systemd-nspawn(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | EXAMPLES | EXIT STATUS | SEE ALSO | NOTES | COLOPHON

SYSTEMD-NSPAWN(1)            systemd-nspawn            SYSTEMD-NSPAWN(1)

NAME         top

       systemd-nspawn - Spawn a command or OS in a light-weight
       container

SYNOPSIS         top

       systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]

       systemd-nspawn --boot [OPTIONS...] [ARGS...]

DESCRIPTION         top

       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 starting the container (see os-release(5)). It might be
       necessary to add this file to the container tree manually if the
       OS of the container is too old to contain this file
       out-of-the-box.

       systemd-nspawn may be invoked directly from the interactive
       command line or run as system service in the background. In this
       mode each container instance runs as its own service instance; a
       default template unit file systemd-nspawn@.service is provided to
       make this easy, taking the container name as instance identifier.
       Note that different default options apply when systemd-nspawn is
       invoked by the template unit file than interactively on the
       command line. Most importantly the template unit file makes use
       of the --boot which is not the default in case systemd-nspawn is
       invoked from the interactive command line. Further differences
       with the defaults are documented along with the various supported
       options below.

       The machinectl(1) tool may be used to execute a number of
       operations on containers. In particular it provides easy-to-use
       commands to run containers as system services using the
       systemd-nspawn@.service template unit file.

       Along with each container a settings file with the .nspawn suffix
       may exist, containing additional settings to apply when running
       the container. See systemd.nspawn(5) for details. Settings files
       override the default options used by the systemd-nspawn@.service
       template unit file, making it usually unnecessary to alter this
       template file directly.

       Note that systemd-nspawn will mount file systems private to the
       container to /dev/, /run/ and similar. These will not be visible
       outside of the container, and their contents will be lost when
       the container exits.

       Note that running two systemd-nspawn containers from the same
       directory tree will not make processes in them see each other.
       The PID namespace separation of the two containers is complete
       and the containers will share very few runtime objects except for
       the underlying file system. Use machinectl(1)'s login or shell
       commands to request an additional login session in a running
       container.

       systemd-nspawn implements the Container Interface[1]
       specification.

       While running, containers invoked with systemd-nspawn are
       registered with the systemd-machined(8) service that keeps track
       of running containers, and provides programming interfaces to
       interact with them.

OPTIONS         top

       If option -b is specified, the arguments are used as arguments
       for the init program. Otherwise, COMMAND specifies the program to
       launch in the container, and the remaining arguments are used as
       arguments for this program. If --boot is not used and no
       arguments are specified, a shell is launched in the container.

       The following options are understood:

       -q, --quiet
           Turns off any status output by the tool itself. When this
           switch is used, the only output from nspawn will be the
           console output of the container OS itself.

       --settings=MODE
           Controls whether systemd-nspawn shall search for and use
           additional per-container settings from .nspawn files. Takes a
           boolean or the special values override or trusted.

           If enabled (the default), a settings file named after the
           machine (as specified with the --machine= setting, or derived
           from the directory or image file name) with the suffix
           .nspawn is searched in /etc/systemd/nspawn/ and
           /run/systemd/nspawn/. If it is found there, its settings are
           read and used. If it is not found there, it is subsequently
           searched in the same directory as the image file or in the
           immediate parent of the root directory of the container. In
           this case, if the file is found, its settings will be also
           read and used, but potentially unsafe settings are ignored.
           Note that in both these cases, settings on the command line
           take precedence over the corresponding settings from loaded
           .nspawn files, if both are specified. Unsafe settings are
           considered all settings that elevate the container's
           privileges or grant access to additional resources such as
           files or directories of the host. For details about the
           format and contents of .nspawn files, consult
           systemd.nspawn(5).

           If this option is set to override, the file is searched, read
           and used the same way, however, the order of precedence is
           reversed: settings read from the .nspawn file will take
           precedence over the corresponding command line options, if
           both are specified.

           If this option is set to trusted, the file is searched, read
           and used the same way, but regardless of being found in
           /etc/systemd/nspawn/, /run/systemd/nspawn/ or next to the
           image file or container root directory, all settings will
           take effect, however, command line arguments still take
           precedence over corresponding settings.

           If disabled, no .nspawn file is read and no settings except
           the ones on the command line are in effect.

   Image Options
       -D, --directory=
           Directory to use as file system root for the container.

           If neither --directory=, nor --image= is specified the
           directory is determined by searching for a directory named
           the same as the machine name specified with --machine=. See
           machinectl(1) section "Files and Directories" for the precise
           search path.

           If neither --directory=, --image=, nor --machine= are
           specified, the current directory will be used. May not be
           specified together with --image=.

       --template=
           Directory or "btrfs" subvolume to use as template for the
           container's root directory. If this is specified and the
           container's root directory (as configured by --directory=)
           does not yet exist it is created as "btrfs" snapshot (if
           supported) or plain directory (otherwise) and populated from
           this template tree. Ideally, the specified template path
           refers to the root of a "btrfs" subvolume, in which case a
           simple copy-on-write snapshot is taken, and populating the
           root directory is instant. If the specified template path
           does not refer to the root of a "btrfs" subvolume (or not
           even to a "btrfs" file system at all), the tree is copied
           (though possibly in a 'reflink' copy-on-write scheme — if the
           file system supports that), which can be substantially more
           time-consuming. Note that the snapshot taken is of the
           specified directory or subvolume, including all
           subdirectories and subvolumes below it, but excluding any
           sub-mounts. May not be specified together with --image= or
           --ephemeral.

           Note that this switch leaves hostname, machine ID and all
           other settings that could identify the instance unmodified.

       -x, --ephemeral
           If specified, the container is run with a temporary snapshot
           of its file system that is removed immediately when the
           container terminates. May not be specified together with
           --template=.

           Note that this switch leaves hostname, machine ID and all
           other settings that could identify the instance unmodified.
           Please note that — as with --template= — taking the temporary
           snapshot is more efficient on file systems that support
           subvolume snapshots or 'reflinks' natively ("btrfs" or new
           "xfs") than on more traditional file systems that do not
           ("ext4"). Note that the snapshot taken is of the specified
           directory or subvolume, including all subdirectories and
           subvolumes below it, but excluding any sub-mounts.

           With this option no modifications of the container image are
           retained. Use --volatile= (described below) for other
           mechanisms to restrict persistency of container images during
           runtime.

       -i, --image=
           Disk image to mount the root directory for the container
           from. Takes a path to a regular file or to a block device
           node. The file or block device must contain either:

           •   An MBR partition table with a single partition of type
               0x83 that is marked bootable.

           •   A GUID partition table (GPT) with a single partition of
               type 0fc63daf-8483-4772-8e79-3d69d8477de4.

           •   A GUID partition table (GPT) with a marked root partition
               which is mounted as the root directory of the container.
               Optionally, GPT images may contain a home and/or a server
               data partition which are mounted to the appropriate
               places in the container. All these partitions must be
               identified by the partition types defined by the
               Discoverable Partitions Specification[2].

           •   No partition table, and a single file system spanning the
               whole image.

           On GPT images, if an EFI System Partition (ESP) is
           discovered, it is automatically mounted to /efi (or /boot as
           fallback) in case a directory by this name exists and is
           empty.

           Partitions encrypted with LUKS are automatically decrypted.
           Also, on GPT images dm-verity data integrity hash partitions
           are set up if the root hash for them is specified using the
           --root-hash= option.

