Provided by: lxc_6.0.3-1ubuntu1_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 support for 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.idmap 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 use single dots. This means complex configuration keys such as
lxc.net.0 expose various subkeys such as lxc.net.0.type, lxc.net.0.link, lxc.net.0.ipv6.address, 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.uts.name
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.signal.halt
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.signal.reboot
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.signal.stop
specify the signal used to stop the container
INIT COMMAND
Sets the command to use as the init system for the containers.
lxc.execute.cmd
Absolute path from container rootfs to the binary to run by default. This mostly makes sense for
lxc-execute.
lxc.init.cmd
Absolute path from container rootfs to the binary to use as init. This mostly makes sense for lxc-
start. Default is /sbin/init.
INIT WORKING DIRECTORY
Sets the absolute path inside the container as the working directory for the containers. LXC will switch
to this directory before executing init.
lxc.init.cwd
Absolute path inside the container to use as the working directory.
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 containers. Defaults to: UID(0), GID(0)
lxc.init.uid
UID to use for init.
lxc.init.gid
GID to use for init.
CORE SCHEDULING
Core scheduling defines if the container payload is marked as being schedulable on the same core. Doing
so will cause the kernel scheduler to ensure that tasks that are not in the same group never run
simultaneously on a core. This can serve as an extra security measure to prevent the container payload
from using cross hyper thread attacks.
lxc.sched.core
The only allowed values are 0 and 1. Set this to 1 to create a core scheduling domain for the
container or 0 to not create one. If not set explicitly no core scheduling domain will be created
for the container.
PROC
Configure proc filesystem for the container.
lxc.proc.[proc file name]
Specify the proc file name to be set. The file names available are those listed under /proc/PID/.
Example:
lxc.proc.oom_score_adj = 10
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.net
may be used without a value to clear all previous network options.
lxc.net.[i].type
specify what kind of network virtualization to be used for the container. Must be specified
before any other option(s) on the net device. Multiple networks can be specified by using an
additional index i after all lxc.net.* keys. For example, lxc.net.0.type = veth and lxc.net.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.net.0.link = br0 will belong to
lxc.net.0.type. Currently, the different virtualization types can be:
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 on the host. lxc.net.[i].veth.mode specifies the mode the veth parent will use on the
host. The accepted modes are bridge and router. The mode defaults to bridge if not specified.
In bridge mode the host side is attached to a bridge specified by the lxc.net.[i].link option. If
the bridge link 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. In router mode static routes are
created on the host for the container's IP addresses pointing to the host side veth interface.
Additionally Proxy ARP and Proxy NDP entries are added on the host side veth interface for the
gateway IPs defined in the container to allow the container to reach the host. 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.net.[i].veth.pair option (except for unprivileged containers where this option is ignored for
security reasons). Static routes can be added on the host pointing to the container using the
lxc.net.[i].veth.ipv4.route and lxc.net.[i].veth.ipv6.route options. Several lines specify
several routes. The route is in format x.y.z.t/m, eg. 192.168.1.0/24. In bridge mode untagged
VLAN membership can be set with the lxc.net.[i].veth.vlan.id option. It accepts a special value of
'none' indicating that the container port should be removed from the bridge's default untagged
VLAN. The lxc.net.[i].veth.vlan.tagged.id option can be specified multiple times to set the
container's bridge port membership to one or more tagged VLANs.
vlan: a vlan interface is linked with the interface specified by the lxc.net.[i].link and assigned
to the container. The vlan identifier is specified with the option lxc.net.[i].vlan.id.
macvlan: a macvlan interface is linked with the interface specified by the lxc.net.[i].link and
assigned to the container. lxc.net.[i].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.
