systemd.nspawn — Container settings
/etc/systemd/nspawn/machine.nspawn
/run/systemd/nspawn/machine.nspawn
/var/lib/machines/machine.nspawn
An nspawn container settings file (suffix .nspawn) contains runtime
configuration for a local container, and is used by
systemd-nspawn(1).
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, similarly to other configuration files supported by
the systemd project. See
systemd.syntax(7) for an
overview.
.nspawn File Discovery¶Files are searched for 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 for in /etc/systemd/nspawn/ and
/run/systemd/nspawn/. If found there, the settings are read and all of them take
full effect (but may still be overridden by corresponding command line arguments). Otherwise, the file
will then be searched for 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 files 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 for how the files are searched and
interpreted may be configured with
systemd-nspawn's --settings=
switch, see
systemd-nspawn(1)
for details.
Settings files may include an [Exec] section, which carries various execution parameters:
Boot=¶Takes a boolean argument, which 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. This option may not be combined with
ProcessTwo=yes. This option is specified by default in the
systemd-nspawn@.service template unit.
Ephemeral=¶Takes a boolean argument, which defaults to off, If enabled, the container is run with
a temporary snapshot of its file system that is removed immediately when the container terminates.
This is equivalent to the --ephemeral command line switch. See
systemd-nspawn(1) for details
about the specific options supported.
ProcessTwo=¶Takes a boolean argument, which defaults to off. If enabled, the specified program is run as
PID 2. A stub init process is run as PID 1. This setting corresponds to the --as-pid2 switch
on the systemd-nspawn command line. This option may not be combined with
Boot=yes.
Parameters=¶Takes a whitespace-separated list of arguments. Single ("'") and
double (""") quotes may be used around arguments with whitespace. 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.
Note: Boot=no, Parameters=a b "c c" is the same as
systemd-nspawn a b "c c", and Boot=yes, Parameters=b 'c c'
is the same as systemd-nspawn --boot b 'c c'.
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.
WorkingDirectory=¶Selects the working directory for the process invoked in the container. Expects an absolute
path in the container's file system namespace. This corresponds to the --chdir= command line
switch.
PivotRoot=¶Selects a directory to pivot to / inside the container when starting up.
Takes a single path, or a pair of two paths separated by a colon. Both paths must be absolute, and are resolved
in the container's file system namespace. This corresponds to the --pivot-root= 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. If the special value "all" is passed, all
capabilities are retained (or dropped).
These settings change the bounding set of capabilities which
also limits the ambient capabilities as given with the
AmbientCapability=.
AmbientCapability=¶Takes a space-separated list of Linux process
capabilities (see
capabilities(7)
for details). The AmbientCapability= setting
specifies capabilities which will be passed to the started program
in the inheritable and ambient capability sets. This will grant
these capabilities to this process. This setting correspond to
the --ambient-capability= command line switch.
The value "all" is not supported for this
setting.
The setting of AmbientCapability= must
be covered by the bounding set settings which were established by
Capability= and DropCapability=.
Note that AmbientCapability= is a privileged
setting (see above).
NoNewPrivileges=¶Takes a boolean argument that controls the PR_SET_NO_NEW_PRIVS flag for
the container payload. This is equivalent to the
--no-new-privileges= command line switch. See
systemd-nspawn(1) for
details.
KillSignal=¶Specify the process signal to send to the
container's PID 1 when nspawn itself receives SIGTERM, in
order to trigger an orderly shutdown of the container.
Defaults to SIGRTMIN+3 if Boot= is used
(on systemd-compatible init systems SIGRTMIN+3 triggers an
orderly shutdown). For a list of valid signals, see
signal(7).
Personality=¶Configures the kernel personality for the
container. This is equivalent to the
--personality= switch.
MachineID=¶Configures the 128-bit machine ID (UUID) to pass to
the container. This is equivalent to the
--uuid= command line switch. This option is
privileged (see above).
PrivateUsers=¶Configures support for usernamespacing. This is equivalent to the
--private-users= command line switch, and takes the same options. This option is privileged
(see above). This option is the default if the systemd-nspawn@.service template unit file
is used.
NotifyReady=¶Configures support for notifications from the container's init process. This is equivalent to
the --notify-ready= command line switch, and takes the same parameters. See
systemd-nspawn(1) for details
about the specific options supported.
