SYSTEMD-NSPAWN(1) systemd-nspawn SYSTEMD-NSPAWN(1)
NAME
systemd-nspawn - Spawn a command or OS in a light-weight container
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 OS 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
booting a 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 option 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.
Rather 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 --boot 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:
-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.
--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.
Image Options
-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 'reflink' copy-on-write scheme — if
the file system supports that), which can be substantially more
time-consuming. Note that the snapshot taken is of the specified
directory or subvolume, including all subdirectories and subvolumes
below it, but excluding any sub-mounts. May not be specified
together with --image= or --ephemeral.
Note that this switch leaves hostname, 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 hostname, machine ID and all other
settings that could identify the instance unmodified. Please note
that — as with --template= — taking the temporary snapshot is more
efficient on file systems that support subvolume snapshots or
'reflinks' natively ("btrfs" or new "xfs") than on more traditional
file systems that do not ("ext4"). Note that the snapshot taken is
of the specified directory or subvolume, including all
subdirectories and subvolumes below it, but excluding any
sub-mounts.
With this option no modifications of the container image are
retained. Use --volatile= (described below) for other mechanisms to
restrict persistency of container images during runtime.
-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:
• An MBR partition table with a single partition of type 0x83
that is marked bootable.
• A GUID partition table (GPT) with a single partition of type
0fc63daf-8483-4772-8e79-3d69d8477de4.
• 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].
• 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.
Single file system images (i.e. file systems without a surrounding
partition table) can be opened using dm-verity if the integrity
data is passed using the --root-hash= and --verity-data= (and
optionally --root-hash-sig=) options.
Any other partitions, such as foreign partitions or swap partitions
are not mounted. May not be specified together with --directory=,
--template=.
--oci-bundle=
Takes the path to an OCI runtime bundle to invoke, as specified in
the OCI Runtime Specification[3]. In this case no .nspawn file is
loaded, and the root directory and various settings are read from
the OCI runtime JSON data (but data passed on the command line
takes precedence).
--read-only
Mount the container's root file system (and any other file systems
container in the container image) read-only. This has no effect on
additional mounts made with --bind=, --tmpfs= and similar options.
This mode is implied if the container image file or directory is
marked read-only itself. It is also implied if --volatile= is used.
In this case the container image on disk is strictly read-only,
while changes are permitted but kept non-persistently in memory
only. For further details, see below.
--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
writable "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 overlay the read-only root file system is
combined with a writable tmpfs instance through "overlayfs", so
that it appears at it normally would, but any changes are applied
to the temporary file system only and lost when the container is
terminated. When the mode parameter is specified as no (the
default), the whole OS tree is made available writable (unless
--read-only is specified, see above).
Note that if one of the volatile modes is chosen, its effect is
limited to the root file system (or /var/ in case of state), and
any other mounts placed in the hierarchy are unaffected —
regardless if they are established automatically (e.g. the EFI
system partition that might be mounted to /efi/ or /boot/) or
explicitly (e.g. through an additional command line option such as
--bind=, see below). This means, even if --volatile=overlay is used
changes to /efi/ or /boot/ are prohibited in case such a partition
exists in the container image operated on, and even if
--volatile=state is used the hypothetical file /etc/foobar is
potentially writable if --bind=/etc/foobar if used to mount it from
outside the read-only container /etc/ directory.
The --ephemeral option is closely related to this setting, and
provides similar behaviour by making a temporary, ephemeral copy of
the whole OS image and executing that. For further details, see
above.
The --tmpfs= and --overlay= options provide similar functionality,
but for specific sub-directories of the OS image only. For details,
see below.
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 setting this option 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 automatically populate
/var/ (and /etc/ in case of "--volatile=yes"). Specifically, this
means that operating systems that follow the historic split of
/bin/ and /lib/ (and related directories) from /usr/ (i.e. where
the former are not symlinks into the latter) are not supported by
"--volatile=yes" as container payload. The overlay option does not
require any particular preparations in the OS, but do note that
"overlayfs" behaviour differs from regular file systems in a number
of ways, and hence compatibility is limited.
