| SYSTEMD-NSPAWN(1) | systemd-nspawn | SYSTEMD-NSPAWN(1) |
.SH "NAME" systemd-nspawn - Spawn a command or OS in a lightweight
container
.SH "SYNOPSIS"
.HP 360u
systemd-nspawn
[OPTIONS...]
[COMMAND [ARGS...]]
.HP 360u
systemd-nspawn
--boot
[OPTIONS...]
[ARGS...]
.SH "DESCRIPTION"
.PP 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.
.PP 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.
.PP In contrast to chroot(1) systemd-nspawn may be used
to boot full Linux-based operating systems in a container.
.PP 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.
.PP 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.
.PP 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.
.PP systemd-nspawn may be invoked directly from the interactive
command line or run as system service in the background. In this mode each
container instance runs as its own service instance; a default template unit
file systemd-nspawn@.service is provided to make this easy, taking the
container name as instance identifier. Note that different default options
apply when systemd-nspawn is invoked by the template unit file than
interactively on the command line. Most importantly the template unit file
makes use of the --boot option which is not the default in case
systemd-nspawn is invoked from the interactive command line. Further
differences with the defaults are documented along with the various
supported options below.
.PP The machinectl(1) tool may be used to execute a number of
operations on containers. In particular it provides easy-to-use commands to
run containers as system services using the systemd-nspawn@.service template
unit file.
.PP Along with each container a settings file with the .nspawn suffix may
exist, containing additional settings to apply when running the container.
See systemd.nspawn(5) for details. Settings files override the
default options used by the systemd-nspawn@.service template unit file,
making it usually unnecessary to alter this template file directly.
.PP 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.
.PP 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.
.PP systemd-nspawn implements the Container Interface[1]
specification.
.PP 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.
.SH "UNPRIVILEGED OPERATION"
.PP 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:
.PP When running in unprivileged mode, some needed functionality is provided
via systemd-mountfsd.service(8) and
systemd-nsresourced.service(8).
.SH "OPTIONS"
.PP 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.
.PP The following options are understood:
.PP -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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.SS "Image Options"
.PP -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=.
.RE
.PP --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.
.RE
.PP -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.
.RE
.PP -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:
.sp
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.
.RE
.PP --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.
.RE
.PP --mstack=
Mount stack to mount the root directory for the container from. Takes a path
to a directory implementing systemd.mstack(7). This may be used to
run a container of an overlayfs assembled from a number of layers, possibly
writable and augmented with additional bind mounts.
Added in version 260.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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(1) 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.
.RE
.SS "Execution Options"
.PP -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.
.RE
.PP -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):
.sp
Table 1. Invocation Mode
| Switch | Explanation |
| Neither --as-pid2 nor --boot specified | The passed parameters 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
systemd-nspawn@.service template unit file is used.
When --boot is used, the passed parameters are processed the same way
the kernel processes its command line before handing it to PID 1: any
KEY=VALUE assignment whose KEY does not contain a . is exported as an
environment variable for PID 1 (with - in the key replaced by _, as if
specified via --setenv=), while all other parameters (including
systemd.*= assignments) are passed as arguments to the init program.
.RE
.PP --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.
.RE
.PP -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.
.RE
.PP -u, --uid=
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. This option was previously named
--user=. The old name is still accepted but deprecated. The short
option -u is compatible with both old and new versions of
systemd-nspawn.
Note that if credentials are used in combination with a non-root
--uid= (e.g.: --set-credential= or --load-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.
.RE
.PP --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.
.RE
.PP --notify-ready=
Configures support for notifications from the container's init process.
--notify-ready= takes a boolean. If false systemd-nspawn
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.)
If systemd-nspawn itself is invoked with a $NOTIFY_SOCKET set
in its environment (i.e. it is itself supervised by a service manager that
uses the sd_notify(3) protocol), FDSTORE=1 and FDSTOREREMOVE=1
messages received from the container payload (along with any accompanying
file descriptors and FDNAME= tag) are forwarded one level up to the
enveloping service manager. This allows the file descriptor store of
services running inside the container to be preserved across container
restarts (and, transitively, across restarts, re-execs, soft-reboots and
LUO-based kexecs of any outer service manager), provided
FileDescriptorStoreMax=/FileDescriptorStorePreserve=yes are
configured on the unit running systemd-nspawn. See the File
Descriptor Store[4] documentation for details.
