Provided by: systemd-container_242-7ubuntu3_amd64 bug

NAME

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

SYNOPSIS

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

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

DESCRIPTION

       systemd-nspawn may be used to run a command or OS in a light-weight namespace container.
       In many ways it is similar to chroot(1), but more powerful since it fully virtualizes the
       file system hierarchy, as well as the process tree, the various IPC subsystems and the
       host and domain name.

       systemd-nspawn may be invoked on any directory tree containing an operating system tree,
       using the --directory= command line option. By using the --machine= option an OS tree is
       automatically searched for in a couple of locations, most importantly in
       /var/lib/machines, the suggested directory to place OS container images installed on the
       system.

       In contrast to chroot(1) systemd-nspawn may be used to boot full Linux-based operating
       systems in a container.

       systemd-nspawn limits access to various kernel interfaces in the container to read-only,
       such as /sys, /proc/sys or /sys/fs/selinux. The host's network interfaces and the system
       clock may not be changed from within the container. Device nodes may not be created. The
       host system cannot be rebooted and kernel modules may not be loaded from within the
       container.

       Use a tool like dnf(8), debootstrap(8), or pacman(8) to set up an OS directory tree
       suitable as file system hierarchy for systemd-nspawn containers. See the Examples section
       below for details on suitable invocation of these commands.

       As a safety check systemd-nspawn will verify the existence of /usr/lib/os-release or
       /etc/os-release in the container tree before 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

       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 host name, 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 host name, 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.

           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 also /etc in case of "--volatile=yes". 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, the root hash is read from it and
           automatically used, also as formatted hexadecimal characters.

       --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
           ┌─────────────────────────────┬──────────────────────────────────┐
           │SwitchExplanation                      │
           ├─────────────────────────────┼──────────────────────────────────┤
           │Neither --as-pid2 nor --boot │ The passed parameters are        │
           │specified                    │ interpreted as the command line, │
           │                             │ which is executed as PID 1 in    │
           │                             │ the container.                   │
           ├─────────────────────────────┼──────────────────────────────────┤
           │--as-pid2 specified          │ The passed parameters are        │
           │                             │ interpreted as the command line, │
           │                             │ which is executed as PID 2 in    │
           │                             │ the container. A stub init       │
           │                             │ process is run as PID 1.         │
           ├─────────────────────────────┼──────────────────────────────────┤
           │--boot specified             │ An init program is automatically │
           │                             │ searched for and run as PID 1 in │
           │                             │ the container. The passed        │
           │                             │ parameters are used as           │
           │                             │ invocation parameters for this   │
           │                             │ process.                         │
           └─────────────────────────────┴──────────────────────────────────┘
           Note that --boot is the default mode of operation if the systemd-nspawn@.service
           template unit file is used.

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

       -E NAME=VALUE, --setenv=NAME=VALUE
           Specifies an environment variable 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 omitted, or true, 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. If this
               mode is used the number of UIDs/GIDs assigned to the container for use is 65536,
               and the UID/GID of the root directory must be a multiple of 65536.

            3. If the parameter is false, user namespacing is turned off. This is the default.

            4. The special value "pick" turns on user namespacing. In this case the UID/GID range
               is automatically chosen. As first step, the file owner of the root directory of
               the container's directory tree is read, and it is checked that it is currently not
               used by the system otherwise (in particular, that no other container is 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. This setting implies --private-users-chown (see
               below), which 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-chown
           If specified, all files and directories in the container's directory tree will
           adjusted so that they are owned to the appropriate UIDs/GIDs selected for the
           container (see above). This operation is potentially expensive, as it involves
           descending and iterating through the full directory tree of the container. Besides
           actual file ownership, file ACLs are adjusted as well.

           This 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-chown, 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-chown (or -U) on the file
           system by redoing the operation with the first UID of 0:

               systemd-nspawn ... --private-users=0 --private-users-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 host namespace. Note that
           --network-interface= implies --private-network. This option may be used more than once
           to add multiple network interfaces to the container.

       --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.

       --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.