           Single file system images (i.e. file systems without a
           surrounding partition table) can be opened using dm-verity if
           the integrity data is passed using the --root-hash= and
           --verity-data= (and optionally --root-hash-sig=) options.

           Any other partitions, such as foreign partitions or swap
           partitions are not mounted. May not be specified together
           with --directory=, --template=.

       --oci-bundle=
           Takes the path to an OCI runtime bundle to invoke, as
           specified in the OCI Runtime Specification[3]. In this case
           no .nspawn file is loaded, and the root directory and various
           settings are read from the OCI runtime JSON data (but data
           passed on the command line takes precedence).

       --read-only
           Mount the container's root file system (and any other file
           systems container in the container image) read-only. This has
           no effect on additional mounts made with --bind=, --tmpfs=
           and similar options. This mode is implied if the container
           image file or directory is marked read-only itself. It is
           also implied if --volatile= is used. In this case the
           container image on disk is strictly read-only, while changes
           are permitted but kept non-persistently in memory only. For
           further details, see below.

       --volatile, --volatile=MODE
           Boots the container in volatile mode. When no mode parameter
           is passed or when mode is specified as yes, full volatile
           mode is enabled. This means the root directory is mounted as
           a mostly unpopulated "tmpfs" instance, and /usr/ from the OS
           tree is mounted into it in read-only mode (the system thus
           starts up with read-only OS image, but pristine state and
           configuration, any changes are lost on shutdown). When the
           mode parameter is specified as state, the OS tree is mounted
           read-only, but /var/ is mounted as a writable "tmpfs"
           instance into it (the system thus starts up with read-only OS
           resources and configuration, but pristine state, and any
           changes to the latter are lost on shutdown). When the mode
           parameter is specified as overlay the read-only root file
           system is combined with a writable tmpfs instance through
           "overlayfs", so that it appears at it normally would, but any
           changes are applied to the temporary file system only and
           lost when the container is terminated. When the mode
           parameter is specified as no (the default), the whole OS tree
           is made available writable (unless --read-only is specified,
           see above).

           Note that if one of the volatile modes is chosen, its effect
           is limited to the root file system (or /var/ in case of
           state), and any other mounts placed in the hierarchy are
           unaffected — regardless if they are established automatically
           (e.g. the EFI system partition that might be mounted to /efi/
           or /boot/) or explicitly (e.g. through an additional command
           line option such as --bind=, see below). This means, even if
           --volatile=overlay is used changes to /efi/ or /boot/ are
           prohibited in case such a partition exists in the container
           image operated on, and even if --volatile=state is used the
           hypothetical file /etc/foobar is potentially writable if
           --bind=/etc/foobar if used to mount it from outside the
           read-only container /etc/ directory.

           The --ephemeral option is closely related to this setting,
           and provides similar behaviour by making a temporary,
           ephemeral copy of the whole OS image and executing that. For
           further details, see above.

           The --tmpfs= and --overlay= options provide similar
           functionality, but for specific sub-directories of the OS
           image only. For details, see below.

           This option provides similar functionality for containers as
           the "systemd.volatile=" kernel command line switch provides
           for host systems. See kernel-command-line(7) for details.

           Note that setting this option to yes or state will only work
           correctly with operating systems in the container that can
           boot up with only /usr/ mounted, and are able to
           automatically populate /var/ (and /etc/ in case of
           "--volatile=yes"). Specifically, this means that operating
           systems that follow the historic split of /bin/ and /lib/
           (and related directories) from /usr/ (i.e. where the former
           are not symlinks into the latter) are not supported by
           "--volatile=yes" as container payload. The overlay option
           does not require any particular preparations in the OS, but
           do note that "overlayfs" behaviour differs from regular file
           systems in a number of ways, and hence compatibility is
           limited.

       --root-hash=
           Takes a data integrity (dm-verity) root hash specified in
           hexadecimal. This option enables data integrity checks using
           dm-verity, if the used image contains the appropriate
           integrity data (see above). The specified hash must match the
           root hash of integrity data, and is usually at least 256 bits
           (and hence 64 formatted hexadecimal characters) long (in case
           of SHA256 for example). If this option is not specified, but
           the image file carries the "user.verity.roothash" extended
           file attribute (see xattr(7)), then the root hash is read
           from it, also as formatted hexadecimal characters. If the
           extended file attribute is not found (or is not supported by
           the underlying file system), but a file with the .roothash
           suffix is found next to the image file, bearing otherwise the
           same name (except if the image has the .raw suffix, in which
           case the root hash file must not have it in its name), the
           root hash is read from it and automatically used, also as
           formatted hexadecimal characters.

           Note that this configures the root hash for the root file
           system. Disk images may also contain separate file systems
           for the /usr/ hierarchy, which may be Verity protected as
           well. The root hash for this protection may be configured via
           the "user.verity.usrhash" extended file attribute or via a
           .usrhash file adjacent to the disk image, following the same
           format and logic as for the root hash for the root file
           system described here. Note that there's currently no switch
           to configure the root hash for the /usr/ from the command
           line.

           Also see the RootHash= option in systemd.exec(5).

       --root-hash-sig=
           Takes a PKCS7 signature of the --root-hash= option. The
           semantics are the same as for the RootHashSignature= option,
           see systemd.exec(5).

       --verity-data=
           Takes the path to a data integrity (dm-verity) file. This
           option enables data integrity checks using dm-verity, if a
           root-hash is passed and if the used image itself does not
           contains the integrity data. The integrity data must be
           matched by the root hash. If this option is not specified,
           but a file with the .verity suffix is found next to the image
           file, bearing otherwise the same name (except if the image
           has the .raw suffix, in which case the verity data file must
           not have it in its name), the verity data is read from it and
           automatically used.

       --pivot-root=
           Pivot the specified directory to / inside the container, and
           either unmount the container's old root, or pivot it to
           another specified directory. Takes one of: a path argument —
           in which case the specified path will be pivoted to / and the
           old root will be unmounted; or a colon-separated pair of new
           root path and pivot destination for the old root. The new
           root path will be pivoted to /, and the old / will be pivoted
           to the other directory. Both paths must be absolute, and are
           resolved in the container's file system namespace.

           This is for containers which have several bootable
           directories in them; for example, several OSTree[4]
           deployments. It emulates the behavior of the boot loader and
           initial RAM disk which normally select which directory to
           mount as the root and start the container's PID 1 in.

   Execution Options
       -a, --as-pid2
           Invoke the shell or specified program as process ID (PID) 2
           instead of PID 1 (init). By default, if neither this option
           nor --boot is used, the selected program is run as the
           process with PID 1, a mode only suitable for programs that
           are aware of the special semantics that the process with PID
           1 has on UNIX. For example, it needs to reap all processes
           reparented to it, and should implement sysvinit compatible
           signal handling (specifically: it needs to reboot on SIGINT,
           reexecute on SIGTERM, reload configuration on SIGHUP, and so
           on). With --as-pid2 a minimal stub init process is run as PID
           1 and the selected program is executed as PID 2 (and hence
           does not need to implement any special semantics). The stub
           init process will reap processes as necessary and react
           appropriately to signals. It is recommended to use this mode
           to invoke arbitrary commands in containers, unless they have
           been modified to run correctly as PID 1. Or in other words:
           this switch should be used for pretty much all commands,
           except when the command refers to an init or shell
           implementation, as these are generally capable of running
           correctly as PID 1. This option may not be combined with
           --boot.