Added in version 231.
.RE
.PP --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.
.RE
.SS "System Identity Options"
.PP -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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.SS "Property Options"
.PP -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.
.RE
.PP --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.
.RE
.PP --register=
Controls whether the container is registered with systemd-machined(8).
Takes a boolean argument or auto, and defaults to auto. 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. When set to auto,
registration is attempted but failures are ignored.
Added in version 209.
.RE
.PP --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.
.RE
.SS "User Namespacing Options"
.PP --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:
.sp
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.
.RE
.PP --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 or --private-users=managed 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.
.RE
.PP --private-users-delegate=
Takes a non-negative integer. Requests that the specified number of
additional 64K UID/GID ranges are delegated into the container's user
namespace. These delegated ranges are mapped 1:1 (i.e. the same UID/GID
values are used inside and outside the user namespace) and can be used by
nested containers to allocate their own transient UID/GID ranges via
systemd-nsresourced.service(8).
This option requires --private-users=managed, as the delegation is
performed by systemd-nsresourced.service(8) as part of the user
namespace allocation. The maximum number of delegated ranges is 16. Defaults
to 0, i.e. no delegation.
When this option is used with a non-zero value, the
systemd-nsresourced.service(8) Varlink socket
(/run/systemd/io.systemd.NamespaceResource) is automatically bind-mounted
into the container along with the necessary discovery symlinks in
/run/systemd/userdb/ and /run/varlink/registry/. This allows processes
inside the container to contact systemd-nsresourced on the host in
order to allocate nested user namespaces from the delegated ranges.
Added in version 260.
.RE
.PP -U
If the kernel supports the user namespaces feature, equivalent to
--private-users=pick --private-users-ownership=auto, otherwise
equivalent to --private-users=no.
Note that -U is the default if the systemd-nspawn@.service template
unit file is used.
Note: it is possible to undo the effect of
--private-users-ownership=chown (or -U) on the file system by
redoing the operation with the first UID of 0:
systemd-nspawn ... --private-users=0 --private-users-ownership=chown
Added in version 230.
.RE
.SS "Networking Options"
.PP --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.
.RE
.PP --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 systemd-nspawn@.service unit file instance, it
might hence make sense to add a unit file drop-in to the service instance
(e.g. /etc/systemd/system/systemd-nspawn@foobar.service.d/50-network.conf)
with contents like the following:
[Unit] Wants=sys-subsystem-net-devices-ens1.device After=sys-subsystem-net-devices-ens1.device
This will make sure that activation of the container service will be delayed
until the ens1 network interface has shown up. This is required since
hardware probing is fully asynchronous, and network interfaces might be
discovered only later during the boot process, after the container would
normally be started without these explicit dependencies.
Added in version 209.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP -n, --network-veth
Create a virtual Ethernet link (veth) between host and container. The host
side of the Ethernet link will be available as a network interface named
after the container's name (as specified with --machine=), prefixed
with ve-. The container side of the Ethernet link will be named host0. The
--network-veth option implies --private-network.
Note that systemd-networkd.service(8) includes by default a network
file /usr/lib/systemd/network/80-container-ve.network matching the host-side
interfaces created this way, which contains settings to enable automatic
address provisioning on the created virtual link via DHCP, as well as
automatic IP routing onto the host's external network interfaces. It also
contains /usr/lib/systemd/network/80-container-host0.network matching the
container-side interface created this way, containing settings to enable
client side address assignment via DHCP. In case systemd-networkd is running
on both the host and inside the container, automatic IP communication from
the container to the host is thus available, with further connectivity to
the external network.
Note that --network-veth is the default if the systemd-nspawn@.service
template unit file is used.
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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP -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.
.RE
.SS "Security Options"
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --restrict-address-families=
Restrict the socket address families accessible to the container. Takes a
space-separated list of address family names, such as AF_INET,
AF_INET6 or AF_UNIX. When prefixed with ~ the listed address
families will be prohibited, otherwise they will be permitted (allowlisted).
