|
NAME | QUICK START | OVERVIEW | REQUIREMENTS | FUNCTIONAL SPECIFICATION | BUGS | SEE ALSO | AUTHOR | COLOPHON |
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 template, it may work.
/usr/local/bin/lxc-execute -n foo -f
/usr/local/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 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.
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.
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.
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-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)
Daniel Lezcano <daniel.lezcano@free.fr>
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
2017-07-05. 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 2017-07-05 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-usernsexec(1), lxc-wait(1), lxc.container.conf(5), lxc.system.conf(5), lxc(7)