gz
system          ubuntu-19.04-standard_19.04-1_amd64.tar.gz
system          ubuntu-19.10-standard_19.10-1_amd64.tar.gz
----

Before you can use such a template, you need to download them into one of your
storages. You can simply use storage `local` for that purpose. For clustered
installations, it is preferred to use a shared storage so that all nodes can
access those images.

----
# pveam download local debian-10.0-standard_10.0-1_amd64.tar.gz
----

You are now ready to create containers using that image, and you can list all
downloaded images on storage `local` with:

----
# pveam list local
local:vztmpl/debian-10.0-standard_10.0-1_amd64.tar.gz  219.95MB
----

The above command shows you the full {pve} volume identifiers. They include the
storage name, and most other {pve} commands can use them. For example you can
delete that image later with:

----
# pveam remove local:vztmpl/debian-10.0-standard_10.0-1_amd64.tar.gz
----

[[pct_container_storage]]
Container Storage
-----------------

The {pve} LXC container storage model is more flexible than traditional
container storage models. A container can have multiple mount points. This
makes it possible to use the best suited storage for each application.

For example the root file system of the container can be on slow and cheap
storage while the database can be on fast and distributed storage via a second
mount point. See section <<pct_mount_points, Mount Points>> for further
details.

Any storage type supported by the {pve} storage library can be used. This means
that containers can be stored on local (for example `lvm`, `zfs` or directory),
shared external (like `iSCSI`, `NFS`) or even distributed storage systems like
Ceph. Advanced storage features like snapshots or clones can be used if the
underlying storage supports them. The `vzdump` backup tool can use snapshots to
provide consistent container backups.

Furthermore, local devices or local directories can be mounted directly using
'bind mounts'. This gives access to local resources inside a container with
practically zero overhead. Bind mounts can be used as an easy way to share data
between containers.


FUSE Mounts
~~~~~~~~~~~

WARNING: Because of existing issues in the Linux kernel's freezer subsystem the
usage of FUSE mounts inside a container is strongly advised against, as
containers need to be frozen for suspend or snapshot mode backups.

If FUSE mounts cannot be replaced by other mounting mechanisms or storage
technologies, it is possible to establish the FUSE mount on the Proxmox host
and use a bind mount point to make it accessible inside the container.


Using Quotas Inside Containers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Quotas allow to set limits inside a container for the amount of disk space that
each user can use.

NOTE: This only works on ext4 image based storage types and currently only
works with privileged containers.

Activating the `quota` option causes the following mount options to be used for
a mount point:
`usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0`

This allows quotas to be used like on any other system. You can initialize the
`/aquota.user` and `/aquota.group` files by running:

----
# quotacheck -cmug /
# quotaon /
----

Then edit the quotas using the `edquota` command. Refer to the documentation of
the distribution running inside the container for details.

NOTE: You need to run the above commands for every mount point by passing the
mount point's path instead of just `/`.


Using ACLs Inside Containers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The standard Posix **A**ccess **C**ontrol **L**ists are also available inside
containers. ACLs allow you to set more detailed file ownership than the
traditional user/group/others model.


Backup of Container mount points
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To include a mount point in backups, enable the `backup` option for it in the
container configuration. For an existing mount point `mp0`

----
mp0: guests:subvol-100-disk-1,mp=/root/files,size=8G
----

add `backup=1` to enable it.

----
mp0: guests:subvol-100-disk-1,mp=/root/files,size=8G,backup=1
----

NOTE: When creating a new mount point in the GUI, this option is enabled by
default.

To disable backups for a mount point, add `backup=0` in the way described
above, or uncheck the *Backup* checkbox on the GUI.

Replication of Containers mount points
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, additional mount points are replicated when the Root Disk is
replicated. If you want the {pve} storage replication mechanism to skip a mount
point, you can set the *Skip replication* option for that mount point.
As of {pve} 5.0, replication requires a storage of type `zfspool`. Adding a
mount point to a different type of storage when the container has replication
configured requires to have *Skip replication* enabled for that mount point.

[[pct_settings]]
Container Settings
------------------

[[pct_general]]
General Settings
~~~~~~~~~~~~~~~~

[thumbnail="screenshot/gui-create-ct-general.png"]

General settings of a container include

* the *Node* : the physical server on which the container will run
* the *CT ID*: a unique number in this {pve} installation used to identify your
  container
* *Hostname*: the hostname of the container
* *Resource Pool*: a logical group of containers and VMs
* *Password*: the root password of the container
* *SSH Public Key*: a public key for connecting to the root account over SSH
* *Unprivileged container*: this option allows to choose at creation time
  if you want to create a privileged or unprivileged container.

