lxc(7) — Linux manual page


LXC(7)                                                                LXC(7)

NAME         top

       lxc - linux containers

OVERVIEW         top

       The container technology is actively being pushed into the mainstream
       Linux kernel. It provides resource management through control groups
       and resource isolation via namespaces.

       lxc, aims to use these new functionalities to provide a userspace
       container object which provides full resource isolation and resource
       control for an applications or a full system.

       lxc is small enough to easily manage a container with simple command
       lines and complete enough to be used for other purposes.

REQUIREMENTS         top

       The kernel version >= 3.10 shipped with the distros, will work with
       lxc, this one will have less functionalities but enough to be

       lxc relies on a set of functionalities provided by the kernel. The
       helper script lxc-checkconfig will give you information about your
       kernel configuration, required, and missing features.


       A container is an object isolating some resources of the host, for
       the application or system running in it.

       The application / system will be launched inside a container
       specified by a configuration that is either initially created or
       passed as a parameter of the commands.

       How to run an application in a container

       Before running an application, you should know what are the resources
       you want to isolate. The default configuration is to isolate PIDs,
       the sysv IPC and mount points. If you want to run a simple shell
       inside a container, a basic configuration is needed, especially if
       you want to share the rootfs. If you want to run an application like
       sshd, you should provide a new network stack and a new hostname. If
       you want to avoid conflicts with some files eg.  /var/run/httpd.pid,
       you should remount /var/run with an empty directory. If you want to
       avoid the conflicts in all the cases, you can specify a rootfs for
       the container. The rootfs can be a directory tree, previously bind
       mounted with the initial rootfs, so you can still use your distro but
       with your own /etc and /home

       Here is an example of directory tree for sshd:

       [root@lxc sshd]$ tree -d rootfs

       |-- bin
       |-- dev
       |   |-- pts
       |   `-- shm
       |       `-- network
       |-- etc
       |   `-- ssh
       |-- lib
       |-- proc
       |-- root
       |-- sbin
       |-- sys
       |-- usr
       `-- var
           |-- empty
           |   `-- sshd
           |-- lib
           |   `-- empty
           |       `-- sshd
           `-- run
               `-- sshd

       and the mount points file associated with it:

            [root@lxc sshd]$ cat fstab

            /lib /home/root/sshd/rootfs/lib none ro,bind 0 0
            /bin /home/root/sshd/rootfs/bin none ro,bind 0 0
            /usr /home/root/sshd/rootfs/usr none ro,bind 0 0
            /sbin /home/root/sshd/rootfs/sbin none ro,bind 0 0

       How to run a system in a container

       Running a system inside a container is paradoxically easier than
       running an application. Why? Because you don't have to care about the
       resources to be isolated, everything needs to be isolated, the other
       resources are specified as being isolated but without configuration
       because the container will set them up. eg. the ipv4 address will be
       setup by the system container init scripts. Here is an example of the
       mount points file:

            [root@lxc debian]$ cat fstab

            /dev /home/root/debian/rootfs/dev none bind 0 0
            /dev/pts /home/root/debian/rootfs/dev/pts  none bind 0 0

       When the container is created, it contains the configuration
       information. When a process is launched, the container will be
       starting and running. When the last process running inside the
       container exits, the container is stopped.

       In case of failure when the container is initialized, it will pass
       through the aborting state.

         | STOPPED |<---------------
          ---------                 |
              |                     |
            start                   |
              |                     |
              V                     |
          ----------                |
         | STARTING |--error-       |
          ----------         |      |
              |              |      |
              V              V      |
          ---------    ----------   |
         | RUNNING |  | ABORTING |  |
          ---------    ----------   |
              |              |      |
         no process          |      |
              |              |      |
              V              |      |
          ----------         |      |
         | STOPPING |<-------       |
          ----------                |
              |                     |

       The container is configured through a configuration file, the format
       of the configuration file is described in lxc.conf(5)

       A persistent container object can be created via the lxc-create
       command. It takes a container name as parameter and optional
       configuration file and template. The name is used by the different
       commands to refer to this container. The lxc-destroy command will
       destroy the container object.

              lxc-create -n foo
              lxc-destroy -n foo

       It is not mandatory to create a container object before starting it.
       The container can be directly started with a configuration file as

       When the container has been created, it is ready to run an
       application / system. This is the purpose of the lxc-execute and lxc-
       start commands. If the container was not created before starting the
       application, the container will use the configuration file passed as
       parameter to the command, and if there is no such parameter either,
       then it will use a default isolation. If the application ended, the
       container will be stopped, but if needed the lxc-stop command can be
       used to stop the container.

       Running an application inside a container is not exactly the same
       thing as running a system. For this reason, there are two different
       commands to run an application into a container:

              lxc-execute -n foo [-f config] /bin/bash
              lxc-start -n foo [-f config] [/bin/bash]

       The lxc-execute command will run the specified command into a
       container via an intermediate process, lxc-init.  This lxc-init after
       launching the specified command, will wait for its end and all other
       reparented processes. (to support daemons in the container). In other
       words, in the container, lxc-init has PID 1 and the first process of
       the application has PID 2.