       -b, --boot
           Automatically search for an init program and invoke it as PID
           1, instead of a shell or a user supplied program. If this
           option is used, arguments specified on the command line are
           used as arguments for the init program. This option may not
           be combined with --as-pid2.

           The following table explains the different modes of
           invocation and relationship to --as-pid2 (see above):

           Table 1. Invocation Mode
           ┌──────────────────────┬──────────────────────────┐
           │Switch                Explanation              │
           ├──────────────────────┼──────────────────────────┤
           │Neither --as-pid2 nor │ The passed parameters    │
           │--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
           systemd-nspawn@.service template unit file is used.

       --chdir=
           Change to the specified working directory before invoking the
           process in the container. Expects an absolute path in the
           container's file system namespace.

       -E NAME=VALUE, --setenv=NAME=VALUE
           Specifies an environment variable assignment to pass to the
           init process in the container, in the format "NAME=VALUE".
           This may be used to override the default variables or to set
           additional variables. This parameter may be used more than
           once.

       -u, --user=
           After transitioning into the container, change to the
           specified user defined in the container's user database. Like
           all other systemd-nspawn features, this is not a security
           feature and provides protection against accidental
           destructive operations only.

       --kill-signal=
           Specify the process signal to send to the container's PID 1
           when nspawn itself receives SIGTERM, in order to trigger an
           orderly shutdown of the container. Defaults to SIGRTMIN+3 if
           --boot is used (on systemd-compatible init systems SIGRTMIN+3
           triggers an orderly shutdown). If --boot is not used and this
           option is not specified the container's processes are
           terminated abruptly via SIGKILL. For a list of valid signals,
           see signal(7).

       --notify-ready=
           Configures support for notifications from the container's
           init process.  --notify-ready= takes a boolean (no and yes).
           With option no systemd-nspawn notifies systemd with a
           "READY=1" message when the init process is created. With
           option yes systemd-nspawn waits for the "READY=1" message
           from the init process in the container before sending its own
           to systemd. For more details about notifications see
           sd_notify(3).

   System Identity Options
       -M, --machine=
           Sets the machine name for this container. This name may be
           used to identify this container during its runtime (for
           example in tools like machinectl(1) and similar), and is used
           to initialize the container's hostname (which the container
           can choose to override, however). If not specified, the last
           component of the root directory path of the container is
           used, possibly suffixed with a random identifier in case
           --ephemeral mode is selected. If the root directory selected
           is the host's root directory the host's hostname is used as
           default instead.

       --hostname=
           Controls the hostname to set within the container, if
           different from the machine name. Expects a valid hostname as
           argument. If this option is used, the kernel hostname of the
           container will be set to this value, otherwise it will be
           initialized to the machine name as controlled by the
           --machine= option described above. The machine name is used
           for various aspect of identification of the container from
           the outside, the kernel hostname configurable with this
           option is useful for the container to identify itself from
           the inside. It is usually a good idea to keep both forms of
           identification synchronized, in order to avoid confusion. It
           is hence recommended to avoid usage of this option, and use
           --machine= exclusively. Note that regardless whether the
           container's hostname is initialized from the name set with
           --hostname= or the one set with --machine=, the container can
           later override its kernel hostname freely on its own as well.

       --uuid=
           Set the specified UUID for the container. The init system
           will initialize /etc/machine-id from this if this file is not
           set yet. Note that this option takes effect only if
           /etc/machine-id in the container is unpopulated.

   Property Options
       -S, --slice=
           Make the container part of the specified slice, instead of
           the default machine.slice. This applies only if the machine
           is run in its own scope unit, i.e. if --keep-unit isn't used.

       --property=
           Set a unit property on the scope unit to register for the
           machine. This applies only if the machine is run in its own
           scope unit, i.e. if --keep-unit isn't used. Takes unit
           property assignments in the same format as systemctl
           set-property. This is useful to set memory limits and similar
           for container.

       --register=
           Controls whether the container is registered with
           systemd-machined(8). Takes a boolean argument, which defaults
           to "yes". This option should be enabled when the container
           runs a full Operating System (more specifically: a system and
           service manager as PID 1), and is useful to ensure that the
           container is accessible via machinectl(1) and shown by tools
           such as ps(1). If the container does not run a service
           manager, it is recommended to set this option to "no".

       --keep-unit
           Instead of creating a transient scope unit to run the
           container in, simply use the service or scope unit
           systemd-nspawn has been invoked in. If --register=yes is set
           this unit is registered with systemd-machined(8). This switch
           should be used if systemd-nspawn is invoked from within a
           service unit, and the service unit's sole purpose is to run a
           single systemd-nspawn container. This option is not available
           if run from a user session.

           Note that passing --keep-unit disables the effect of --slice=
           and --property=. Use --keep-unit and --register=no in
           combination to disable any kind of unit allocation or
           registration with systemd-machined.

   User Namespacing Options
       --private-users=
           Controls user namespacing. If enabled, the container will run
           with its own private set of UNIX user and group ids (UIDs and
           GIDs). This involves mapping the private UIDs/GIDs used in
           the container (starting with the container's root user 0 and
           up) to a range of UIDs/GIDs on the host that are not used for
           other purposes (usually in the range beyond the host's
           UID/GID 65536). The parameter may be specified as follows:

            1. If one or two colon-separated numbers are specified, user
               namespacing is turned on. The first parameter specifies
               the first host UID/GID to assign to the container, the
               second parameter specifies the number of host UIDs/GIDs
               to assign to the container. If the second parameter is
               omitted, 65536 UIDs/GIDs are assigned.

            2. If the parameter is "yes", user namespacing is turned on.
               The UID/GID range to use is determined automatically from
               the file ownership of the root directory of the
               container's directory tree. To use this option, make sure
               to prepare the directory tree in advance, and ensure that
               all files and directories in it are owned by UIDs/GIDs in
               the range you'd like to use. Also, make sure that used
               file ACLs exclusively reference UIDs/GIDs in the
               appropriate range. In this mode, the number of UIDs/GIDs
               assigned to the container is 65536, and the owner UID/GID
               of the root directory must be a multiple of 65536.

            3. If the parameter is "no", user namespacing is turned off.
               This is the default.

            4. If the parameter is "identity", user namespacing is
               employed with an identity mapping for the first 65536
               UIDs/GIDs. This is mostly equivalent to
               --private-users=0:65536. While it does not provide
               UID/GID isolation, since all host and container UIDs/GIDs
               are chosen identically it does provide process capability
               isolation, and hence is often a good choice if proper
               user namespacing with distinct UID maps is not
               appropriate.

            5. The special value "pick" turns on user namespacing. In
               this case the UID/GID range is automatically chosen. As
               first step, the file owner UID/GID of the root directory
               of the container's directory tree is read, and it is
               checked that no other container is currently using it. If
               this check is successful, the UID/GID range determined
               this way is used, similar to the behavior if "yes" is
               specified. If the check is not successful (and thus the
               UID/GID range indicated in the root directory's file
               owner is already used elsewhere) a new – currently unused
               – UID/GID range of 65536 UIDs/GIDs is randomly chosen
               between the host UID/GIDs of 524288 and 1878982656,
               always starting at a multiple of 65536, and, if possible,
               consistently hashed from the machine name. This setting
               implies --private-users-ownership=auto (see below), which
               possibly has the effect that the files and directories in
               the container's directory tree will be owned by the
               appropriate users of the range picked. Using this option
               makes user namespace behavior fully automatic. Note that
               the first invocation of a previously unused container
               image might result in picking a new UID/GID range for it,
               and thus in the (possibly expensive) file ownership
               adjustment operation. However, subsequent invocations of
               the container will be cheap (unless of course the picked
               UID/GID range is assigned to a different use by then).

