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 --boot [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 may be invoked on any directory tree containing an
operating system tree, using the --directory= command line option. By
using the --machine= option an OS tree is automatically searched for in
a couple of locations, most importantly in /var/lib/machines, the
suggested directory to place container images installed on the system.
In contrast to chroot(1) systemd-nspawn may be used to boot full
Linux-based operating systems in a container.
systemd-nspawn limits access to various kernel interfaces in the
container to read-only, such as /sys, /proc/sys or /sys/fs/selinux. The
host's 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.
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. See the Examples section below for details on suitable
invocation of these commands.
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.
systemd-nspawn may be invoked directly from the interactive command
line or run as system service in the background. In this mode each
container instance runs as its own service instance; a default template
unit file systemd-nspawn@.service is provided to make this easy, taking
the container name as instance identifier. Note that different default
options apply when systemd-nspawn is invoked by the template unit file
than interactively on the command line. Most importantly the template
unit file makes use of the --boot which is not the default in case
systemd-nspawn is invoked from the interactive command line. Further
differences with the defaults are documented along with the various
supported options below.
The machinectl(1) tool may be used to execute a number of operations on
containers. In particular it provides easy-to-use commands to run
containers as system services using the systemd-nspawn@.service
template unit file.
Along with each container a settings file with the .nspawn suffix may
exist, containing additional settings to apply when running the
container. See systemd.nspawn(5) for details. Settings files override
the default options used by the systemd-nspawn@.service template unit
file, making it usually unnecessary to alter this template file
directly.
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 or shell commands to request an additional
login session in a running container.
systemd-nspawn implements the Container Interface[1] specification.
While running, containers invoked with systemd-nspawn are registered
with the systemd-machined(8) service that keeps track of running
containers, and provides programming interfaces to interact with them.
OPTIONS
If option -b is specified, the arguments are used as arguments for the
init program. Otherwise, COMMAND specifies the program to launch in the
container, and the remaining arguments are used as arguments for this
program. If --boot 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" snapshot (if supported) or plain
directory (otherwise) 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 (though possibly in a copy-on-write scheme -- if the file
system supports that), which can be substantially more
time-consuming. 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 snapshot of its
file system that is removed immediately when the container
terminates. May not be specified together with --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:
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].
o No partition table, and a single file system spanning the whole
image.
On GPT images, if an EFI System Partition (ESP) is discovered, it
is automatically mounted to /efi (or /boot as fallback) in case a
directory by this name exists and is empty.
Partitions encrypted with LUKS are automatically decrypted. Also,
on GPT images dm-verity data integrity hash partitions are set up
if the root hash for them is specified using the --root-hash=
option.
Any other partitions, such as foreign partitions or swap partitions
are not mounted. May not be specified together with --directory=,
--template=.
--root-hash=
Takes a data integrity (dm-verity) root hash specified in
hexadecimal. This option enables data integrity checks using
dm-verity, if the used image contains the appropriate integrity
data (see above). The specified hash must match the root hash of
integrity data, and is usually at least 256 bits (and hence 64
formatted hexadecimal characters) long (in case of SHA256 for
example). If this option is not specified, but the image file
carries the "user.verity.roothash" extended file attribute (see
xattr(7)), then the root hash is read from it, also as formatted
hexadecimal characters. If the extended file attribute is not found
(or is not supported by the underlying file system), but a file
with the .roothash suffix is found next to the image file, bearing
otherwise the same name, the root hash is read from it and
automatically used, also as formatted hexadecimal characters.
-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 program is run as the 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 program 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.
-b, --boot
Automatically search for an init program 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 program. This option may not be combined with
--as-pid2.
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 the command |
| | line, which is executed as |
| | PID 1 in the container. |
+----------------------+----------------------------+
|--as-pid2 specified | The passed parameters are |
| | interpreted as the command |
| | line, which is executed as |
| | PID 2 in the container. A |
| | stub init process is run |
| | as PID 1. |
+----------------------+----------------------------+
|--boot specified | An init program is |
| | automatically searched for |
| | and run as PID 1 in the |
| | container. The passed |
| | parameters are used as |
| | invocation parameters for |
| | this process. |
+----------------------+----------------------------+
Note that --boot is the default mode of operation if the
systemd-nspawn@.service template unit file is used.
