~ubuntu-branches/ubuntu/quantal/lxc/quantal-201206191543

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.TH "LXC" "7" "02 March 2012" "Version 0.8.0-rc1" ""

.SH NAME

lxc \- linux containers

.SH "QUICK START"

.PP

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.

\fB/usr/bin/lxc-execute -n foo -f

/usr/share/doc/lxc/examples/lxc-macvlan.conf /bin/bash\fR

.SH "OVERVIEW"

.PP

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.

.PP

The linux containers, \fBlxc\fR, aims to use these

new functionalities to provide an userspace container object

which provides full resource isolation and resource control for

an applications or a system.

.PP

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 \fBlxc\fR is small enough to easily

manage a container with simple command lines and complete enough

to be used for other purposes.

.SH "REQUIREMENTS"

.PP

The \fBlxc\fR relies on a set of functionalities

provided by the kernel which needs to be active. Depending of

the missing functionalities the \fBlxc\fR will

work with a restricted number of functionalities or will simply

fails.

.PP

The following list gives the kernel features to be enabled in

the kernel to have the full features container:

.nf

	    * 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

.fi

.PP

The kernel version >= 2.6.27 shipped with the distros, will

work with \fBlxc\fR, this one will have less

functionalities but enough to be interesting.

With the kernel 2.6.29, \fBlxc\fR is fully

functional.

The helper script \fBlxc-checkconfig\fR will give

you information about your kernel configuration.

.PP

Before using the \fBlxc\fR, your system should be

configured with the file capabilities, otherwise you will need

to run the \fBlxc\fR commands as root.

.PP

The control group can be mounted anywhere, eg:

\fBmount -t cgroup cgroup /cgroup\fR\&.

If you want to dedicate a specific cgroup mount point

for \fBlxc\fR, that is to have different cgroups

mounted at different places with different options but

let \fBlxc\fR to use one location, you can bind

the mount point with the \fBlxc\fR name, eg:

\fBmount -t cgroup lxc /cgroup4lxc\fR or

\fBmount -t cgroup -ons,cpuset,freezer,devices

lxc /cgroup4lxc\fR

.SH "FUNCTIONAL SPECIFICATION"

.PP

A container is an object isolating some resources of the host,

for the application or system running in it.

.PP

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.

.PP

How to run an application in a container ?

.PP

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 \fBsshd\fR, you

should provide a new network stack and a new hostname. If you

want to avoid conflicts with some files

eg. \fI/var/run/httpd.pid\fR, you should

remount \fI/var/run\fR 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 \fI/etc\fR and \fI/home\fR

.PP

Here is an example of directory tree

for \fBsshd\fR:

.nf

[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

.fi

and the mount points file associated with it:

.nf

	[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

.fi

.PP

How to run a system in a container ?

.PP

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:

.nf

	[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

.fi

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.

.nf

	/etc/resolv.conf /home/root/debian/rootfs/etc/resolv.conf none bind 0 0

.fi

.SS "CONTAINER LIFE CYCLE"

.PP

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.

.PP

In case of failure when the container is initialized, it will

pass through the aborting state.

.nf

   ---------

  | STOPPED |<---------------

   ---------                 |

       |                     |

     start                   |

       |                     |

       V                     |

   ----------                |

  | STARTING |--error-       |

   ----------         |      |

       |              |      |

       V              V      |

   ---------    ----------   |

  | RUNNING |  | ABORTING |  |

   ---------    ----------   |

       |              |      |

  no process          |      |

       |              |      |

       V              |      |

   ----------         |      |

  | STOPPING |<-------       |

   ----------                |

       |                     |

        ---------------------

.fi

.SS "CONFIGURATION"

.PP

The container is configured through a configuration

file, the format of the configuration file is described in 

\fB\fIlxc.conf\fB\fR(5)

.SS "CREATING / DESTROYING CONTAINER  (PERSISTENT CONTAINER)"

.PP

A persistent container object can be

created via the \fBlxc-create\fR

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 \fBlxc-destroy\fR command will

destroy the container object.

.nf

	  lxc-create -n foo

	  lxc-destroy -n foo

.fi

.SS "VOLATILE CONTAINER"

.PP

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.

.SS "STARTING / STOPPING CONTAINER"

.PP

When the container has been created, it is ready to run an

application / system.

This is the purpose of the \fBlxc-execute\fR and

\fBlxc-start\fR 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 \fBlxc-stop\fR command can

be used to kill the still running application.

.PP

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:

.nf

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

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

.fi

.PP

\fBlxc-execute\fR command will run the

specified command into the container via an intermediate

process, \fBlxc-init\fR\&.

This lxc-init after launching  the specified command,

will wait for its end and all other reparented processes.

(that allows to support daemons in the container).

In other words, in the

container, \fBlxc-init\fR has the pid 1 and the

first process of the application has the pid 2.

