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, the user namespace, and the control groups are supported.

Each option in the configuration file has the form key = value fitting in one line. The '#' character means the line is a comment. List options, like capabilities and cgroups options, can be used with no value to clear any previously defined values of that option.

CONFIGURATION

In order to ease administration of multiple related containers, it is possible to have a container configuration file cause another file to be loaded. For instance, network configuration can be defined in one common file which is included by multiple containers. Then, if the containers are moved to another host, only one file may need to be updated.

lxc.include

Specify the file to be included. The included file must be in the same valid lxc configuration file format.

ARCHITECTURE

Allows one to set the architecture for the container. For example, set a 32bits architecture for a container running 32bits binaries on a 64bits host. This fixes the container scripts which rely on the architecture to do some work like downloading the packages.

lxc.arch

Specify the architecture for the container.

Valid options are x86, i686, x86_64, amd64

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

HALT SIGNAL

Allows one to specify signal name or number, sent by lxc-stop to the container's init process to cleanly shutdown the container. Different init systems could use different signals to perform clean shutdown sequence. This option allows the signal to be specified in kill(1) fashion, e.g. SIGPWR, SIGRTMIN+14, SIGRTMAX-10 or plain number. The default signal is SIGPWR.

lxc.haltsignal

specify the signal used to halt the container

REBOOT SIGNAL

Allows one to specify signal name or number, sent by lxc-stop to reboot the container. This option allows signal to be specified in kill(1) fashion, e.g. SIGTERM, SIGRTMIN+14, SIGRTMAX-10 or plain number. The default signal is SIGINT.

lxc.rebootsignal

specify the signal used to reboot the container

STOP SIGNAL

Allows one to specify signal name or number, sent by lxc-stop to forcibly shutdown the container. This option allows signal to be specified in kill(1) fashion, e.g. SIGKILL, SIGRTMIN+14, SIGRTMAX-10 or plain number. The default signal is SIGKILL.

lxc.stopsignal

specify the signal used to stop the container

INIT COMMAND

Sets the command to use as the init system for the containers. This option is ignored when using lxc-execute. Defaults to: /sbin/init

lxc.init_cmd

Absolute path from container rootfs to the binary to use as init.

INIT ID

Sets the UID/GID to use for the init system, and subsequent command, executed by lxc-execute. These options are only used when lxc-execute is started in a private user namespace. Defaults to: UID(0), GID(0)

lxc.init_uid

UID to use within a private user namesapce for init.

lxc.init_gid

GID to use within a private user namesapce for init.

EPHEMERAL

Allows one to specify whether a container will be destroyed on shutdown.

lxc.ephemeral

The only allowed values are 0 and 1. Set this to 1 to destroy a container on shutdown.

NETWORK

The network section defines how the network is virtualized in the container. The network virtualization acts at layer two. In order to use the network virtualization, parameters must be specified to define the network interfaces of the container. Several virtual interfaces can be assigned and used in a container even if the system has only one physical network interface.

lxc.network

may be used without a value to clear all previous network options.

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. In this way, several network virtualization types can be specified for the same container, as well as assigning several network interfaces for one container. The different virtualization types can be:

none: will cause the container to share the host's network namespace. This means the host network devices are usable in the container. It also means that if both the container and host have upstart as init, 'halt' in a container (for instance) will shut down the host.

empty: will create only the loopback interface.

veth: a virtual ethernet pair device is created with one side assigned to the container and the other side attached to a bridge specified by the lxc.network.link option. If the bridge is not specified, then the veth pair device will be created but not attached to any bridge. Otherwise, the bridge has to be created on the system before starting the container. lxc won't handle any configuration outside of the container. By default, lxc chooses a name for the network device belonging to the outside of the container, but if you wish to handle this name yourselves, you can tell lxc to set a specific name with the lxc.network.veth.pair option (except for unprivileged containers where this option is ignored for security reasons).

