NAME | QUICK START | OVERVIEW | REQUIREMENTS | FUNCTIONAL SPECIFICATION | BUGS | SEE ALSO | AUTHOR | COLOPHON

LXC(7)                                                                LXC(7)

NAME         top

       lxc - linux containers

QUICK START         top

       You are in a hurry, and you don't want to read this man page. Ok,
       without warranty, here are the commands to launch a shell inside a
       container with a predefined configuration template, it may work.
       /usr/local/bin/lxc-execute -n foo -f
       /usr/local/share/doc/lxc/examples/lxc-macvlan.conf /bin/bash

OVERVIEW         top

       The container technology is actively being pushed into the mainstream
       linux kernel. It provides the resource management through the control
       groups aka process containers and resource isolation through the
       namespaces.

       The linux containers, 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 system.

       The first objective of this project is to make the life easier for
       the kernel developers involved in the containers project and
       especially to continue working on the Checkpoint/Restart new
       features. The 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 lxc relies on a set of functionalities provided by the kernel
       which needs to be active. Depending of the missing functionalities
       the lxc will work with a restricted number of functionalities or will
       simply fail.

       The following list gives the kernel features to be enabled in the
       kernel to have the full features container:

                * General setup
                  * Control Group support
                    -> Namespace cgroup subsystem
                    -> Freezer cgroup subsystem
                    -> Cpuset support
                    -> Simple CPU accounting cgroup subsystem
                    -> Resource counters
                      -> Memory resource controllers for Control Groups
                  * Group CPU scheduler
                    -> Basis for grouping tasks (Control Groups)
                  * Namespaces support
                    -> UTS namespace
                    -> IPC namespace
                    -> User namespace
                    -> Pid namespace
                    -> Network namespace
                * Device Drivers
                  * Character devices
                    -> Support multiple instances of devpts
                  * Network device support
                    -> MAC-VLAN support
                    -> Virtual ethernet pair device
                * Networking
                  * Networking options
                    -> 802.1d Ethernet Bridging
                * Security options
                  -> File POSIX Capabilities

       The kernel version >= 2.6.32 shipped with the distros, will work with
       lxc, this one will have less functionalities but enough to be
       interesting.  The helper script lxc-checkconfig will give you
       information about your kernel configuration.

       The control group can be mounted anywhere, eg: mount -t cgroup cgroup
       /cgroup.  It is however recommended to use cgmanager, cgroup-lite or
       systemd to mount the cgroup hierarchy under /sys/fs/cgroup.

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 parameter of the starting 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 the
       pids, the sysv ipc and the 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 need 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

       More information can be added to the container to facilitate the
       configuration. For example, make accessible from the container the
       resolv.conf file belonging to the host.

            /etc/resolv.conf /home/root/debian/rootfs/etc/resolv.conf 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 CONTAINER  (PERSISTENT CONTAINER)
       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 to start 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 is
       ended, the container will be stopped also, but if needed the lxc-stop
       command can be used to kill the still running application.

       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]

       lxc-execute command will run the specified command into the 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 the pid 1 and the first process of the
       application has the pid 2.

       lxc-start command will run directly the specified command into 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

   CONNECT TO AN AVAILABLE TTY
       If the container is configured with the ttys, it is possible to
       access it through them. It is up to the container to provide a set of
       available tty to be used by the following command. When the tty is
       lost, it is possible to reconnect 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 cgroup freezer 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 into a specific container. For this reason, the following
       commands may be useful:

              lxc-ls
              lxc-info -n foo

       lxc-ls lists the containers of the system.

       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 accept 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 he went to
       the background.

              # 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"

   SETTING THE CONTROL GROUP FOR CONTAINER
       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.

BUGS         top

       The lxc is still in development, so the command syntax and the API
       can change. The version 1.0.0 will be the frozen version.

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>

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
       2017-03-13.  If you discover any rendering problems in this HTML ver‐
       sion 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 man‐
       ual page), send a mail to man-pages@man7.org

Version 2.0.0                    2017-03-13                           LXC(7)