systemd-nspawn(1)
NAME
systemd-nspawn - Spawn a namespace container for debugging, testing and building
SYNOPSIS
systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]] systemd-nspawn --boot [OPTIONS...] [ARGS...]
DESCRIPTION
systemd-nspawn may be used to run a command or OS in a light-weight namespace container. In many ways it is similar to chroot(1), but more powerful since it fully virtualizes the file system hierarchy, as well as the process tree, the various IPC subsystems and the host and domain name. systemd-nspawn may be invoked on any directory tree containing an operating system tree, using the --directory= command line option. By using the --machine= option an OS tree is automatically searched for in a couple of locations, most importantly in /var/lib/machines, the suggested directory to place container images installed on the system. In contrast to chroot(1) systemd-nspawn may be used to boot full Linux-based operating systems in a container. systemd-nspawn limits access to various kernel interfaces in the container to read-only, such as /sys, /proc/sys or /sys/fs/selinux. The host's network interfaces and the system clock may not be changed from within the container. Device nodes may not be created. The host system cannot be rebooted and kernel modules may not be loaded from within the container. Use a tool like dnf(8), debootstrap(8), or pacman(8) to set up an OS directory tree suitable as file system hierarchy for systemd-nspawn containers. See the Examples section below for details on suitable invocation of these commands. As a safety check systemd-nspawn will verify the existence of /usr/lib/os-release or /etc/os-release in the container tree before starting the container (see os-release(5)). It might be necessary to add this file to the container tree manually if the OS of the container is too old to contain this file out-of-the-box. systemd-nspawn may be invoked directly from the interactive command line or run as system service in the background. In this mode each container instance runs as its own service instance; a default template unit file systemd-nspawn@.service is provided to make this easy, taking the container name as instance identifier. Note that different default options apply when systemd-nspawn is invoked by the template unit file than interactively on the command line. Most importantly the template unit file makes use of the --boot which is not the default in case systemd-nspawn is invoked from the interactive command line. Further differences with the defaults are documented along with the various supported options below. The machinectl(1) tool may be used to execute a number of operations on containers. In particular it provides easy-to-use commands to run containers as system services using the systemd-nspawn@.service template unit file. Along with each container a settings file with the .nspawn suffix may exist, containing additional settings to apply when running the container. See systemd.nspawn(5) for details. Settings files override the default options used by the systemd-nspawn@.service template unit file, making it usually unnecessary to alter this template file directly. Note that systemd-nspawn will mount file systems private to the container to /dev, /run and similar. These will not be visible outside of the container, and their contents will be lost when the container exits. Note that running two systemd-nspawn containers from the same directory tree will not make processes in them see each other. The PID namespace separation of the two containers is complete and the containers will share very few runtime objects except for the underlying file system. Use machinectl(1)'s login or shell commands to request an additional login session in a running container. systemd-nspawn implements the Container Interface[1] specification. While running, containers invoked with systemd-nspawn are registered with the systemd-machined(8) service that keeps track of running containers, and provides programming interfaces to interact with them.
OPTIONS
If option -b is specified, the arguments are used as arguments for the
init binary. Otherwise, COMMAND specifies the program to launch in the
container, and the remaining arguments are used as arguments for this
program. If --boot is not used and no arguments are specified, a shell
is launched in the container.
The following options are understood:
-D, --directory=
Directory to use as file system root for the container.
If neither --directory=, nor --image= is specified the directory is
determined by searching for a directory named the same as the
machine name specified with --machine=. See machinectl(1) section
"Files and Directories" for the precise search path.
If neither --directory=, --image=, nor --machine= are specified,
the current directory will be used. May not be specified together
with --image=.
--template=
Directory or "btrfs" subvolume to use as template for the
container's root directory. If this is specified and the
container's root directory (as configured by --directory=) does not
yet exist it is created as "btrfs" subvolume and populated from
this template tree. Ideally, the specified template path refers to
the root of a "btrfs" subvolume, in which case a simple
copy-on-write snapshot is taken, and populating the root directory
is instant. If the specified template path does not refer to the
root of a "btrfs" subvolume (or not even to a "btrfs" file system
at all), the tree is copied, which can be substantially more
time-consuming. Note that if this option is used the container's
root directory (in contrast to the template directory!) must be
located on a "btrfs" file system, so that the "btrfs" subvolume may
be created. May not be specified together with --image= or
--ephemeral.