--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.
--pivot-root=
Pivot the specified directory to / inside the container, and either
unmount the container's old root, or pivot it to another specified
directory. Takes one of: a path argument -- in which case the
specified path will be pivoted to / and the old root will be
unmounted; or a colon-separated pair of new root path and pivot
destination for the old root. The new root path will be pivoted to
/, and the old / will be pivoted to the other directory. Both paths
must be absolute, and are resolved in the container's file system
namespace.
This is for containers which have several bootable directories in
them; for example, several OSTree[3] deployments. It emulates the
behavior of the boot loader and initial RAM disk which normally
select which directory to mount as the root and start the
container's PID 1 in.
-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.
--hostname=
Controls the hostname to set within the container, if different
from the machine name. Expects a valid hostname as argument. If
this option is used, the kernel hostname of the container will be
set to this value, otherwise it will be initialized to the machine
name as controlled by the --machine= option described above. The
machine name is used for various aspect of identification of the
container from the outside, the kernel hostname configurable with
this option is useful for the container to identify itself from the
inside. It is usually a good idea to keep both forms of
identification synchronized, in order to avoid confusion. It is
hence recommended to avoid usage of this option, and use --machine=
exclusively. Note that regardless whether the container's hostname
is initialized from the name set with --hostname= or the one set
with --machine=, the container can later override its kernel
hostname freely on its own as well.
--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.
Note that this option takes effect only if /etc/machine-id in the
container is unpopulated.
-S, --slice=
Make the container part of the specified slice, instead of the
default machine.slice. This applies only if the machine is run in
its own scope unit, i.e. if --keep-unit isn't used.
--property=
Set a unit property on the scope unit to register for the machine.
This applies only if the machine is run in its own scope unit, i.e.
if --keep-unit isn't used. Takes unit property assignments in the
same format as systemctl set-property. This is useful to set memory
limits and similar for container.
--private-users=
Controls user namespacing. If enabled, the container will run with
its own private set of UNIX user and group ids (UIDs and GIDs).
This involves mapping the private UIDs/GIDs used in the container
(starting with the container's root user 0 and up) to a range of
UIDs/GIDs on the host that are not used for other purposes (usually
in the range beyond the host's UID/GID 65536). The parameter may be
specified as follows:
1. If one or two colon-separated numbers are specified, user
namespacing is turned on. The first parameter specifies the
first host UID/GID to assign to the container, the second
parameter specifies the number of host UIDs/GIDs to assign to
the container. If the second parameter is omitted, 65536
UIDs/GIDs are assigned.
2. If the parameter is omitted, or true, user namespacing is
turned on. The UID/GID range to use is determined automatically
from the file ownership of the root directory of the
container's directory tree. To use this option, make sure to
prepare the directory tree in advance, and ensure that all
files and directories in it are owned by UIDs/GIDs in the range
you'd like to use. Also, make sure that used file ACLs
exclusively reference UIDs/GIDs in the appropriate range. If
this mode is used the number of UIDs/GIDs assigned to the
container for use is 65536, and the UID/GID of the root
directory must be a multiple of 65536.
3. If the parameter is false, user namespacing is turned off. This
is the default.
4. The special value "pick" turns on user namespacing. In this
case the UID/GID range is automatically chosen. As first step,
the file owner of the root directory of the container's
directory tree is read, and it is checked that it is currently
not used by the system otherwise (in particular, that no other
container is using it). If this check is successful, the
UID/GID range determined this way is used, similar to the
behavior if "yes" is specified. If the check is not successful
(and thus the UID/GID range indicated in the root directory's
file owner is already used elsewhere) a new - currently unused
- UID/GID range of 65536 UIDs/GIDs is randomly chosen between
the host UID/GIDs of 524288 and 1878982656, always starting at
a multiple of 65536. This setting implies --private-users-chown
(see below), which has the effect that the files and
directories in the container's directory tree will be owned by
the appropriate users of the range picked. Using this option
makes user namespace behavior fully automatic. Note that the
first invocation of a previously unused container image might
result in picking a new UID/GID range for it, and thus in the
(possibly expensive) file ownership adjustment operation.