--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 (except if the image has the .raw suffix,
in which case the root hash file must not have it in its name), the
root hash is read from it and automatically used, also as formatted
hexadecimal characters.
Note that this configures the root hash for the root file system.
Disk images may also contain separate file systems for the /usr/
hierarchy, which may be Verity protected as well. The root hash for
this protection may be configured via the "user.verity.usrhash"
extended file attribute or via a .usrhash file adjacent to the disk
image, following the same format and logic as for the root hash for
the root file system described here. Note that there's currently no
switch to configure the root hash for the /usr/ from the command
line.
Also see the RootHash= option in systemd.exec(5).
--root-hash-sig=
Takes a PKCS7 signature of the --root-hash= option. The semantics
are the same as for the RootHashSignature= option, see
systemd.exec(5).
--verity-data=
Takes the path to a data integrity (dm-verity) file. This option
enables data integrity checks using dm-verity, if a root-hash is
passed and if the used image itself does not contains the integrity
data. The integrity data must be matched by the root hash. If this
option is not specified, but a file with the .verity suffix is
found next to the image file, bearing otherwise the same name
(except if the image has the .raw suffix, in which case the verity
data file must not have it in its name), the verity data is read
from it and automatically used.
--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[4] deployments. It emulates the
behavior of the boot loader and the initrd which normally select
which directory to mount as the root and start the container's PID
1 in.
Execution Options
-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.
-E NAME[=VALUE], --setenv=NAME[=VALUE]
Specifies an environment variable to pass to the init process in
the container. This may be used to override the default variables
or to set additional variables. It may be used more than once to
set multiple variables. When "=" and VALUE are omitted, the value
of the variable with the same name in the program environment will
be used.
-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.
--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 abruptly via SIGKILL. For
a list of valid signals, see signal(7).
--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).
--suppress-sync=
Expects a boolean argument. If true, turns off any form of on-disk
file system synchronization for the container payload. This means
all system calls such as sync(2), fsync(), syncfs(), ... will
execute no operation, and the O_SYNC/O_DSYNC flags to open(2) and
related calls will be made unavailable. This is potentially
dangerous, as assumed data integrity guarantees to the container
payload are not actually enforced (i.e. data assumed to have been
written to disk might be lost if the system is shut down
abnormally). However, this can dramatically improve container
runtime performance – as long as these guarantees are not required
or desirable, for example because any data written by the container
is of temporary, redundant nature, or just an intermediary artifact
that will be further processed and finalized by a later step in a
pipeline. Defaults to false.
System Identity Options
-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.
Property Options
-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 the container.
--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.
User Namespacing Options
--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 "yes", 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. In this mode, the number of UIDs/GIDs
assigned to the container is 65536, and the owner UID/GID of
the root directory must be a multiple of 65536.
3. If the parameter is "no", user namespacing is turned off. This
is the default.
4. If the parameter is "identity", user namespacing is employed
with an identity mapping for the first 65536 UIDs/GIDs. This is
mostly equivalent to --private-users=0:65536. While it does not
provide UID/GID isolation, since all host and container
UIDs/GIDs are chosen identically it does provide process
capability isolation, and hence is often a good choice if
proper user namespacing with distinct UID maps is not
appropriate.
5. The special value "pick" turns on user namespacing. In this
case the UID/GID range is automatically chosen. As first step,
the file owner UID/GID of the root directory of the container's
directory tree is read, and it is checked that no other
container is currently using it. If this check is successful,
the UID/GID range determined this way is used, similarly 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, and, if possible, consistently hashed from
the machine name. This setting implies
--private-users-ownership=auto (see below), which possibly 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-ownership=
Controls how to adjust the container image's UIDs and GIDs to match
the UID/GID range chosen with --private-users=, see above. Takes
one of "off" (to leave the image as is), "chown" (to recursively
chown() the container's directory tree as needed), "map" (in order
to use transparent ID mapping mounts) or "auto" for automatically
using "map" where available and "chown" where not.