Use the special value none to prohibit all address families. This option may
be specified more than once, in which case the configured lists are
combined. If both a positive and a negative list are configured, the
negative list takes precedence over the positive list.
Note that currently this option defaults to no restrictions, i.e. all address
families are accessible. In a future version of systemd, the default will be
changed to restrict address families to AF_INET, AF_INET6 and
AF_UNIX. Use --restrict-address-families= (with an empty
argument) or set RestrictAddressFamilies= in a .nspawn file to opt
out of filtering explicitly.
Added in version 261.
.RE
.PP -Z, --selinux-context=
Sets the SELinux security context to be used to label processes in the
container.
Added in version 209.
.RE
.PP -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.
.RE
.SS "Resource Options"
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.SS "Integration Options"
.PP --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.
.RE
.PP --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.
.RE
.PP --link-journal=
Control whether the container's journal shall be made visible to the host
system. If enabled, allows viewing the container's journal files from the
host (but not vice versa). Takes one of no, host, try-host, guest,
try-guest, auto. If no, the journal is not linked. If host, the journal
files are stored on the host file system (beneath
/var/log/journal/machine-id) and the subdirectory is bind-mounted
into the container at the same location. If guest, the journal files are
stored on the guest file system (beneath /var/log/journal/machine-id)
and the subdirectory is symlinked into the host at the same location.
try-host and try-guest do the same but do not fail if the host does not have
persistent journaling enabled, or if the container is in the
--ephemeral mode. If auto (the default), and the right subdirectory
of /var/log/journal exists, it will be bind mounted into the container. If
the subdirectory does not exist, no linking is performed. Effectively,
booting a container once with guest or host will link the journal
persistently if further on the default of auto is used.
Note that --link-journal=try-guest is the default if the
systemd-nspawn@.service template unit file is used.
Added in version 187.
.RE
.PP -j
Equivalent to --link-journal=try-guest.
Added in version 187.
.RE
.PP --forward-journal=
Forward the container's journal to the host by starting
systemd-journal-remote(8) listening on a Unix socket that is
bind-mounted into the container. The container's systemd-journald(8)
connects to the socket via the journal.forward_to_socket credential
and streams journal entries to the host in real-time. Takes a path to a
journal file or directory where the received entries will be stored. If the
path ends in .journal, entries are written to a single file; otherwise,
entries are split per host into the specified directory.
Added in version 261.
.RE
.PP --forward-journal-max-use=BYTES,
--forward-journal-keep-free=BYTES,
--forward-journal-max-file-size=BYTES,
--forward-journal-max-files=N
These options configure the corresponding settings of
systemd-journal-remote(8) when forwarding journal entries from the
container. See journal-remote.conf(5) for the descriptions of these
settings.
Added in version 261.
.RE
.SS "Mount Options"
.PP --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:
.sp
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.
.RE
.PP --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
two things:
.sp
The combination of the two 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.
.RE
.PP --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.
.sp
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.
.RE
.PP --bind-user-group=NAME
When used with --bind-user=, includes the specified group as an
auxiliary group in the user records of users bound into the container. Takes
a group name.
Note: This will not check whether the specified groups exist in the
container.
This operation is only supported in combination with --bind-user=.
Added in version 259.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.SS "Input/Output Options"
.PP --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.
.RE
.PP --pipe, -P
Equivalent to --console=pipe.
Added in version 242.
.RE
.PP --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.
.RE
.SS "Credentials"
.PP --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.
.RE
.SS "Other"
.PP --system, --user
Specify whether to run in system or user scope. This controls which service
manager and machined instance to interact with, as well as operational
defaults such as user namespace mode and private networking. If neither is
specified, --system is implied when running as root, --user
otherwise.
Note: for backwards compatibility, --user followed by a positional
argument is interpreted as the deprecated --user=NAME
form (now --uid=). To use --user for scope selection when
positional arguments follow, separate them with --.
Added in version 261.
.RE
.PP --no-pager
Do not pipe output into a pager.