       The lxc-start command will directly run the specified command in the
       container. The PID of the first process is 1. If no command is
       specified lxc-start will run the command defined in lxc.init.cmd or
       if not set, /sbin/init.

       To summarize, lxc-execute is for running an application and lxc-start
       is better suited for running a system.

       If the application is no longer responding, is inaccessible or is not
       able to finish by itself, a wild lxc-stop command will kill all the
       processes in the container without pity.

              lxc-stop -n foo -k

       If the container is configured with ttys, it is possible to access it
       through them. It is up to the container to provide a set of available
       ttys to be used by the following command. When the tty is lost, it is
       possible to reconnect to it without login again.

              lxc-console -n foo -t 3

       Sometime, it is useful to stop all the processes belonging to a
       container, eg. for job scheduling. The commands:

              lxc-freeze -n foo

       will put all the processes in an uninteruptible state and

              lxc-unfreeze -n foo

       will resume them.

       This feature is enabled if the freezer cgroup v1 controller is
       enabled in the kernel.

       When there are a lot of containers, it is hard to follow what has
       been created or destroyed, what is running or what are the PIDs
       running in a specific container. For this reason, the following
       commands may be useful:

              lxc-ls -f
              lxc-info -n foo

       lxc-ls lists containers.

       lxc-info gives information for a specific container.

       Here is an example on how the combination of these commands allows
       one to list all the containers and retrieve their state.

              for i in $(lxc-ls -1); do
                lxc-info -n $i

       It is sometime useful to track the states of a container, for example
       to monitor it or just to wait for a specific state in a script.

       lxc-monitor command will monitor one or several containers. The
       parameter of this command accepts a regular expression for example:

              lxc-monitor -n "foo|bar"

       will monitor the states of containers named 'foo' and 'bar', and:

              lxc-monitor -n ".*"

       will monitor all the containers.

       For a container 'foo' starting, doing some work and exiting, the
       output will be in the form:

       'foo' changed state to [STARTING]
       'foo' changed state to [RUNNING]
       'foo' changed state to [STOPPING]
       'foo' changed state to [STOPPED]

       lxc-wait command will wait for a specific state change and exit. This
       is useful for scripting to synchronize the launch of a container or
       the end. The parameter is an ORed combination of different states.
       The following example shows how to wait for a container if it
       successfully started as a daemon.

              # launch lxc-wait in background
              lxc-wait -n foo -s STOPPED &

              # this command goes in background
              lxc-execute -n foo mydaemon &

              # block until the lxc-wait exits
              # and lxc-wait exits when the container
              # is STOPPED
              wait $LXC_WAIT_PID
              echo "'foo' is finished"

       The container is tied with the control groups, when a container is
       started a control group is created and associated with it. The
       control group properties can be read and modified when the container
       is running by using the lxc-cgroup command.

       lxc-cgroup command is used to set or get a control group subsystem
       which is associated with a container. The subsystem name is handled
       by the user, the command won't do any syntax checking on the
       subsystem name, if the subsystem name does not exists, the command
       will fail.

              lxc-cgroup -n foo cpuset.cpus

       will display the content of this subsystem.

              lxc-cgroup -n foo cpu.shares 512

       will set the subsystem to the specified value.

SEE ALSO         top

       lxc(7), lxc-create(1), lxc-copy(1), lxc-destroy(1), lxc-start(1),
       lxc-stop(1), lxc-execute(1), lxc-console(1), lxc-monitor(1),
       lxc-wait(1), lxc-cgroup(1), lxc-ls(1), lxc-info(1), lxc-freeze(1),
       lxc-unfreeze(1), lxc-attach(1), lxc.conf(5)

AUTHOR         top

       Daniel Lezcano <daniel.lezcano@free.fr>

       Christian Brauner <christian.brauner@ubuntu.com>

       Serge Hallyn <serge@hallyn.com>

       Stéphane Graber <stgraber@ubuntu.com>

COLOPHON         top

       This page is part of the lxc (Linux containers) project.  Information
       about the project can be found at ⟨http://linuxcontainers.org/⟩.  If
       you have a bug report for this manual page, send it to
       lxc-devel@lists.linuxcontainers.org.  This page was obtained from the
       project's upstream Git repository ⟨git://github.com/lxc/lxc⟩ on
       2020-11-01.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-10-28.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Version 4.0.0-devel              2020-11-01                           LXC(7)

Pages that refer to this page: lxc-attach(1)lxc-autostart(1)lxc-cgroup(1)lxc-checkconfig(1)lxc-checkpoint(1)lxc-config(1)lxc-console(1)lxc-copy(1)lxc-create(1)lxc-destroy(1)lxc-device(1)lxc-execute(1)lxc-freeze(1)lxc-info(1)lxc-ls(1)lxc-monitor(1)lxc-snapshot(1)lxc-start(1)lxc-stop(1)lxc-top(1)lxc-unfreeze(1)lxc-unshare(1)lxc-update-config(1)lxc-usernsexec(1)lxc-wait(1)lxc.container.conf(5)lxc.system.conf(5)lxc(7)