If "chown" is selected, all files and directories in the
container's directory tree will be adjusted so that they are owned
by the appropriate UIDs/GIDs selected for the container (see
above). This operation is potentially expensive, as it involves
iterating through the full directory tree of the container. Besides
actual file ownership, file ACLs are adjusted as well.
Typically "map" is the best choice, since it transparently maps
UIDs/GIDs in memory as needed without modifying the image, and
without requiring an expensive recursive adjustment operation.
However, it is not available for all file systems, currently.
The --private-users-ownership=auto 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-ownership=auto, 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-ownership=chown (or -U) on the file system by
redoing the operation with the first UID of 0:
systemd-nspawn ... --private-users=0 --private-users-ownership=chown
Networking Options
--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-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 calling namespace. Note that --network-interface=
implies --private-network. This option may be used more than once
to add multiple network interfaces to the container.
Note that any network interface specified this way must already
exist at the time the container is started. If the container shall
be started automatically at boot via a systemd-nspawn@.service unit
file instance, it might hence make sense to add a unit file drop-in
to the service instance (e.g.
/etc/systemd/system/systemd-nspawn@foobar.service.d/50-network.conf)
with contents like the following:
[Unit]
Wants=sys-subsystem-net-devices-ens1.device
After=sys-subsystem-net-devices-ens1.device
This will make sure that activation of the container service will
be delayed until the "ens1" network interface has shown up. This is
required since hardware probing is fully asynchronous, and network
interfaces might be discovered only later during the boot process,
after the container would normally be started without these
explicit dependencies.
--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.
As with --network-interface=, the underlying Ethernet network
interface must already exist at the time the container is started,
and thus similar unit file drop-ins as described above might be
useful.
--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.
As with --network-interface=, the underlying Ethernet network
interface must already exist at the time the container is started,
and thus similar unit file drop-ins as described above might be
useful.
-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 /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
/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.
Note that on Linux network interface names may have a length of 15
characters at maximum, while container names may have a length up
to 64 characters. As this option derives the host-side interface
name from the container name the name is possibly truncated. Thus,
care needs to be taken to ensure that interface names remain unique
in this case, or even better container names are generally not
chosen longer than 12 characters, to avoid the truncation. If the
name is truncated, systemd-nspawn will automatically append a
4-digit hash value to the name to reduce the chance of collisions.
However, the hash algorithm is not collision-free. (See
systemd.net-naming-scheme(7) for details on older naming algorithms
for this interface). Alternatively, the --network-veth-extra=
option may be used, which allows free configuration of the
host-side interface name independently of the container name — but
might require a bit more additional configuration in case bridging
in a fashion similar to --network-bridge= is desired.
--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-". Regardless of the used naming prefix the same
network interface name length limits imposed by Linux apply, along
with the complications this creates (for details see above).
As with --network-interface=, the underlying bridge network
interface must already exist at the time the container is started,
and thus similar unit file drop-ins as described above might be
useful.
--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 /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.
--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=.
-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=.
Security Options
--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.
If the special value of "help" is passed, the program will print
known capability names and exit.
This option sets the bounding set of capabilities which also limits
the ambient capabilities as given with the --ambient-capability=.
--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).
If the special value of "help" is passed, the program will print
known capability names and exit.
This option sets the bounding set of capabilities which also limits
the ambient capabilities as given with the --ambient-capability=.
--ambient-capability=
Specify one or more additional capabilities to pass in the
inheritable and ambient set to the program started within the
container. The value "all" is not supported for this setting.
All capabilities specified here must be in the set allowed with the
--capability= and --drop-capability= options. Otherwise, an error
message will be shown.
This option cannot be combined with the boot mode of the container
(as requested via --boot).
If the special value of "help" is passed, the program will print
known capability names and exit.
--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 allow list (as opposed to a deny
list!), and this command line option hence adds or removes entries
from the default allow list, depending on the "~" prefix. Note that
the applied system call filter is also altered implicitly if
additional capabilities are passed using the --capabilities=.
-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.
Resource Options
--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.
--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.
