systemd/man/systemd-nspawn.xml

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<refentry id="systemd-nspawn">

        <refentryinfo>
                <title>systemd-nspawn</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>systemd-nspawn</refentrytitle>
                <manvolnum>1</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd-nspawn</refname>
                <refpurpose>Spawn a namespace container for debugging, testing and building</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <cmdsynopsis>
                        <command>systemd-nspawn</command>
                        <arg choice="opt" rep="repeat">OPTIONS</arg>
                        <arg choice="opt"><replaceable>COMMAND</replaceable>
                        <arg choice="opt" rep="repeat">ARGS</arg>
                        </arg>
                </cmdsynopsis>
                <cmdsynopsis>
                        <command>systemd-nspawn</command>
                        <arg choice="plain">-b</arg>
                        <arg choice="opt" rep="repeat">OPTIONS</arg>
                        <arg choice="opt" rep="repeat">ARGS</arg>
                </cmdsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><command>systemd-nspawn</command> may be used to
                run a command or OS in a light-weight namespace
                container. In many ways it is similar to
                <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                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.</para>

                <para><command>systemd-nspawn</command> limits access
                to various kernel interfaces in the container to
                read-only, such as <filename>/sys</filename>,
                <filename>/proc/sys</filename> or
                <filename>/sys/fs/selinux</filename>. 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.</para>

                <para>Note that even though these security precautions
                are taken <command>systemd-nspawn</command> 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.</para>

                <para>In contrast to
                <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry> <command>systemd-nspawn</command>
                may be used to boot full Linux-based operating systems
                in a container.</para>

                <para>Use a tool like
                <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                or
                <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                to set up an OS directory tree suitable as file system
                hierarchy for <command>systemd-nspawn</command>
                containers.</para>

                <para>Note that <command>systemd-nspawn</command> will
                mount file systems private to the container to
                <filename>/dev</filename>,
                <filename>/run</filename> and similar. These will
                not be visible outside of the container, and their
                contents will be lost when the container exits.</para>

                <para>Note that running two
                <command>systemd-nspawn</command> 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
                <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
                <command>login</command> command to request an
                additional login prompt in a running container.</para>

                <para><command>systemd-nspawn</command> implements the
                <ulink
                url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
                Interface</ulink> specification.</para>

                <para>As a safety check
                <command>systemd-nspawn</command> will verify the
                existence of <filename>/etc/os-release</filename> in
                the container tree before starting the container (see
                <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>). 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.</para>
        </refsect1>

        <refsect1>
                <title>Incompatibility with Auditing</title>

                <para>Note that the kernel auditing subsystem is
                currently broken when used together with
                containers. We hence recommend turning it off entirely
                by booting with <literal>audit=0</literal> on the
                kernel command line, or by turning it off at kernel
                build time. If auditing is enabled in the kernel,
                operating systems booted in an nspawn container might
                refuse log-in attempts.</para>
        </refsect1>

        <refsect1>
                <title>Options</title>

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

                <para>The following options are understood:</para>

                <variablelist>
                        <varlistentry>
                                <term><option>-h</option></term>
                                <term><option>--help</option></term>

                                <listitem><para>Prints a short help
                                text and exits.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--version</option></term>

                                <listitem><para>Prints a version string
                                and exits.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-D</option></term>
                                <term><option>--directory=</option></term>

                                <listitem><para>Directory to use as
                                file system root for the namespace
                                container. If omitted, the current
                                directory will be
                                used.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-b</option></term>
                                <term><option>--boot</option></term>

                                <listitem><para>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
                                <option>--share-system</option>.
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-u</option></term>
                                <term><option>--user=</option></term>

                                <listitem><para>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.
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-M</option></term>
                                <term><option>--machine=</option></term>

                                <listitem><para>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.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--slice=</option></term>

                                <listitem><para>Make the container
                                part of the specified slice, instead
                                of the
                                <filename>machine.slice</filename>.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-Z</option></term>
                                <term><option>--selinux-context=</option></term>

                                <listitem><para>Sets the SELinux
                                security context to be used to label
                                processes in the container.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-L</option></term>
                                <term><option>--selinux-apifs-context=</option></term>

                                <listitem><para>Sets the SELinux security
                                context to be used to label files in
                                the virtual API file systems in the
                                container.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--uuid=</option></term>

                                <listitem><para>Set the specified UUID
                                for the container. The init system
                                will initialize
                                <filename>/etc/machine-id</filename>
                                from this if this file is not set yet.
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--private-network</option></term>

                                <listitem><para>Turn off networking in
                                the container. This makes all network
                                interfaces unavailable in the
                                container, with the exception of the
                                loopback device.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--read-only</option></term>

                                <listitem><para>Mount the root file
                                system read-only for the
                                container.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--capability=</option></term>

