systemd Developer Lennart Poettering lennart@poettering.net systemd-nspawn 1 systemd-nspawn Spawn a namespace container for debugging, testing and building systemd-nspawn OPTIONS COMMAND ARGS systemd-nspawn -b OPTIONS ARGS systemd-nspawn may be used to run a command or OS in a light-weight namespace container. In many ways it is similar to chroot1, 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 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. The intended use of this program is debugging and testing as well as building of packages, distributions and software involved with boot and systems management. In contrast to chroot1 systemd-nspawn may be used to boot full Linux-based operating systems in a container. Use a tool like yum8, debootstrap8, or pacman8 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 machinectl1's login command to request an additional login prompt in a running container. systemd-nspawn implements the Container Interface specification. As a safety check systemd-nspawn will verify the existence of /etc/os-release in the container tree before starting the container (see os-release5). 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. 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 specifed, a shell is launched in the container. The following options are understood: -h --help Prints a short help text and exits. --version Prints a version string and exits. -D --directory= Directory to use as file system root for the namespace container. If omitted, the current directory will be used. -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= Run the command under specified user, create home directory and cd into it. As rest of systemd-nspawn, this is not the security feature and limits against accidental changes only. -M --machine= Sets the machine name for this container. This name may be used to identify this container on the host, 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 of the container is used. --slice= Make the container part of the specified slice, instead of the machine.slice. -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. --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. --private-network Turn off networking in the container. This makes all network interfaces unavailable in the container, with the exception of the loopback device and those specified with --network-interface=. 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 move 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. --read-only Mount the root file system read-only for the container. --capability= List one or more additional capabilities to grant the container. Takes a comma-separated list of capability names, see capabilities7 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). --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, 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. 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=guest. --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. The --bind-ro= option creates read-only bind mount. --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. -q --quiet Turns off any status output by the tool itself. When this switch is used, then the only output by nspawn will be the console output of the container OS itself. --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-machined8. 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 machinectl1 and shown by tools such as ps1. 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 in systemd-machined8. This has no effect if --register=no is used. This switch should be used if systemd-nspawn is invoked from within an 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. # yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum 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. # 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. # pacstrap -c -d ~/arch-tree/ base # systemd-nspawn -bD ~/arch-tree/ This installs a mimimal Arch Linux distribution into the directory ~/arch-tree/ and then boots an OS in a namespace container in it. # mv ~/arch-tree /var/lib/container/arch # systemctl enable systemd-nspawn@arch.service # systemctl start systemd-nspawn@arch.service This makes the Arch Linux container part of the multi-user.target on the host. # btrfs subvolume snapshot / /.tmp # systemd-nspawn --private-network -D /.tmp -b This runs a copy of the host system in a btrfs snapshot. # 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 This runs a container with SELinux sandbox security contexts. The exit code of the program executed in the container is returned. systemd1, chroot1, yum8, debootstrap8, pacman8, systemd.slice5, machinectl1