Integration Options
--resolv-conf=
Configures how /etc/resolv.conf inside of the container shall be
handled (i.e. DNS configuration synchronization from host to
container). Takes one of "off", "copy-host", "copy-static",
"copy-uplink", "copy-stub", "replace-host", "replace-static",
"replace-uplink", "replace-stub", "bind-host", "bind-static",
"bind-uplink", "bind-stub", "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, unless the file exists already and is
not a regular file (e.g. a symlink). Similarly, if "replace-host"
is used the file is copied, replacing any existing inode, including
symlinks. Similarly, if "bind-host" is used, the file is bind
mounted from the host into the container.
If set to "copy-static", "replace-static" or "bind-static" the
static resolv.conf file supplied with systemd-resolved.service(8)
(specifically: /usr/lib/systemd/resolv.conf) is copied or bind
mounted into the container.
If set to "copy-uplink", "replace-uplink" or "bind-uplink" the
uplink resolv.conf file managed by systemd-resolved.service
(specifically: /run/systemd/resolve/resolv.conf) is copied or bind
mounted into the container.
If set to "copy-stub", "replace-stub" or "bind-stub" the stub
resolv.conf file managed by systemd-resolved.service (specifically:
/run/systemd/resolve/stub-resolv.conf) is copied or bind mounted
into the container.
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 running its stub resolv.conf file is
used, and if not the host's /etc/resolv.conf file. In the latter
cases the file is copied if the image is writable, and bind mounted
otherwise.
It's recommended to use "copy-..." or "replace-..." 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. Similarly, if "bind" is used, the file
is bind mounted from the host into the container. If set to
"symlink", a symlink is created pointing from /etc/localtime in the
container to the timezone file in 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".
--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, or if the container is
in the --ephemeral mode. 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.
Mount Options
--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. If the
source path is not absolute, it is resolved relative to the current
working directory. The --bind-ro= option creates read-only bind
mounts. 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.
Mount options are comma-separated. rbind and norbind control
whether to create a recursive or a regular bind mount. Defaults to
"rbind". noidmap, idmap, and rootidmap control ID mapping.
Using idmap or rootidmap requires support by the source filesystem
for user/group ID mapped mounts. Defaults to "noidmap". With x
being the container's UID range offset, y being the length of the
container's UID range, and p being the owner UID of the bind mount
source inode on the host:
• If noidmap is used, any user z in the range 0 ... y seen from
inside of the container is mapped to x + z in the x ... x + y
range on the host. All host users outside of that range are
mapped to nobody inside the container.
• If idmap is used, any user z in the UID range 0 ... y as seen
from inside the container is mapped to the same z in the same 0
... y range on the host. All host users outside of that range
are mapped to nobody inside the container.
• If rootidmap is used, the user 0 seen from inside of the
container is mapped to p on the host. All host users outside of
that range are mapped to nobody inside the container.
Whichever ID mapping option is used, the same mapping will be used
for users and groups IDs. If rootidmap is used, the group owning
the bind mounted directory will have no effect
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=. Alternatively
you can use the "idmap" mount option to map the filesystem IDs.
--bind-user=
Binds the home directory of the specified user on the host into the
container. Takes the name of an existing user on the host as
argument. May be used multiple times to bind multiple users into
the container. This does three things:
1. The user's home directory is bind mounted from the host into
/run/host/home/.
2. An additional UID/GID mapping is added that maps the host
user's UID/GID to a container UID/GID, allocated from the
60514...60577 range.
3. A JSON user and group record is generated in /run/userdb/ that
describes the mapped user. It contains a minimized
representation of the host's user record, adjusted to the
UID/GID and home directory path assigned to the user in the
container. The nss-systemd(8) glibc NSS module will pick up
these records from there and make them available in the
container's user/group databases.
The combination of the three operations above ensures that it is
possible to log into the container using the same account
information as on the host. The user is only mapped transiently,
while the container is running, and the mapping itself does not
result in persistent changes to the container (except maybe for log
messages generated at login time, and similar). Note that in
particular the UID/GID assignment in the container is not made
persistently. If the user is mapped transiently, it is best to not
allow the user to make persistent changes to the container. If the
user leaves files or directories owned by the user, and those
UIDs/GIDs are reused during later container invocations (possibly
with a different --bind-user= mapping), those files and directories
will be accessible to the "new" user.