           It is recommended to assign at least 65536 UIDs/GIDs to each
           container, so that the usable UID/GID range in the container
           covers 16 bit. For best security, do not assign overlapping
           UID/GID ranges to multiple containers. It is hence a good
           idea to use the upper 16 bit of the host 32-bit UIDs/GIDs as
           container identifier, while the lower 16 bit encode the
           container UID/GID used. This is in fact the behavior enforced
           by the --private-users=pick option.

           When user namespaces are used, the GID range assigned to each
           container is always chosen identical to the UID range.

           In most cases, using --private-users=pick is the recommended
           option as it enhances container security massively and
           operates fully automatically in most cases.

           Note that the picked UID/GID range is not written to
           /etc/passwd or /etc/group. In fact, the allocation of the
           range is not stored persistently anywhere, except in the file
           ownership of the files and directories of the container.

           Note that when user namespacing is used file ownership on
           disk reflects this, and all of the container's files and
           directories are owned by the container's effective user and
           group IDs. This means that copying files from and to the
           container image requires correction of the numeric UID/GID
           values, according to the UID/GID shift applied.

       --private-users-ownership=
           Controls how to adjust the container image's UIDs and GIDs to
           match the UID/GID range chosen with --private-users=, see
           above. Takes one of "off" (to leave the image as is), "chown"
           (to recursively chown() the container's directory tree as
           needed), "map" (in order to use transparent ID mapping
           mounts) or "auto" for automatically using "map" where
           available and "chown" where not.

           If "chown" is selected, all files and directories in the
           container's directory tree will be adjusted so that they are
           owned by the appropriate UIDs/GIDs selected for the container
           (see above). This operation is potentially expensive, as it
           involves iterating through the full directory tree of the
           container. Besides actual file ownership, file ACLs are
           adjusted as well.

           Typically "map" is the best choice, since it transparently
           maps UIDs/GIDs in memory as needed without modifying the
           image, and without requiring an expensive recursive
           adjustment operation. However, it is not available for all
           file systems, currently.

           The --private-users-ownership=auto option is implied if
           --private-users=pick is used. This option has no effect if
           user namespacing is not used.

       -U
           If the kernel supports the user namespaces feature,
           equivalent to --private-users=pick
           --private-users-ownership=auto, otherwise equivalent to
           --private-users=no.

           Note that -U is the default if the systemd-nspawn@.service
           template unit file is used.

           Note: it is possible to undo the effect of
           --private-users-ownership=chown (or -U) on the file system by
           redoing the operation with the first UID of 0:

               systemd-nspawn ... --private-users=0 --private-users-ownership=chown

   Networking Options
       --private-network
           Disconnect networking of the container from the host. This
           makes all network interfaces unavailable in the container,
           with the exception of the loopback device and those specified
           with --network-interface= and configured with --network-veth.
           If this option is specified, the CAP_NET_ADMIN capability
           will be added to the set of capabilities the container
           retains. The latter may be disabled by using
           --drop-capability=. If this option is not specified (or
           implied by one of the options listed below), the container
           will have full access to the host network.

       --network-interface=
           Assign the specified network interface to the container. This
           will remove the specified interface from the calling
           namespace and place it in the container. When the container
           terminates, it is moved back to the calling namespace. Note
           that --network-interface= implies --private-network. This
           option may be used more than once to add multiple network
           interfaces to the container.

           Note that any network interface specified this way must
           already exist at the time the container is started. If the
           container shall be started automatically at boot via a
           systemd-nspawn@.service unit file instance, it might hence
           make sense to add a unit file drop-in to the service instance
           (e.g.
           /etc/systemd/system/systemd-nspawn@foobar.service.d/50-network.conf)
           with contents like the following:

               [Unit]
               Wants=sys-subsystem-net-devices-ens1.device
               After=sys-subsystem-net-devices-ens1.device

           This will make sure that activation of the container service
           will be delayed until the "ens1" network interface has shown
           up. This is required since hardware probing is fully
           asynchronous, and network interfaces might be discovered only
           later during the boot process, after the container would
           normally be started without these explicit dependencies.

       --network-macvlan=
           Create a "macvlan" interface of the specified Ethernet
           network interface and add it to the container. A "macvlan"
           interface is a virtual interface that adds a second MAC
           address to an existing physical Ethernet link. The interface
           in the container will be named after the interface on the
           host, prefixed with "mv-". Note that --network-macvlan=
           implies --private-network. This option may be used more than
           once to add multiple network interfaces to the container.

           As with --network-interface=, the underlying Ethernet network
           interface must already exist at the time the container is
           started, and thus similar unit file drop-ins as described
           above might be useful.

       --network-ipvlan=
           Create an "ipvlan" interface of the specified Ethernet
           network interface and add it to the container. An "ipvlan"
           interface is a virtual interface, similar to a "macvlan"
           interface, which uses the same MAC address as the underlying
           interface. The interface in the container will be named after
           the interface on the host, prefixed with "iv-". Note that
           --network-ipvlan= implies --private-network. This option may
           be used more than once to add multiple network interfaces to
           the container.

           As with --network-interface=, the underlying Ethernet network
           interface must already exist at the time the container is
           started, and thus similar unit file drop-ins as described
           above might be useful.

       -n, --network-veth
           Create a virtual Ethernet link ("veth") between host and
           container. The host side of the Ethernet link will be
           available as a network interface named after the container's
           name (as specified with --machine=), prefixed with "ve-". The
           container side of the Ethernet link will be named "host0".
           The --network-veth option implies --private-network.

           Note that systemd-networkd.service(8) includes by default a
           network file /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.

       --network-veth-extra=
           Adds an additional virtual Ethernet link between host and
           container. Takes a colon-separated pair of host interface
           name and container interface name. The latter may be omitted
           in which case the container and host sides will be assigned
           the same name. This switch is independent of --network-veth,
           and — in contrast — may be used multiple times, and allows
           configuration of the network interface names. Note that
           --network-bridge= has no effect on interfaces created with
           --network-veth-extra=.

       --network-bridge=
           Adds the host side of the Ethernet link created with
           --network-veth to the specified Ethernet bridge interface.
           Expects a valid network interface name of a bridge device as
           argument. Note that --network-bridge= implies --network-veth.
           If this option is used, the host side of the Ethernet link
           will use the "vb-" prefix instead of "ve-". Regardless of the
           used naming prefix the same network interface name length
           limits imposed by Linux apply, along with the complications
           this creates (for details see above).

           As with --network-interface=, the underlying bridge network
           interface must already exist at the time the container is
           started, and thus similar unit file drop-ins as described
           above might be useful.

       --network-zone=
           Creates a virtual Ethernet link ("veth") to the container and
           adds it to an automatically managed Ethernet bridge
           interface. The bridge interface is named after the passed
           argument, prefixed with "vz-". The bridge interface is
           automatically created when the first container configured for
           its name is started, and is automatically removed when the
           last container configured for its name exits. Hence, each
           bridge interface configured this way exists only as long as
           there's at least one container referencing it running. This
           option is very similar to --network-bridge=, besides this
           automatic creation/removal of the bridge device.