ipvlan: an ipvlan interface is linked with the interface specified by the lxc.net.[i].link and
assigned to the container. lxc.net.[i].ipvlan.mode specifies the mode the ipvlan will use to
communicate between different ipvlan on the same upper device. The accepted modes are l3, l3s and
l2. It defaults to l3 mode. In l3 mode TX processing up to L3 happens on the stack instance
attached to the dependent device and packets are switched to the stack instance of the parent
device for the L2 processing and routing from that instance will be used before packets are queued
on the outbound device. In this mode the dependent devices will not receive nor can send multicast
/ broadcast traffic. In l3s mode TX processing is very similar to the L3 mode except that
iptables (conn-tracking) works in this mode and hence it is L3-symmetric (L3s). This will have
slightly less performance but that shouldn't matter since you are choosing this mode over plain-L3
mode to make conn-tracking work. In l2 mode TX processing happens on the stack instance attached
to the dependent device and packets are switched and queued to the parent device to send devices
out. In this mode the dependent devices will RX/TX multicast and broadcast (if applicable) as
well. lxc.net.[i].ipvlan.isolation specifies the isolation mode. The accepted isolation values
are bridge, private and vepa. It defaults to bridge. In bridge isolation mode dependent devices
can cross-talk among themselves apart from talking through the parent device. In private
isolation mode the port is set in private mode. i.e. port won't allow cross communication between
dependent devices. In vepa isolation mode the port is set in VEPA mode. i.e. port will offload
switching functionality to the external entity as described in 802.1Qbg.
phys: an already existing interface specified by the lxc.net.[i].link is assigned to the
container.
lxc.net.[i].flags
Specify an action to do for the network.
up: activates the interface.
lxc.net.[i].link
Specify the interface to be used for real network traffic.
lxc.net.[i].l2proxy
Controls whether layer 2 IP neighbour proxy entries will be added to the lxc.net.[i].link
interface for the IP addresses of the container. Can be set to 0 or 1. Defaults to 0. When used
with IPv4 addresses, the following sysctl values need to be set: net.ipv4.conf.[link].forwarding=1
When used with IPv6 addresses, the following sysctl values need to be set:
net.ipv6.conf.[link].proxy_ndp=1 net.ipv6.conf.[link].forwarding=1
lxc.net.[i].mtu
Specify the maximum transfer unit for this interface.
lxc.net.[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.net.[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.net.[i].ipv4.address
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. You can optionally
specify the broadcast address after the IP address, e.g. 192.168.1.123/24 255.255.255.255.
Otherwise it is automatically calculated from the IP address.
lxc.net.[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.net.[i].link option) and use that as
the gateway. auto is only available when using the veth, macvlan and ipvlan network types. Can
also have the special value of dev, which means to set the default gateway as a device route.
This is primarily for use with layer 3 network modes, such as IPVLAN.
lxc.net.[i].ipv6.address
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.net.[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.net.[i].link option) and use that as
the gateway. auto is only available when using the veth, macvlan and ipvlan network types. Can
also have the special value of dev, which means to set the default gateway as a device route.
This is primarily for use with layer 3 network modes, such as IPVLAN.
lxc.net.[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.
In addition to the information available to all hooks. The following information is provided to
the script:
• LXC_HOOK_TYPE: the hook type. This is either 'up' or 'down'.
• LXC_HOOK_SECTION: the section type 'net'.
• LXC_NET_TYPE: the network type. This is one of the valid network types listed here (e.g. 'vlan',
'macvlan', 'ipvlan', 'veth').
• LXC_NET_PARENT: the parent device on the host. This is only set for network types 'mavclan',
'veth', 'phys'.
• LXC_NET_PEER: the name of the peer device on the host. This is only set for 'veth' network
types. Note that this information is only available when lxc.hook.version is set to 1.
Whether this information is provided in the form of environment variables or as arguments to the script
depends on the value of lxc.hook.version. If set to 1 then information is provided in the form of
environment variables. If set to 0 information is provided as arguments to the script.
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.net.[i].script.down
Add a configuration option to specify a script to be executed before destroying the network used
from the host side.
In addition to the information available to all hooks. The following information is provided to
the script:
• LXC_HOOK_TYPE: the hook type. This is either 'up' or 'down'.
• LXC_HOOK_SECTION: the section type 'net'.
• LXC_NET_TYPE: the network type. This is one of the valid network types listed here (e.g. 'vlan',
'macvlan', 'ipvlan', 'veth').
• LXC_NET_PARENT: the parent device on the host. This is only set for network types 'mavclan',
'veth', 'phys'.
• LXC_NET_PEER: the name of the peer device on the host. This is only set for 'veth' network
types. Note that this information is only available when lxc.hook.version is set to 1.
