Provided by: lxc1_2.0.11-0ubuntu1~16.04.3_amd64 
NAME
lxc.container.conf - LXC container configuration file
DESCRIPTION
LXC is the well-known and heavily tested low-level Linux container runtime. It is in active development
since 2008 and has proven itself in critical production environments world-wide. Some of its core
contributors are the same people that helped to implement various well-known containerization features
inside the Linux kernel.
LXC's main focus is system containers. That is, containers which offer an environment as close as
possible as the one you'd get from a VM but without the overhead that comes with running a separate
kernel and simulating all the hardware.
This is achieved through a combination of kernel security features such as namespaces, mandatory access
control and control groups.
LXC has supports unprivileged containers. Unprivileged containers are containers that are run without any
privilege. This requires support for user namespaces in the kernel that the container is run on. LXC was
the first runtime to support unprivileged containers after user namespaces were merged into the mainline
kernel.
In essence, user namespaces isolate given sets of UIDs and GIDs. This is achieved by establishing a
mapping between a range of UIDs and GIDs on the host to a different (unprivileged) range of UIDs and GIDs
in the container. The kernel will translate this mapping in such a way that inside the container all UIDs
and GIDs appear as you would expect from the host whereas on the host these UIDs and GIDs are in fact
unprivileged. For example, a process running as UID and GID 0 inside the container might appear as UID
and GID 100000 on the host. The implementation and working details can be gathered from the corresponding
user namespace man page. UID and GID mappings can be defined with the lxc.id_map key.
Linux containers are defined with a simple configuration file. 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.
LXC namespaces configuration keys by using single dots. This means complex configuration keys such as
lxc.network expose various subkeys such as lxc.network.type, lxc.network.link, lxc.network.ipv6, and
others for even more fine-grained configuration.
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.
Some 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 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 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 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 commands. Note that using a non-root uid
when booting a system container will likely not work due to missing privileges. Setting the UID/GID is
mostly useful when running application container. Defaults to: UID(0), GID(0)
lxc.init_uid
UID to use for init.
lxc.init_gid
GID to use 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.[i].type
specify what kind of network virtualization to be used for the container. Multiple networks can
be specified by using an additional index i after all lxc.network.* keys. For example,
lxc.network.0.type = veth and lxc.network.1.type = veth specify two different networks of the same
type. All keys sharing the same index i will be treated as belonging to the same network. For
example, lxc.network.0.link = br0 will belong to lxc.network.0.type. Currently, 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.[i].flags
Specify an action to do for the network.
up: activates the interface.
lxc.network.[i].link
Specify the interface to be used for real network traffic.
lxc.network.[i].mtu
Specify the maximum transfer unit for this interface.
lxc.network.[i].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.[i].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.[i].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.[i].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.[i].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.[i].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.[i].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.[i].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. Note, when specifying 'none' and creating a device node for the console in
the container at /dev/console or bind-mounting the hosts's /dev/console into the container at
/dev/console the container will have direct access to the hosts's /dev/console. This is dangerous
when the container has write access to the device and should thus be used with caution.
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. Note that LXC
will move any bind-mounts or device nodes for /dev/console into this directory.
/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
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 supports mount
propagation, such as rslave or rprivate, and adds two additional mount options. 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 in those hierarchies 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:mixed:force: The force option will cause LXC to perform the cgroup mounts for the
container under all circumstances. Otherwise it is similar to cgroup:mixed. This is mainly
useful when the cgroup namespaces are enabled where LXC will normally leave mounting cgroups to
the init binary of the container since it is perfectly safe to do so.
• cgroup:ro: similar to cgroup:mixed, but everything will be mounted read-only.
• cgroup:ro:force: The force option will cause LXC to perform the cgroup mounts for the container
under all circumstances. Otherwise it is similar to cgroup:ro. This is mainly useful when the
cgroup namespaces are enabled where LXC will normally leave mounting cgroups to the init binary
of the container since it is perfectly safe to do so.
• 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:rw:force: The force option will cause LXC to perform the cgroup mounts for the container
under all circumstances. Otherwise it is similar to cgroup:rw. This is mainly useful when the
cgroup namespaces are enabled where LXC will normally leave mounting cgroups to the init binary
of the container since it is perfectly safe to do so.
• 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
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.
• LXC_CGNS_AWARE: indicated whether the container is cgroup namespace aware.
• LXC_LOG_LEVEL: the container's log level.
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/log/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.0.type = veth
lxc.network.0.flags = up
lxc.network.0.link = br0
lxc.network.0.hwaddr = 4a:49:43:49:79:bf
lxc.network.0.ipv4 = 10.2.3.5/24 10.2.3.255
lxc.network.0.ipv6 = 2003:db8:1:0:214:1234:fe0b:3597
lxc.network.0.ipv6 = 2003:db8:1:0:214:5432:feab:3588
lxc.network.1.type = macvlan
lxc.network.1.flags = up
lxc.network.1.link = eth0
lxc.network.1.hwaddr = 4a:49:43:49:79:bd
lxc.network.1.ipv4 = 10.2.3.4/24
lxc.network.1.ipv4 = 192.168.10.125/24
lxc.network.1.ipv6 = 2003:db8:1:0:214:1234:fe0b:3596
lxc.network.2.type = phys
lxc.network.2.flags = up
lxc.network.2.link = dummy0
lxc.network.2.hwaddr = 4a:49:43:49:79:ff
lxc.network.2.ipv4 = 10.2.3.6/24
lxc.network.2.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
SEE ALSO
chroot(1), pivot_root(8), fstab(5), capabilities(7)
SEE ALSO
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)
AUTHOR
Daniel Lezcano <daniel.lezcano@free.fr>
2019-04-09 lxc.container.conf(5)