SystemCallFilter=¶Configures the system call filter applied to containers. This is equivalent to the
--system-call-filter= command line switch, and takes the same list parameter. See
systemd-nspawn(1) for
details.
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=, LimitRTTIME=¶Configures various types of resource limits applied to containers. This is equivalent to the
--rlimit= command line switch, and takes the same arguments. See
systemd-nspawn(1) for
details.
OOMScoreAdjust=¶Configures the OOM score adjustment value. This is equivalent to the
--oom-score-adjust= command line switch, and takes the same argument. See
systemd-nspawn(1) for
details.
CPUAffinity=¶Configures the CPU affinity. This is equivalent to the --cpu-affinity= command
line switch, and takes the same argument. See
systemd-nspawn(1) for
details.
Hostname=¶Configures the kernel hostname set for the container. This is equivalent to the
--hostname= command line switch, and takes the same argument. See
systemd-nspawn(1) for
details.
ResolvConf=¶Configures how /etc/resolv.conf in the container shall be handled. This is
equivalent to the --resolv-conf= command line switch, and takes the same argument. See
systemd-nspawn(1) for
details.
Timezone=¶Configures how /etc/localtime in the container shall be handled. This is
equivalent to the --timezone= command line switch, and takes the same argument. See
systemd-nspawn(1) for
details.
LinkJournal=¶Configures how to link host and container journal setups. This is equivalent to the
--link-journal= command line switch, and takes the same parameter. See
systemd-nspawn(1) for
details.
SuppressSync=¶Configures whether to suppress disk synchronization for the container payload. This
is equivalent to the --suppress-sync= command line switch, and takes the same
parameter. See
systemd-nspawn(1)
for details.
Settings files may include a [Files] section, which carries various parameters configuring the file system of the container:
ReadOnly=¶Takes a boolean argument, which 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).
BindUser=¶Binds a user from the host into the container. This option is equivalent to the
command line switch --bind-user=, 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).
Inaccessible=¶Masks the specified file or directory in the container, by over-mounting it with an empty file
node of the same type with the most restrictive access mode. Takes a file system path as argument. This option
may be used multiple times to mask multiple files or directories. This option is equivalent to the command line
switch --inaccessible=, see
systemd-nspawn(1) for details
about the specific options supported. This setting is privileged (see above).
Overlay=, OverlayReadOnly=¶Adds an overlay mount point. Takes a colon-separated list of paths. This option may be used
multiple times to configure multiple overlay mounts. This option is equivalent to the command line switches
--overlay= and --overlay-ro=, see
systemd-nspawn(1) for details
about the specific options supported. This setting is privileged (see above).
PrivateUsersOwnership=¶Configures whether the ownership of the files and directories in the container tree
shall be adjusted to the UID/GID range used, if necessary and user namespacing is enabled. This is
equivalent to the --private-users-ownership= command line switch. This option is
privileged (see above).
Settings files may include a [Network] section, which carries various parameters configuring the network connectivity of the container:
Private=¶Takes a boolean argument, which 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). This option is the default if the
systemd-nspawn@.service template unit file is used.
VirtualEthernetExtra=¶Takes a colon-separated pair of interface names. Configures an additional virtual
Ethernet connection ("veth") between host and the container. The first specified
name is the interface name on the host, the second the interface name in the container. The latter
may be omitted in which case it is set to the same name as the host side interface. This setting
implies Private=yes. This setting corresponds to the
--network-veth-extra= command line switch, and may be used multiple times. It is
independent of VirtualEthernet=. Note that this option is unrelated to the
Bridge= setting below, and thus any connections created this way are not
automatically added to any bridge device on the host side. This option is privileged (see
above).
Interface=¶Takes a space-separated list of interfaces to add to the container.
The interface object is defined either by a single interface name, referencing the name on the host,
or a colon-separated pair of interfaces, in which case the first one references the name on the host,
and the second one the name in 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. The interface object is defined either by a single interface name, referencing the name
on the host, or a colon-separated pair of interfaces, in which case the first one references the name
on the host, and the second one the name in 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).
Zone=¶Takes a network zone 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 an automatically managed bridge interface named after the passed argument, prefixed with
"vz-". This option corresponds to the --network-zone= 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).