The user/group record mapping only works if the container contains
systemd 249 or newer, with nss-systemd properly configured in
nsswitch.conf. See nss-systemd(8) for details.
Note that the user record propagated from the host into the
container will contain the UNIX password hash of the user, so that
seamless logins in the container are possible. If the container is
less trusted than the host it's hence important to use a strong
UNIX password hash function (e.g. yescrypt or similar, with the
"$y$" hash prefix).
When binding a user from the host into the container checks are
executed to ensure that the username is not yet known in the
container. Moreover, it is checked that the UID/GID allocated for
it is not currently defined in the user/group databases of the
container. Both checks directly access the container's /etc/passwd
and /etc/group, and thus might not detect existing accounts in
other databases.
This operation is only supported in combination with
--private-users=/-U.
--inaccessible=
Make the specified path inaccessible in the container. This
over-mounts the specified path (which must exist in the container)
with a file node of the same type that is empty and has the most
restrictive access mode supported. This is an effective way to mask
files, directories and other file system objects from the container
payload. This option may be used more than once in case all
specified paths are masked.
--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). Backslash escapes are interpreted in
the path, so "\:" may be used to embed colons in the path.
Note that this option cannot be used to replace the root file
system of the container with a temporary file system. However, the
--volatile= option described below provides similar functionality,
with a focus on implementing stateless operating system images.
--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 an 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 "--overlay=+/var::/var" in order to automatically
overlay a writable temporary directory on a read-only /var/
directory. If a source path is not absolute, it is resolved
relative to the current working directory.
For details about overlay file systems, see Overlay Filesystem[5].
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.
Note that this option cannot be used to replace the root file
system of the container with an overlay file system. However, the
--volatile= option described above provides similar functionality,
with a focus on implementing stateless operating system images.
Input/Output Options
--console=MODE
Configures how to set up standard input, output and error output
for the container payload, as well as the /dev/console device for
the container. Takes one of interactive, read-only, passive, pipe
or autopipe. If interactive, a pseudo-TTY is allocated and made
available as /dev/console in the container. It is then
bi-directionally connected to the standard input and output passed
to systemd-nspawn. read-only is similar but only the output of the
container is propagated and no input from the caller is read. If
passive, a pseudo TTY is allocated, but it is not connected
anywhere. In pipe mode no pseudo TTY is allocated, but the standard
input, output and error output file descriptors passed to
systemd-nspawn are passed on — as they are — to the container
payload, see the following paragraph. Finally, autopipe mode
operates like interactive when systemd-nspawn is invoked on a
terminal, and like pipe otherwise. Defaults to interactive if
systemd-nspawn is invoked from a terminal, and read-only otherwise.
In pipe mode, /dev/console will not exist in the container. This
means that the container payload generally cannot be a full init
system as init systems tend to require /dev/console to be
available. On the other hand, in this mode container invocations
can be used within shell pipelines. This is because intermediary
pseudo TTYs do not permit independent bidirectional propagation of
the end-of-file (EOF) condition, which is necessary for shell
pipelines to work correctly. Note that the pipe mode should be
used carefully, as passing arbitrary file descriptors to less
trusted container payloads might open up unwanted interfaces for
access by the container payload. For example, if a passed file
descriptor refers to a TTY of some form, APIs such as TIOCSTI may
be used to synthesize input that might be used for escaping the
container. Hence pipe mode should only be used if the payload is
sufficiently trusted or when the standard input/output/error output
file descriptors are known safe, for example pipes.
--pipe, -P
Equivalent to --console=pipe.
Credentials
--load-credential=ID:PATH, --set-credential=ID:VALUE
Pass a credential to the container. These two options correspond to
the LoadCredential= and SetCredential= settings in unit files. See
systemd.exec(5) for details about these concepts, as well as the
syntax of the option's arguments.
Note: when systemd-nspawn runs as systemd system service it can
propagate the credentials it received via
LoadCredential=/SetCredential= to the container payload. A systemd
service manager running as PID 1 in the container can further
propagate them to the services it itself starts. It is thus
possible to easily propagate credentials from a parent service
manager to a container manager service and from there into its
payload. This can even be done recursively.
