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NAME | SYNOPSIS | DESCRIPTION | UNPRIVILEGED OPERATION | OPTIONS | HOTKEYS | ENVIRONMENT | EXAMPLES | EXIT STATUS | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-NSPAWN(1) systemd-nspawn SYSTEMD-NSPAWN(1)
systemd-nspawn - Spawn a command or OS in a lightweight container
systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]
systemd-nspawn --boot [OPTIONS...] [ARGS...]
systemd-nspawn may be used to run a command or OS in a lightweight
namespace container. In many ways it is similar to chroot(1), but
more powerful since it virtualizes the file system hierarchy, as
well as the process tree, the various IPC subsystems, and the host
and domain names.
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. This sandbox
can easily be circumvented from within the container if user
namespaces are not used. This means that untrusted code must
always be run in a user namespace, see the discussion of the
--private-users= option below.
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 [email protected] 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
[email protected] 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 [email protected]
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.
systemd-nspawn may be invoked with or without privileges. The full
functionality is currently only available when invoked with
privileges. When invoked without privileges, various limitations
apply, including, but not limited to:
• Only disk image based containers are supported (i.e.
--image=). Directory based ones (i.e. --directory=) are not
supported.
• Machine registration via --machine= is not supported.
• Only --private-network and --network-veth networking modes are
supported.
When running in unprivileged mode, some needed functionality is
provided via systemd-mountfsd.service(8) and
systemd-nsresourced.service(8).
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.
Added in version 209.
--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.
Added in version 226.
--cleanup
Clean up left-over mounts and underlying mount points used by
the container, and exit without invoking any containers. This
may be useful when the previous invocation of systemd-nspawn
was unexpectedly terminated. This requires at least one of
-M/--machine=, -D/--directory=, or -i/--image= to determine
the mounts to be cleaned up.
Added in version 257.
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.
In place of the directory path a ".v/" versioned directory may
be specified, see systemd.v(7) for details.
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.
Added in version 219.
-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.
Added in version 219.
-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=.
In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.
Added in version 211.
--image-policy=policy
Takes an image policy string as argument, as per
systemd.image-policy(7). The policy is enforced when operating
on the disk image specified via --image=, see above. If not
specified, defaults to
"root=verity+signed+encrypted+unprotected+absent:usr=verity+signed+encrypted+unprotected+absent:home=encrypted+unprotected+absent:srv=encrypted+unprotected+absent:esp=unprotected+absent:xbootldr=unprotected+absent:tmp=encrypted+unprotected+absent:var=encrypted+unprotected+absent",
i.e. all recognized file systems in the image are used, but
not the swap partition.
Added in version 254.
--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).
Added in version 242.
--read-only
Mount the container's root file system (and any other file
systems contained 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 of whether 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 is 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.
Added in version 216.
--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).
Added in version 233.
--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).
Added in version 246.
--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
contain 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.
Added in version 246.
--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.
Added in version 233.
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.
Added in version 229.
-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 │
│ --boot specified │ are 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
[email protected] 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.
Added in version 229.
-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.
Added in version 209.
-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.
Note that if credentials are used in combination with a
non-root --user= (e.g.: --set-credential=, --load-credential=
or --import-credential=), then --no-new-privileges=yes must be
used, and --boot or --as-pid2 must not be used, as the
credentials would otherwise be unreadable by the container due
to missing privileges after switching to the specified user.
--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).
Added in version 220.
--notify-ready=
Configures support for notifications from the container's init
process. --notify-ready= takes a boolean. If false
systemd-vmpawn notifies the calling service manager with a
"READY=1" message when the init process is created. If true it
waits for a "READY=1" message from the init process in the VM
before sending its own to the service manager. For more
details about notifications see sd_notify(3).
Defaults to false. (Note that this is unlike the option of the
same name to systemd-vmspawn(1) that defaults to true.)
Added in version 231.
--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.
Added in version 250.
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.
Added in version 202.
--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.
Added in version 239.
--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 is not used.
Added in version 206.
--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 is not 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.
Added in version 220.