However, subsequent invocations of the container will be cheap
(unless of course the picked UID/GID range is assigned to a
different use by then).
It is recommended to assign at least 65536 UIDs/GIDs to each
container, so that the usable UID/GID range in the container covers
16 bit. For best security, do not assign overlapping UID/GID ranges
to multiple containers. It is hence a good idea to use the upper 16
bit of the host 32-bit UIDs/GIDs as container identifier, while the
lower 16 bit encode the container UID/GID used. This is in fact the
behavior enforced by the --private-users=pick option.
When user namespaces are used, the GID range assigned to each
container is always chosen identical to the UID range.
In most cases, using --private-users=pick is the recommended option
as it enhances container security massively and operates fully
automatically in most cases.
Note that the picked UID/GID range is not written to /etc/passwd or
/etc/group. In fact, the allocation of the range is not stored
persistently anywhere, except in the file ownership of the files
and directories of the container.
Note that when user namespacing is used file ownership on disk
reflects this, and all of the container's files and directories are
owned by the container's effective user and group IDs. This means
that copying files from and to the container image requires
correction of the numeric UID/GID values, according to the UID/GID
shift applied.
--private-users-chown
If specified, all files and directories in the container's
directory tree will adjusted so that they are owned to the
appropriate UIDs/GIDs selected for the container (see above). This
operation is potentially expensive, as it involves descending and
iterating through the full directory tree of the container. Besides
actual file ownership, file ACLs are adjusted as well.
This option is implied if --private-users=pick is used. This option
has no effect if user namespacing is not used.
-U
If the kernel supports the user namespaces feature, equivalent to
--private-users=pick --private-users-chown, otherwise equivalent to
--private-users=no.
Note that -U is the default if the systemd-nspawn@.service template
unit file is used.
Note: it is possible to undo the effect of --private-users-chown
(or -U) on the file system by redoing the operation with the first
UID of 0:
systemd-nspawn ... --private-users=0 --private-users-chown
--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=. If this option is not
specified (or implied by one of the options listed below), the
container will have full access to the host network.
--network-namespace-path=
Takes the path to a file representing a kernel network namespace
that the container shall run in. The specified path should refer to
a (possibly bind-mounted) network namespace file, as exposed by the
kernel below /proc/$PID/ns/net. This makes the container enter the
given network namespace. One of the typical use cases is to give a
network namespace under /run/netns created by ip-netns(8), for
example, --network-namespace-path=/run/netns/foo. Note that this
option cannot be used together with other network-related options,
such as --private-network or --network-interface=.
--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". The --network-veth option
implies --private-network.
Note that systemd-networkd.service(8) includes by default a network
file /usr/lib/systemd/network/80-container-ve.network matching the
host-side interfaces created this way, which contains settings to
enable automatic address provisioning on the created virtual link
via DHCP, as well as automatic IP routing onto the host's external
network interfaces. It also contains
/usr/lib/systemd/network/80-container-host0.network matching the
container-side interface created this way, containing settings to
enable client side address assignment via DHCP. In case
systemd-networkd is running on both the host and inside the
container, automatic IP communication from the container to the
host is thus available, with further connectivity to the external
network.
Note that --network-veth is the default if the
systemd-nspawn@.service template unit file is used.
--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 Ethernet bridge interface. Expects a valid network
interface name of a bridge device as argument. 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-".
--network-zone=
Creates a virtual Ethernet link ("veth") to the container and adds
it to an automatically managed Ethernet bridge interface. The
bridge interface is named after the passed argument, prefixed with
"vz-". The bridge interface is automatically created when the first
container configured for its name is started, and is automatically
removed when the last container configured for its name exits.
Hence, each bridge interface configured this way exists only as
long as there's at least one container referencing it running. This
option is very similar to --network-bridge=, besides this automatic
creation/removal of the bridge device.
