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lxc.conf

NAME

lxc.conf - linux container configuration file

DESCRIPTION

The linux containers (lxc) are always created before being used. This creation defines a set of system resources to be virtualized / isolated when a process is using the container. By default, the pids, sysv ipc and mount points are virtualized and isolated. The other system resources are shared across containers, until they are explicitly defined in the configuration file. For example, if there is no network configuration, the network will be shared between the creator of the container and the container itself, but if the network is specified, a new network stack is created for the container and the container can no longer use the network of its ancestor.

The configuration file defines the different system resources to be assigned for the container. At present, the utsname, the network, the mount points, the root file system and the control groups are supported.

Each option in the configuration file has the form key = value fitting in one line. The '#' caracter means the line is a comment.

HOSTNAME

The utsname section defines the hostname to be set for the container. That means the container can set its own hostname without changing the one from the system. That makes the hostname private for the container.

lxc.utsname

specify the hostname for the container

NETWORK

The network section defines how the network is virtualized in the container. The network virtualization acts at the layer two, so in order to use the network, a few information should be specified to define the network interfaces to be used by the container. Several virtual interfaces can be assigned and used in a container either if the system has only one physical network interface.

lxc.network.type

specify what kind of network virtualization to be used for the container. Each time a lxc.network.type field is found a new round of network configuration begins. By this way several network virtualization can be specified for the same container, as well as assigning several network interfaces for one container. The different virtualization types can be:

empty: a new network stack is created for the container, but it will not contain any network interface.

veth: a new network stack is created, a peer network device is created with one side assigned to the container and the other side attached to a bridge specified by the lxc.network.link. The bridge has to be setup before on the system, lxc won't handle configuration outside of the container.

macvlan: a new network stack is created, a macvlan interface is linked with the interface specified by the lxc.network.link and assigned to the container.

phys: a new network stack is created and the interface specified by the lxc.network.link is assigned to the container.

lxc.network.flags

specify an action to do for the network.

up: activates the interface.

lxc.network.link

specify the interface to be used for real network traffic.

lxc.network.name

the interface name is dynamically allocated, but if an other name is needed because the configuration files being used by the container use a generic name, eg. eth0, this option will rename the interface in the container.

lxc.network.hwaddr

the interface mac address is dynamically allocated by default to the virtual interface, but in some case, this is needed to resolve a mac address conflict or to have always the same link-locak ipv6 address.

lxc.network.ipv4

specify the ipv4 address to assign to the virtualized interface. Several lines specify several ipv4 addresses. The address is in format x.y.z.t/m, eg. 192.168.1.123/24.

lxc.network.ipv6

specify the ipv6 address to assign to the virtualized interface. Several lines specify several ipv6 addresses. The address is in format x::y/m, eg. 2003:db8:1:0:214:1234:fe0b:3596/64

NEW PSEUDO TTY INSTANCE (DEVPTS)

For stricter isolation the container can have its own private instance of the pseudo tty.

lxc.pts

Specify the container should have a new pseudo tty instance making this private to it. The value specified is ignored for but it is preferable to specify a consistent value representing the maximum number of pseudo tty allowed for pts instance either if it is ignored for now.

CONSOLE THROUGH THE TTYS

If the container is configured with a root filesystem and the inittab file is setup to launch a getty on the ttys. This option will specify the number of ttys to be available for the container. The number of getty in the inittab file of the container and the number of tty specified in this configuration file should be equal, otherwise the getty will die and respawn indefinitly giving annoying messages on the console.

lxc.tty

Specify the number of tty to make available to the container.

MOUNT POINTS

The mount points section specifies the different places to be mounted. These mount points will be private to the container and won't be visible by the processes running outside of the container. This is useful to mount /etc, /var or /home for examples.

lxc.mount

specify a file location in the fstab format, containing the mount informations.

ROOT FILE SYSTEM

The root file system is the location where the container will chroot.

lxc.rootfs

specify a file location containing the new file tree for a root file system.

CONTROL GROUP

The control group section contains the configuration for the different subsystem. lxc does not check the correctness of the subsystem name. This has the inconvenient to have the error being detected at runtime, but the advantage to support any future subsystem.

lxc.cgroup.[subsystem name]

specify the control group value to be set. This field is the identifier to tell the following keyword is the literal name of the control group subsystem, eg. lxc.cgroup.cpuset.cpus

EXAMPLES

NETWORK

This configuration sets up a container to use a veth pair device with one side plugged to a bridge br0 (which has been configured before on the system by the administrator). The virtual network device visible in the container is renamed to eth0.

lxc.utsname = myhostname

lxc.network.type = veth

lxc.network.flags = up

lxc.network.link = br0

lxc.network.name = eth0

lxc.network.hwaddr = 4a:49:43:49:79:bf

lxc.network.ipv4 = 1.2.3.5/24

lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597

CONTROL GROUP

This configuration will setup several control groups for the application, cpuset.cpus restricts usage of the defined cpu, cpus.share prioritize the control group, devices.allow makes usable the specified devices.

lxc.cgroup.cpuset.cpus = 0,1

lxc.cgroup.cpu.shares = 1234

lxc.cgroup.devices.deny = a

lxc.cgroup.devices.allow = c 1:3 rw

lxc.cgroup.devices.allow = b 8:0 rw

COMPLEX CONFIGURATION

This example show a complex configuration making a complex network stack, using the control groups, setting a new hostname, mounting some locations and a changing the root file system.

lxc.utsname = complex

lxc.network.type = veth

lxc.network.flags = up

lxc.network.link = br0

lxc.network.hwaddr = 4a:49:43:49:79:bf

lxc.network.ipv4 = 1.2.3.5/24

lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597

lxc.network.ipv6 = 2003:db8:1:0:214:5432:feab:3588

lxc.network.type = macvlan

lxc.network.flags = up

lxc.network.link = eth0

lxc.network.hwaddr = 4a:49:43:49:79:bd

lxc.network.ipv4 = 1.2.3.4/24

lxc.network.ipv4 = 192.168.10.125/24

lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3596

lxc.network.type = phys

lxc.network.flags = up

lxc.network.link = dummy0

lxc.network.hwaddr = 4a:49:43:49:79:ff

lxc.network.ipv4 = 1.2.3.6/24

lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3297

lxc.cgroup.cpuset.cpus = 0,1

lxc.cgroup.cpu.shares = 1234

lxc.cgroup.devices.deny = a

lxc.cgroup.devices.allow = c 1:3 rw

lxc.cgroup.devices.allow = b 8:0 rw

lxc.mount = /etc/fstab.complex

lxc.rootfs = /mnt/rootfs.complex

SEE ALSO

lxc-create(1), lxc-execute(1), chroot(1), pivot_root(8), fstab(5)

AUTHOR

Daniel Lezcano <daniel.lezcano@free.fr>