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 limits access to various kernel interfaces in the
container to read-only, such as /sys, /proc/sys or /sys/fs/selinux.
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.
Note that even though these security precautions are taken
systemd-nspawn is not suitable for fully secure container setups.
Many of the security features may be circumvented and are hence
primarily useful to avoid accidental changes to the host system from
In contrast to chroot(1)systemd-nspawn may be used to boot full
Linux-based operating systems in a 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
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
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 command to request
an additional login prompt in a running container.
systemd-nspawn implements the Container Interface specification.
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.
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 -b is not used and no arguments are specified, a
shell is launched in the container.
The following options are understood:
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
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.
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.
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
· 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 PartitionsSpecification.
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.
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
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 or --share-system.
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 command │
│ │ line, which is executed │
│ │ as PID 1 in the │
│ │ container. │
│--as-pid2 specified │ The passed parameters are │
│ │ interpreted as command │
│ │ line, which are 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. │
Change to the specified working directory before invoking the
process in the container. Expects an absolute path in the
container's file system namespace.
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
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.
Set the specified UUID for the container. The init system will
initialize /etc/machine-id from this if this file is not set yet.
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.
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.
Enables user namespacing. If enabled, the container will run with
its own private set of Unix user and group ids (UIDs and GIDs).
Takes none, one or two colon-separated parameters: the first
parameter specifies the first host UID to assign to the
container, the second parameter specifies the number of host UIDs
to assign to the container. If the second parameter is omitted,
65536 UIDs are assigned. If the first parameter is also omitted
(and hence no parameter passed at all), the first UID assigned to
the container is read from the owner of the root directory of the
container's directory tree. By default, no user namespacing is
Note that user namespacing currently requires OS trees that are
prepared for the UID shift that is being applied: UIDs and GIDs
used for file ownership or in file ACL entries must be shifted to
the container UID base that is used during container runtime.
It is recommended to assign at least 65536 UIDs to each
container, so that the usable UID range in the container covers
16 bit. For best security, do not assign overlapping UID ranges
to multiple containers. It is hence a good idea to use the upper
16 bit of the host 32-bit UIDs as container identifier, while the
lower 16 bit encode the container UID used.
When user namespaces are used, the GID range assigned to each
container is always chosen identical to the UID range.
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=.
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
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
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.
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". Note that
--network-veth implies --private-network.
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=.
Adds the host side of the Ethernet link created with
--network-veth to the specified bridge. 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-".
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 or --network-bridge=.
Sets the SELinux security context to be used to label processes
in the container.
Sets the SELinux security context to be used to label files in
the virtual API file systems in the container.
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.
Specify one or more additional capabilities to drop for the
container. This allows running the container with fewer
capabilities than the default (see above).
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). Takes a signal name like "SIGHUP", "SIGTERM"
or similar as argument.
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
journalling 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.
Equivalent to --link-journal=try-guest.
Mount the root file system read-only for the container.
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.
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.
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
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
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
For details about overlay file systems, see overlayfs.txt.
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.
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.
Allows the container to share certain system facilities with the
host. More specifically, this turns off PID namespacing, UTS
namespacing and IPC namespacing, and thus allows the guest to see
and interact more easily with processes outside of the container.
Note that using this option makes it impossible to start up a
full Operating System in the container, as an init system cannot
operate in this mode. It is only useful to run specific programs
or applications this way, without involving an init system in the
container. This option implies --register=no. This option may not
be combined with --boot.
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". Note that --share-system implies --register=no.
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
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.
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.
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 resources, but pristine state and configuration, any
changes to the either 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,
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
If disabled, no .nspawn file is read and no settings except the
ones on the command line are in effect.
Print a short help text and exit.
Print a short version string and exit.
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/21/Cloud/Images/x86_64/Fedora-Cloud-Base-20141203-21.x86_64.raw.xz
# systemd-nspawn -M Fedora-Cloud-Base-20141203-21
This downloads an image using machinectl(1) and opens a shell in it.
Example 2. Build and boot a minimal Fedora distribution in acontainer
# 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
Example 3. Spawn a shell in a container of a minimal Debian unstabledistribution
# 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
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
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2016-03-15. 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
systemd 229 SYSTEMD-NSPAWN(1)