Whether this information is provided in the form of environment variables or as arguments to the script
depends on the value of lxc.hook.version. If set to 1 then information is provided in the form of
environment variables. If set to 0 information is provided as arguments to the script.
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.pty.max
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 pty 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.buffer.size
Setting this option instructs liblxc to allocate an in-memory ringbuffer. The container's console
output will be written to the ringbuffer. Note that ringbuffer must be at least as big as a
standard page size. When passed a value smaller than a single page size liblxc will allocate a
ringbuffer of a single page size. A page size is usually 4KB. The keyword 'auto' will cause
liblxc to allocate a ringbuffer of 128KB. When manually specifying a size for the ringbuffer the
value should be a power of 2 when converted to bytes. Valid size prefixes are 'KB', 'MB', 'GB'.
(Note that all conversions are based on multiples of 1024. That means 'KB' == 'KiB', 'MB' ==
'MiB', 'GB' == 'GiB'. Additionally, the case of the suffix is ignored, i.e. 'kB', 'KB' and 'Kb'
are treated equally.)
lxc.console.size
Setting this option instructs liblxc to place a limit on the size of the console log file
specified in lxc.console.logfile. Note that size of the log file must be at least as big as a
standard page size. When passed a value smaller than a single page size liblxc will set the size
of log file to a single page size. A page size is usually 4KB. The keyword 'auto' will cause
liblxc to place a limit of 128KB on the log file. When manually specifying a size for the log
file the value should be a power of 2 when converted to bytes. Valid size prefixes are 'KB', 'MB',
'GB'. (Note that all conversions are based on multiples of 1024. That means 'KB' == 'KiB', 'MB' ==
'MiB', 'GB' == 'GiB'. Additionally, the case of the suffix is ignored, i.e. 'kB', 'KB' and 'Kb'
are treated equally.) If users want to mirror the console ringbuffer on disk they should set
lxc.console.size equal to lxc.console.buffer.size.
lxc.console.logfile
Specify a path to a file where the console output will be written. Note that in contrast to the
on-disk ringbuffer logfile this file will keep growing potentially filling up the users disks if
not rotated and deleted. This problem can also be avoided by using the in-memory ringbuffer
options lxc.console.buffer.size and lxc.console.buffer.logfile.
lxc.console.rotate
Whether to rotate the console logfile specified in lxc.console.logfile. Users can send an API
request to rotate the logfile. Note that the old logfile will have the same name as the original
with the suffix ".1" appended. Users wishing to prevent the console log file from filling the
disk should rotate the logfile and delete it if unneeded. This problem can also be avoided by
using the in-memory ringbuffer options lxc.console.buffer.size and lxc.console.buffer.logfile.
lxc.console.path
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.max
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.tty.dir
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 by default, unless defined in
lxc.autodev.tmpfs.size) 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.
lxc.autodev.tmpfs.size
Set this to define the size of the /dev tmpfs. The default value is 500000 (500K). If the
parameter is used but without value, the default value is used.
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 their home directory at just the right time.
lxc.mount.fstab
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 rshared or rprivate, and adds three 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. relative source path is taken to be relative to the mounted container root. For
instance,
dev/null proc/kcore none bind,relative 0 0
Will expand dev/null to ${LXC_ROOTFS_MOUNT}/dev/null, and mount it to proc/kcore inside the
container.
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: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-full: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-full:ro: similar to cgroup-full:mixed, but everything will be mounted read-only.
• cgroup-full: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-full: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-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: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-full: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-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.path
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. For overlay 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.path before pivoting. This is to ensure success of the
pivot_root(8) syscall. Any directory suffices, the default should generally work.
lxc.rootfs.options
Specify extra mount options to use when mounting the rootfs. The format of the mount options
corresponds to the format used in fstab. In addition, LXC supports the custom idmap= mount option.
This option can be used to tell LXC to create an idmapped mount for the container's rootfs. This
is useful when the user doesn't want to recursively chown the rootfs of the container to match the
idmapping of the user namespace the container is going to use. Instead an idmapped mount can be
used to handle this. The argument for idmap= can either be a path pointing to a user namespace
file that LXC will open and use to idmap the rootfs or the special value "container" which will
instruct LXC to use the container's user namespace to idmap the rootfs.
lxc.rootfs.managed
Set this to 0 to indicate that LXC is not managing the container storage, then LXC will not modify
the container storage. The default is 1.