vlan: a vlan interface is linked with the interface specified by the lxc.network.link and assigned to the container. The vlan identifier is specified with the option lxc.network.vlan.id.

macvlan: a macvlan interface is linked with the interface specified by the lxc.network.link and assigned to the container. lxc.network.macvlan.mode specifies the mode the macvlan will use to communicate between different macvlan on the same upper device. The accepted modes are private, vepa, bridge and passthru. In private mode, the device never communicates with any other device on the same upper_dev (default). In vepa mode, the new Virtual Ethernet Port Aggregator (VEPA) mode, it assumes that the adjacent bridge returns all frames where both source and destination are local to the macvlan port, i.e. the bridge is set up as a reflective relay. Broadcast frames coming in from the upper_dev get flooded to all macvlan interfaces in VEPA mode, local frames are not delivered locally. In bridge mode, it provides the behavior of a simple bridge between different macvlan interfaces on the same port. Frames from one interface to another one get delivered directly and are not sent out externally. Broadcast frames get flooded to all other bridge ports and to the external interface, but when they come back from a reflective relay, we don't deliver them again. Since we know all the MAC addresses, the macvlan bridge mode does not require learning or STP like the bridge module does. In passthru mode, all frames received by the physical interface are forwarded to the macvlan interface. Only one macvlan interface in passthru mode is possible for one physical interface.

phys: an already existing 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.mtu

specify the maximum transfer unit for this interface.

lxc.network.name

the interface name is dynamically allocated, but if another 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 cases, this is needed to resolve a mac address conflict or to always have the same link-local ipv6 address. Any "x" in address will be replaced by random value, this allows setting hwaddr templates.

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. The broadcast address should be specified on the same line, right after the ipv4 address.

lxc.network.ipv4.gateway

specify the ipv4 address to use as the gateway inside the container. The address is in format x.y.z.t, eg. 192.168.1.123. Can also have the special value auto, which means to take the primary address from the bridge interface (as specified by the lxc.network.link option) and use that as the gateway. auto is only available when using the veth and macvlan network types.

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

lxc.network.ipv6.gateway

specify the ipv6 address to use as the gateway inside the container. The address is in format x::y, eg. 2003:db8:1:0::1 Can also have the special value auto, which means to take the primary address from the bridge interface (as specified by the lxc.network.link option) and use that as the gateway. auto is only available when using the veth and macvlan network types.

lxc.network.script.up

add a configuration option to specify a script to be executed after creating and configuring the network used from the host side. The following arguments are passed to the script: container name and config section name (net) Additional arguments depend on the config section employing a script hook; the following are used by the network system: execution context (up), network type (empty/veth/macvlan/phys), Depending on the network type, other arguments may be passed: veth/macvlan/phys. And finally (host-sided) device name.

Standard output from the script is logged at debug level. Standard error is not logged, but can be captured by the hook redirecting its standard error to standard output.

lxc.network.script.down

add a configuration option to specify a script to be executed before destroying the network used from the host side. The following arguments are passed to the script: container name and config section name (net) Additional arguments depend on the config section employing a script hook; the following are used by the network system: execution context (down), network type (empty/veth/macvlan/phys), Depending on the network type, other arguments may be passed: veth/macvlan/phys. And finally (host-sided) device name.

Standard output from the script is logged at debug level. Standard error is not logged, but can be captured by the hook redirecting its standard error to standard output.

NEW PSEUDO TTY INSTANCE (DEVPTS)

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

lxc.pts

If set, the container will have a new pseudo tty instance, making this private to it. The value specifies the maximum number of pseudo ttys allowed for a pts instance (this limitation is not implemented yet).

CONTAINER SYSTEM CONSOLE

If the container is configured with a root filesystem and the inittab file is setup to use the console, you may want to specify where the output of this console goes.

lxc.console.logfile

Specify a path to a file where the console output will be written.

lxc.console

Specify a path to a device to which the console will be attached. The keyword 'none' will simply disable the console. This is dangerous once if have a rootfs with a console device file where the application can write, the messages will fall in the host.