Note that this switch leaves host name, machine ID and all other
settings that could identify the instance unmodified.
-x, --ephemeral
If specified, the container is run with a temporary "btrfs"
snapshot of its root directory (as configured with --directory=),
that is removed immediately when the container terminates. This
option is only supported if the root file system is "btrfs". May
not be specified together with --image= or --template=.
Note that this switch leaves host name, machine ID and all other
settings that could identify the instance unmodified.
-i, --image=
Disk image to mount the root directory for the container from.
Takes a path to a regular file or to a block device node. The file
or block device must contain either:
* An MBR partition table with a single partition of type 0x83
that is marked bootable.
* A GUID partition table (GPT) with a single partition of type
0fc63daf-8483-4772-8e79-3d69d8477de4.
* A GUID partition table (GPT) with a marked root partition which
is mounted as the root directory of the container. Optionally,
GPT images may contain a home and/or a server data partition
which are mounted to the appropriate places in the container.
All these partitions must be identified by the partition types
defined by the Discoverable Partitions Specification[2].
Any other partitions, such as foreign partitions, swap partitions
or EFI system partitions are not mounted. May not be specified
together with --directory=, --template= or --ephemeral.
-a, --as-pid2
Invoke the shell or specified program as process ID (PID) 2 instead
of PID 1 (init). By default, if neither this option nor --boot is
used, the selected binary is run as process with PID 1, a mode only
suitable for programs that are aware of the special semantics that
the process with PID 1 has on UNIX. For example, it needs to reap
all processes reparented to it, and should implement sysvinit
compatible signal handling (specifically: it needs to reboot on
SIGINT, reexecute on SIGTERM, reload configuration on SIGHUP, and
so on). With --as-pid2 a minimal stub init process is run as PID 1
and the selected binary is executed as PID 2 (and hence does not
need to implement any special semantics). The stub init process
will reap processes as necessary and react appropriately to
signals. It is recommended to use this mode to invoke arbitrary
commands in containers, unless they have been modified to run
correctly as PID 1. Or in other words: this switch should be used
for pretty much all commands, except when the command refers to an
init or shell implementation, as these are generally capable of
running correctly as PID 1. This option may not be combined with
--boot.
-b, --boot
Automatically search for an init binary and invoke it as PID 1,
instead of a shell or a user supplied program. If this option is
used, arguments specified on the command line are used as arguments
for the init binary. This option may not be combined with
--as-pid2.
The following table explains the different modes of invocation and
relationship to --as-pid2 (see above):
Table 1. Invocation Mode
Switch Explanation
Neither --as-pid2 nor The passed parameters are
--boot specified interpreted as the command
line, which is executed as
PID 1 in the container.
--as-pid2 specified The passed parameters are
interpreted as the command
line, which is executed as
PID 2 in the container. A
stub init process is run
as PID 1.
--boot specified An init binary as
automatically searched and
run as PID 1 in the
container. The passed
parameters are used as
invocation parameters for
this process.
Note that --boot is the default mode of operation if the
systemd-nspawn@.service template unit file is used.
--chdir=
Change to the specified working directory before invoking the
process in the container. Expects an absolute path in the
container's file system namespace.
-u, --user=
After transitioning into the container, change to the specified
user-defined in the container's user database. Like all other
systemd-nspawn features, this is not a security feature and
provides protection against accidental destructive operations only.
-M, --machine=
Sets the machine name for this container. This name may be used to
identify this container during its runtime (for example in tools
like machinectl(1) and similar), and is used to initialize the
container's hostname (which the container can choose to override,
however). If not specified, the last component of the root
directory path of the container is used, possibly suffixed with a
random identifier in case --ephemeral mode is selected. If the root
directory selected is the host's root directory the host's hostname
is used as default instead.
--uuid=
Set the specified UUID for the container. The init system will
initialize /etc/machine-id from this if this file is not set yet.