CONTROL GROUPS ("CGROUPS")
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.
The kernel implementation of cgroups has changed significantly over the years. With Linux 4.5 support for
a new cgroup filesystem was added usually referred to as "cgroup2" or "unified hierarchy". Since then the
old cgroup filesystem is usually referred to as "cgroup1" or the "legacy hierarchies". Please see the
cgroups manual page for a detailed explanation of the differences between the two versions.
LXC distinguishes settings for the legacy and the unified hierarchy by using different configuration key
prefixes. To alter settings for controllers in a legacy hierarchy the key prefix lxc.cgroup. must be used
and in order to alter the settings for a controller in the unified hierarchy the lxc.cgroup2. key must be
used. Note that LXC will ignore lxc.cgroup. settings on systems that only use the unified hierarchy.
Conversely, it will ignore lxc.cgroup2. options on systems that only use legacy hierarchies.
At its core a cgroup hierarchy is a way to hierarchically organize processes. Usually a cgroup hierarchy
will have one or more "controllers" enabled. A "controller" in a cgroup hierarchy is usually responsible
for distributing a specific type of system resource along the hierarchy. Controllers include the "pids"
controller, the "cpu" controller, the "memory" controller and others. Some controllers however do not
fall into the category of distributing a system resource, instead they are often referred to as "utility"
controllers. One utility controller is the device controller. Instead of distributing a system resource
it allows one to manage device access.
In the legacy hierarchy the device controller was implemented like most other controllers as a set of
files that could be written to. These files where named "devices.allow" and "devices.deny". The legacy
device controller allowed the implementation of both "allowlists" and "denylists".
An allowlist is a device program that by default blocks access to all devices. In order to access
specific devices "allow rules" for particular devices or device classes must be specified. In contrast, a
denylist is a device program that by default allows access to all devices. In order to restrict access to
specific devices "deny rules" for particular devices or device classes must be specified.
In the unified cgroup hierarchy the implementation of the device controller has completely changed.
Instead of files to read from and write to a eBPF program of BPF_PROG_TYPE_CGROUP_DEVICE can be attached
to a cgroup. Even though the kernel implementation has changed completely LXC tries to allow for the same
semantics to be followed in the legacy device cgroup and the unified eBPF-based device controller. The
following paragraphs explain the semantics for the unified eBPF-based device controller.
As mentioned the format for specifying device rules for the unified eBPF-based device controller is the
same as for the legacy cgroup device controller; only the configuration key prefix has changed.
Specifically, device rules for the legacy cgroup device controller are specified via
lxc.cgroup.devices.allow and lxc.cgroup.devices.deny whereas for the cgroup2 eBPF-based device controller
lxc.cgroup2.devices.allow and lxc.cgroup2.devices.deny must be used.
• A denylist device rule
lxc.cgroup2.devices.deny = a
will cause LXC to instruct the kernel to block access to all devices by default. To grant access to
devices allow device rules must be added via the lxc.cgroup2.devices.allow key. This is referred to as
a "allowlist" device program.
• An allowlist device rule
lxc.cgroup2.devices.allow = a
will cause LXC to instruct the kernel to allow access to all devices by default. To deny access to
devices deny device rules must be added via lxc.cgroup2.devices.deny key. This is referred to as a
"denylist" device program.
• Specifying any of the aforementioned two rules will cause all previous rules to be cleared, i.e. the
device list will be reset.
• When an allowlist program is requested, i.e. access to all devices is blocked by default, specific deny
rules for individual devices or device classes are ignored.
• When a denylist program is requested, i.e. access to all devices is allowed by default, specific allow
rules for individual devices or device classes are ignored.
For example the set of rules:
lxc.cgroup2.devices.deny = a
lxc.cgroup2.devices.allow = c *:* m
lxc.cgroup2.devices.allow = b *:* m
lxc.cgroup2.devices.allow = c 1:3 rwm
implements an allowlist device program, i.e. the kernel will block access to all devices not specifically
allowed in this list. This particular program states that all character and block devices may be created
but only /dev/null might be read or written.