           This setting makes it easy to place multiple related
           containers on a common, virtual Ethernet-based broadcast
           domain, here called a "zone". Each container may only be part
           of one zone, but each zone may contain any number of
           containers. Each zone is referenced by its name. Names may be
           chosen freely (as long as they form valid network interface
           names when prefixed with "vz-"), and it is sufficient to pass
           the same name to the --network-zone= switch of the various
           concurrently running containers to join them in one zone.

           Note that systemd-networkd.service(8) includes by default a
           network file /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.

       --network-namespace-path=
           Takes the path to a file representing a kernel network
           namespace that the container shall run in. The specified path
           should refer to a (possibly bind-mounted) network namespace
           file, as exposed by the kernel below /proc/$PID/ns/net. This
           makes the container enter the given network namespace. One of
           the typical use cases is to give a network namespace under
           /run/netns created by ip-netns(8), for example,
           --network-namespace-path=/run/netns/foo. Note that this
           option cannot be used together with other network-related
           options, such as --private-network or --network-interface=.

       -p, --port=
           If private networking is enabled, maps an IP port on the host
           onto an IP port on the container. Takes a protocol specifier
           (either "tcp" or "udp"), separated by a colon from a host
           port number in the range 1 to 65535, separated by a colon
           from a container port number in the range from 1 to 65535.
           The protocol specifier and its separating colon may be
           omitted, in which case "tcp" is assumed. The container port
           number and its colon may be omitted, in which case the same
           port as the host port is implied. This option is only
           supported if private networking is used, such as with
           --network-veth, --network-zone= --network-bridge=.

   Security Options
       --capability=
           List one or more additional capabilities to grant the
           container. Takes a comma-separated list of capability names,
           see capabilities(7) for more information. Note that the
           following capabilities will be granted in any way:
           CAP_AUDIT_CONTROL, CAP_AUDIT_WRITE, CAP_CHOWN,
           CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER,
           CAP_FSETID, CAP_IPC_OWNER, CAP_KILL, CAP_LEASE,
           CAP_LINUX_IMMUTABLE, CAP_MKNOD, CAP_NET_BIND_SERVICE,
           CAP_NET_BROADCAST, CAP_NET_RAW, CAP_SETFCAP, CAP_SETGID,
           CAP_SETPCAP, CAP_SETUID, CAP_SYS_ADMIN, CAP_SYS_BOOT,
           CAP_SYS_CHROOT, CAP_SYS_NICE, CAP_SYS_PTRACE,
           CAP_SYS_RESOURCE, CAP_SYS_TTY_CONFIG. Also CAP_NET_ADMIN is
           retained if --private-network is specified. If the special
           value "all" is passed, all capabilities are retained.

           If the special value of "help" is passed, the program will
           print known capability names and exit.

           This option sets the bounding set of capabilities which also
           limits the ambient capabilities as given with the
           --ambient-capability=.

       --drop-capability=
           Specify one or more additional capabilities to drop for the
           container. This allows running the container with fewer
           capabilities than the default (see above).

           If the special value of "help" is passed, the program will
           print known capability names and exit.

           This option sets the bounding set of capabilities which also
           limits the ambient capabilities as given with the
           --ambient-capability=.

       --ambient-capability=
           Specify one or more additional capabilities to pass in the
           inheritable and ambient set to the program started within the
           container. The value "all" is not supported for this setting.

           All capabilities specified here must be in the set allowed
           with the --capability= and --drop-capability= options.
           Otherwise, an error message will be shown.

           This option cannot be combined with the boot mode of the
           container (as requested via --boot).

           If the special value of "help" is passed, the program will
           print known capability names and exit.

       --no-new-privileges=
           Takes a boolean argument. Specifies the value of the
           PR_SET_NO_NEW_PRIVS flag for the container payload. Defaults
           to off. When turned on the payload code of the container
           cannot acquire new privileges, i.e. the "setuid" file bit as
           well as file system capabilities will not have an effect
           anymore. See prctl(2) for details about this flag.

       --system-call-filter=
           Alter the system call filter applied to containers. Takes a
           space-separated list of system call names or group names (the
           latter prefixed with "@", as listed by the syscall-filter
           command of systemd-analyze(1)). Passed system calls will be
           permitted. The list may optionally be prefixed by "~", in
           which case all listed system calls are prohibited. If this
           command line option is used multiple times the configured
           lists are combined. If both a positive and a negative list
           (that is one system call list without and one with the "~"
           prefix) are configured, the negative list takes precedence
           over the positive list. Note that systemd-nspawn always
           implements a system call allow list (as opposed to a deny
           list!), and this command line option hence adds or removes
           entries from the default allow list, depending on the "~"
           prefix. Note that the applied system call filter is also
           altered implicitly if additional capabilities are passed
           using the --capabilities=.

       -Z, --selinux-context=
           Sets the SELinux security context to be used to label
           processes in the container.

       -L, --selinux-apifs-context=
           Sets the SELinux security context to be used to label files
           in the virtual API file systems in the container.

   Resource Options
       --rlimit=
           Sets the specified POSIX resource limit for the container
           payload. Expects an assignment of the form "LIMIT=SOFT:HARD"
           or "LIMIT=VALUE", where LIMIT should refer to a resource
           limit type, such as RLIMIT_NOFILE or RLIMIT_NICE. The SOFT
           and HARD fields should refer to the numeric soft and hard
           resource limit values. If the second form is used, VALUE may
           specify a value that is used both as soft and hard limit. In
           place of a numeric value the special string "infinity" may be
           used to turn off resource limiting for the specific type of
           resource. This command line option may be used multiple times
           to control limits on multiple limit types. If used multiple
           times for the same limit type, the last use wins. For details
           about resource limits see setrlimit(2). By default resource
           limits for the container's init process (PID 1) are set to
           the same values the Linux kernel originally passed to the
           host init system. Note that some resource limits are enforced
           on resources counted per user, in particular RLIMIT_NPROC.
           This means that unless user namespacing is deployed (i.e.
           --private-users= is used, see above), any limits set will be
           applied to the resource usage of the same user on all local
           containers as well as the host. This means particular care
           needs to be taken with these limits as they might be
           triggered by possibly less trusted code. Example:
           "--rlimit=RLIMIT_NOFILE=8192:16384".

       --oom-score-adjust=
           Changes the OOM ("Out Of Memory") score adjustment value for
           the container payload. This controls /proc/self/oom_score_adj
           which influences the preference with which this container is
           terminated when memory becomes scarce. For details see
           proc(5). Takes an integer in the range -1000...1000.

       --cpu-affinity=
           Controls the CPU affinity of the container payload. Takes a
           comma separated list of CPU numbers or number ranges (the
           latter's start and end value separated by dashes). See
           sched_setaffinity(2) for details.

       --personality=
           Control the architecture ("personality") reported by uname(2)
           in the container. Currently, only "x86" and "x86-64" are
           supported. This is useful when running a 32-bit container on
           a 64-bit host. If this setting is not used, the personality
           reported in the container is the same as the one reported on
           the host.

   Integration Options
       --resolv-conf=
           Configures how /etc/resolv.conf inside of the container shall
           be handled (i.e. DNS configuration synchronization from host
           to container). Takes one of "off", "copy-host",
           "copy-static", "copy-uplink", "copy-stub", "replace-host",
           "replace-static", "replace-uplink", "replace-stub",
           "bind-host", "bind-static", "bind-uplink", "bind-stub",
           "delete" or "auto".