Note that this option takes effect only if /etc/machine-id in the
container is unpopulated.
--slice=
Make the container part of the specified slice, instead of the
default machine.slice. This is only applies if the machine is run
in its own scope unit, i.e. if --keep-unit is not used.
--property=
Set a unit property on the scope unit to register for the machine.
This only applies if the machine is run in its own scope unit, i.e.
if --keep-unit is not used. Takes unit property assignments in the
same format as systemctl set-property. This is useful to set memory
limits and similar for machines.
--private-users=
Controls user namespacing. If enabled, the container will run with
its own private set of UNIX user and group ids (UIDs and GIDs).
This involves mapping the private UIDs/GIDs used in the container
(starting with the container's root user 0 and up) to a range of
UIDs/GIDs on the host that are not used for other purposes (usually
in the range beyond the host's UID/GID 65536). The parameter may be
specified as follows:
1. If one or two colon-separated numbers are specified, user
namespacing is turned on. The first parameter specifies the
first host UID/GID to assign to the container, the second
parameter specifies the number of host UIDs/GIDs to assign to
the container. If the second parameter is omitted, 65536
UIDs/GIDs are assigned.
2. If the parameter is omitted, or true, user namespacing is
turned on. The UID/GID range to use is determined automatically
from the file ownership of the root directory of the
container's directory tree. To use this option, make sure to
prepare the directory tree in advance, and ensure that all
files and directories in it are owned by UIDs/GIDs in the range
you'd like to use. Also, make sure that used file ACLs
exclusively reference UIDs/GIDs in the appropriate range. If
this mode is used the number of UIDs/GIDs assigned to the
container for use is 65536, and the UID/GID of the root
directory must be a multiple of 65536.
3. If the parameter is false, user namespacing is turned off. This
is the default.
4. The special value "pick" turns on user namespacing. In this
case the UID/GID range is automatically chosen. As first step,
the file owner of the root directory of the container's
directory tree is read, and it is checked that it is currently
not used by the system otherwise (in particular, that no other
container is using it). If this check is successful, the
UID/GID range determined this way is used, similar to the
behavior if "yes" is specified. If the check is not successful
(and thus the UID/GID range indicated in the root directory's
file owner is already used elsewhere) a new -- currently unused
-- UID/GID range of 65536 UIDs/GIDs is randomly chosen between
the host UID/GIDs of 524288 and 1878982656, always starting at
a multiple of 65536. This setting implies --private-users-chown
(see below), which has the effect that the files and
directories in the container's directory tree will be owned by
the appropriate users of the range picked. Using this option
makes user namespace behavior fully automatic. Note that the
first invocation of a previously unused container image might
result in picking a new UID/GID range for it, and thus in the
(possibly expensive) file ownership adjustment operation.
However, subsequent invocations of the container will be cheap
(unless of course the picked UID/GID range is assigned to a
different use by then).
It is recommended to assign at least 65536 UIDs/GIDs to each
container, so that the usable UID/GID range in the container covers
16 bit. For best security, do not assign overlapping UID/GID ranges
to multiple containers. It is hence a good idea to use the upper 16
bit of the host 32-bit UIDs/GIDs as container identifier, while the
lower 16 bit encode the container UID/GID used. This is in fact the
behavior enforced by the --private-users=pick option.
When user namespaces are used, the GID range assigned to each
container is always chosen identical to the UID range.
In most cases, using --private-users=pick is the recommended option
as it enhances container security massively and operates fully
automatically in most cases.
Note that the picked UID/GID range is not written to /etc/passwd or
/etc/group. In fact, the allocation of the range is not stored
persistently anywhere, except in the file ownership of the files
and directories of the container.
--private-users-chown
If specified, all files and directories in the container's
directory tree will adjusted so that they are owned to the
appropriate UIDs/GIDs selected for the container (see above). This
operation is potentially expensive, as it involves descending and
iterating through the full directory tree of the container. Besides
actual file ownership, file ACLs are adjusted as well.
This option is implied if --private-users=pick is used. This option
has no effect if user namespacing is not used.
-U
If the kernel supports the user namespaces feature, equivalent to
--private-users=pick --private-users-chown, otherwise equivalent to
--private-users=no.