Unprivileged Containers
^^^^^^^^^^^^^^^^^^^^^^^

Unprivileged containers use a new kernel feature called user namespaces.
The root UID 0 inside the container is mapped to an unprivileged user outside
the container. This means that most security issues (container escape, resource
abuse, etc.) in these containers will affect a random unprivileged user, and
would be a generic kernel security bug rather than an LXC issue. The LXC team
thinks unprivileged containers are safe by design.

This is the default option when creating a new container.

NOTE: If the container uses systemd as an init system, please be aware the
systemd version running inside the container should be equal to or greater than
220.


Privileged Containers
^^^^^^^^^^^^^^^^^^^^^

Security in containers is achieved by using mandatory access control
('AppArmor'), 'seccomp' filters and namespaces. The LXC team considers this
kind of container as unsafe, and they will not consider new container escape
exploits to be security issues worthy of a CVE and quick fix.  That's why
privileged containers should only be used in trusted environments.

Although it is not recommended, AppArmor can be disabled for a container. This
brings security risks with it. Some syscalls can lead to privilege escalation
when executed within a container if the system is misconfigured or if a LXC or
Linux Kernel vulnerability exists.

To disable AppArmor for a container, add the following line to the container
configuration file located at `/etc/pve/lxc/CTID.conf`:

----
lxc.apparmor_profile = unconfined
----

WARNING: Please note that this is not recommended for production use.


[[pct_cpu]]
CPU
~~~

[thumbnail="screenshot/gui-create-ct-cpu.png"]

You can restrict the number of visible CPUs inside the container using the
`cores` option. This is implemented using the Linux 'cpuset' cgroup
(**c**ontrol *group*).
A special task inside `pvestatd` tries to distribute running containers among
available CPUs periodically.
To view the assigned CPUs run the following command:

----
# pct cpusets
 ---------------------
 102:              6 7
 105:      2 3 4 5
 108:  0 1
 ---------------------
----

Containers use the host kernel directly. All tasks inside a container are
handled by the host CPU scheduler. {pve} uses the Linux 'CFS' (**C**ompletely
**F**air **S**cheduler) scheduler by default, which has additional bandwidth
control options.

[horizontal]

`cpulimit`: :: You can use this option to further limit assigned CPU time.
Please note that this is a floating point number, so it is perfectly valid to
assign two cores to a container, but restrict overall CPU consumption to half a
core.
+
----
cores: 2
cpulimit: 0.5
----

`cpuunits`: :: This is a relative weight passed to the kernel scheduler. The
larger the number is, the more CPU time this container gets. Number is relative
to the weights of all the other running containers. The default is 1024. You
can use this setting to prioritize some containers.


[[pct_memory]]
Memory
~~~~~~

[thumbnail="screenshot/gui-create-ct-memory.png"]

Container memory is controlled using the cgroup memory controller.

[horizontal]

`memory`: :: Limit overall memory usage. This corresponds to the
`memory.limit_in_bytes` cgroup setting.

`swap`: :: Allows the container to use additional swap memory from the host
swap space. This corresponds to the `memory.memsw.limit_in_bytes` cgroup
setting, which is set to the sum of both value (`memory + swap`).


