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. 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 /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 specifed, 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= are
specified, the current directory will
be used. May not be specified together with
--image=.
-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 a GUID
Partition Table with a root partition
which is mounted as the root directory
of the container. Optionally, it 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. Any
other partitions, such as foreign
partitions, swap partitions or EFI
system partitions are not mounted. May
not be specified together with
--directory=.
-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. This option may not be
combined with
--share-system.
-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 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.
--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.
--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-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-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-".
-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).
--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/)
and the subdirectory is bind-mounted
into the container at the same
location. If "machine-idguest",
the journal files are stored on the
guest file system (beneath
/var/log/journal/)
and the subdirectory is symlinked into the host
at the same location. If
"machine-idauto" (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.
--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. 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
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.
--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.
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, 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.
-h, --help¶--version¶# 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.
# mv ~/arch-tree /var/lib/container/arch # systemctl enable systemd-nspawn@arch.service # systemctl start systemd-nspawn@arch.service
This makes the Arch Linux container part of the
multi-user.target on the host.
# btrfs subvolume snapshot / /.tmp # systemd-nspawn --private-network -D /.tmp -b
This runs a copy of the host system in a btrfs snapshot.
# 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 runs a container with SELinux sandbox security contexts.