.PP

\fBlxc-start\fR command will run directly the specified

command into the container.

The pid of the first process is 1. If no command is

specified \fBlxc-start\fR will

run \fI/sbin/init\fR\&.

.PP

To summarize, \fBlxc-execute\fR is for running

an application and \fBlxc-start\fR is better suited for

running a system.

.PP

If the application is no longer responding, is inaccessible or is

not able to finish by itself, a

wild \fBlxc-stop\fR command will kill all the

processes in the container without pity.

.nf

	  lxc-stop -n foo

.fi

.SS "CONNECT TO AN AVAILABLE TTY"

.PP

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.

.nf

	  lxc-console -n foo -t 3

.fi

.SS "FREEZE / UNFREEZE CONTAINER"

.PP

Sometime, it is useful to stop all the processes belonging to

a container, eg. for job scheduling. The commands:

.nf

	  lxc-freeze -n foo

.fi

will put all the processes in an uninteruptible state and 

.nf

	  lxc-unfreeze -n foo

.fi

will resume them.

.PP

This feature is enabled if the cgroup freezer is enabled in the

kernel.

.SS "GETTING INFORMATION ABOUT CONTAINER"

.PP

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 usefull:

.nf

	  lxc-ls

	  lxc-ps --name foo

	  lxc-info -n foo

.fi

.PP

\fBlxc-ls\fR lists the containers of the

system. The command is a script built on top

of \fBls\fR, so it accepts the options of the ls

commands, eg:

.nf

	  lxc-ls -C1

.fi

will display the containers list in one column or:

.nf

	  lxc-ls -l

.fi

will display the containers list and their permissions.

.PP

\fBlxc-ps\fR will display the pids for a specific

container. Like \fBlxc-ls\fR, \fBlxc-ps\fR

is built on top of \fBps\fR and accepts the same

options, eg:

.nf

lxc-ps --name foo --forest

.fi

will display the processes hierarchy for the processes

belonging the 'foo' container.

.nf

lxc-ps --lxc

.fi

will display all the containers and their processes.

.PP

\fBlxc-info\fR gives informations for a specific

container, at present time, only the state of the container is

displayed.

.PP

Here is an example on how the combination of these commands

allow to list all the containers and retrieve their state.

.nf

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

	    lxc-info -n $i

	  done

.fi

And displaying all the pids of all the containers:

.nf

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

	    lxc-ps --name $i --forest

	  done

.fi

.PP

\fBlxc-netstat\fR display network information for

a specific container. This command is built on top of

the \fBnetstat\fR command and will accept its

options

.PP

The following command will display the socket informations for

the container 'foo'.

.nf

	  lxc-netstat -n foo -tano

.fi

.SS "MONITORING CONTAINER"

.PP

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.

.PP

\fBlxc-monitor\fR command will monitor one or

several containers. The parameter of this command accept a

regular expression for example:

.nf

	  lxc-monitor -n "foo|bar"

.fi

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

.nf

	  lxc-monitor -n ".*"

.fi

will monitor all the containers.

.PP

For a container 'foo' starting, doing some work and exiting,

the output will be in the form:

.nf

\&'foo' changed state to [STARTING]

\&'foo' changed state to [RUNNING]

\&'foo' changed state to [STOPPING]

\&'foo' changed state to [STOPPED]

.fi

.PP

\fBlxc-wait\fR 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.

.nf

	  # 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"

.fi

.SS "SETTING THE CONTROL GROUP FOR CONTAINER"

.PP

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.

.PP

\fBlxc-cgroup\fR 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.

.PP

.nf

	  lxc-cgroup -n foo cpuset.cpus

.fi

will display the content of this subsystem.

.nf

	  lxc-cgroup -n foo cpu.shares 512

.fi

will set the subsystem to the specified value.

.SH "BUGS"

.PP

The \fBlxc\fR is still in development, so the

command syntax and the API can change. The version 1.0.0 will be

the frozen version.

.SH "SEE ALSO"

.PP

\fBlxc\fR(1),

\fBlxc-create\fR(1),

\fBlxc-destroy\fR(1),

\fBlxc-start\fR(1),

\fBlxc-stop\fR(1),

\fBlxc-execute\fR(1),

\fBlxc-kill\fR(1),

\fBlxc-console\fR(1),

\fBlxc-monitor\fR(1),

\fBlxc-wait\fR(1),

\fBlxc-cgroup\fR(1),

\fBlxc-ls\fR(1),

\fBlxc-ps\fR(1),

\fBlxc-info\fR(1),

\fBlxc-freeze\fR(1),

\fBlxc-unfreeze\fR(1),

\fBlxc-attach\fR(1),

\fBlxc.conf\fR(5)

.SH "AUTHOR"

.PP

Daniel Lezcano <daniel.lezcano@free.fr>