Man page of lxc.container.conf

lxc.container.conf

Section: (5)
Updated: 2021-06-03
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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.

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:

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. Note that unprivileged containers do not work with this setting due to an inability to mount sysfs. An unsafe workaround would be to bind mount the host's sysfs.

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.

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.

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 his 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 hierachies.

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 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.cgroup.devices.allow and lxc.cgroup.devices.deny must be used.

•

A allowlist 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.

•

A denylist 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 aformentioned 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 a 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 = dummy0
        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

AUTHOR

Daniel Lezcano <daniel.lezcano@free.fr>

Index

NAME

DESCRIPTION

CONFIGURATION
ARCHITECTURE
HOSTNAME
HALT SIGNAL
REBOOT SIGNAL
STOP SIGNAL
INIT COMMAND
INIT WORKING DIRECTORY
INIT ID
PROC
EPHEMERAL
NETWORK
NEW PSEUDO TTY INSTANCE (DEVPTS)
CONTAINER SYSTEM CONSOLE
CONSOLE THROUGH THE TTYS
CONSOLE DEVICES LOCATION
/DEV DIRECTORY
MOUNT POINTS
ROOT FILE SYSTEM
CONTROL GROUPS ("CGROUPS")
CAPABILITIES
NAMESPACES
RESOURCE LIMITS
SYSCTL
APPARMOR PROFILE
SELINUX CONTEXT
KERNEL KEYRING
SECCOMP CONFIGURATION
PR_SET_NO_NEW_PRIVS
UID MAPPINGS
CONTAINER HOOKS
CONTAINER HOOKS ENVIRONMENT VARIABLES
LOGGING
AUTOSTART
AUTOSTART AND SYSTEM BOOT
CONTAINER ENVIRONMENT

EXAMPLES

NETWORK
UID/GID MAPPING
CONTROL GROUP
COMPLEX CONFIGURATION

SEE ALSO

AUTHOR

This document was created by man2html, using the manual pages.
Time: 04:45:25 GMT, December 18, 2024