CONSOLE THROUGH THE TTYS

This option is useful if the container is configured with a root filesystem and the inittab file is setup to launch a getty on the ttys. The option specifies the number of ttys to be available for the container. The number of gettys in the inittab file of the container should not be greater than the number of ttys specified in this option, otherwise the excess getty sessions will die and respawn indefinitely giving annoying messages on the console or in /var/log/messages.

lxc.tty

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

CONSOLE DEVICES LOCATION

LXC consoles are provided through Unix98 PTYs created on the host and bind-mounted over the expected devices in the container. By default, they are bind-mounted over /dev/console and /dev/ttyN. This can prevent package upgrades in the guest. Therefore you can specify a directory location (under /dev under which LXC will create the files and bind-mount over them. These will then be symbolically linked to /dev/console and /dev/ttyN. A package upgrade can then succeed as it is able to remove and replace the symbolic links.

lxc.devttydir

Specify a directory under /dev under which to create the container console devices.

/DEV DIRECTORY

By default, lxc creates a few symbolic links (fd,stdin,stdout,stderr) in the container's /dev directory but does not automatically create device node entries. This allows the container's /dev to be set up as needed in the container rootfs. If lxc.autodev is set to 1, then after mounting the container's rootfs LXC will mount a fresh tmpfs under /dev (limited to 500k) and fill in a minimal set of initial devices. This is generally required when starting a container containing a "systemd" based "init" but may be optional at other times. Additional devices in the containers /dev directory may be created through the use of the lxc.hook.autodev hook.

lxc.autodev

Set this to 0 to stop LXC from mounting and populating a minimal /dev when starting the container.

ENABLE KMSG SYMLINK

Enable creating /dev/kmsg as symlink to /dev/console. This defaults to 0.

lxc.kmsg

Set this to 1 to enable /dev/kmsg symlinking.

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.

NOTE - LXC will generally ensure that mount targets and relative bind-mount sources are properly confined under the container root, to avoid attacks involving over-mounting host directories and files. (Symbolic links in absolute mount sources are ignored) However, if the container configuration first mounts a directory which is under the control of the container user, such as /home/joe, into the container at some path, and then mounts under path, then a TOCTTOU attack would be possible where the container user modifies a symbolic link under his home directory at just the right time.

lxc.mount

specify a file location in the fstab format, containing the mount information. The mount target location can and in most cases should be a relative path, which will become relative to the mounted container root. For instance,

proc proc proc nodev,noexec,nosuid 0 0
.fi
Will mount a proc filesystem under the container's /proc,
regardless of where the root filesystem comes from. This
is resilient to block device backed filesystems as well as
container cloning.
Note that when mounting a filesystem from an
image file or block device the third field (fs_vfstype)
cannot be auto as with
mount(8)
but must be explicitly specified.

lxc.mount.entry

specify a mount point corresponding to a line in the fstab format. Moreover lxc add two options to mount. optional don't fail if mount does not work. create=dir or create=file to create dir (or file) when the point will be mounted.

lxc.mount.auto

specify which standard kernel file systems should be automatically mounted. This may dramatically simplify the configuration. The file systems are:

• proc:mixed (or proc): mount /proc as read-write, but remount /proc/sys and /proc/sysrq-trigger read-only for security / container isolation purposes.
• proc:rw: mount /proc as read-write
• sys:mixed (or sys): mount /sys as read-only but with /sys/devices/virtual/net writable.
• sys:ro: mount /sys as read-only for security / container isolation purposes.
• sys:rw: mount /sys as read-write
• cgroup:mixed: mount a tmpfs to /sys/fs/cgroup, create directories for all hierarchies to which the container is added, create subdirectories there with the name of the cgroup, and bind-mount the container's own cgroup into that directory. The container will be able to write to its own cgroup directory, but not the parents, since they will be remounted read-only.
• cgroup:ro: similar to cgroup:mixed, but everything will be mounted read-only.
• cgroup:rw: similar to cgroup:mixed, but everything will be mounted read-write. Note that the paths leading up to the container's own cgroup will be writable, but will not be a cgroup filesystem but just part of the tmpfs of /sys/fs/cgroup
• cgroup (without specifier): defaults to cgroup:rw if the container retains the CAP_SYS_ADMIN capability, cgroup:mixed otherwise.
• cgroup-full:mixed: mount a tmpfs to /sys/fs/cgroup, create directories for all hierarchies to which the container is added, bind-mount the hierarchies from the host to the container and make everything read-only except the container's own cgroup. Note that compared to cgroup, where all paths leading up to the container's own cgroup are just simple directories in the underlying tmpfs, here /sys/fs/cgroup/$hierarchy will contain the host's full cgroup hierarchy, albeit read-only outside the container's own cgroup. This may leak quite a bit of information into the container.
• cgroup-full:ro: similar to cgroup-full:mixed, but everything will be mounted read-only.
• cgroup-full:rw: similar to cgroup-full:mixed, but everything will be mounted read-write. Note that in this case, the container may escape its own cgroup. (Note also that if the container has CAP_SYS_ADMIN support and can mount the cgroup filesystem itself, it may do so anyway.)
• cgroup-full (without specifier): defaults to cgroup-full:rw if the container retains the CAP_SYS_ADMIN capability, cgroup-full:mixed otherwise.

If cgroup namespaces are enabled, then any cgroup auto-mounting request will be ignored, since the container can mount the filesystems itself, and automounting can confuse the container init. Note that if automatic mounting of the cgroup filesystem is enabled, the tmpfs under /sys/fs/cgroup will always be mounted read-write (but for the :mixed and :ro cases, the individual hierarchies, /sys/fs/cgroup/$hierarchy, will be read-only). This is in order to work around a quirk in Ubuntu's mountall(8) command that will cause containers to wait for user input at boot if /sys/fs/cgroup is mounted read-only and the container can't remount it read-write due to a lack of CAP_SYS_ADMIN. Examples: lxc.mount.auto = proc sys cgroup lxc.mount.auto = proc:rw sys:rw cgroup-full:rw

ROOT FILE SYSTEM

The root file system of the container can be different than that of the host system.

lxc.rootfs

specify the root file system for the container. It can be an image file, a directory or a block device. If not specified, the container shares its root file system with the host.

For directory or simple block-device backed containers, a pathname can be used. If the rootfs is backed by a nbd device, then nbd:file:1 specifies that file should be attached to a nbd device, and partition 1 should be mounted as the rootfs. nbd:file specifies that the nbd device itself should be mounted. overlayfs:/lower:/upper specifies that the rootfs should be an overlay with /upper being mounted read-write over a read-only mount of /lower. aufs:/lower:/upper does the same using aufs in place of overlayfs. For both overlayfs and aufs multiple /lower directories can be specified. loop:/file tells lxc to attach /file to a loop device and mount the loop device.

lxc.rootfs.mount

where to recursively bind lxc.rootfs before pivoting. This is to ensure success of the pivot_root(8) syscall. Any directory suffices, the default should generally work.

lxc.rootfs.options

extra mount options to use when mounting the rootfs.

lxc.rootfs.backend

specify the rootfs backend type to use, for instance 'dir' or 'zfs'. While this can be guessed by lxc at container startup, doing so takes time. Specifying it here avoids extra processing.