Note that -U is the default if the systemd-nspawn@.service template
unit file is used.
Note: it is possible to undo the effect of --private-users-chown
(or -U) on the file system by redoing the operation with the first
UID of 0:
systemd-nspawn ... --private-users=0 --private-users-chown
--private-network
Disconnect networking of the container from the host. This makes
all network interfaces unavailable in the container, with the
exception of the loopback device and those specified with
--network-interface= and configured with --network-veth. If this
option is specified, the CAP_NET_ADMIN capability will be added to
the set of capabilities the container retains. The latter may be
disabled by using --drop-capability=.
--network-interface=
Assign the specified network interface to the container. This will
remove the specified interface from the calling namespace and place
it in the container. When the container terminates, it is moved
back to the host namespace. Note that --network-interface= implies
--private-network. This option may be used more than once to add
multiple network interfaces to the container.
--network-macvlan=
Create a "macvlan" interface of the specified Ethernet network
interface and add it to the container. A "macvlan" interface is a
virtual interface that adds a second MAC address to an existing
physical Ethernet link. The interface in the container will be
named after the interface on the host, prefixed with "mv-". Note
that --network-macvlan= implies --private-network. This option may
be used more than once to add multiple network interfaces to the
container.
--network-ipvlan=
Create an "ipvlan" interface of the specified Ethernet network
interface and add it to the container. An "ipvlan" interface is a
virtual interface, similar to a "macvlan" interface, which uses the
same MAC address as the underlying interface. The interface in the
container will be named after the interface on the host, prefixed
with "iv-". Note that --network-ipvlan= implies --private-network.
This option may be used more than once to add multiple network
interfaces to the container.
-n, --network-veth
Create a virtual Ethernet link ("veth") between host and container.
The host side of the Ethernet link will be available as a network
interface named after the container's name (as specified with
--machine=), prefixed with "ve-". The container side of the
Ethernet link will be named "host0". The --network-veth option
implies --private-network.
Note that systemd-networkd.service(8) includes by default a network
file /lib/systemd/network/80-container-ve.network matching the
host-side interfaces created this way, which contains settings to
enable automatic address provisioning on the created virtual link
via DHCP, as well as automatic IP routing onto the host's external
network interfaces. It also contains
/lib/systemd/network/80-container-host0.network matching the
container-side interface created this way, containing settings to
enable client side address assignment via DHCP. In case
systemd-networkd is running on both the host and inside the
container, automatic IP communication from the container to the
host is thus available, with further connectivity to the external
network.
Note that --network-veth is the default if the
systemd-nspawn@.service template unit file is used.
--network-veth-extra=
Adds an additional virtual Ethernet link between host and
container. Takes a colon-separated pair of host interface name and
container interface name. The latter may be omitted in which case
the container and host sides will be assigned the same name. This
switch is independent of --network-veth, and --- in contrast --- may be
used multiple times, and allows configuration of the network
interface names. Note that --network-bridge= has no effect on
interfaces created with --network-veth-extra=.
--network-bridge=
Adds the host side of the Ethernet link created with --network-veth
to the specified Ethernet bridge interface. Expects a valid network
interface name of a bridge device as argument. Note that
--network-bridge= implies --network-veth. If this option is used,
the host side of the Ethernet link will use the "vb-" prefix
instead of "ve-".
--network-zone=
Creates a virtual Ethernet link ("veth") to the container and adds
it to an automatically managed Ethernet bridge interface. The
bridge interface is named after the passed argument, prefixed with
"vz-". The bridge interface is automatically created when the first
container configured for its name is started, and is automatically
removed when the last container configured for its name exits.
Hence, each bridge interface configured this way exists only as
long as there's at least one container referencing it running. This
option is very similar to --network-bridge=, besides this automatic
creation/removal of the bridge device.
This setting makes it easy to place multiple related containers on
a common, virtual Ethernet-based broadcast domain, here called a
"zone". Each container may only be part of one zone, but each zone
may contain any number of containers. Each zone is referenced by
its name. Names may be chosen freely (as long as they form valid
network interface names when prefixed with "vz-"), and it is
sufficient to pass the same name to the --network-zones= switch of
the various concurrently running containers to join them in one
zone.
