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 -b [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 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 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.
The intended use of this program is debugging and testing as well as building of packages,
distributions and software involved with boot and systems management.
In contrast to chroot(1) systemd-nspawn may be used to boot full Linux-based operating
systems in a container.
Use a tool like yum(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. It is however possible to enter an existing container, see Example 4 below.
systemd-nspawn implements the Container Interface specification.
As a safety check systemd-nspawn will verify the existence of /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.
INCOMPATIBILITY WITH AUDITING
Note that the kernel auditing subsystem is currently broken when used together with
containers. We hence recommend turning it off entirely by booting with "audit=0" on the
kernel command line, or by turning it off at kernel build time. If auditing is enabled in
the kernel, operating systems booted in an nspawn container might refuse log-in attempts.
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
specifed, a shell is launched in the container.
The following options are understood:
Prints a short help text and exits.
Prints a version string and exits.
Directory to use as file system root for the namespace container. If omitted, the
current directory will be used.
Automatically search for an init binary and invoke it 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.
Run the command under specified user, create home directory and cd into it. As rest of
systemd-nspawn, this is not the security feature and limits against accidental changes
Sets the machine name for this container. This name may be used to identify this
container on the host, 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 of the container is used.
Make the container part of the specified slice, instead of the machine.slice.
Set the specified UUID for the container. The init system will initialize
/etc/machine-id from this if this file is not set yet.
Turn off networking in the container. This makes all network interfaces unavailable in
the container, with the exception of the loopback device.
Mount the root file system read-only for 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.
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", "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. 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=guest.
Bind mount a file or directory from the host into the container. Either takes 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. The --bind-ro= option creates read-only bind mount.
# yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum 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.
# 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.
# pacstrap -c -d ~/arch-tree/ base
# systemd-nspawn -bD ~/arch-tree/
This installs a mimimal Arch Linux distribution into the directory ~/arch-tree/ and then
boots an OS in a namespace container in it.
To enter the container, PID of one of the processes sharing the new namespaces must be
used. systemd-nspawn prints the PID (as viewed from the outside) of the launched process,
and it can be used to enter the container.
# nsenter -m -u -i -n -p -t $PID
nsenter(1) is part of util-linux. Kernel support for entering namespaces was added in
# mv ~/arch-tree /var/lib/container/arch
# systemctl enable email@example.com
# systemctl start firstname.lastname@example.org
This makes the Arch Linux container part of the multi-user.target on the host.
The exit code of the program executed in the container is returned.
systemd(1), chroot(1), unshare(1), yum(8), debootstrap(8), pacman(8), systemd.slice(5)
1. Container Interface
systemd 208 SYSTEMD-NSPAWN(1)