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NAME | SYNOPSIS | DESCRIPTION | UNPRIVILEGED OPERATION | OPTIONS | 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 light-weight
container
systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]
systemd-nspawn --boot [OPTIONS...] [ARGS...]
systemd-nspawn may be used to run a command or OS in a
light-weight namespace container. In many ways it is similar to
chroot(1), but more powerful since it fully virtualizes the file
system hierarchy, as well as the process tree, the various IPC
subsystems and the host and domain name.
systemd-nspawn 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 [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.
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 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.
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 (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).
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 isn't 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 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.
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. 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.
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) 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.
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/.
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.
Added in version 249.
--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.
$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 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.
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=40 --installroot=/var/lib/machines/f40 \
--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/f40
This installs a minimal Fedora distribution into the directory
/var/lib/machines/f40 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 f40.
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
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. 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
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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 257~devel SYSTEMD-NSPAWN(1)
Pages that refer to this page: bootctl(1), coredumpctl(1), importctl(1), journalctl(1), machinectl(1), systemctl(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.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-machined.service(8), systemd-nsresourced.service(8), systemd-sysext(8), systemd-sysusers(8), systemd-tmpfiles(8)
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