SYSTEMD.NSPAWN(5)

NAME
systemd.nspawn - Container settings

SYNOPSIS

/etc/systemd/nspawn/machine.nspawn

/run/systemd/nspawn/machine.nspawn

/var/lib/machines/machine.nspawn

DESCRIPTION

An nspawn container settings file (suffix .nspawn) encodes additional runtime information about a local container, and is searched, read and used by systemd-nspawn(1) when starting a container. Files of this type are named after the containers they define settings for. They are optional, and only required for containers whose execution environment shall differ from the defaults. Files of this type mostly contain settings that may also be set on the systemd-nspawn command line, and make it easier to persistently attach specific settings to specific containers. The syntax of these files is inspired by .desktop files following the XDG Desktop Entry Specification[1], which are in turn inspired by Microsoft Windows .ini files.

Boolean arguments used in these settings files can be written in various formats. For positive settings the strings 1, yes, true and on are equivalent. For negative settings, the strings 0, no, false and off are equivalent.

Empty lines and lines starting with # or ; are ignored. This may be used for commenting. Lines ending in a backslash are concatenated with the following line while reading and the backslash is replaced by a space character. This may be used to wrap long lines.

.NSPAWN FILE DISCOVERY

Files are searched by appending the .nspawn suffix to the machine name of the container, as specified with the --machine= switch of systemd-nspawn, or derived from the directory or image file name. This file is first searched in /etc/systemd/nspawn/ and /run/systemd/nspawn/. If found in these directories its settings are read and all of them take full effect (but are possibly overridden by corresponding command line arguments). If not found the file will then be searched next to the image file or in the immediate parent of the root directory of the container. If the file is found there only a subset of the settings will take effect however. All settings that possibly elevate privileges or grant additional access to resources of the host (such as files or directories) are ignored. To which options this applies is documented below.

Persistent settings file created and maintained by the administrator (and thus trusted) should be placed in /etc/systemd/nspawn/, while automatically downloaded (and thus potentially untrusted) settings files are placed in /var/lib/machines/ instead (next to the container images), where their security impact is limited. In order to add privileged settings to .nspawn files acquired from the image vendor it is recommended to copy the settings files into /etc/systemd/nspawn/ and edit them there, so that the privileged options become available. The precise algorithm how the files are searched and interpreted may be configured with systemd-nspawn's --settings= switch, see systemd-nspawn(1) for details.

[EXEC] SECTION OPTIONS

Settings files may include an "[Exec]" section, which carries various execution parameters:

Boot=
    Takes a boolean argument, defaults to off. If enabled systemd-nspawn will automatically search for an init executable and invoke it. In this case the specified parameters using Parameters= are passed as additional arguments to the init process. This setting corresponds to the --boot switch on the systemd-nspawn command line.

Parameters=
    Takes a space separated list of arguments. This is either a command line, beginning with the binary name to execute, or – if Boot= is enabled – the list of arguments to pass to the init process. This setting corresponds to the command line parameters passed on the systemd-nspawn command line.

Environment=
    Takes an environment variable assignment consisting of key and value, separated by "=". Sets an environment variable for the main process invoked in the container. This setting may be used multiple times to set multiple environment variables. It corresponds to the --setenv= command line switch.

User=
    Takes a UNIX user name. Specifies the user name to invoke the main process of the container as. This user must be known in the container's user database. This corresponds to the --user= command line switch.

Capability=, DropCapability=
    Takes a space separated list of Linux process capabilities (see capabilities(7) for details). The Capability= setting specifies additional capabilities to pass on top of the default set of capabilities. The DropCapability= setting specifies capabilities to drop from the default set. These settings correspond to the --capability= and --drop-capability= command line switches. Note that Capability= is a privileged setting, and only takes effect in .nspawn files in /etc/systemd/nspawn/ and /run/system/nspawn/ (see above). On the other hand DropCapability= takes effect in all cases.

Personality=
    Configures the kernel personality for the container. This is equivalent to the --personality= switch.

MachineID=
    Configures the 128bit machine ID (UUID) to pass to the container. This is equivalent to the --uuid= command line switch. This option is privileged (see above).

[FILES] SECTION OPTIONS

Settings files may include a "[Files]" section, which carries various parameters configuring the file system of the container:

ReadOnly=
    Takes a boolean argument, defaults to off. If specified the container will be run with a read-only file system. This setting corresponds to the --read-only command line switch.

Volatile=
    Takes a boolean argument, or the special value "state". This configures whether to run the container with volatile state and/or configuration. This option is equivalent to --volatile=, see systemd-nspawn(1) for details about the specific options supported.

Bind=, BindReadOnly=
    Adds a bind mount from the host into the container. Takes a single path, a pair of two paths separated by a colon, or a triplet of two paths plus an option string separated by colons. This option may be used multiple times to configure multiple bind mounts. This option is equivalent to the command line switches --bind= and --bind-ro=, see systemd-nspawn(1) for details about the specific options supported. This setting is privileged (see above).

TemporaryFileSystem=
    Adds a "tmpfs" mount to the container. Takes a path or a pair of path and option string, separated by a colon. This option may be used multiple times to configure multiple "tmpfs" mounts. This option is equivalent to the command line switch --tmpfs=, see systemd-nspawn(1) for details about the specific options supported. This setting is privileged (see above).

[NETWORK] SECTION OPTIONS

Settings files may include a "[Network]" section, which carries various parameters configuring the network connectivity of the container:

Private=
    Takes a boolean argument, defaults to off. If enabled the container will run in its own network namespace and not share network interfaces and configuration with the host. This setting corresponds to the --private-network command line switch.

VirtualEthernet=
    Takes a boolean argument. Configures whether to create a virtual ethernet connection ("veth") between host and the container. This setting implies Private=yes. This setting corresponds to the --network-veth command line switch. This option is privileged (see above).

Interface=
    Takes a space separated list of interfaces to add to the container. This option corresponds to the --network-interface= command line switch and implies Private=yes. This option is privileged (see above).

MACVLAN=, IPVLAN=
    Takes a space separated list of interfaces to add MACLVAN or IPVLAN interfaces to, which are then added to the container. These options correspond to the --network-macvlan= and --network-ipvlan= command line switches and imply Private=yes. These options are privileged (see above).

Bridge=
    Takes an interface name. This setting implies VirtualEthernet=yes and Private=yes and has the effect that the host side of the created virtual Ethernet link is connected to the specified bridge interface. This option corresponds to the --network-bridge= command line switch. This option is privileged (see above).

Port=
    Exposes a TCP or UDP port of the container on the host. This option corresponds to the --port= command line switch, see systemd-nspawn(1) for the precise syntax of the argument this option takes. This option is privileged (see above).

SEE ALSO

systemd(1), systemd-nspawn(1), systemd.directives(7)

NOTES

1.  XDG Desktop Entry Specification
    http://standards.freedesktop.org/desktop-entry-spec/latest/