This setting makes it easy to place multiple related containers on
a common, virtual Ethernet-based broadcast domain, here called a
"zone". Each container may only be part of one zone, but each zone
may contain any number of containers. Each zone is referenced by
its name. Names may be chosen freely (as long as they form valid
network interface names when prefixed with "vz-"), and it is
sufficient to pass the same name to the --network-zone= switch of
the various concurrently running containers to join them in one
zone.
Note that systemd-networkd.service(8) includes by default a network
file /usr/lib/systemd/network/80-container-vz.network matching the
bridge interfaces created this way, which contains settings to
enable automatic address provisioning on the created virtual
network via DHCP, as well as automatic IP routing onto the host's
external network interfaces. Using --network-zone= is hence in most
cases fully automatic and sufficient to connect multiple local
containers in a joined broadcast domain to the host, with further
connectivity to the external network.
-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, --network-zone= --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_AUDIT_CONTROL,
CAP_AUDIT_WRITE, CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER, CAP_KILL, CAP_LEASE,
CAP_LINUX_IMMUTABLE, CAP_MKNOD, CAP_NET_BIND_SERVICE,
CAP_NET_BROADCAST, CAP_NET_RAW, CAP_SETFCAP, CAP_SETGID,
CAP_SETPCAP, CAP_SETUID, CAP_SYS_ADMIN, CAP_SYS_BOOT,
CAP_SYS_CHROOT, CAP_SYS_NICE, CAP_SYS_PTRACE, CAP_SYS_RESOURCE,
CAP_SYS_TTY_CONFIG. 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).
--no-new-privileges=
Takes a boolean argument. Specifies the value of the
PR_SET_NO_NEW_PRIVS flag for the container payload. Defaults to
off. When turned on the payload code of the container cannot
acquire new privileges, i.e. the "setuid" file bit as well as file
system capabilities will not have an effect anymore. See prctl(2)
for details about this flag.
--system-call-filter=
Alter the system call filter applied to containers. Takes a
space-separated list of system call names or group names (the
latter prefixed with "@", as listed by the syscall-filter command
of systemd-analyze(1)). Passed system calls will be permitted. The
list may optionally be prefixed by "~", in which case all listed
system calls are prohibited. If this command line option is used
multiple times the configured lists are combined. If both a
positive and a negative list (that is one system call list without
and one with the "~" prefix) are configured, the negative list
takes precedence over the positive list. Note that systemd-nspawn
always implements a system call whitelist (as opposed to a
blacklist), and this command line option hence adds or removes
entries from the default whitelist, depending on the "~" prefix.
Note that the applied system call filter is also altered implicitly
if additional capabilities are passed using the --capabilities=.
--rlimit=
Sets the specified POSIX resource limit for the container payload.
Expects an assignment of the form "LIMIT=SOFT:HARD" or
"LIMIT=VALUE", where LIMIT should refer to a resource limit type,
such as RLIMIT_NOFILE or RLIMIT_NICE. The SOFT and HARD fields
should refer to the numeric soft and hard resource limit values. If
the second form is used, VALUE may specify a value that is used
both as soft and hard limit. In place of a numeric value the
special string "infinity" may be used to turn off resource limiting
for the specific type of resource. This command line option may be
used multiple times to control limits on multiple limit types. If
used multiple times for the same limit type, the last use wins. For
details about resource limits see setrlimit(2). By default resource
limits for the container's init process (PID 1) are set to the same
values the Linux kernel originally passed to the host init system.
Note that some resource limits are enforced on resources counted
per user, in particular RLIMIT_NPROC. This means that unless user
namespacing is deployed (i.e. --private-users= is used, see
above), any limits set will be applied to the resource usage of the
same user on all local containers as well as the host. This means
particular care needs to be taken with these limits as they might
be triggered by possibly less trusted code. Example:
"--rlimit=RLIMIT_NOFILE=8192:16384".
--oom-score-adjust=
Changes the OOM ("Out Of Memory") score adjustment value for the
container payload. This controls /proc/self/oom_score_adj which
influences the preference with which this container is terminated
when memory becomes scarce. For details see proc(5). Takes an
integer in the range -1000...1000.