If we instead switch to the following set of rules:
lxc.cgroup2.devices.allow = a
lxc.cgroup2.devices.deny = c *:* m
lxc.cgroup2.devices.deny = b *:* m
lxc.cgroup2.devices.deny = c 1:3 rwm
then LXC would instruct the kernel to implement a denylist, i.e. the kernel will allow access to all
devices not specifically denied in this list. This particular program states that no character devices or
block devices might be created and that /dev/null is not allow allowed to be read, written, or created.
Now consider the same program but followed by a "global rule" which determines the type of device program
(allowlist or denylist) as explained above:
lxc.cgroup2.devices.allow = a
lxc.cgroup2.devices.deny = c *:* m
lxc.cgroup2.devices.deny = b *:* m
lxc.cgroup2.devices.deny = c 1:3 rwm
lxc.cgroup2.devices.allow = a
The last line will cause LXC to reset the device list without changing the type of device program.
If we specify:
lxc.cgroup2.devices.allow = a
lxc.cgroup2.devices.deny = c *:* m
lxc.cgroup2.devices.deny = b *:* m
lxc.cgroup2.devices.deny = c 1:3 rwm
lxc.cgroup2.devices.deny = a
instead then the last line will cause LXC to reset the device list and switch from an allowlist program
to a denylist program.
lxc.cgroup.[controller name].[controller file]
Specify the control group value to be set on a legacy cgroup hierarchy. The controller name is the
literal name of the control group. 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
lxc.cgroup2.[controller name].[controller file]
Specify the control group value to be set on the unified cgroup hierarchy. The controller name is
the literal name of the control group. 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.cgroup2.memory.high
lxc.cgroup.dir
specify a directory or path in which the container's cgroup will be created. For example, setting
lxc.cgroup.dir = my-cgroup/first for a container named "c1" will create the container's cgroup as
a sub-cgroup of "my-cgroup". For example, if the user's current cgroup "my-user" is located in the
root cgroup of the cpuset controller in a cgroup v1 hierarchy this would create the cgroup
"/sys/fs/cgroup/cpuset/my-user/my-cgroup/first/c1" for the container. Any missing cgroups will be
created by LXC. This presupposes that the user has write access to its current cgroup.
lxc.cgroup.dir.container
This is similar to lxc.cgroup.dir, but must be used together with lxc.cgroup.dir.monitor and
affects only the container's cgroup path. This option is mutually exclusive with lxc.cgroup.dir.
Note that the final path the container attaches to may be extended further by the
lxc.cgroup.dir.container.inner option.
lxc.cgroup.dir.monitor
This is the monitor process counterpart to lxc.cgroup.dir.container.
lxc.cgroup.dir.monitor.pivot
On container termination the PID of the monitor process is attached to this cgroup. This path
should not be a subpath of any other configured cgroup dir to ensure proper removal of other
cgroup paths on container termination.
lxc.cgroup.dir.container.inner
Specify an additional subdirectory where the cgroup namespace will be created. With this option,
the cgroup limits will be applied to the outer path specified in lxc.cgroup.dir.container, which
is not accessible from within the container, making it possible to better enforce limits for
privileged containers in a way they cannot override them. This only works in conjunction with the
lxc.cgroup.dir.container and lxc.cgroup.dir.monitor options and has otherwise no effect.
lxc.cgroup.relative
Set this to 1 to instruct LXC to never escape to the root cgroup. This makes it easy for users to
adhere to restrictions enforced by cgroup2 and systemd. Specifically, this makes it possible to
run LXC containers as systemd services.
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.
NAMESPACES
A namespace can be cloned (lxc.namespace.clone), kept (lxc.namespace.keep) or shared
(lxc.namespace.share.[namespace identifier]).
lxc.namespace.clone
Specify namespaces which the container is supposed to be created with. The namespaces to create
are specified as a space separated list. Each namespace must correspond to one of the standard
namespace identifiers as seen in the /proc/PID/ns directory. When lxc.namespace.clone is not
explicitly set all namespaces supported by the kernel and the current configuration will be used.
To create a new mount, net and ipc namespace set lxc.namespace.clone=mount net ipc.
lxc.namespace.keep
Specify namespaces which the container is supposed to inherit from the process that created it.
