Provided by: systemd-container_229-4ubuntu21.31_amd64 
NAME
systemd-nspawn - Spawn a namespace container for debugging, testing and building
SYNOPSIS
systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]
systemd-nspawn -b [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 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 the container.
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 containers.
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
command to request an additional login prompt in a running container.
systemd-nspawn implements the Container Interface[1] 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.
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 -b 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 or
--share-system.
-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 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 --boot │ The passed parameters are interpreted │
│specified │ 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. │
└─────────────────────────────┴───────────────────────────────────────┘
--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.
--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=
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 applied.
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.
--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". Note
that --network-veth implies --private-network.
--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 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-".
-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 or
--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). Takes a signal name like
"SIGHUP", "SIGTERM" or similar as argument.
--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 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.
-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.
--setenv=
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.
--share-system
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.
--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". Note that --share-system implies --register=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 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, 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.
-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/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 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