In order to embed binary data into the credential data for
--set-credential=, use C-style escaping (i.e. "\n" to embed a
newline, or "\x00" to embed a NUL byte). Note that the invoking
shell might already apply unescaping once, hence this might require
double escaping!.
The systemd-sysusers.service(8) and systemd-firstboot(1) services
read credentials configured this way for the purpose of configuring
the container's root user's password and shell, as well as system
locale, keymap and timezone during the first boot process of the
container. This is particularly useful in combination with
--volatile=yes where every single boot appears as first boot, since
configuration applied to /etc/ is lost on container reboot cycles.
See the respective man pages for details. Example:
# systemd-nspawn -i image.raw \
--volatile=yes \
--set-credential=firstboot.locale:de_DE.UTF-8 \
--set-credential=passwd.hashed-password.root:'$y$j9T$yAuRJu1o5HioZAGDYPU5d.$F64ni6J2y2nNQve90M/p0ZP0ECP/qqzipNyaY9fjGpC' \
-b
The above command line will invoke the specified image file
image.raw in volatile mode, i.e. with empty /etc/ and /var/. The
container payload will recognize this as a first boot, and will
invoke systemd-firstboot.service, which then reads the two passed
credentials to configure the system's initial locale and root
password.
Other
--no-pager
Do not pipe output into a pager.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
ENVIRONMENT
$SYSTEMD_LOG_LEVEL
The maximum log level of emitted messages (messages with a higher
log level, i.e. less important ones, will be suppressed). Either
one of (in order of decreasing importance) emerg, alert, crit, err,
warning, notice, info, debug, or an integer in the range 0...7. See
syslog(3) for more information.
$SYSTEMD_LOG_COLOR
A boolean. If true, messages written to the tty will be colored
according to priority.
This setting is only useful when messages are written directly to
the terminal, because journalctl(1) and other tools that display
logs will color messages based on the log level on their own.
$SYSTEMD_LOG_TIME
A boolean. If true, console log messages will be prefixed with a
timestamp.
This setting is only useful when messages are written directly to
the terminal or a file, because journalctl(1) and other tools that
display logs will attach timestamps based on the entry metadata on
their own.
$SYSTEMD_LOG_LOCATION
A boolean. If true, messages will be prefixed with a filename and
line number in the source code where the message originates.
Note that the log location is often attached as metadata to journal
entries anyway. Including it directly in the message text can
nevertheless be convenient when debugging programs.
$SYSTEMD_LOG_TID
A boolean. If true, messages will be prefixed with the current
numerical thread ID (TID).
Note that the this information is attached as metadata to journal
entries anyway. Including it directly in the message text can
nevertheless be convenient when debugging programs.
$SYSTEMD_LOG_TARGET
The destination for log messages. One of console (log to the
attached tty), console-prefixed (log to the attached tty but with
prefixes encoding the log level and "facility", see syslog(3), kmsg
(log to the kernel circular log buffer), journal (log to the
journal), journal-or-kmsg (log to the journal if available, and to
kmsg otherwise), auto (determine the appropriate log target
automatically, the default), null (disable log output).
$SYSTEMD_PAGER
Pager to use when --no-pager is not given; overrides $PAGER. If
neither $SYSTEMD_PAGER nor $PAGER are set, a set of well-known
pager implementations are tried in turn, including less(1) and
more(1), until one is found. If no pager implementation is
discovered no pager is invoked. Setting this environment variable
to an empty string or the value "cat" is equivalent to passing
--no-pager.
Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER (as well
as $PAGER) will be silently ignored.
$SYSTEMD_LESS
Override the options passed to less (by default "FRSXMK").
Users might want to change two options in particular:
K
This option instructs the pager to exit immediately when Ctrl+C
is pressed. To allow less to handle Ctrl+C itself to switch
back to the pager command prompt, unset this option.
If the value of $SYSTEMD_LESS does not include "K", and the
pager that is invoked is less, Ctrl+C will be ignored by the
executable, and needs to be handled by the pager.
