lxc(7) — Linux manual page

NAME | OVERVIEW | REQUIREMENTS | FUNCTIONAL SPECIFICATION | SEE ALSO | AUTHOR | COLOPHON

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 interesting.

       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.

FUNCTIONAL SPECIFICATION         top

       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

       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

   CONTAINER LIFE CYCLE
       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 |<-------       |
          ----------                |
              |                     |
               ---------------------

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

   CREATING / DESTROYING CONTAINERS
       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

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

   STARTING / STOPPING CONTAINER
       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

   CONNECT TO AN AVAILABLE TTY
       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

   FREEZE / UNFREEZE CONTAINER
       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.

   GETTING INFORMATION ABOUT CONTAINER
       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
              done

   MONITORING CONTAINER
       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 &
              LXC_WAIT_PID=$!

              # 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"

   CGROUP SETTINGS FOR CONTAINERS
       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 2021-08-27.  (At that time, the
       date of the most recent commit that was found in the repository
       was 2021-08-26.)  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
       man-pages@man7.org

Version 4.0.0-devel            2021-08-26                         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)