--cpu-affinity=
Controls the CPU affinity of the container payload. Takes a comma
separated list of CPU numbers or number ranges (the latter's start
and end value separated by dashes). See sched_setaffinity(2) for
details.
--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). If --boot is not used and this option is not specified
the container's processes are terminated abrubtly via SIGKILL. For
a list of valid signals, see signal(7).
--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 journaling 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.
Note that --link-journal=try-guest is the default if the
systemd-nspawn@.service template unit file is used.
-j
Equivalent to --link-journal=try-guest.
--resolv-conf=
Configures how /etc/resolv.conf inside of the container (i.e. DNS
configuration synchronization from host to container) shall be
handled. Takes one of "off", "copy-host", "copy-static",
"bind-host", "bind-static", "delete" or "auto". If set to "off" the
/etc/resolv.conf file in the container is left as it is included in
the image, and neither modified nor bind mounted over. If set to
"copy-host", the /etc/resolv.conf file from the host is copied into
the container. Similar, if "bind-host" is used, the file is bind
mounted from the host into the container. If set to "copy-static"
the static resolv.conf file supplied with systemd-
resolved.service(8) is copied into the container, and
correspondingly "bind-static" bind mounts it there. If set to
"delete" the /etc/resolv.conf file in the container is deleted if
it exists. Finally, if set to "auto" the file is left as it is if
private networking is turned on (see --private-network). Otherwise,
if systemd-resolved.service is connectible its static resolv.conf
file is used, and if not the host's /etc/resolv.conf file is used.
In the latter cases the file is copied if the image is writable,
and bind mounted otherwise. It's recommended to use "copy" if the
container shall be able to make changes to the DNS configuration on
its own, deviating from the host's settings. Otherwise "bind" is
preferable, as it means direct changes to /etc/resolv.conf in the
container are not allowed, as it is a read-only bind mount (but
note that if the container has enough privileges, it might simply
go ahead and unmount the bind mount anyway). Note that both if the
file is bind mounted and if it is copied no further propagation of
configuration is generally done after the one-time early
initialization (this is because the file is usually updated through
copying and renaming). Defaults to "auto".
--timezone=
Configures how /etc/localtime inside of the container (i.e. local
timezone synchronization from host to container) shall be handled.
Takes one of "off", "copy", "bind", "symlink", "delete" or "auto".
If set to "off" the /etc/localtime file in the container is left as
it is included in the image, and neither modified nor bind mounted
over. If set to "copy" the /etc/localtime file of the host is
copied into the container. Similar, if "bind" is used, it is bind
mounted from the host into the container. If set to "symlink" a
symlink from /etc/localtime in the container is created pointing to
the matching the timezone file of the container that matches the
timezone setting on the host. If set to "delete" the file in the
container is deleted, should it exist. If set to "auto" and the
/etc/localtime file of the host is a symlink, then "symlink" mode
is used, and "copy" otherwise, except if the image is read-only in
which case "bind" is used instead. Defaults to "auto".
--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. The source path
may optionally be prefixed with a "+" character. If so, the source
path is taken relative to the image's root directory. This permits
setting up bind mounts within the container image. The source path
may be specified as empty string, in which case a temporary
directory below the host's /var/tmp directory is used. It is
automatically removed when the container is shut down. Mount
options are comma-separated and currently, only rbind and norbind
are allowed, controlling whether to create a recursive or a regular
bind mount. 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.
Note that when this option is used in combination with
--private-users, the resulting mount points will be owned by the
nobody user. That's because the mount and its files and directories
continue to be owned by the relevant host users and groups, which
do not exist in the container, and thus show up under the wildcard
UID 65534 (nobody). If such bind mounts are created, it is
recommended to make them read-only, using --bind-ro=.
--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.
The source paths may optionally be prefixed with "+" character. If
so they are taken relative to the image's root directory. The
uppermost source path may also be specified as empty string, in
which case a temporary directory below the host's /var/tmp is used.