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 disadvantage of not detecting configuration errors until the container is started, but has the advantage of permitting any future subsystem.

lxc.cgroup.[subsystem name]

specify the control group value to be set. The subsystem name is the literal name of the control group subsystem. The permitted names and the syntax of their values is not dictated by LXC, instead it depends on the features of the Linux kernel running at the time the container is started, eg. lxc.cgroup.cpuset.cpus

CAPABILITIES

The capabilities can be dropped in the container if this one is run as root.

lxc.cap.drop

Specify the capability to be dropped in the container. A single line defining several capabilities with a space separation is allowed. The format is the lower case of the capability definition without the "CAP_" prefix, eg. CAP_SYS_MODULE should be specified as sys_module. See capabilities(7). If used with no value, lxc will clear any drop capabilities specified up to this point.

lxc.cap.keep

Specify the capability to be kept in the container. All other capabilities will be dropped. When a special value of "none" is encountered, lxc will clear any keep capabilities specified up to this point. A value of "none" alone can be used to drop all capabilities.

APPARMOR PROFILE

If lxc was compiled and installed with apparmor support, and the host system has apparmor enabled, then the apparmor profile under which the container should be run can be specified in the container configuration. The default is lxc-container-default-cgns if the host kernel is cgroup namespace aware, or lxc-container-default othewise.

lxc.aa_profile

Specify the apparmor profile under which the container should be run. To specify that the container should be unconfined, use

lxc.aa_profile = unconfined

If the apparmor profile should remain unchanged (i.e. if you are nesting containers and are already confined), then use

lxc.aa_profile = unchanged

lxc.aa_allow_incomplete

Apparmor profiles are pathname based. Therefore many file restrictions require mount restrictions to be effective against a determined attacker. However, these mount restrictions are not yet implemented in the upstream kernel. Without the mount restrictions, the apparmor profiles still protect against accidental damager.

If this flag is 0 (default), then the container will not be started if the kernel lacks the apparmor mount features, so that a regression after a kernel upgrade will be detected. To start the container under partial apparmor protection, set this flag to 1.

SELINUX CONTEXT

If lxc was compiled and installed with SELinux support, and the host system has SELinux enabled, then the SELinux context under which the container should be run can be specified in the container configuration. The default is unconfined_t, which means that lxc will not attempt to change contexts. See /usr/share/lxc/selinux/lxc.te for an example policy and more information.

lxc.se_context

Specify the SELinux context under which the container should be run or unconfined_t. For example

lxc.se_context = system_u:system_r:lxc_t:s0:c22

SECCOMP CONFIGURATION

A container can be started with a reduced set of available system calls by loading a seccomp profile at startup. The seccomp configuration file must begin with a version number on the first line, a policy type on the second line, followed by the configuration.

Versions 1 and 2 are currently supported. In version 1, the policy is a simple whitelist. The second line therefore must read "whitelist", with the rest of the file containing one (numeric) sycall number per line. Each syscall number is whitelisted, while every unlisted number is blacklisted for use in the container

In version 2, the policy may be blacklist or whitelist, supports per-rule and per-policy default actions, and supports per-architecture system call resolution from textual names.

An example blacklist policy, in which all system calls are allowed except for mknod, which will simply do nothing and return 0 (success), looks like:

2
blacklist
mknod errno 0
.fi

lxc.seccomp

Specify a file containing the seccomp configuration to load before the container starts.

UID MAPPINGS

A container can be started in a private user namespace with user and group id mappings. For instance, you can map userid 0 in the container to userid 200000 on the host. The root user in the container will be privileged in the container, but unprivileged on the host. Normally a system container will want a range of ids, so you would map, for instance, user and group ids 0 through 20,000 in the container to the ids 200,000 through 220,000.

lxc.id_map

Four values must be provided. First a character, either 'u', or 'g', to specify whether user or group ids are being mapped. Next is the first userid as seen in the user namespace of the container. Next is the userid as seen on the host. Finally, a range indicating the number of consecutive ids to map.

CONTAINER HOOKS

Container hooks are programs or scripts which can be executed at various times in a container's lifetime.

When a container hook is executed, information is passed both as command line arguments and through environment variables. The arguments are:

• Container name.
• Section (always 'lxc').
• The hook type (i.e. 'clone' or 'pre-mount').
• Additional arguments. In the case of the clone hook, any extra arguments passed to lxc-clone will appear as further arguments to the hook. In the case of the stop hook, paths to filedescriptors for each of the container's namespaces along with their types are passed.

