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 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 debootstrap8 or mock1 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. If no arguments are passed the container is set up and a shell started in it, otherwise the passed command and arguments are executed in it. The following options are understood: --help -h Prints a short help text and exits. --directory= -D Directory to use as file system root for the namespace container. If omitted the current directory will be used. --boot -b Automatically search for an init binary and invoke it instead of a shell or a user supplied program. --user= -u 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. --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. --controllers= -C Makes the container appear in other hierarchies that the name=systemd:/ one. Takes a comma-separated list of controllers. --private-network Turn off networking in the container. This makes all network interfaces unavailable in the container, with the exception of the loopback device. # 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. # mock --init # systemd-nspawn -D /var/lib/mock/fedora-rawhide-x86_64/root/ /sbin/init systemd.log_level=debug This installs a minimal Fedora distribution into a subdirectory of /var/lib/mock/ and then boots an OS in a namespace container in it, with systemd as init system, configured for debug logging. The exit code of the program executed in the container is returned. systemd1, chroot1, debootstrap8, mock1