           If set to "off" the /etc/resolv.conf file in the container is
           left as it is included in the image, and neither modified nor
           bind mounted over.

           If set to "copy-host", the /etc/resolv.conf file from the
           host is copied into the container, unless the file exists
           already and is not a regular file (e.g. a symlink). Similar,
           if "replace-host" is used the file is copied, replacing any
           existing inode, including symlinks. Similar, if "bind-host"
           is used, the file is bind mounted from the host into the
           container.

           If set to "copy-static", "replace-static" or "bind-static"
           the static resolv.conf file supplied with
           systemd-resolved.service(8) (specifically:
           /usr/lib/systemd/resolv.conf) is copied or bind mounted into
           the container.

           If set to "copy-uplink", "replace-uplink" or "bind-uplink"
           the uplink resolv.conf file managed by
           systemd-resolved.service (specifically:
           /run/systemd/resolve/resolv.conf) is copied or bind mounted
           into the container.

           If set to "copy-stub", "replace-stub" or "bind-stub" the stub
           resolv.conf file managed by systemd-resolved.service
           (specifically: /run/systemd/resolve/stub-resolv.conf) is
           copied or bind mounted into the container.

           If set to "delete" the /etc/resolv.conf file in the container
           is deleted if it exists.

           Finally, if set to "auto" the file is left as it is if
           private networking is turned on (see --private-network).
           Otherwise, if systemd-resolved.service is running its stub
           resolv.conf file is used, and if not the host's
           /etc/resolv.conf file. In the latter cases the file is copied
           if the image is writable, and bind mounted otherwise.

           It's recommended to use "copy-..."  or "replace-..."  if the
           container shall be able to make changes to the DNS
           configuration on its own, deviating from the host's settings.
           Otherwise "bind" is preferable, as it means direct changes to
           /etc/resolv.conf in the container are not allowed, as it is a
           read-only bind mount (but note that if the container has
           enough privileges, it might simply go ahead and unmount the
           bind mount anyway). Note that both if the file is bind
           mounted and if it is copied no further propagation of
           configuration is generally done after the one-time early
           initialization (this is because the file is usually updated
           through copying and renaming). Defaults to "auto".

       --timezone=
           Configures how /etc/localtime inside of the container (i.e.
           local timezone synchronization from host to container) shall
           be handled. Takes one of "off", "copy", "bind", "symlink",
           "delete" or "auto". If set to "off" the /etc/localtime file
           in the container is left as it is included in the image, and
           neither modified nor bind mounted over. If set to "copy" the
           /etc/localtime file of the host is copied into the container.
           Similarly, if "bind" is used, the file is bind mounted from
           the host into the container. If set to "symlink", a symlink
           is created pointing from /etc/localtime in the container to
           the timezone file in the container that matches the timezone
           setting on the host. If set to "delete", the file in the
           container is deleted, should it exist. If set to "auto" and
           the /etc/localtime file of the host is a symlink, then
           "symlink" mode is used, and "copy" otherwise, except if the
           image is read-only in which case "bind" is used instead.
           Defaults to "auto".

       --link-journal=
           Control whether the container's journal shall be made visible
           to the host system. If enabled, allows viewing the
           container's journal files from the host (but not vice versa).
           Takes one of "no", "host", "try-host", "guest", "try-guest",
           "auto". If "no", the journal is not linked. If "host", the
           journal files are stored on the host file system (beneath
           /var/log/journal/machine-id) and the subdirectory is
           bind-mounted into the container at the same location. If
           "guest", the journal files are stored on the guest file
           system (beneath /var/log/journal/machine-id) and the
           subdirectory is symlinked into the host at the same location.
           "try-host" and "try-guest" do the same but do not fail if the
           host does not have persistent journaling enabled. If "auto"
           (the default), and the right subdirectory of /var/log/journal
           exists, it will be bind mounted into the container. If the
           subdirectory does not exist, no linking is performed.
           Effectively, booting a container once with "guest" or "host"
           will link the journal persistently if further on the default
           of "auto" is used.

           Note that --link-journal=try-guest is the default if the
           systemd-nspawn@.service template unit file is used.

       -j
           Equivalent to --link-journal=try-guest.

   Mount Options
       --bind=, --bind-ro=
           Bind mount a file or directory from the host into the
           container. Takes one of: a path argument — in which case the
           specified path will be mounted from the host to the same path
           in the container, or a colon-separated pair of paths — in
           which case the first specified path is the source in the
           host, and the second path is the destination in the
           container, or a colon-separated triple of source path,
           destination path and mount options. The source path may
           optionally be prefixed with a "+" character. If so, the
           source path is taken relative to the image's root directory.
           This permits setting up bind mounts within the container
           image. The source path may be specified as empty string, in
           which case a temporary directory below the host's /var/tmp/
           directory is used. It is automatically removed when the
           container is shut down. Mount options are comma-separated and
           currently, only rbind and norbind are allowed, controlling
           whether to create a recursive or a regular bind mount.
           Defaults to "rbind". Backslash escapes are interpreted, so
           "\:" may be used to embed colons in either path. This option
           may be specified multiple times for creating multiple
           independent bind mount points. The --bind-ro= option creates
           read-only bind mounts.

           Note that when this option is used in combination with
           --private-users, the resulting mount points will be owned by
           the nobody user. That's because the mount and its files and
           directories continue to be owned by the relevant host users
           and groups, which do not exist in the container, and thus
           show up under the wildcard UID 65534 (nobody). If such bind
           mounts are created, it is recommended to make them read-only,
           using --bind-ro=.

       --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/hosts/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 host's user account inside the
           container as if it was local to the container. 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 generated log messages 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 recycled during later container invocations
           (possibly with a different --bind-user= mapping), those files
           and directories will be accessible to the "new" user.

           The user/group record mapping only works if the container
           contains systemd 249 or newer, with nss-systemd properly
           configured in nsswitch.conf. See nss-systemd(8) for details.

           Note that the user record propagated from the host into the
           container will contain the UNIX password hash of the user, so
           that seamless logins in the container are possible. If the
           container is less trusted than the host it's hence important
           to use a strong UNIX password hash function (e.g. yescrypt or
           similar, with the "$y$" hash prefix).

           When binding a user from the host into the container checks
           are executed to ensure that the username is not yet known in
           the container. Moreover, it is checked that the UID/GID
           allocated for it is not currently defined in the user/group
           databases of the container. Both checks directly access the
           container's /etc/passwd and /etc/group, and thus might not
           detect existing accounts in other databases.

           This operation is only supported in combination with
           --private-users=/-U.

       --inaccessible=
           Make the specified path inaccessible in the container. This
           over-mounts the specified path (which must exist in the
           container) with a file node of the same type that is empty
           and has the most restrictive access mode supported. This is
           an effective way to mask files, directories and other file
           system objects from the container payload. This option may be
           used more than once in case all specified paths are masked.

       --tmpfs=
           Mount a tmpfs file system into the container. Takes a single
           absolute path argument that specifies where to mount the
           tmpfs instance to (in which case the directory access mode
           will be chosen as 0755, owned by root/root), or optionally a
           colon-separated pair of path and mount option string that is
           used for mounting (in which case the kernel default for
           access mode and owner will be chosen, unless otherwise
           specified). Backslash escapes are interpreted in the path, so
           "\:" may be used to embed colons in the path.

           Note that this option cannot be used to replace the root file
           system of the container with a temporary file system.
           However, the --volatile= option described below provides
           similar functionality, with a focus on implementing stateless
           operating system images.