The namespaces to keep are specified as a space separated list. Each namespace must correspond to
one of the standard namespace identifiers as seen in the /proc/PID/ns directory. The
lxc.namespace.keep is a denylist option, i.e. it is useful when enforcing that containers must
keep a specific set of namespaces.
To keep the network, user and ipc namespace set lxc.namespace.keep=user net ipc.
Note that sharing pid namespaces will likely not work with most init systems.
Note that if the container requests a new user namespace and the container wants to inherit the
network namespace it needs to inherit the user namespace as well.
lxc.namespace.share.[namespace identifier]
Specify a namespace to inherit from another container or process. The [namespace identifier]
suffix needs to be replaced with one of the namespaces that appear in the /proc/PID/ns directory.
To inherit the namespace from another process set the lxc.namespace.share.[namespace identifier]
to the PID of the process, e.g. lxc.namespace.share.net=42.
To inherit the namespace from another container set the lxc.namespace.share.[namespace identifier]
to the name of the container, e.g. lxc.namespace.share.pid=c3.
To inherit the namespace from another container located in a different path than the standard
liblxc path set the lxc.namespace.share.[namespace identifier] to the full path to the container,
e.g. lxc.namespace.share.user=/opt/c3.
In order to inherit namespaces the caller needs to have sufficient privilege over the process or
container.
Note that sharing pid namespaces between system containers will likely not work with most init
systems.
Note that if two processes are in different user namespaces and one process wants to inherit the
other's network namespace it usually needs to inherit the user namespace as well.
Note that without careful additional configuration of an LSM, sharing user+pid namespaces with a
task may allow that task to escalate privileges to that of the task calling liblxc.
lxc.time.offset.boot
Specify a positive or negative offset for the boottime clock. The format accepts hours (h),
minutes (m), seconds (s), milliseconds (ms), microseconds (us), and nanoseconds (ns).
lxc.time.offset.monotonic
Specify a positive or negative offset for the monotonic clock. The format accepts hours (h),
minutes (m), seconds (s), milliseconds (ms), microseconds (us), and nanoseconds (ns).
RESOURCE LIMITS
The soft and hard resource limits for the container can be changed. Unprivileged containers can only
lower them. Resources which are not explicitly specified will be inherited.
lxc.prlimit.[limit name]
Specify the resource limit to be set. A limit is specified as two colon separated values which are
either numeric or the word 'unlimited'. A single value can be used as a shortcut to set both soft
and hard limit to the same value. The permitted names the "RLIMIT_" resource names in lowercase
without the "RLIMIT_" prefix, eg. RLIMIT_NOFILE should be specified as "nofile". See setrlimit(2).
If used with no value, lxc will clear the resource limit specified up to this point. A resource
with no explicitly configured limitation will be inherited from the process starting up the
container.
SYSCTL
Configure kernel parameters for the container.
lxc.sysctl.[kernel parameters name]
Specify the kernel parameters to be set. The parameters available are those listed under
/proc/sys/. Note that not all sysctls are namespaced. Changing Non-namespaced sysctls will cause
the system-wide setting to be modified. sysctl(8). If used with no value, lxc will clear the
parameters specified up to this point.
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 otherwise.
lxc.apparmor.profile
Specify the apparmor profile under which the container should be run. To specify that the
container should be unconfined, use
lxc.apparmor.profile = unconfined
If the apparmor profile should remain unchanged (i.e. if you are nesting containers and are
already confined), then use
lxc.apparmor.profile = unchanged
If you instruct LXC to generate the apparmor profile, then use
lxc.apparmor.profile = generated
lxc.apparmor.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.
lxc.apparmor.allow_nesting
If set this to 1, causes the following changes. When generated apparmor profiles are used, they
will contain the necessary changes to allow creating a nested container. In addition to the usual
mount points, /dev/.lxc/proc and /dev/.lxc/sys will contain procfs and sysfs mount points without
the lxcfs overlays, which, if generated apparmor profiles are being used, will not be
read/writable directly.
lxc.apparmor.raw
A list of raw AppArmor profile lines to append to the profile. Only valid when using generated
profiles.