[[pct_mount_points]]
Mount Points
~~~~~~~~~~~~

[thumbnail="screenshot/gui-create-ct-root-disk.png"]

The root mount point is configured with the `rootfs` property. You can
configure up to 256 additional mount points. The corresponding options are
called `mp0` to `mp255`. They can contain the following settings:

include::pct-mountpoint-opts.adoc[]

Currently there are three types of mount points: storage backed mount points,
bind mounts, and device mounts.

.Typical container `rootfs` configuration
----
rootfs: thin1:base-100-disk-1,size=8G
----


Storage Backed Mount Points
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Storage backed mount points are managed by the {pve} storage subsystem and come
in three different flavors:

- Image based: these are raw images containing a single ext4 formatted file
  system.
- ZFS subvolumes: these are technically bind mounts, but with managed storage,
  and thus allow resizing and snapshotting.
- Directories: passing `size=0` triggers a special case where instead of a raw
  image a directory is created.

NOTE: The special option syntax `STORAGE_ID:SIZE_IN_GB` for storage backed
mount point volumes will automatically allocate a volume of the specified size
on the specified storage. For example, calling

----
pct set 100 -mp0 thin1:10,mp=/path/in/container
----

will allocate a 10GB volume on the storage `thin1` and replace the volume ID
place holder `10` with the allocated volume ID, and setup the moutpoint in the
container at `/path/in/container`


Bind Mount Points
^^^^^^^^^^^^^^^^^

Bind mounts allow you to access arbitrary directories from your Proxmox VE host
inside a container. Some potential use cases are:

- Accessing your home directory in the guest
- Accessing an USB device directory in the guest
- Accessing an NFS mount from the host in the guest

Bind mounts are considered to not be managed by the storage subsystem, so you
cannot make snapshots or deal with quotas from inside the container. With
unprivileged containers you might run into permission problems caused by the
user mapping and cannot use ACLs.

NOTE: The contents of bind mount points are not backed up when using `vzdump`.

WARNING: For security reasons, bind mounts should only be established using
source directories especially reserved for this purpose, e.g., a directory
hierarchy under `/mnt/bindmounts`. Never bind mount system directories like
`/`, `/var` or `/etc` into a container - this poses a great security risk.

NOTE: The bind mount source path must not contain any symlinks.

For example, to make the directory `/mnt/bindmounts/shared` accessible in the
container with ID `100` under the path `/shared`, use a configuration line like
`mp0: /mnt/bindmounts/shared,mp=/shared` in `/etc/pve/lxc/100.conf`.
Alternatively, use `pct set 100 -mp0 /mnt/bindmounts/shared,mp=/shared` to
achieve the same result.


Device Mount Points
^^^^^^^^^^^^^^^^^^^

Device mount points allow to mount block devices of the host directly into the
container. Similar to bind mounts, device mounts are not managed by {PVE}'s
storage subsystem, but the `quota` and `acl` options will be honored.

NOTE: Device mount points should only be used under special circumstances. In
most cases a storage backed mount point offers the same performance and a lot
more features.

NOTE: The contents of device mount points are not backed up when using
`vzdump`.


[[pct_container_network]]
Network
~~~~~~~

[thumbnail="screenshot/gui-create-ct-network.png"]

You can configure up to 10 network interfaces for a single container.
The corresponding options are called `net0` to `net9`, and they can contain the
following setting:

include::pct-network-opts.adoc[]


[[pct_startup_and_shutdown]]
Automatic Start and Shutdown of Containers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To automatically start a container when the host system boots, select the
option 'Start at boot' in the 'Options' panel of the container in the web
interface or run the following command:

----
# pct set CTID -onboot 1
----

.Start and Shutdown Order
// use the screenshot from qemu - its the same
[thumbnail="screenshot/gui-qemu-edit-start-order.png"]

If you want to fine tune the boot order of your containers, you can use the
following parameters:

* *Start/Shutdown order*: Defines the start order priority. For example, set it
  to 1 if you want the CT to be the first to be started. (We use the reverse
  startup order for shutdown, so a container with a start order of 1 would be
  the last to be shut down)
* *Startup delay*: Defines the interval between this container start and
  subsequent containers starts. For example, set it to 240 if you want to wait
  240 seconds before starting other containers.
* *Shutdown timeout*: Defines the duration in seconds {pve} should wait
  for the container to be offline after issuing a shutdown command.
  By default this value is set to 60, which means that {pve} will issue a
  shutdown request, wait 60s for the machine to be offline, and if after 60s
  the machine is still online will notify that the shutdown action failed.

Please note that containers without a Start/Shutdown order parameter will
always start after those where the parameter is set, and this parameter only
makes sense between the machines running locally on a host, and not
cluster-wide.