Note that systemd-networkd.service(8) includes by default a network
file /lib/systemd/network/80-container-vz.network matching the
bridge interfaces created this way, which contains settings to
enable automatic address provisioning on the created virtual
network via DHCP, as well as automatic IP routing onto the host's
external network interfaces. Using --network-zone= is hence in most
cases fully automatic and sufficient to connect multiple local
containers in a joined broadcast domain to the host, with further
connectivity to the external network.
-p, --port=
If private networking is enabled, maps an IP port on the host onto
an IP port on the container. Takes a protocol specifier (either
"tcp" or "udp"), separated by a colon from a host port number in
the range 1 to 65535, separated by a colon from a container port
number in the range from 1 to 65535. The protocol specifier and its
separating colon may be omitted, in which case "tcp" is assumed.
The container port number and its colon may be omitted, in which
case the same port as the host port is implied. This option is only
supported if private networking is used, such as with
--network-veth, --network-zone= --network-bridge=.
-Z, --selinux-context=
Sets the SELinux security context to be used to label processes in
the container.
-L, --selinux-apifs-context=
Sets the SELinux security context to be used to label files in the
virtual API file systems in the container.
--capability=
List one or more additional capabilities to grant the container.
Takes a comma-separated list of capability names, see
capabilities(7) for more information. Note that the following
capabilities will be granted in any way: CAP_CHOWN,
CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, CAP_FSETID,
CAP_IPC_OWNER, CAP_KILL, CAP_LEASE, CAP_LINUX_IMMUTABLE,
CAP_NET_BIND_SERVICE, CAP_NET_BROADCAST, CAP_NET_RAW, CAP_SETGID,
CAP_SETFCAP, CAP_SETPCAP, CAP_SETUID, CAP_SYS_ADMIN,
CAP_SYS_CHROOT, CAP_SYS_NICE, CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
CAP_SYS_RESOURCE, CAP_SYS_BOOT, CAP_AUDIT_WRITE, CAP_AUDIT_CONTROL.
Also CAP_NET_ADMIN is retained if --private-network is specified.
If the special value "all" is passed, all capabilities are
retained.
--drop-capability=
Specify one or more additional capabilities to drop for the
container. This allows running the container with fewer
capabilities than the default (see above).
--kill-signal=
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).
--link-journal=
Control whether the container's journal shall be made visible to
the host system. If enabled, allows viewing the container's journal
files from the host (but not vice versa). Takes one of "no",
"host", "try-host", "guest", "try-guest", "auto". If "no", the
journal is not linked. If "host", the journal files are stored on
the host file system (beneath /var/log/journal/machine-id) and the
subdirectory is bind-mounted into the container at the same
location. If "guest", the journal files are stored on the guest
file system (beneath /var/log/journal/machine-id) and the
subdirectory is symlinked into the host at the same location.
"try-host" and "try-guest" do the same but do not fail if the host
does not have persistent journaling enabled. If "auto" (the
default), and the right subdirectory of /var/log/journal exists, it
will be bind mounted into the container. If the subdirectory does
not exist, no linking is performed. Effectively, booting a
container once with "guest" or "host" will link the journal
persistently if further on the default of "auto" is used.
Note that --link-journal=try-guest is the default if the
systemd-nspawn@.service template unit file is used.
-j
Equivalent to --link-journal=try-guest.
--read-only
Mount the root file system read-only for the container.
--bind=, --bind-ro=
Bind mount a file or directory from the host into the container.
Takes one of: a path argument --- in which case the specified path
will be mounted from the host to the same path in the container ---,
or a colon-separated pair of paths --- in which case the first
specified path is the source in the host, and the second path is
the destination in the container ---, or a colon-separated triple of
source path, destination path and mount options. Mount options are
comma-separated and currently, only "rbind" and "norbind" are
allowed. Defaults to "rbind". Backslash escapes are interpreted, so
"\:" may be used to embed colons in either path. This option may be
specified multiple times for creating multiple independent bind
mount points. The --bind-ro= option creates read-only bind mounts.