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

           Note that systemd-networkd.service(8) includes by default a network file
           /lib/systemd/network/80-container-ve.network matching the host-side interfaces created
           this way, which contains settings to enable automatic address provisioning on the
           created virtual link via DHCP, as well as automatic IP routing onto the host's
           external network interfaces. It also contains
           /lib/systemd/network/80-container-host0.network matching the container-side interface
           created this way, containing settings to enable client side address assignment via
           DHCP. In case systemd-networkd is running on both the host and inside the container,
           automatic IP communication from the container to the host is thus available, with
           further connectivity to the external network.

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

           Note that on Linux network interface names may have a length of 15 characters at
           maximum, while container names may have a length up to 64 characters. As this option
           derives the host-side interface name from the container name the name is possibly
           truncated. Thus, care needs to be taken to ensure that interface names remain unique
           in this case, or even better container names are generally not chosen longer than 12
           characters, to avoid the truncation. 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).

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

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

           Note that systemd-networkd.service(8) includes by default a network file
           /lib/systemd/network/80-container-vz.network matching the bridge interfaces created
           this way, which contains settings to enable automatic address provisioning on the
           created virtual network via DHCP, as well as automatic IP routing onto the host's
           external network interfaces. Using --network-zone= is hence in most cases fully
           automatic and sufficient to connect multiple local containers in a joined broadcast
           domain to the host, with further connectivity to the external network.

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

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

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

       --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).

       --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 whitelist (as opposed to a blacklist), and this command line option hence adds or
           removes entries from the default whitelist, 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 (i.e. DNS configuration
           synchronization from host to container) shall be handled. Takes one of "off",
           "copy-host", "copy-static", "bind-host", "bind-static", "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. Similar, if
           "bind-host" is used, the file is bind mounted from the host into the container. If set
           to "copy-static" the static resolv.conf file supplied with systemd-resolved.service(8)
           is copied into the container, and correspondingly "bind-static" bind mounts it there.
           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 connectible its
           static resolv.conf file is used, and if not the host's /etc/resolv.conf file is used.
           In the latter cases the file is copied if the image is writable, and bind mounted
           otherwise. It's recommended to use "copy" 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. Similar, if "bind" is used, it is bind mounted from the host into the
           container. If set to "symlink" a symlink from /etc/localtime in the container is
           created pointing to the matching the timezone file of 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=.

       --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 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 the "--overlay=+/var::/var"
           option 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 or pipe. 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.
           In passive mode a pseudo TTY is allocated, but it is not connected anywhere. Finally,
           in pipe mode no pseudo TTY is allocated, but the passed standard input, output and
           error output file descriptors are passed on — as they are — to the container payload.
           In this mode /dev/console will not exist in the container. Note that in this mode 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. Defaults to interactive if systemd-nspawn is
           invoked from a terminal, and read-only otherwise.

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

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

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

       --version
           Print a short version string and exit.

ENVIRONMENT

       $SYSTEMD_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").

           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. This allows less to handle Ctrl+C
           itself.

       $SYSTEMD_LESSCHARSET
           Override the charset passed to less (by default "utf-8", if the invoking terminal is
           determined to be UTF-8 compatible).

EXAMPLES

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

           # machinectl pull-raw --verify=no \
                 https://download.fedoraproject.org/pub/fedora/linux/releases/28/Cloud/x86_64/images/Fedora-Cloud-Base-28-1.1.x86_64.raw.xz
           # systemd-nspawn -M Fedora-Cloud-Base-28-1.1.x86_64.raw

       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=28 --installroot=/var/lib/machines/f28 \
                 --disablerepo='*' --enablerepo=fedora --enablerepo=updates install \
                 systemd passwd dnf fedora-release vim-minimal
           # systemd-nspawn -bD /var/lib/machines/f28

       This installs a minimal Fedora distribution into the directory /var/lib/machines/f28 and
       then boots an OS in a namespace container in it. Because the installation is located
       underneath the standard /var/lib/machines/ directory, it is also possible to start the
       machine using systemd-nspawn -M f28.

       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 in a namespace container in it.

       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 -d ~/arch-tree/ base
           # systemd-nspawn -bD ~/arch-tree/

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

       Example 5. Install the OpenSUSE Tumbleweed rolling distribution

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

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

           # systemd-nspawn -D / -xb

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

       Example 7. Run a container with SELinux sandbox security contexts

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

       Example 8. Run a container with an OSTree deployment

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

EXIT STATUS

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

SEE ALSO

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

NOTES

        1. Container Interface
           https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface

        2. Discoverable Partitions Specification
           https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/

        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