X
This option instructs the pager to not send termcap
initialization and deinitialization strings to the terminal. It
is set by default to allow command output to remain visible in
the terminal even after the pager exits. Nevertheless, this
prevents some pager functionality from working, in particular
paged output cannot be scrolled with the mouse.
Note that setting the regular $LESS environment variable has no
effect for less invocations by systemd tools.
See less(1) for more discussion.
$SYSTEMD_LESSCHARSET
Override the charset passed to less (by default "utf-8", if the
invoking terminal is determined to be UTF-8 compatible).
Note that setting the regular $LESSCHARSET environment variable has
no effect for less invocations by systemd tools.
$SYSTEMD_PAGERSECURE
Takes a boolean argument. When true, the "secure" mode of the pager
is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE is not set
at all, secure mode is enabled if the effective UID is not the same
as the owner of the login session, see geteuid(2) and
sd_pid_get_owner_uid(3). In secure mode, LESSSECURE=1 will be set
when invoking the pager, and the pager shall disable commands that
open or create new files or start new subprocesses. When
$SYSTEMD_PAGERSECURE is not set at all, pagers which are not known
to implement secure mode will not be used. (Currently only less(1)
implements secure mode.)
Note: when commands are invoked with elevated privileges, for
example under sudo(8) or pkexec(1), care must be taken to ensure
that unintended interactive features are not enabled. "Secure" mode
for the pager may be enabled automatically as describe above.
Setting SYSTEMD_PAGERSECURE=0 or not removing it from the inherited
environment allows the user to invoke arbitrary commands. Note that
if the $SYSTEMD_PAGER or $PAGER variables are to be honoured,
$SYSTEMD_PAGERSECURE must be set too. It might be reasonable to
completely disable the pager using --no-pager instead.
$SYSTEMD_COLORS
Takes a boolean argument. When true, systemd and related utilities
will use colors in their output, otherwise the output will be
monochrome. Additionally, the variable can take one of the
following special values: "16", "256" to restrict the use of colors
to the base 16 or 256 ANSI colors, respectively. This can be
specified to override the automatic decision based on $TERM and
what the console is connected to.
$SYSTEMD_URLIFY
The value must be a boolean. Controls whether clickable links
should be generated in the output for terminal emulators supporting
this. This can be specified to override the decision that systemd
makes based on $TERM and other conditions.
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/37/Cloud/x86_64/images/Fedora-Cloud-Base-37-1.7.x86_64.raw.xz \
Fedora-Cloud-Base-37-1.7.x86-64
# systemd-nspawn -M Fedora-Cloud-Base-37-1.7.x86-64
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=37 --installroot=/var/lib/machines/f37 \
--repo=fedora --repo=updates --setopt=install_weak_deps=False install \
passwd dnf fedora-release vim-minimal util-linux systemd systemd-networkd
# systemd-nspawn -bD /var/lib/machines/f37
This installs a minimal Fedora distribution into the directory
/var/lib/machines/f37 and then boots that OS in a namespace container.
Because the installation is located underneath the standard
/var/lib/machines/ directory, it is also possible to start the machine
using systemd-nspawn -M f37.
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 from this image in a namespace
container.
debootstrap supports Debian[7], Ubuntu[8], and Tanglu[9] 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 ~/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://systemd.io/CONTAINER_INTERFACE
2. Discoverable Partitions Specification
https://systemd.io/DISCOVERABLE_PARTITIONS
3. OCI Runtime Specification
https://github.com/opencontainers/runtime-spec/blob/master/spec.md
4. OSTree
https://ostree.readthedocs.io/en/latest/
5. Overlay Filesystem
https://docs.kernel.org/filesystems/overlayfs.html
6. Fedora
https://getfedora.org
7. Debian
https://www.debian.org
8. Ubuntu
https://www.ubuntu.com
9. Tanglu
https://www.tanglu.org
10. Arch Linux
https://www.archlinux.org
11. OpenSUSE Tumbleweed
https://software.opensuse.org/distributions/tumbleweed
systemd 252 SYSTEMD-NSPAWN(1)
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