SYSTEMD-NSPAWN(1) systemd-nspawn SYSTEMD-NSPAWN(1)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 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[1] 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.
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 specifed, a shell is
launched in the container.
The following options are understood:
-h, --help
Prints a short help text and exits.
--version
Prints a version string and exits.
-D, --directory=
Directory to use as file system root for the namespace container.
If omitted, the current directory will be used.
-b, --boot
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.
-u, --user=
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 only.
-M, --machine=
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.
--slice=
Make the container part of the specified slice, instead of the
machine.slice.
--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.
--private-network
Turn off networking in the container. This makes all network
interfaces unavailable in the container, with the exception of the
loopback device.
--read-only
Mount the root file system read-only for 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.
--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", "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.
-j
Equivalent to --link-journal=guest.
--bind=, --bind-ro=
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.
EXAMPLE 1
# 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.
EXAMPLE 2
# 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 3
# 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.
EXAMPLE 4
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[2]. Kernel support for entering
namespaces was added in Linux 3.8.
EXIT STATUS
The exit code of the program executed in the container is returned.
SEE ALSOsystemd(1), chroot(1), unshare(1), yum(8), debootstrap(8), pacman(8),
systemd.slice(5)NOTES
1. Container Interface
http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
2. util-linux
https://github.com/karelzak/util-linux
systemd 207SYSTEMD-NSPAWN(1)