       --overlay=, --overlay-ro=
           Combine multiple directory trees into one overlay file system
           and mount it into the container. Takes a list of
           colon-separated paths to the directory trees to combine and
           the destination mount point.

           Backslash escapes are interpreted in the paths, so "\:" may
           be used to embed colons in the paths.

           If three or more paths are specified, then the last specified
           path is the destination mount point in the container, all
           paths specified before refer to directory trees on the host
           and are combined in the specified order into one overlay file
           system. The left-most path is hence the lowest directory
           tree, the second-to-last path the highest directory tree in
           the stacking order. If --overlay-ro= is used instead of
           --overlay=, a read-only overlay file system is created. If a
           writable overlay file system is created, all changes made to
           it are written to the highest directory tree in the stacking
           order, i.e. the second-to-last specified.

           If only two paths are specified, then the second specified
           path is used both as the top-level directory tree in the
           stacking order as seen from the host, as well as the mount
           point for the overlay file system in the container. At least
           two paths have to be specified.

           The source paths may optionally be prefixed with "+"
           character. If so they are taken relative to the image's root
           directory. The uppermost source path may also be specified as
           an empty string, in which case a temporary directory below
           the host's /var/tmp/ is used. The directory is removed
           automatically when the container is shut down. This behaviour
           is useful in order to make read-only container directories
           writable while the container is running. For example, use
           "--overlay=+/var::/var" in order to automatically overlay a
           writable temporary directory on a read-only /var/ directory.

           For details about overlay file systems, see overlayfs.txt[5].
           Note that the semantics of overlay file systems are
           substantially different from normal file systems, in
           particular regarding reported device and inode information.
           Device and inode information may change for a file while it
           is being written to, and processes might see out-of-date
           versions of files at times. Note that this switch
           automatically derives the "workdir=" mount option for the
           overlay file system from the top-level directory tree, making
           it a sibling of it. It is hence essential that the top-level
           directory tree is not a mount point itself (since the working
           directory must be on the same file system as the top-most
           directory tree). Also note that the "lowerdir=" mount option
           receives the paths to stack in the opposite order of this
           switch.

           Note that this option cannot be used to replace the root file
           system of the container with an overlay file system. However,
           the --volatile= option described above provides similar
           functionality, with a focus on implementing stateless
           operating system images.

   Input/Output Options
       --console=MODE
           Configures how to set up standard input, output and error
           output for the container payload, as well as the /dev/console
           device for the container. Takes one of interactive,
           read-only, passive, pipe or autopipe. If interactive, a
           pseudo-TTY is allocated and made available as /dev/console in
           the container. It is then bi-directionally connected to the
           standard input and output passed to systemd-nspawn.
           read-only is similar but only the output of the container is
           propagated and no input from the caller is read. If passive,
           a pseudo TTY is allocated, but it is not connected anywhere.
           In pipe mode no pseudo TTY is allocated, but the standard
           input, output and error output file descriptors passed to
           systemd-nspawn are passed on — as they are — to the container
           payload, see the following paragraph. Finally, autopipe mode
           operates like interactive when systemd-nspawn is invoked on a
           terminal, and like pipe otherwise. Defaults to interactive if
           systemd-nspawn is invoked from a terminal, and read-only
           otherwise.

           In pipe mode, /dev/console will not exist in the container.
           This means that the container payload generally cannot be a
           full init system as init systems tend to require /dev/console
           to be available. On the other hand, in this mode container
           invocations can be used within shell pipelines. This is
           because intermediary pseudo TTYs do not permit independent
           bidirectional propagation of the end-of-file (EOF) condition,
           which is necessary for shell pipelines to work correctly.
           Note that the pipe mode should be used carefully, as passing
           arbitrary file descriptors to less trusted container payloads
           might open up unwanted interfaces for access by the container
           payload. For example, if a passed file descriptor refers to a
           TTY of some form, APIs such as TIOCSTI may be used to
           synthesize input that might be used for escaping the
           container. Hence pipe mode should only be used if the payload
           is sufficiently trusted or when the standard
           input/output/error output file descriptors are known safe,
           for example pipes.

       --pipe, -P
           Equivalent to --console=pipe.

   Credentials
       --load-credential=ID:PATH, --set-credential=ID:VALUE
           Pass a credential to the container. These two options
           correspond to the LoadCredential= and SetCredential= settings
           in unit files. See systemd.exec(5) for details about these
           concepts, as well as the syntax of the option's arguments.

           Note: when systemd-nspawn runs as systemd system service it
           can propagate the credentials it received via
           LoadCredential=/SetCredential= to the container payload. A
           systemd service manager running as PID 1 in the container can
           further propagate them to the services it itself starts. It
           is thus possible to easily propagate credentials from a
           parent service manager to a container manager service and
           from there into its payload. This can even be done
           recursively.

           In order to embed binary data into the credential data for
           --set-credential= use C-style escaping (i.e.  "\n" to embed a
           newline, or "\x00" to embed a NUL byte. Note that the
           invoking shell might already apply unescaping once, hence
           this might require double escaping!).

           The systemd-sysusers.service(8) and systemd-firstboot(1)
           services read credentials configured this way for the purpose
           of configuring the container's root user's password and
           shell, as well as system locale, keymap and timezone during
           the first boot process of the container. This is particularly
           useful in combination with --volatile=yes where every single
           boot appears as first boot, since configuration applied to
           /etc/ is lost on container reboot cycles. See the respective
           man pages for details. Example:

               # systemd-nspawn -i image.raw \
                       --volatile=yes \
                       --set-credential=firstboot.locale:de_DE.UTF-8 \
                       --set-credential=passwd.hashed-password.root:'$y$j9T$yAuRJu1o5HioZAGDYPU5d.$F64ni6J2y2nNQve90M/p0ZP0ECP/qqzipNyaY9fjGpC' \
                       -b

           The above command line will invoke the specified image file
           image.raw in volatile mode, i.e with an empty /etc/ and
           /var/, so that the container's payload recognizes this as
           first boot condition, and will invoke
           systemd-firstboot.service, which then read the two passed
           credentials to configure the system's initial locale and root
           password.

   Other
       --no-pager
           Do not pipe output into a pager.

       -h, --help
           Print a short help text and exit.

       --version
           Print a short version string and exit.

ENVIRONMENT         top

       $SYSTEMD_LOG_LEVEL
           The maximum log level of emitted messages (messages with a
           higher log level, i.e. less important ones, will be
           suppressed). Either one of (in order of decreasing
           importance) emerg, alert, crit, err, warning, notice, info,
           debug, or an integer in the range 0...7. See syslog(3) for
           more information.

       $SYSTEMD_LOG_COLOR
           A boolean. If true, messages written to the tty will be
           colored according to priority.

           This setting is only useful when messages are written
           directly to the terminal, because journalctl(1) and other
           tools that display logs will color messages based on the log
           level on their own.

       $SYSTEMD_LOG_TIME
           A boolean. If true, console log messages will be prefixed
           with a timestamp.

           This setting is only useful when messages are written
           directly to the terminal or a file, because journalctl(1) and
           other tools that display logs will attach timestamps based on
           the entry metadata on their own.

       $SYSTEMD_LOG_LOCATION
           A boolean. If true, messages will be prefixed with a filename
           and line number in the source code where the message
           originates.

           Note that the log location is often attached as metadata to
           journal entries anyway. Including it directly in the message
           text can nevertheless be convenient when debugging programs.

