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lxc(7)                                                                                     lxc(7)

       lxc - linux containers

       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 tem‐
       plate,  it  may  work.   /usr/bin/lxc-execute  -n  foo -f /usr/share/doc/lxc/examples/lxc-
       macvlan.conf /bin/bash

       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 appli‐
       cations 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 Check‐
       point/Restart new features. The lxc is small enough to easily manage a container with sim‐
       ple command lines and complete enough to be used for other purposes.

       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  num‐
       ber 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 >= 2.6.27 shipped with the distros, will work with lxc, this  one  will
       have  less  functionalities  but enough to be interesting.  With the kernel 2.6.29, lxc is
       fully functional.  The helper script lxc-checkconfig will give you information about  your
       kernel configuration.

       Before  using the lxc, your system should be configured with the file capabilities, other‐
       wise you will need to run the lxc commands as root.

       The control group can be mounted anywhere, eg: mount -t cgroup  cgroup  /cgroup.   If  you
       want  to dedicate a specific cgroup mount point for lxc, that is to have different cgroups
       mounted at different places with different options but let lxc to use  one  location,  you
       can  bind  the mount point with the lxc name, eg: mount -t cgroup lxc /cgroup4lxc or mount
       -t cgroup -ons,cpuset,freezer,devices lxc /cgroup4lxc

       A container is an object isolating some resources of the host, for the application or sys‐
       tem 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,  espe‐
       cially  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  con‐
       tainer.  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 need
       to be isolated, the other resources are specified as being isolated but without configura‐
       tion  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  exam‐
       ple, 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

       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

         | 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 con‐
       tainer 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 to start it.  The container can be
       directly started with a configuration file as parameter.

       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  sys‐
       tem.  For  this reason, there are two different commands to run an application into a con‐

              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 /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

       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  com‐
       mand. When the tty is lost, it is possible to reconnect 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 cgroup freezer 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 into a specific container. For
       this reason, the following commands may be useful:

              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 allow to list all the contain‐
       ers 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
       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

              '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 &

              # 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 syn‐
       tax  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.

       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.

       lxc(7), lxc-create(1), lxc-destroy(1), lxc-start(1), lxc-stop(1), lxc-execute(1), lxc-con‐
       sole(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)

       Daniel Lezcano <daniel.lezcano AT free.fr>

Version 1.0.6                      Sat Apr 29 06:45:43 UTC 2017                            lxc(7)

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