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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | EXIT STATUS | SEE ALSO | NOTES | COLOPHON |
SYSTEMD-NSPAWN(1) systemd-nspawn SYSTEMD-NSPAWN(1)
systemd-nspawn - Spawn a namespace container for debugging, testing
and building
systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]
systemd-nspawn --boot [OPTIONS...] [ARGS...]
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.
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" snapshot (if supported) or
plain directory (otherwise) 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 (though possibly in a copy-on-write scheme —
if the file system supports that), which can be substantially
more time-consuming. 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 snapshot of
its file system that is removed immediately when the container
terminates. May not be specified together with --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].
· No partition table, and a single file system spanning the
whole image.
On GPT images, if an EFI System Partition (ESP) is discovered, it
is automatically mounted to /efi (or /boot as fallback) in case a
directory by this name exists and is empty.
Partitions encrypted with LUKS are automatically decrypted. Also,
on GPT images dm-verity data integrity hash partitions are set up
if the root hash for them is specified using the --root-hash=
option.
Any other partitions, such as foreign partitions or swap
partitions are not mounted. May not be specified together with
--directory=, --template=.
--root-hash=
Takes a data integrity (dm-verity) root hash specified in
hexadecimal. This option enables data integrity checks using
dm-verity, if the used image contains the appropriate integrity
data (see above). The specified hash must match the root hash of
integrity data, and is usually at least 256 bits (and hence 64
formatted hexadecimal characters) long (in case of SHA256 for
example). If this option is not specified, but the image file
carries the "user.verity.roothash" extended file attribute (see
xattr(7)), then the root hash is read from it, also as formatted
hexadecimal characters. If the extended file attribute is not
found (or is not supported by the underlying file system), but a
file with the .roothash suffix is found next to the image file,
bearing otherwise the same name, the root hash is read from it
and automatically used, also as formatted hexadecimal characters.
-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.
--pivot-root=
Pivot the specified directory to / inside the container, and
either unmount the container's old root, or pivot it to another
specified directory. Takes one of: a path argument — in which
case the specified path will be pivoted to / and the old root
will be unmounted; or a colon-separated pair of new root path and
pivot destination for the old root. The new root path will be
pivoted to /, and the old / will be pivoted to the other
directory. Both paths must be absolute, and are resolved in the
container's file system namespace.
This is for containers which have several bootable directories in
them; for example, several OSTree[3] deployments. It emulates the
behavior of the boot loader and initial RAM disk which normally
select which directory to mount as the root and start the
container's PID 1 in.
-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 applies only if the machine is run in
its own scope unit, i.e. if --keep-unit isn't used.
--property=
Set a unit property on the scope unit to register for the
machine. This applies only if the machine is run in its own scope
unit, i.e. if --keep-unit isn't used. Takes unit property
assignments in the same format as systemctl set-property. This is
useful to set memory limits and similar for container.
--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.
Note that when user namespacing is used file ownership on disk
reflects this, and all of the container's files and directories
are owned by the container's effective user and group IDs. This
means that copying files from and to the container image requires
correction of the numeric UID/GID values, according to the
UID/GID shift applied.
--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 /usr/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
/usr/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-zone= 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 /usr/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. The source path
may optionally be prefixed with a "+" character. If so, the
source path is taken relative to the image's root directory. This
permits setting up bind mounts within the container image. The
source path may be specified as empty string, in which case a
temporary directory below the host's /var/tmp directory is used.
It is automatically removed when the container is shut down.
Mount options are comma-separated and currently, only rbind and
norbind are allowed, controlling whether to create a recursive or
a regular bind mount. 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.
The source paths may optionally be prefixed with "+" character.
If so they are taken relative to the image's root directory. The
uppermost source path may also be specified as empty string, in
which case a temporary directory below the host's /var/tmp is
used. The directory is removed automatically when the container
is shut down. This behaviour is useful in order to make read-only
container directories writable while the container is running.
For example, use the "--overlay=+/var::/var" option in order to
automatically overlay a writable temporary directory on a
read-only /var directory.
For details about overlay file systems, see overlayfs.txt[4].
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: a system and service
manager as PID 1), 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 a service manager, 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.
Note that passing --keep-unit disables the effect of --slice= and
--property=.
--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.
This option provides similar functionality for containers as the
"systemd.volatile=" kernel command line switch provides for host
systems. See kernel-command-line(7) for details.
Note that enabling this setting will only work correctly with
operating systems in the container that can boot up with only
/usr mounted, and are able to automatically populate /var, and
also /etc in case of "--volatile=yes".
--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.
Example 1. Download a Fedora image and start a shell in it
# machinectl pull-raw --verify=no \
https://download.fedoraproject.org/pub/fedora/linux/releases/25/CloudImages/x86_64/images/Fedora-Cloud-Base-25-1.3.x86_64.raw.xz
# systemd-nspawn -M Fedora-Cloud-Base-25-1.3.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=25 --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. Install the OpenSUSE Tumbleweed rolling distribution
# zypper --root=/var/lib/machines/tumbleweed ar -c \
https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
# zypper --root=/var/lib/machines/tumbleweed refresh
# zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
systemd shadow zypper openSUSE-release vim
# systemd-nspawn -M tumbleweed passwd root
# systemd-nspawn -M tumbleweed -b
Example 6. Boot into an ephemeral snapshot of the host system
# systemd-nspawn -D / -xb
This runs a copy of the host system in a snapshot which is removed
immediately when the container exits. All file system changes made
during runtime will be lost on shutdown, hence.
Example 7. 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
Example 8. Run a container with an OSTree deployment
# systemd-nspawn -b -i ~/image.raw \
--pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
--bind=+/sysroot/ostree/deploy/$OS/var:/var
The exit code of the program executed in the container is returned.
systemd(1), systemd.nspawn(5), chroot(1), dnf(8), debootstrap(8),
pacman(8), zypper(8), systemd.slice(5), machinectl(1), btrfs(8)
1. Container Interface
https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
2. Discoverable Partitions Specification
https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/
3. OSTree
https://ostree.readthedocs.io/en/latest/
4. overlayfs.txt
https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SYSTEMD-NSPAWN(1)
Pages that refer to this page: machinectl(1), systemd-cgls(1), systemd-detect-virt(1), systemd.nspawn(5), systemd.directives(7), systemd.index(7), systemd-importd.service(8), systemd-machined.service(8)