       $SYSTEMD_LOG_TID
           A boolean. If true, messages will be prefixed with the
           current numerical thread ID (TID).

           Note that the this information is attached as metadata to
           journal entries anyway. Including it directly in the message
           text can nevertheless be convenient when debugging programs.

       $SYSTEMD_LOG_TARGET
           The destination for log messages. One of console (log to the
           attached tty), console-prefixed (log to the attached tty but
           with prefixes encoding the log level and "facility", see
           syslog(3), kmsg (log to the kernel circular log buffer),
           journal (log to the journal), journal-or-kmsg (log to the
           journal if available, and to kmsg otherwise), auto (determine
           the appropriate log target automatically, the default), null
           (disable log output).

       $SYSTEMD_PAGER
           Pager to use when --no-pager is not given; overrides $PAGER.
           If neither $SYSTEMD_PAGER nor $PAGER are set, a set of
           well-known pager implementations are tried in turn, including
           less(1) and more(1), until one is found. If no pager
           implementation is discovered no pager is invoked. Setting
           this environment variable to an empty string or the value
           "cat" is equivalent to passing --no-pager.

       $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.

           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).

       $SYSTEMD_PAGERSECURE
           Takes a boolean argument. When true, the "secure" mode of the
           pager is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE
           is not set at all, secure mode is enabled if the effective
           UID is not the same as the owner of the login session, see
           geteuid(2) and sd_pid_get_owner_uid(3). In secure mode,
           LESSSECURE=1 will be set when invoking the pager, and the
           pager shall disable commands that open or create new files or
           start new subprocesses. When $SYSTEMD_PAGERSECURE is not set
           at all, pagers which are not known to implement secure mode
           will not be used. (Currently only less(1) implements secure
           mode.)

           Note: when commands are invoked with elevated privileges, for
           example under sudo(8) or pkexec(1), care must be taken to
           ensure that unintended interactive features are not enabled.
           "Secure" mode for the pager may be enabled automatically as
           describe above. Setting SYSTEMD_PAGERSECURE=0 or not removing
           it from the inherited environment allows the user to invoke
           arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER
           variables are to be honoured, $SYSTEMD_PAGERSECURE must be
           set too. It might be reasonable to completely disable the
           pager using --no-pager instead.

       $SYSTEMD_COLORS
           Takes a boolean argument. When true, systemd and related
           utilities will use colors in their output, otherwise the
           output will be monochrome. Additionally, the variable can
           take one of the following special values: "16", "256" to
           restrict the use of colors to the base 16 or 256 ANSI colors,
           respectively. This can be specified to override the automatic
           decision based on $TERM and what the console is connected to.

       $SYSTEMD_URLIFY
           The value must be a boolean. Controls whether clickable links
           should be generated in the output for terminal emulators
           supporting this. This can be specified to override the
           decision that systemd makes based on $TERM and other
           conditions.

EXAMPLES         top

       Example 1. Download a Fedora image and start a shell in it

           # machinectl pull-raw --verify=no \
                 https://download.fedoraproject.org/pub/fedora/linux/releases/34/Cloud/x86_64/images/Fedora-Cloud-Base-34-1.2.x86_64.raw.xz \
                 Fedora-Cloud-Base-34-1.2.x86-64
           # systemd-nspawn -M Fedora-Cloud-Base-34-1.2.x86-64

       This downloads an image using machinectl(1) and opens a shell in
       it.

       Example 2. Build and boot a minimal Fedora distribution in a
       container

           # dnf -y --releasever=34 --installroot=/var/lib/machines/f34 \
                 --disablerepo='*' --enablerepo=fedora --enablerepo=updates install \
                 systemd passwd dnf fedora-release vim-minimal glibc-minimal-langpack
           # systemd-nspawn -bD /var/lib/machines/f34

       This installs a minimal Fedora distribution into the directory
       /var/lib/machines/f34 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 f34.

       Example 3. Spawn a shell in a container of a minimal Debian
       unstable distribution

           # debootstrap unstable ~/debian-tree/
           # systemd-nspawn -D ~/debian-tree/

       This installs a minimal Debian unstable distribution into the
       directory ~/debian-tree/ and then spawns a shell from this image
       in a namespace container.

       debootstrap supports Debian[7], Ubuntu[8], and Tanglu[9] out of
       the box, so the same command can be used to install any of those.
       For other distributions from the Debian family, a mirror has to
       be specified, see debootstrap(8).

       Example 4. Boot a minimal Arch Linux distribution in a container

           # pacstrap -c ~/arch-tree/ base
           # systemd-nspawn -bD ~/arch-tree/

       This installs a minimal Arch Linux distribution into the
       directory ~/arch-tree/ and then boots an OS in a namespace
       container in it.

       Example 5. Install the OpenSUSE Tumbleweed rolling distribution

           # zypper --root=/var/lib/machines/tumbleweed ar -c \
                 https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
           # zypper --root=/var/lib/machines/tumbleweed refresh
           # zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
                 systemd shadow zypper openSUSE-release vim
           # systemd-nspawn -M tumbleweed passwd root
           # systemd-nspawn -M tumbleweed -b

       Example 6. Boot into an ephemeral snapshot of the host system

           # systemd-nspawn -D / -xb

       This runs a copy of the host system in a snapshot which is
       removed immediately when the container exits. All file system
       changes made during runtime will be lost on shutdown, hence.

       Example 7. Run a container with SELinux sandbox security contexts

           # chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
           # systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 \
                 -Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh

       Example 8. Run a container with an OSTree deployment

           # systemd-nspawn -b -i ~/image.raw \
                 --pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
                 --bind=+/sysroot/ostree/deploy/$OS/var:/var

EXIT STATUS         top

       The exit code of the program executed in the container is
       returned.

SEE ALSO         top

       systemd(1), systemd.nspawn(5), chroot(1), dnf(8), debootstrap(8),
       pacman(8), zypper(8), systemd.slice(5), machinectl(1), btrfs(8)

NOTES         top

        1. Container Interface
           https://systemd.io/CONTAINER_INTERFACE

        2. Discoverable Partitions Specification
           https://systemd.io/DISCOVERABLE_PARTITIONS

        3. OCI Runtime Specification
           https://github.com/opencontainers/runtime-spec/blob/master/spec.md

        4. OSTree
           https://ostree.readthedocs.io/en/latest/

        5. overlayfs.txt
           https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt

        6. Fedora
           https://getfedora.org

        7. Debian
           https://www.debian.org

        8. Ubuntu
           https://www.ubuntu.com

        9. Tanglu
           https://www.tanglu.org

       10. Arch Linux
           https://www.archlinux.org

       11. OpenSUSE Tumbleweed
           https://software.opensuse.org/distributions/tumbleweed

COLOPHON         top

       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 2021-06-20.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-06-19.)  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
       man-pages@man7.org

systemd 249                                            SYSTEMD-NSPAWN(1)

Pages that refer to this page: journalctl(1)machinectl(1)systemd-cgls(1)systemd-detect-virt(1)systemd-dissect(1)systemd-firstboot(1)org.freedesktop.import1(5)repart.d(5)systemd.nspawn(5)systemd.directives(7)systemd.index(7)systemd.net-naming-scheme(7)nss-mymachines(8)nss-systemd(8)systemd-importd.service(8)systemd-machined.service(8)systemd-sysext(8)systemd-sysusers(8)systemd-tmpfiles(8)