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

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

NAME         top

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

SYNOPSIS         top

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

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

DESCRIPTION         top

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

       systemd-nspawn 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), yum(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         top

       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 as /var/lib/machines/ suffixed by the machine name
           as specified with --machine=. 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.

       -b, --boot
           Automatically search for an init binary and invoke it 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
           --share-system.

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

       --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.

           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, 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=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 mostly
           unpopulated "tmpfs" instance, and /usr from the OS tree is
           mounted into it, read-only (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 "tmpfs" instance into it (the
           system thus starts up with read-only OS resources and
           configuration, but pristine state, 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.

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

       --version
           Print a short version string and exit.

EXAMPLES         top

       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=21 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora 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         top

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

SEE ALSO         top

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

NOTES         top

        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

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see 
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository
       (git://anongit.freedesktop.org/systemd/systemd) on 2015-07-23.  If
       you discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for the
       page, or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page), send a
       mail to man-pages@man7.org

systemd 222                                                SYSTEMD-NSPAWN(1)