The following environment variables are set:

• LXC_NAME: is the container's name.
• LXC_ROOTFS_MOUNT: the path to the mounted root filesystem.
• LXC_CONFIG_FILE: the path to the container configuration file.
• LXC_SRC_NAME: in the case of the clone hook, this is the original container's name.
• LXC_ROOTFS_PATH: this is the lxc.rootfs entry for the container. Note this is likely not where the mounted rootfs is to be found, use LXC_ROOTFS_MOUNT for that.

Standard output from the hooks is logged at debug level. Standard error is not logged, but can be captured by the hook redirecting its standard error to standard output.

lxc.hook.pre-start

A hook to be run in the host's namespace before the container ttys, consoles, or mounts are up.

lxc.hook.pre-mount

A hook to be run in the container's fs namespace but before the rootfs has been set up. This allows for manipulation of the rootfs, i.e. to mount an encrypted filesystem. Mounts done in this hook will not be reflected on the host (apart from mounts propagation), so they will be automatically cleaned up when the container shuts down.

lxc.hook.mount

A hook to be run in the container's namespace after mounting has been done, but before the pivot_root.

lxc.hook.autodev

A hook to be run in the container's namespace after mounting has been done and after any mount hooks have run, but before the pivot_root, if lxc.autodev == 1. The purpose of this hook is to assist in populating the /dev directory of the container when using the autodev option for systemd based containers. The container's /dev directory is relative to the ${LXC_ROOTFS_MOUNT} environment variable available when the hook is run.

lxc.hook.start

A hook to be run in the container's namespace immediately before executing the container's init. This requires the program to be available in the container.

lxc.hook.stop

A hook to be run in the host's namespace with references to the container's namespaces after the container has been shut down. For each namespace an extra argument is passed to the hook containing the namespace's type and a filename that can be used to obtain a file descriptor to the corresponding namespace, separated by a colon. The type is the name as it would appear in the /proc/PID/ns directory. For instance for the mount namespace the argument usually looks like mnt:/proc/PID/fd/12.

lxc.hook.post-stop

A hook to be run in the host's namespace after the container has been shut down.

lxc.hook.clone

A hook to be run when the container is cloned to a new one. See lxc-clone(1) for more information.

lxc.hook.destroy

A hook to be run when the container is destroyed.

CONTAINER HOOKS ENVIRONMENT VARIABLES

A number of environment variables are made available to the startup hooks to provide configuration information and assist in the functioning of the hooks. Not all variables are valid in all contexts. In particular, all paths are relative to the host system and, as such, not valid during the lxc.hook.start hook.

LXC_NAME

The LXC name of the container. Useful for logging messages in common log environments. [-n]

LXC_CONFIG_FILE

Host relative path to the container configuration file. This gives the container to reference the original, top level, configuration file for the container in order to locate any additional configuration information not otherwise made available. [-f]

LXC_CONSOLE

The path to the console output of the container if not NULL. [-c] [lxc.console]

LXC_CONSOLE_LOGPATH

The path to the console log output of the container if not NULL. [-L]

LXC_ROOTFS_MOUNT

The mount location to which the container is initially bound. This will be the host relative path to the container rootfs for the container instance being started and is where changes should be made for that instance. [lxc.rootfs.mount]

LXC_ROOTFS_PATH

The host relative path to the container root which has been mounted to the rootfs.mount location. [lxc.rootfs]

LXC_SRC_NAME

Only for the clone hook. Is set to the original container name.

LXC_TARGET

Only for the stop hook. Is set to "stop" for a container shutdown or "reboot" for a container reboot.

LXC_CGNS_AWARE

If unset, then this version of lxc is not aware of cgroup namespaces. If set, it will be set to 1, and lxc is aware of cgroup namespaces. Note this does not guarantee that cgroup namespaces are enabled in the kernel. This is used by the lxcfs mount hook.