--tmpfs=
Mount a tmpfs file system into the container. Takes a single
absolute path argument that specifies where to mount the tmpfs
instance to (in which case the directory access mode will be chosen
as 0755, owned by root/root), or optionally a colon-separated pair
of path and mount option string that is used for mounting (in which
case the kernel default for access mode and owner will be chosen,
unless otherwise specified). This option is particularly useful for
mounting directories such as /var as tmpfs, to allow state-less
systems, in particular when combined with --read-only. Backslash
escapes are interpreted in the path, so "\:" may be used to embed
colons in the path.
--overlay=, --overlay-ro=
Combine multiple directory trees into one overlay file system and
mount it into the container. Takes a list of colon-separated paths
to the directory trees to combine and the destination mount point.
Backslash escapes are interpreted in the paths, so "\:" may be used
to embed colons in the paths.
If three or more paths are specified, then the last specified path
is the destination mount point in the container, all paths
specified before refer to directory trees on the host and are
combined in the specified order into one overlay file system. The
left-most path is hence the lowest directory tree, the
second-to-last path the highest directory tree in the stacking
order. If --overlay-ro= is used instead of --overlay=, a read-only
overlay file system is created. If a writable overlay file system
is created, all changes made to it are written to the highest
directory tree in the stacking order, i.e. the second-to-last
specified.
If only two paths are specified, then the second specified path is
used both as the top-level directory tree in the stacking order as
seen from the host, as well as the mount point for the overlay file
system in the container. At least two paths have to be specified.
For details about overlay file systems, see overlayfs.txt[3]. Note
that the semantics of overlay file systems are substantially
different from normal file systems, in particular regarding
reported device and inode information. Device and inode information
may change for a file while it is being written to, and processes
might see out-of-date versions of files at times. Note that this
switch automatically derives the "workdir=" mount option for the
overlay file system from the top-level directory tree, making it a
sibling of it. It is hence essential that the top-level directory
tree is not a mount point itself (since the working directory must
be on the same file system as the top-most directory tree). Also
note that the "lowerdir=" mount option receives the paths to stack
in the opposite order of this switch.
-E NAME=VALUE, --setenv=NAME=VALUE
Specifies an environment variable assignment to pass to the init
process in the container, in the format "NAME=VALUE". This may be
used to override the default variables or to set additional
variables. This parameter may be used more than once.
--register=
Controls whether the container is registered with systemd-
machined(8). Takes a boolean argument, which defaults to "yes".
This option should be enabled when the container runs a full
Operating System (more specifically: an init system), and is useful
to ensure that the container is accessible via machinectl(1) and
shown by tools such as ps(1). If the container does not run an init
system, it is recommended to set this option to "no".
--keep-unit
Instead of creating a transient scope unit to run the container in,
simply register the service or scope unit systemd-nspawn has been
invoked in with systemd-machined(8). This has no effect if
--register=no is used. This switch should be used if systemd-nspawn
is invoked from within a service unit, and the service unit's sole
purpose is to run a single systemd-nspawn container. This option is
not available if run from a user session.
--personality=
Control the architecture ("personality") reported by uname(2) in
the container. Currently, only "x86" and "x86-64" are supported.
This is useful when running a 32-bit container on a 64-bit host. If
this setting is not used, the personality reported in the container
is the same as the one reported on the host.
-q, --quiet
Turns off any status output by the tool itself. When this switch is
used, the only output from nspawn will be the console output of the
container OS itself.
--volatile, --volatile=MODE
Boots the container in volatile mode. When no mode parameter is
passed or when mode is specified as yes, full volatile mode is
enabled. This means the root directory is mounted as a mostly
unpopulated "tmpfs" instance, and /usr from the OS tree is mounted
into it in read-only mode (the system thus starts up with read-only
OS image, but pristine state and configuration, any changes are
lost on shutdown). When the mode parameter is specified as state,
the OS tree is mounted read-only, but /var is mounted as a "tmpfs"
instance into it (the system thus starts up with read-only OS
resources and configuration, but pristine state, and any changes to
the latter are lost on shutdown). When the mode parameter is
specified as no (the default), the whole OS tree is made available
writable.