Hookscripts
~~~~~~~~~~~

You can add a hook script to CTs with the config property `hookscript`.

----
# pct set 100 -hookscript local:snippets/hookscript.pl
----

It will be called during various phases of the guests lifetime.  For an example
and documentation see the example script under
`/usr/share/pve-docs/examples/guest-example-hookscript.pl`.

Security Considerations
-----------------------

Containers use the kernel of the host system. This exposes an attack surface
for malicious users. In general, full virtual machines provide better
isolation. This should be considered if containers are provided to unkown or
untrusted people.

To reduce the attack surface, LXC uses many security features like AppArmor,
CGroups and kernel namespaces.

AppArmor profiles are used to restrict access to possibly dangerous actions.
Some system calls, i.e. `mount`, are prohibited from execution.

To trace AppArmor activity, use:

----
# dmesg | grep apparmor
----

Guest Operating System Configuration
------------------------------------

{pve} tries to detect the Linux distribution in the container, and modifies
some files. Here is a short list of things done at container startup:

set /etc/hostname:: to set the container name

modify /etc/hosts:: to allow lookup of the local hostname

network setup:: pass the complete network setup to the container

configure DNS:: pass information about DNS servers

adapt the init system:: for example, fix the number of spawned getty processes

set the root password:: when creating a new container

rewrite ssh_host_keys:: so that each container has unique keys

randomize crontab:: so that cron does not start at the same time on all containers

Changes made by {PVE} are enclosed by comment markers:

----
# --- BEGIN PVE ---
<data>
# --- END PVE ---
----

Those markers will be inserted at a reasonable location in the file. If such a
section already exists, it will be updated in place and will not be moved.

Modification of a file can be prevented by adding a `.pve-ignore.` file for it.
For instance, if the file `/etc/.pve-ignore.hosts` exists then the `/etc/hosts`
file will not be touched. This can be a simple empty file created via:

----
# touch /etc/.pve-ignore.hosts
----

Most modifications are OS dependent, so they differ between different
distributions and versions. You can completely disable modifications by
manually setting the `ostype` to `unmanaged`.

OS type detection is done by testing for certain files inside the
container. {pve} first checks the `/etc/os-release` file
footnote:[/etc/os-release replaces the multitude of per-distribution
release files https://manpages.debian.org/stable/systemd/os-release.5.en.html].
If that file is not present, or it does not contain a clearly recognizable
distribution identifier the following distribution specific release files are
checked.

Ubuntu:: inspect /etc/lsb-release (`DISTRIB_ID=Ubuntu`)

Debian:: test /etc/debian_version

Fedora:: test /etc/fedora-release

RedHat or CentOS:: test /etc/redhat-release

ArchLinux:: test /etc/arch-release

Alpine:: test /etc/alpine-release

Gentoo:: test /etc/gentoo-release

NOTE: Container start fails if the configured `ostype` differs from the auto
detected type.


Backup and Restore
------------------


Container Backup
~~~~~~~~~~~~~~~~

It is possible to use the `vzdump` tool for container backup. Please refer to
the `vzdump` manual page for details.


Restoring Container Backups
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Restoring container backups made with `vzdump` is possible using the `pct
restore` command. By default, `pct restore` will attempt to restore as much of
the backed up container configuration as possible. It is possible to override
the backed up configuration by manually setting container options on the
command line (see the `pct` manual page for details).

NOTE: `pvesm extractconfig` can be used to view the backed up configuration
contained in a vzdump archive.

There are two basic restore modes, only differing by their handling of mount
points:


``Simple'' Restore Mode
^^^^^^^^^^^^^^^^^^^^^^^

If neither the `rootfs` parameter nor any of the optional `mpX` parameters are
explicitly set, the mount point configuration from the backed up configuration
file is restored using the following steps:

. Extract mount points and their options from backup
. Create volumes for storage backed mount points (on storage provided with the
  `storage` parameter, or default local storage if unset)
. Extract files from backup archive
. Add bind and device mount points to restored configuration (limited to root
  user)

NOTE: Since bind and device mount points are never backed up, no files are
restored in the last step, but only the configuration options. The assumption
is that such mount points are either backed up with another mechanism (e.g.,
NFS space that is bind mounted into many containers), or not intended to be
backed up at all.

This simple mode is also used by the container restore operations in the web
interface.


``Advanced'' Restore Mode
^^^^^^^^^^^^^^^^^^^^^^^^^

By setting the `rootfs` parameter (and optionally, any combination of `mpX`
parameters), the `pct restore` command is automatically switched into an
advanced mode. This advanced mode completely ignores the `rootfs` and `mpX`
configuration options contained in the backup archive, and instead only uses
the options explicitly provided as parameters.

This mode allows flexible configuration of mount point settings at restore
time, for example:

* Set target storages, volume sizes and other options for each mount point
  individually
* Redistribute backed up files according to new mount point scheme
* Restore to device and/or bind mount points (limited to root user)


Managing Containers with `pct`
------------------------------

The ``Proxmox Container Toolkit'' (`pct`) is the command line tool to manage
{pve} containers. It enables you to create or destroy containers, as well as
control the container execution (start, stop, reboot, migrate, etc.). It can be
used to set parameters in the config file of a container, for example the
network configuration or memory limits.

CLI Usage Examples
~~~~~~~~~~~~~~~~~~

Create a container based on a Debian template (provided you have already
downloaded the template via the web interface)

----
# pct create 100 /var/lib/vz/template/cache/debian-10.0-standard_10.0-1_amd64.tar.gz
----

Start container 100

----
# pct start 100
----

Start a login session via getty

----
# pct console 100
----

Enter the LXC namespace and run a shell as root user

----
# pct enter 100
----

Display the configuration

----
# pct config 100
----

Add a network interface called `eth0`, bridged to the host bridge `vmbr0`, set
the address and gateway, while it's running

----
# pct set 100 -net0 name=eth0,bridge=vmbr0,ip=192.168.15.147/24,gw=192.168.15.1
----

Reduce the memory of the container to 512MB

----
# pct set 100 -memory 512
----


Obtaining Debugging Logs
~~~~~~~~~~~~~~~~~~~~~~~~

In case `pct start` is unable to start a specific container, it might be
helpful to collect debugging output by running `lxc-start` (replace `ID` with
the container's ID):

----
# lxc-start -n ID -F -l DEBUG -o /tmp/lxc-ID.log
----

This command will attempt to start the container in foreground mode, to stop
the container run `pct shutdown ID` or `pct stop ID` in a second terminal.