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.selinux.context
Specify the SELinux context under which the container should be run or unconfined_t. For example
lxc.selinux.context = system_u:system_r:lxc_t:s0:c22
lxc.selinux.context.keyring
Specify the SELinux context under which the container's keyring should be created. By default this
the same as lxc.selinux.context, or the context lxc is executed under if lxc.selinux.context has
not been set.
lxc.selinux.context.keyring = system_u:system_r:lxc_t:s0:c22
KERNEL KEYRING
The Linux Keyring facility is primarily a way for various kernel components to retain or cache security
data, authentication keys, encryption keys, and other data in the kernel. By default lxc will create a
new session keyring for the started application.
lxc.keyring.session
Disable the creation of new session keyring by lxc. The started application will then inherit the
current session keyring. By default, or when passing the value 1, a new keyring will be created.
lxc.keyring.session = 0
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 allowlist. The second line
therefore must read "allowlist", with the rest of the file containing one (numeric) syscall number per
line. Each syscall number is allowlisted, while every unlisted number is denylisted for use in the
container
In version 2, the policy may be denylist or allowlist, supports per-rule and per-policy default actions,
and supports per-architecture system call resolution from textual names.
An example denylist policy, in which all system calls are allowed except for mknod, which will simply do
nothing and return 0 (success), looks like:
2
denylist
mknod errno 0
ioctl notify
Specifying "errno" as action will cause LXC to register a seccomp filter that will cause a specific errno
to be returned to the caller. The errno value can be specified after the "errno" action word.
Specifying "notify" as action will cause LXC to register a seccomp listener and retrieve a listener file
descriptor from the kernel. When a syscall is made that is registered as "notify" the kernel will
generate a poll event and send a message over the file descriptor. The caller can read this message,
inspect the syscalls including its arguments. Based on this information the caller is expected to send
back a message informing the kernel which action to take. Until that message is sent the kernel will
block the calling process. The format of the messages to read and sent is documented in seccomp itself.
lxc.seccomp.profile
Specify a file containing the seccomp configuration to load before the container starts.
lxc.seccomp.allow_nesting
If this flag is set to 1, then seccomp filters will be stacked regardless of whether a seccomp
profile is already loaded. This allows nested containers to load their own seccomp profile. The
default setting is 0.
lxc.seccomp.notify.proxy
Specify a unix socket to which LXC will connect and forward seccomp events to. The path must be in
the form unix:/path/to/socket or unix:@socket. The former specifies a path-bound unix domain
socket while the latter specifies an abstract unix domain socket.
lxc.seccomp.notify.cookie
An additional string sent along with proxied seccomp notification requests.
PR_SET_NO_NEW_PRIVS
With PR_SET_NO_NEW_PRIVS active execve() promises not to grant privileges to do anything that could not
have been done without the execve() call (for example, rendering the set-user-ID and set-group-ID mode
bits, and file capabilities non-functional). Once set, this bit cannot be unset. The setting of this bit
is inherited by children created by fork() and clone(), and preserved across execve(). Note that
PR_SET_NO_NEW_PRIVS is applied after the container has changed into its intended AppArmor profile or
SElinux context.
lxc.no_new_privs
Specify whether the PR_SET_NO_NEW_PRIVS flag should be set for the container. Set to 1 to
activate.
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.idmap
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, additional information is passed along. The lxc.hook.version argument
can be used to determine if the following arguments are passed as command line arguments or 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 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_CGNS_AWARE: indicator whether the container is cgroup namespace aware.
• LXC_CONFIG_FILE: the path to the container configuration file.
• LXC_HOOK_TYPE: the hook type (e.g. 'clone', 'mount', 'pre-mount'). Note that the existence of this
environment variable is conditional on the value of lxc.hook.version. If it is set to 1 then
LXC_HOOK_TYPE will be set.
• LXC_HOOK_SECTION: the section type (e.g. 'lxc', 'net'). Note that the existence of this environment
variable is conditional on the value of lxc.hook.version. If it is set to 1 then LXC_HOOK_SECTION will
be set.
• LXC_HOOK_VERSION: the version of the hooks. This value is identical to the value of the container's
lxc.hook.version config item. If it is set to 0 then old-style hooks are used. If it is set to 1 then
new-style hooks are used.
• LXC_LOG_LEVEL: the container's log level.