LOGGING

Logging can be configured on a per-container basis. By default, depending upon how the lxc package was compiled, container startup is logged only at the ERROR level, and logged to a file named after the container (with '.log' appended) either under the container path, or under /var/lib/lxc.

Both the default log level and the log file can be specified in the container configuration file, overriding the default behavior. Note that the configuration file entries can in turn be overridden by the command line options to lxc-start.

lxc.loglevel

The level at which to log. The log level is an integer in the range of 0..8 inclusive, where a lower number means more verbose debugging. In particular 0 = trace, 1 = debug, 2 = info, 3 = notice, 4 = warn, 5 = error, 6 = critical, 7 = alert, and 8 = fatal. If unspecified, the level defaults to 5 (error), so that only errors and above are logged.

Note that when a script (such as either a hook script or a network interface up or down script) is called, the script's standard output is logged at level 1, debug.

lxc.logfile

The file to which logging info should be written.

AUTOSTART

The autostart options support marking which containers should be auto-started and in what order. These options may be used by LXC tools directly or by external tooling provided by the distributions.

lxc.start.auto

Whether the container should be auto-started. Valid values are 0 (off) and 1 (on).

lxc.start.delay

How long to wait (in seconds) after the container is started before starting the next one.

lxc.start.order

An integer used to sort the containers when auto-starting a series of containers at once.

lxc.monitor.unshare

If not zero the mount namespace will be unshared from the host before initializing the container (before running any pre-start hooks). This requires the CAP_SYS_ADMIN capability at startup. Default is 0.

lxc.group

A multi-value key (can be used multiple times) to put the container in a container group. Those groups can then be used (amongst other things) to start a series of related containers.

AUTOSTART AND SYSTEM BOOT

Each container can be part of any number of groups or no group at all. Two groups are special. One is the NULL group, i.e. the container does not belong to any group. The other group is the "onboot" group.

When the system boots with the LXC service enabled, it will first attempt to boot any containers with lxc.start.auto == 1 that is a member of the "onboot" group. The startup will be in order of lxc.start.order. If an lxc.start.delay has been specified, that delay will be honored before attempting to start the next container to give the current container time to begin initialization and reduce overloading the host system. After starting the members of the "onboot" group, the LXC system will proceed to boot containers with lxc.start.auto == 1 which are not members of any group (the NULL group) and proceed as with the onboot group.

CONTAINER ENVIRONMENT

If you want to pass environment variables into the container (that is, environment variables which will be available to init and all of its descendents), you can use lxc.environment parameters to do so. Be careful that you do not pass in anything sensitive; any process in the container which doesn't have its environment scrubbed will have these variables available to it, and environment variables are always available via /proc/PID/environ.

This configuration parameter can be specified multiple times; once for each environment variable you wish to configure.

lxc.environment

Specify an environment variable to pass into the container. Example:

              lxc.environment = APP_ENV=production
              lxc.environment = SYSLOG_SERVER=192.0.2.42
            

EXAMPLES

In addition to the few examples given below, you will find some other examples of configuration file in /usr/share/doc/lxc/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 = 10.2.3.5/24 10.2.3.255
        lxc.network.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597
      

UID/GID MAPPING

This configuration will map both user and group ids in the range 0-9999 in the container to the ids 100000-109999 on the host.

        lxc.id_map = u 0 100000 10000
        lxc.id_map = g 0 100000 10000
      

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 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 = 10.2.3.5/24 10.2.3.255
        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 = 10.2.3.4/24
        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 = 10.2.3.6/24
        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.mount.entry = /lib /root/myrootfs/lib none ro,bind 0 0
        lxc.rootfs = /mnt/rootfs.complex
        lxc.cap.drop = sys_module mknod setuid net_raw
        lxc.cap.drop = mac_override
      

AUTHOR

Daniel Lezcano <[email protected]>