The collected debug log is written to `/tmp/lxc-ID.log`.

NOTE: If you have changed the container's configuration since the last start
attempt with `pct start`, you need to run `pct start` at least once to also
update the configuration used by `lxc-start`.

[[pct_migration]]
Migration
---------

If you have a cluster, you can migrate your Containers with

----
# pct migrate <ctid> <target>
----

This works as long as your Container is offline. If it has local volumes or
mount points defined, the migration will copy the content over the network to
the target host if the same storage is defined there.

Running containers cannot live-migrated due to techincal limitations. You can
do a restart migration, which shuts down, moves and then starts a container
again on the target node. As containers are very lightweight, this results
normally only in a downtime of some hundreds of milliseconds.

A restart migration can be done through the web interface or by using the
`--restart` flag with the `pct migrate` command.

A restart migration will shut down the Container and kill it after the
specified timeout (the default is 180 seconds). Then it will migrate the
Container like an offline migration and when finished, it starts the Container
on the target node.

[[pct_configuration]]
Configuration
-------------

The `/etc/pve/lxc/<CTID>.conf` file stores container configuration, where
`<CTID>` is the numeric ID of the given container. Like all other files stored
inside `/etc/pve/`, they get automatically replicated to all other cluster
nodes.

NOTE: CTIDs < 100 are reserved for internal purposes, and CTIDs need to be
unique cluster wide.

.Example Container Configuration
----
ostype: debian
arch: amd64
hostname: www
memory: 512
swap: 512
net0: bridge=vmbr0,hwaddr=66:64:66:64:64:36,ip=dhcp,name=eth0,type=veth
rootfs: local:107/vm-107-disk-1.raw,size=7G
----

The configuration files are simple text files. You can edit them using a normal
text editor, for example, `vi` or `nano`.
This is sometimes useful to do small corrections, but keep in mind that you
need to restart the container to apply such changes.

For that reason, it is usually better to use the `pct` command to generate and
modify those files, or do the whole thing using the GUI.
Our toolkit is smart enough to instantaneously apply most changes to running
containers. This feature is called ``hot plug'', and there is no need to restart
the container in that case.

In cases where a change cannot be hot-plugged, it will be registered as a
pending change (shown in red color in the GUI).
They will only be applied after rebooting the container.


File Format
~~~~~~~~~~~

The container configuration file uses a simple colon separated key/value
format. Each line has the following format:

-----
# this is a comment
OPTION: value
-----

Blank lines in those files are ignored, and lines starting with a `#` character
are treated as comments and are also ignored.

It is possible to add low-level, LXC style configuration directly, for example:

----
lxc.init_cmd: /sbin/my_own_init
----

or

----
lxc.init_cmd = /sbin/my_own_init
----

The settings are passed directly to the LXC low-level tools.


[[pct_snapshots]]
Snapshots
~~~~~~~~~

When you create a snapshot, `pct` stores the configuration at snapshot time
into a separate snapshot section within the same configuration file. For
example, after creating a snapshot called ``testsnapshot'', your configuration
file will look like this:

.Container configuration with snapshot
----
memory: 512
swap: 512
parent: testsnaphot
...

[testsnaphot]
memory: 512
swap: 512
snaptime: 1457170803
...
----

There are a few snapshot related properties like `parent` and `snaptime`. The
`parent` property is used to store the parent/child relationship between
snapshots. `snaptime` is the snapshot creation time stamp (Unix epoch).


[[pct_options]]
Options
~~~~~~~

include::pct.conf.5-opts.adoc[]


Locks
-----

Container migrations, snapshots and backups (`vzdump`) set a lock to prevent
incompatible concurrent actions on the affected container. Sometimes you need
to remove such a lock manually (e.g., after a power failure).

----
# pct unlock <CTID>
----

CAUTION: Only do this if you are sure the action which set the lock is no
longer running.


ifdef::manvolnum[]

Files
------

`/etc/pve/lxc/<CTID>.conf`::

Configuration file for the container '<CTID>'.


include::pve-copyright.adoc[]
endif::manvolnum[]