The directory is removed automatically when the container is shut
down. This behaviour is useful in order to make read-only container
directories writable while the container is running. For example,
use the "--overlay=+/var::/var" option in order to automatically
overlay a writable temporary directory on a read-only /var
directory.
For details about overlay file systems, see overlayfs.txt[4]. 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.
-E NAME=VALUE, --setenv=NAME=VALUE
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.
--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: a system and service manager
as PID 1), 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 a service manager, it is recommended to set
this option to "no".
--keep-unit
Instead of creating a transient scope unit to run the container in,
simply use the service or scope unit systemd-nspawn has been
invoked in. If --register=yes is set this unit is registered with
systemd-machined(8). 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.
Note that passing --keep-unit disables the effect of --slice= and
--property=. Use --keep-unit and --register=no in combination to
disable any kind of unit allocation or registration with
systemd-machined.
--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 image, but pristine state and configuration, any changes 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.
This option provides similar functionality for containers as the
"systemd.volatile=" kernel command line switch provides for host
systems. See kernel-command-line(7) for details.
Note that enabling this setting will only work correctly with
operating systems in the container that can boot up with only /usr
mounted, and are able to automatically populate /var, and also /etc
in case of "--volatile=yes".
--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.
--notify-ready=
Configures support for notifications from the container's init
process. --notify-ready= takes a boolean (no and yes). With option
no systemd-nspawn notifies systemd with a "READY=1" message when
the init process is created. With option yes systemd-nspawn waits
for the "READY=1" message from the init process in the container
before sending its own to systemd. For more details about
notifications see sd_notify(3)).
-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 \
https://download.fedoraproject.org/pub/fedora/linux/releases/28/Cloud/x86_64/images/Fedora-Cloud-Base-28-1.1.x86_64.raw.xz
# systemd-nspawn -M Fedora-Cloud-Base-28-1.1.x86_64.raw
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=28 --installroot=/var/lib/machines/f28 \
--disablerepo='*' --enablerepo=fedora --enablerepo=updates install \
systemd passwd dnf fedora-release vim-minimal
# systemd-nspawn -bD /var/lib/machines/f28
This installs a minimal Fedora distribution into the directory
/var/lib/machines/f28 and then boots an OS in a namespace container in
it. Because the installation is located underneath the standard
/var/lib/machines/ directory, it is also possible to start the machine
using systemd-nspawn -M f28.
Example 3. Spawn a shell in a container of a minimal Debian unstable
distribution
# debootstrap 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.
debootstrap supports Debian[6], Ubuntu[7], and Tanglu[8] out of the
box, so the same command can be used to install any of those. For other
distributions from the Debian family, a mirror has to be specified, see
debootstrap(8).
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. Install the OpenSUSE Tumbleweed rolling distribution
# zypper --root=/var/lib/machines/tumbleweed ar -c \
https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
# zypper --root=/var/lib/machines/tumbleweed refresh
# zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
systemd shadow zypper openSUSE-release vim
# systemd-nspawn -M tumbleweed passwd root
# systemd-nspawn -M tumbleweed -b
Example 6. Boot into an ephemeral snapshot of the host system
# systemd-nspawn -D / -xb
This runs a copy of the host system in a snapshot which is removed
immediately when the container exits. All file system changes made
during runtime will be lost on shutdown, hence.
Example 7. 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
Example 8. Run a container with an OSTree deployment
# systemd-nspawn -b -i ~/image.raw \
--pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
--bind=+/sysroot/ostree/deploy/$OS/var:/var
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), zypper(8), systemd.slice(5), machinectl(1), btrfs(8)
NOTES
1. Container Interface
https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface
2. Discoverable Partitions Specification
https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/
3. OSTree
https://ostree.readthedocs.io/en/latest/
4. overlayfs.txt
https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt
5. Fedora
https://getfedora.org
6. Debian
https://www.debian.org
7. Ubuntu
https://www.ubuntu.com
8. Tanglu
https://www.tanglu.org
9. Arch Linux
https://www.archlinux.org
10. OpenSUSE Tumbleweed
https://software.opensuse.org/distributions/tumbleweed
systemd 239 SYSTEMD-NSPAWN(1)
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