--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".
Added in version 209.
--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.
Added in version 209.
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. 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).
4. If the parameter is "no", user namespacing is turned off.
This is the default when systemd-nspawn is invoked
directly. (Note that the [email protected] unit
enables private users.) This option is not secure and must
not be used to run untrusted code.
5. 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, but may be useful if proper user namespacing
with distinct UID maps is not possible. This option is not
secure and must not be used to run untrusted code.
6. If the parameter is "managed", user namespacing is
employed with in managed mode, i.e. allocation of a UID
range is delegated to systemd-nsresourced.service(8). This
mode is selected by default if invoked unprivileged, but
can also be requested explicitly when privileged. In this
mode a 64K UID range is automatically picked.
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 bits. 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 bits 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, --private-users=managed (or when privileged
--private-users=pick, too) is the recommended option as user
namespacing is advised for security, and this option massively
enhances container security while operating 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, except possibly in the file
ownership of the files and directories of the container, see
--private-users-ownership=.
Note that when user namespacing is used without UID mapping
(see below) 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.
Note that for fully unprivileged operation in "managed" mode,
any directory image should be owned by the foreign UID range.
Added in version 220.
--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
from UID 0 to the target UID range), "foreign" (the same, but
from the foreign UID range base) or "auto" for automatically
using "map" or "foreign", where available and applicable 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 "foreign" or "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.
systemd-dissect(1)'s --shift switch may be used to shift
UID/GID ownership from or to the 0, foreign or specific
container UID/GID base outside of any systemd-nspawn
invocation.
Added in version 230.
-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 [email protected]
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
Added in version 230.
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.
Either takes a single interface name, referencing the name on
the host, or a colon-separated pair of interfaces, in which
case the first one references the name on the host, and the
second one the name in the container. When the container
terminates, the interface is moved back to the calling
namespace and renamed to its original name. 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
[email protected] unit file instance, it might hence
make sense to add a unit file drop-in to the service instance
(e.g.
/etc/systemd/system/[email protected]/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.
Added in version 209.
--network-macvlan=
Create a "macvlan" interface of the specified Ethernet network
interface and add it to the container. Either takes a single
interface name, referencing the name on the host, or a
colon-separated pair of interfaces, in which case the first
one references the name on the host, and the second one the
name in the container. A "macvlan" interface is a virtual
interface that adds a second MAC address to an existing
physical Ethernet link. If the container interface name is not
defined, 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.
Added in version 211.
--network-ipvlan=
Create an "ipvlan" interface of the specified Ethernet network
interface and add it to the container. Either takes a single
interface name, referencing the name on the host, or a
colon-separated pair of interfaces, in which case the first
one references the name on the host, and the second one the
name in the container. An "ipvlan" interface is a virtual
interface, similar to a "macvlan" interface, which uses the
same MAC address as the underlying interface. If the container
interface name is not defined, 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.
Added in version 219.
-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
[email protected] 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.
Added in version 209.
--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=.
Added in version 228.
--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.
Added in version 209.
--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.
Added in version 230.
--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=.
Added in version 236.
-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=.
Added in version 219.
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=.
Added in version 186.
--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=.
Added in version 209.
--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.
Added in version 248.
--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.
Added in version 239.
--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=.
Added in version 235.
-Z, --selinux-context=
Sets the SELinux security context to be used to label
processes in the container.
Added in version 209.
-L, --selinux-apifs-context=
Sets the SELinux security context to be used to label files in
the virtual API file systems in the container.
Added in version 209.
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".
Added in version 239.
--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.
Added in version 239.
--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.
Added in version 239.
--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.
Added in version 209.
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".
Added in version 239.
--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".
Added in version 239.
--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
[email protected] template unit file is used.
Added in version 187.
-j
Equivalent to --link-journal=try-guest.
Added in version 187.
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, rootidmap and owneridmap
control ID mapping.
Using idmap, rootidmap or owneridmap 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. Other host users 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. Other host users 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. Other host users are
mapped to nobody inside the container.