• LXC_NAME: is the container's name.
• LXC_[NAMESPACE IDENTIFIER]_NS: path under /proc/PID/fd/ to a file descriptor referring to the
container's namespace. For each preserved namespace type there will be a separate environment variable.
These environment variables will only be set if lxc.hook.version is set to 1.
• LXC_ROOTFS_MOUNT: the path to the mounted root filesystem.
• LXC_ROOTFS_PATH: this is the lxc.rootfs.path entry for the container. Note this is likely not where the
mounted rootfs is to be found, use LXC_ROOTFS_MOUNT for that.
• LXC_SRC_NAME: in the case of the clone hook, this is the original container's name.
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.version
To pass the arguments in new style via environment variables set to 1 otherwise set to 0 to pass
them as arguments. This setting affects all hooks arguments that were traditionally passed as
arguments to the script. Specifically, it affects the container name, section (e.g. 'lxc', 'net')
and hook type (e.g. 'clone', 'mount', 'pre-mount') arguments. If new-style hooks are used then
the arguments will be available as environment variables. The container name will be set in
LXC_NAME. (This is set independently of the value used for this config item.) The section will be
set in LXC_HOOK_SECTION and the hook type will be set in LXC_HOOK_TYPE. It also affects how the
paths to file descriptors referring to the container's namespaces are passed. If set to 1 then for
each namespace a separate environment variable LXC_[NAMESPACE IDENTIFIER]_NS will be set. If set
to 0 then the paths will be passed as arguments to the stop hook.
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-host
A hook to be run in the host's namespace after the container has been setup, and immediately
before starting the container init.
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.path]
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.path]
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.log.level
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.log.file
The file to which logging info should be written.
lxc.log.syslog
Send logging info to syslog. It respects the log level defined in lxc.log.level. The argument
should be the syslog facility to use, valid ones are: daemon, local0, local1, local2, local3,
local4, local5, local5, local6, local7.
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. A lower
value means an earlier start.
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.monitor.signal.pdeath
Set the signal to be sent to the container's init when the lxc monitor exits. By default it is set
to SIGKILL which will cause all container processes to be killed when the lxc monitor process
dies. To ensure that containers stay alive even if lxc monitor dies set this to 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
It is possible to inherit host environment variables by setting the name of the variable without a
"=" sign. For example:
lxc.environment = PATH
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.uts.name = myhostname
lxc.net.0.type = veth
lxc.net.0.flags = up
lxc.net.0.link = br0
lxc.net.0.name = eth0
lxc.net.0.hwaddr = 4a:49:43:49:79:bf
lxc.net.0.ipv4.address = 10.2.3.5/24 10.2.3.255
lxc.net.0.ipv6.address = 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.idmap = u 0 100000 10000
lxc.idmap = 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.uts.name = complex
lxc.net.0.type = veth
lxc.net.0.flags = up
lxc.net.0.link = br0
lxc.net.0.hwaddr = 4a:49:43:49:79:bf
lxc.net.0.ipv4.address = 10.2.3.5/24 10.2.3.255
lxc.net.0.ipv6.address = 2003:db8:1:0:214:1234:fe0b:3597
lxc.net.0.ipv6.address = 2003:db8:1:0:214:5432:feab:3588
lxc.net.1.type = macvlan
lxc.net.1.flags = up
lxc.net.1.link = eth0
lxc.net.1.hwaddr = 4a:49:43:49:79:bd
lxc.net.1.ipv4.address = 10.2.3.4/24
lxc.net.1.ipv4.address = 192.168.10.125/24
lxc.net.1.ipv6.address = 2003:db8:1:0:214:1234:fe0b:3596
lxc.net.2.type = phys
lxc.net.2.flags = up
lxc.net.2.link = random0
lxc.net.2.hwaddr = 4a:49:43:49:79:ff
lxc.net.2.ipv4.address = 10.2.3.6/24
lxc.net.2.ipv6.address = 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.fstab = /etc/fstab.complex
lxc.mount.entry = /lib /root/myrootfs/lib none ro,bind 0 0
lxc.rootfs.path = dir:/mnt/rootfs.complex
lxc.rootfs.options = idmap=container
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)
2025-05-10 lxc.container.conf(5)