Provided by: systemd-container_229-4ubuntu4_amd64 bug

NAME

       systemd-nspawn - Spawn a namespace container for debugging, testing and building

SYNOPSIS

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

       systemd-nspawn -b [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 limits access to various kernel interfaces in the container to read-only,
       such as /sys, /proc/sys or /sys/fs/selinux. 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.

       Note that even though these security precautions are taken systemd-nspawn is not suitable
       for fully secure container setups. Many of the security features may be circumvented and
       are hence primarily useful to avoid accidental changes to the host system from the
       container.

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

       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 command to request an additional login prompt in a
       running container.

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

       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.

OPTIONS

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

       The following options are understood:

       -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" subvolume 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, which can be substantially more time-consuming. Note that if
           this option is used the container's root directory (in contrast to the template
           directory!) must be located on a "btrfs" file system, so that the "btrfs" subvolume
           may be created. 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 "btrfs" snapshot of its root
           directory (as configured with --directory=), that is removed immediately when the
           container terminates. This option is only supported if the root file system is
           "btrfs". May not be specified together with --image= or --template=.

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

       -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].

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

       -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 binary is run as
           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 binary 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 or --share-system.

       -b, --boot
           Automatically search for an init binary 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 binary. This option may not be combined with
           --as-pid2 or --share-system.

           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 command line,     │
           │                             │ which is executed as PID 1 in    │
           │                             │ the container.                   │
           ├─────────────────────────────┼──────────────────────────────────┤
           │--as-pid2 specified          │ The passed parameters are        │
           │                             │ interpreted as command line,     │
           │                             │ which are executed as PID 2 in   │
           │                             │ the container. A stub init       │
           │                             │ process is run as PID 1.         │
           ├─────────────────────────────┼──────────────────────────────────┤
           │--boot specified             │ An init binary as automatically  │
           │                             │ searched and run as PID 1 in the │
           │                             │ container. The passed parameters │
           │                             │ are used as invocation           │
           │                             │ parameters for this process.     │
           └─────────────────────────────┴──────────────────────────────────┘

       --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.

       -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.

       -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.

       --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.

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

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

       --private-users=
           Enables user namespacing. If enabled, the container will run with its own private set
           of Unix user and group ids (UIDs and GIDs). Takes none, one or two colon-separated
           parameters: the first parameter specifies the first host UID to assign to the
           container, the second parameter specifies the number of host UIDs to assign to the
           container. If the second parameter is omitted, 65536 UIDs are assigned. If the first
           parameter is also omitted (and hence no parameter passed at all), the first UID
           assigned to the container is read from the owner of the root directory of the
           container's directory tree. By default, no user namespacing is applied.

           Note that user namespacing currently requires OS trees that are prepared for the UID
           shift that is being applied: UIDs and GIDs used for file ownership or in file ACL
           entries must be shifted to the container UID base that is used during container
           runtime.

           It is recommended to assign at least 65536 UIDs to each container, so that the usable
           UID range in the container covers 16 bit. For best security, do not assign overlapping
           UID ranges to multiple containers. It is hence a good idea to use the upper 16 bit of
           the host 32-bit UIDs as container identifier, while the lower 16 bit encode the
           container UID used.

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

       --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=.

       --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". Note that --network-veth implies
           --private-network.

       --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
           bridge. 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-".

       -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 or --network-bridge=.

       -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.

       --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_CHOWN,
           CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
           CAP_KILL, CAP_LEASE, CAP_LINUX_IMMUTABLE, CAP_NET_BIND_SERVICE, CAP_NET_BROADCAST,
           CAP_NET_RAW, CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP, CAP_SETUID, CAP_SYS_ADMIN,
           CAP_SYS_CHROOT, CAP_SYS_NICE, CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG, CAP_SYS_RESOURCE,
           CAP_SYS_BOOT, CAP_AUDIT_WRITE, CAP_AUDIT_CONTROL. 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).

       --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). Takes a signal name like "SIGHUP", "SIGTERM" or similar
           as argument.

       --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 journalling 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.

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

       --read-only
           Mount the root file system read-only for the container.

       --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. Mount options are comma-separated and currently, only "rbind" and
           "norbind" are allowed. 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.

       --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). This option is particularly useful for mounting directories such
           as /var as tmpfs, to allow state-less systems, in particular when combined with
           --read-only. Backslash escapes are interpreted in the path, so "\:" may be used to
           embed colons in the path.

       --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.

           For details about overlay file systems, see overlayfs.txt[3]. 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.

       --setenv=
           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.

       --share-system
           Allows the container to share certain system facilities with the host. More
           specifically, this turns off PID namespacing, UTS namespacing and IPC namespacing, and
           thus allows the guest to see and interact more easily with processes outside of the
           container. Note that using this option makes it impossible to start up a full
           Operating System in the container, as an init system cannot operate in this mode. It
           is only useful to run specific programs or applications this way, without involving an
           init system in the container. This option implies --register=no. This option may not
           be combined with --boot.

       --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: an init system), 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 an init system, it is recommended to set this
           option to "no". Note that --share-system implies --register=no.

       --keep-unit
           Instead of creating a transient scope unit to run the container in, simply register
           the service or scope unit systemd-nspawn has been invoked in with systemd-machined(8).
           This has no effect if --register=no is used. 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.

       --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.

       -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.

       --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 resources, but
           pristine state and configuration, any changes to the either 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 "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 no (the
           default), the whole OS tree is made available writable.

           Note that setting this 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 populate
           /var automatically, as needed.

       --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.

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

       --version
           Print a short version string and exit.

EXAMPLES

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

           # machinectl pull-raw --verify=no http://ftp.halifax.rwth-aachen.de/fedora/linux/releases/21/Cloud/Images/x86_64/Fedora-Cloud-Base-20141203-21.x86_64.raw.xz
           # systemd-nspawn -M Fedora-Cloud-Base-20141203-21

       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=23 --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora --enablerepo=updates install systemd passwd dnf fedora-release vim-minimal
           # systemd-nspawn -bD /srv/mycontainer

       This installs a minimal Fedora distribution into the directory /srv/mycontainer/ and then
       boots an OS in a namespace container in it.

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

           # debootstrap --arch=amd64 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.

       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. Boot into an ephemeral "btrfs" snapshot of the host system

           # systemd-nspawn -D / -xb

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

       Example 6. 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

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),
       systemd.slice(5), machinectl(1), btrfs(8)

NOTES

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

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

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