Note that setting this to yes or state will only work correctly
with operating systems in the container that can boot up with only
/usr mounted, and are able to populate /var automatically, as
needed.
--settings=MODE
Controls whether systemd-nspawn shall search for and use additional
per-container settings from .nspawn files. Takes a boolean or the
special values override or trusted.
If enabled (the default), a settings file named after the machine
(as specified with the --machine= setting, or derived from the
directory or image file name) with the suffix .nspawn is searched
in /etc/systemd/nspawn/ and /run/systemd/nspawn/. If it is found
there, its settings are read and used. If it is not found there, it
is subsequently searched in the same directory as the image file or
in the immediate parent of the root directory of the container. In
this case, if the file is found, its settings will be also read and
used, but potentially unsafe settings are ignored. Note that in
both these cases, settings on the command line take precedence over
the corresponding settings from loaded .nspawn files, if both are
specified. Unsafe settings are considered all settings that elevate
the container's privileges or grant access to additional resources
such as files or directories of the host. For details about the
format and contents of .nspawn files, consult systemd.nspawn(5).
If this option is set to override, the file is searched, read and
used the same way, however, the order of precedence is reversed:
settings read from the .nspawn file will take precedence over the
corresponding command line options, if both are specified.
If this option is set to trusted, the file is searched, read and
used the same way, but regardless of being found in
/etc/systemd/nspawn/, /run/systemd/nspawn/ or next to the image
file or container root directory, all settings will take effect,
however, command line arguments still take precedence over
corresponding settings.
If disabled, no .nspawn file is read and no settings except the
ones on the command line are in effect.
--notify-ready=
Configures support for notifications from the container's init
process. --notify-ready= takes a boolean (no and yes). With option
no systemd-nspawn notifies systemd with a "READY=1" message when
the init process is created. With option yes systemd-nspawn waits
for the "READY=1" message from the init process in the container
before sending its own to systemd. For more details about
notifications see sd_notify(3)).
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
EXAMPLES
Example 1. Download a Fedora image and start a shell in it
# machinectl pull-raw --verify=no http://ftp.halifax.rwth-aachen.de/fedora/linux/releases/24/CloudImages/x86_64/images/Fedora-Cloud-Base-24-1.2.x86_64.raw.xz
# systemd-nspawn -M Fedora-Cloud-Base-24-1.2.x86_64.raw
This downloads an image using machinectl(1) and opens a shell in it.
Example 2. Build and boot a minimal Fedora distribution in a container
# dnf -y --releasever=23 --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora --enablerepo=updates install systemd passwd dnf fedora-release vim-minimal
# systemd-nspawn -bD /srv/mycontainer
This installs a minimal Fedora distribution into the directory
/srv/mycontainer/ and then boots an OS in a namespace container in it.
Example 3. Spawn a shell in a container of a minimal Debian unstable
distribution
# debootstrap --arch=amd64 unstable ~/debian-tree/
# systemd-nspawn -D ~/debian-tree/
This installs a minimal Debian unstable distribution into the directory
~/debian-tree/ and then spawns a shell in a namespace container in it.
Example 4. Boot a minimal Arch Linux distribution in a container
# pacstrap -c -d ~/arch-tree/ base
# systemd-nspawn -bD ~/arch-tree/
This installs a minimal Arch Linux distribution into the directory
~/arch-tree/ and then boots an OS in a namespace container in it.
Example 5. Boot into an ephemeral "btrfs" snapshot of the host system
# systemd-nspawn -D / -xb
This runs a copy of the host system in a "btrfs" snapshot which is
removed immediately when the container exits. All file system changes
made during runtime will be lost on shutdown, hence.
Example 6. Run a container with SELinux sandbox security contexts
# chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
# systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh
EXIT STATUS
The exit code of the program executed in the container is returned.
SEE ALSO
systemd(1), systemd.nspawn(5), chroot(1), dnf(8), debootstrap(8), pacman(8), systemd.slice(5), machinectl(1), btrfs(8)
NOTES
1. Container Interface
http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
2. Discoverable Partitions Specification
http://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/
3. overlayfs.txt
https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt
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