• If owneridmap is used, the owner of the target directory
inside of the container is mapped to p on the host. Other
host users 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 or owneridmap are
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.
Added in version 198.
--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/, using an idmapped mount to map the
host user's UID/GID to its assigned UID/GID in the
container.
2. 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 is 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.
Added in version 249.
--bind-user-shell=
When used with --bind-user=, includes the specified shell in
the user records of users bound into the container. Takes
either a boolean or an absolute path.
• If false (the default), no shell is passed in the user
records for users bound into the container. This causes
bound users to the use the container's default shell.
• If true, the shells specified by the host user records are
included in the user records of all users bound into the
container.
• If passed an absolute path, sets that path as the shell
for user records of all users bound into the container.
Note: This will not check whether the specified shells exist
in the container.
This operation is only supported in combination with
--bind-user=.
Added in version 258.
--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.
Added in version 242.
--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.
Added in version 214.
--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.
Added in version 220.
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.
Added in version 242.
--pipe, -P
Equivalent to --console=pipe.
Added in version 242.
--background=COLOR
Change the terminal background color to the specified ANSI
color as long as the container runs. The color specified
should be an ANSI X3.64 SGR background color, i.e. strings
such as "40", "41", ..., "47", "48;2;...", "48;5;...". See
ANSI Escape Code (Wikipedia)[6] for details. Assign an empty
string to disable any coloring.
Added in version 256.
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.
Added in version 247.
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.
--no-ask-password
Do not query the user for authentication for privileged
operations.
When invoked in interactive mode (i.e. the default
--console=interactive), a few special keyboard shortcuts are
understood that control the container runtime. These shortcuts
need to be typed within 1s to have effect, otherwise they will be
forwarded to the container as regular keypresses.
Ctrl-] Ctrl-] Ctrl-]
Immediately terminate the container, killing all processes.
Ctrl-] Ctrl-] r
Issue a reboot request to the container.
Added in version 258.
Ctrl-] Ctrl-] p
Issue a shutdown request to the container.
Added in version 258.
$SYSTEMD_LOG_LEVEL
The maximum log level of emitted messages (messages with a
higher log level, i.e. less important ones, will be
suppressed). Takes a comma-separated list of values. A value
may be 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. Each value may optionally be prefixed with one of
console, syslog, kmsg or journal followed by a colon to set
the maximum log level for that specific log target (e.g.
SYSTEMD_LOG_LEVEL=debug,console:info specifies to log at debug
level except when logging to the console which should be at
info level). Note that the global maximum log level takes
priority over any per target maximum log levels.
$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_LOG_RATELIMIT_KMSG
Whether to ratelimit kmsg or not. Takes a boolean. Defaults to
"true". If disabled, systemd will not ratelimit messages
written to kmsg.
$SYSTEMD_PAGER, $PAGER
Pager to use when --no-pager is not given. $SYSTEMD_PAGER is
used if set; otherwise $PAGER is used. If neither
$SYSTEMD_PAGER nor $PAGER are set, a set of well-known pager
implementations is tried in turn, including less(1) and
more(1), until one is found. If no pager implementation is
discovered, no pager is invoked. Setting those environment
variables to an empty string or the value "cat" is equivalent
to passing --no-pager.
Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER and
$PAGER can only be used to disable the pager (with "cat" or
""), and are otherwise 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
Common pager commands like less(1), in addition to "paging",
i.e. scrolling through the output, support opening of or
writing to other files and running arbitrary shell commands.
When commands are invoked with elevated privileges, for
example under sudo(8) or pkexec(1), the pager becomes a
security boundary. Care must be taken that only programs with
strictly limited functionality are used as pagers, and
unintended interactive features like opening or creation of
new files or starting of subprocesses are not allowed. "Secure
mode" for the pager may be enabled as described below, if the
pager supports that (most pagers are not written in a way that
takes this into consideration). It is recommended to either
explicitly enable "secure mode" or to completely disable the
pager using --no-pager or PAGER=cat when allowing untrusted
users to execute commands with elevated privileges.
