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.
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 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= is specified the directory is
determined as /var/lib/machines/ suffixed by the machine name as
specified with --machine=. 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.
-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=.
-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:
o An MBR partition table with a single partition of type 0x83
that is marked bootable.
o A GUID partition table (GPT) with a single partition of type
0fc63daf-8483-4772-8e79-3d69d8477de4.
o 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 | 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. |
+----------------------+----------------------------+
-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.
--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-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 ommitted, in which
case the same port as the host port is implied. This option is only
supported if private networking is used, such as --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).
--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.
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.
--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, 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=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 mostly
unpopulated "tmpfs" instance, and /usr from the OS tree is mounted
into it, read-only (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
"tmpfs" instance into it (the system thus starts up with read-only
OS resources and configuration, but pristine state, 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.
-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
# yum -y --releasever=21 --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 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 mimimal 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), chroot(1), yum(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/
systemd 219 SYSTEMD-NSPAWN(1)
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