                                <listitem><para>List one or more
                                additional capabilities to grant the
                                container. Takes a comma-separated
                                list of capability names, see
                                <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                                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.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--drop-capability=</option></term>

                                <listitem><para>Specify one or more
                                additional capabilities to drop for
                                the container. This allows running the
                                container with fewer capabilities than
                                the default (see above).</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--link-journal=</option></term>

                                <listitem><para>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
                                <literal>no</literal>,
                                <literal>host</literal>,
                                <literal>guest</literal>,
                                <literal>auto</literal>. If
                                <literal>no</literal>, the journal is
                                not linked. If <literal>host</literal>,
                                the journal files are stored on the
                                host file system (beneath
                                <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
                                and the subdirectory is bind-mounted
                                into the container at the same
                                location. If <literal>guest</literal>,
                                the journal files are stored on the
                                guest file system (beneath
                                <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
                                and the subdirectory is symlinked into the host
                                at the same location. If
                                <literal>auto</literal> (the default),
                                and the right subdirectory of
                                <filename>/var/log/journal</filename>
                                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
                                <literal>guest</literal> or
                                <literal>host</literal> will link the
                                journal persistently if further on
                                the default of <literal>auto</literal>
                                is used.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-j</option></term>

                                <listitem><para>Equivalent to
                                <option>--link-journal=guest</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--bind=</option></term>
                                <term><option>--bind-ro=</option></term>

                                <listitem><para>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
                                <option>--bind-ro=</option> option
                                creates read-only bind
                                mount.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--setenv=</option></term>

                                <listitem><para>Specifies an
                                environment variable assignment to
                                pass to the init process in the
                                container, in the format
                                <literal>NAME=VALUE</literal>. This
                                may be used to override the default
                                variables or to set additional
                                variables. This parameter may be used
                                more than once.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>-q</option></term>
                                <term><option>--quiet</option></term>

                                <listitem><para>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.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--share-system</option></term>

                                <listitem><para>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
                                <option>--register=no</option>. This
                                option may not be combined with
                                <option>--boot</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><option>--register=</option></term>

                                <listitem><para>Controls whether the
                                container is registered with
                                <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
                                a boolean argument, defaults to
                                <literal>yes</literal>. This option
                                should be enabled when the container
                                runs a full Operating System (more
                                specifically: an init system), and is
                                useful to ensure the container is
                                accesible via
                                <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                                and shown by tools such as
                                <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>. If
                                the container does not run an init
                                system it is recommended to set this
                                option to <literal>no</literal>. Note
                                that <option>--share-system</option>
                                implies
                                <option>--register=no</option>.
                                </para></listitem>
                        </varlistentry>
                </variablelist>

        </refsect1>

        <refsect1>
                <title>Example 1</title>

                <programlisting># yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
# systemd-nspawn -bD /srv/mycontainer</programlisting>

                <para>This installs a minimal Fedora distribution into
                the directory <filename noindex='true'>/srv/mycontainer/</filename> and
                then boots an OS in a namespace container in
                it.</para>
        </refsect1>

        <refsect1>
                <title>Example 2</title>

                <programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
# systemd-nspawn -D ~/debian-tree/</programlisting>

                <para>This installs a minimal Debian unstable
                distribution into the directory
                <filename>~/debian-tree/</filename> and then spawns a
                shell in a namespace container in it.</para>
        </refsect1>

        <refsect1>
                <title>Example 3</title>

                <programlisting># pacstrap -c -d ~/arch-tree/ base
# systemd-nspawn -bD ~/arch-tree/</programlisting>

                <para>This installs a mimimal Arch Linux distribution into
                the directory <filename>~/arch-tree/</filename> and then
                boots an OS in a namespace container in it.</para>
        </refsect1>

        <refsect1>
                <title>Example 4</title>

                <programlisting># mv ~/arch-tree /var/lib/container/arch
# systemctl enable systemd-nspawn@arch.service
# systemctl start systemd-nspawn@arch.service</programlisting>

                <para>This makes the Arch Linux container part of the
                <filename>multi-user.target</filename> on the host.
                </para>
        </refsect1>

        <refsect1>
                <title>Example 5</title>

                <programlisting># btrfs subvolume snapshot / /.tmp
# systemd-nspawn --private-network -D /.tmp -b</programlisting>

                <para>This runs a copy of the host system in a
                btrfs snapshot.</para>
        </refsect1>

        <refsect1>
                <title>Example 6</title>

                <programlisting># 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</programlisting>

                <para>This runs a container with SELinux sandbox security contexts.</para>
        </refsect1>

        <refsect1>
                <title>Exit status</title>

                <para>The exit code of the program executed in the
                container is returned.</para>
        </refsect1>

        <refsect1>
                <title>See Also</title>
                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>