This option takes a boolean argument. When set to true, the
"secure mode" of the pager is enabled. In "secure mode",
LESSSECURE=1 will be set when invoking the pager, which
instructs the pager to disable commands that open or create
new files or start new subprocesses. Currently only less(1) is
known to understand this variable and implement "secure mode".
When set to false, no limitation is placed on the pager.
Setting SYSTEMD_PAGERSECURE=0 or not removing it from the
inherited environment may allow the user to invoke arbitrary
commands.
When $SYSTEMD_PAGERSECURE is not set, systemd tools attempt to
automatically figure out if "secure mode" should be enabled
and whether the pager supports it. "Secure mode" is enabled if
the effective UID is not the same as the owner of the login
session, see geteuid(2) and sd_pid_get_owner_uid(3), or when
running under sudo(8) or similar tools ($SUDO_UID is set [7]).
In those cases, SYSTEMD_PAGERSECURE=1 will be set and pagers
which are not known to implement "secure mode" will not be
used at all. Note that this autodetection only covers the most
common mechanisms to elevate privileges and is intended as
convenience. It is recommended to explicitly set
$SYSTEMD_PAGERSECURE or disable the pager.
Note that if the $SYSTEMD_PAGER or $PAGER variables are to be
honoured, other than to disable the pager,
$SYSTEMD_PAGERSECURE must be set too.
$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.
Example 1. Download an Ubuntu TAR image and open a shell in it
# importctl pull-tar -mN https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64-root.tar.xz
# systemd-nspawn -M jammy-server-cloudimg-amd64-root
This downloads and verifies the specified .tar image, and then
uses systemd-nspawn(1) to open a shell in it.
Example 2. Build and boot a minimal Fedora distribution in a
container
# dnf -y --releasever=42 --installroot=/var/lib/machines/f42 \
--use-host-config --setopt=install_weak_deps=0 \
--repo=fedora --repo=updates install \
passwd dnf fedora-release nano util-linux systemd systemd-networkd
# systemd-nspawn -bD /var/lib/machines/f42
(Omit --use-host-config when using dnf <= 4.) This installs a
minimal Fedora distribution into the directory
/var/lib/machines/f42 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 f42.
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[8], Ubuntu[9], and Tanglu[10] 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
The exit code of the program executed in the container is
returned.
systemd(1), systemd.nspawn(5), chroot(1), dnf(8), debootstrap(8),
pacman(8), zypper(8), systemd.slice(5), machinectl(1),
importctl(1), systemd-mountfsd.service(8),
systemd-nsresourced.service(8), btrfs(8)
1. Container Interface
https://systemd.io/CONTAINER_INTERFACE
2. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification
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. ANSI Escape Code (Wikipedia)
https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters
7. It is recommended for other tools to set and check $SUDO_UID
as appropriate, treating it is a common interface.
8. Debian
https://www.debian.org
9. Ubuntu
https://www.ubuntu.com
10. Tanglu
https://www.tanglu.org
11. Arch Linux
https://www.archlinux.org
12. OpenSUSE Tumbleweed
https://software.opensuse.org/distributions/tumbleweed
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 258~rc2 SYSTEMD-NSPAWN(1)
Pages that refer to this page: bootctl(1), coredumpctl(1), importctl(1), journalctl(1), machinectl(1), systemctl(1), systemd-analyze(1), systemd-cgls(1), systemd-detect-virt(1), systemd-dissect(1), systemd-firstboot(1), systemd-nspawn(1), systemd-vmspawn(1), org.freedesktop.import1(5), repart.d(5), systemd.exec(5), systemd.network(5), systemd.nspawn(5), systemd.directives(7), systemd.image-policy(7), systemd.index(7), systemd.net-naming-scheme(7), systemd.v(7), kernel-install(8), nss-mymachines(8), nss-systemd(8), systemd-importd.service(8), systemd-import-generator(8), systemd-machined.service(8), systemd-nsresourced.service(8), systemd-run-generator(8), systemd-sysext(8), systemd-sysusers(8), systemd-tmpfiles(8)
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