.RE
.PP -h, --help
Print a short help text and exit.
.RE
.PP --version
Print a short version string and exit.
.RE
.PP --no-ask-password
Do not query the user for authentication for privileged operations.
.RE
.SH "HOTKEYS"
.PP 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.
.PP Ctrl-] Ctrl-] Ctrl-]
Immediately terminate the container, killing all processes.
.RE
.PP Ctrl-] Ctrl-] r
Issue a reboot request to the container.
Added in version 258.
.RE
.PP Ctrl-] Ctrl-] p
Issue a shutdown request to the container.
Added in version 258.
.RE
.SH "ENVIRONMENT"
.PP $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.
.RE
.PP $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.
.RE
.PP $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.
.RE
.PP $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.
.RE
.PP $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.
.RE
.PP $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).
.RE
.PP $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.
.RE
.PP $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.
.RE
.PP $SYSTEMD_LESS
Override the options passed to less (by default FRSXMK).
Users might want to change two options in particular:
.PP 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.
.RE
.PP 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.
.RE
.sp
Note that setting the regular $LESS environment variable has no effect
for less invocations by systemd tools.
See less(1) for more discussion.
.RE
.PP $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.
.RE
.PP $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.
.RE
.PP $SYSTEMD_COLORS
Takes a boolean argument, or a special value. By default (unset),
systemd and related utilities will use colors in their output if
possible. If $COLORTERM is set to truecolor or 24bit, 24-bit colors
will be enabled, 256 colors otherwise, unless $NO_COLOR or
$TERM indicates colors are disabled.
.PP true
Same as unset, except that $NO_COLOR is ignored.
.RE
.PP false
The output will be monochrome.
.RE
.PP 16, 256, 24bit
Always use the base 16 ANSI colors, 256 colors, or 24 bit color,
respectively.
.RE
.PP auto-16, auto-256, auto-24bit
Use the given quantity of colours, subject to $TERM, and what the
console is connected to.
.RE
.sp
.RE
.PP $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.
.RE
.SH "EXAMPLES"
.PP 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
.PP This downloads and verifies the specified .tar image, and then uses
systemd-nspawn(1) to open a shell in it.
.PP Example 2. Build and boot a minimal Fedora distribution
in a container
# dnf -y --releasever=44 --installroot=/var/lib/machines/f44 \
--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/f44
.PP (Omit --use-host-config when using dnf <= 4.) This
installs a minimal Fedora distribution into the directory
/var/lib/machines/f44 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 f44.
.PP Example 3. Spawn a shell in a container of a minimal
Debian unstable distribution
# debootstrap unstable ~/debian-tree/ # systemd-nspawn -D ~/debian-tree/
.PP This installs a minimal Debian unstable distribution into the directory
~/debian-tree/ and then spawns a shell from this image in a namespace
container.
.PP debootstrap supports Debian[8], and Ubuntu[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).
.PP Example 4. Boot a minimal Arch Linux distribution in a
container
# pacstrap -c ~/arch-tree/ base # systemd-nspawn -bD ~/arch-tree/
.PP This installs a minimal Arch Linux distribution into the directory
~/arch-tree/ and then boots an OS in a namespace container in it.
.PP 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
.PP Example 6. Boot into an ephemeral snapshot of the host
system
# systemd-nspawn -D / -xb
.PP 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.
.PP 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
.PP 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
.SH "EXIT STATUS"
.PP The exit code of the program executed in the container is returned.
.SH "SEE ALSO"
.PP 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),
systemd.mstack(7), btrfs(8)
NOTES
- 1.
- Container Interface
- 2.
- UAPI.2 Discoverable Partitions Specification
- 3.
- OCI Runtime Specification
- 4.
- File Descriptor Store
- 5.
- Overlay Filesystem
- 6.
- ANSI Escape Code (Wikipedia)
- 7.
-
It is recommended for other tools to set and check $SUDO_UID as appropriate, treating it is a common interface. - 8.
- Debian
- 9.
- Ubuntu
- 10.
- Arch Linux
- 11.
- OpenSUSE Tumbleweed
| systemd 262.2 |