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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 <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">COMMAND</arg> <arg choice="opt" rep="repeat">ARGS</arg></command>

</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>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry> or <citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</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.</para>

</refsect1>

<refsect1>

<title>Options</title>

<para>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:</para>

<variablelist>

<varlistentry>

<term><option>--help</option></term>

<term><option>-h</option></term>

<listitem><para>Prints a short help

text and exits.</para></listitem>

</varlistentry>

<varlistentry>

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

<term><option>-D</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>--boot</option></term>

<term><option>-b</option></term>

<listitem><para>Automatically search

for an init binary and invoke it

instead of a shell or a user supplied

program.</para></listitem>

</varlistentry>

<varlistentry>

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

<term><option>-u</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>--controllers=</option></term>

<term><option>-C</option></term>

<listitem><para>Makes the container appear in

other hierarchies that the name=systemd:/ one.

Takes a comma-separated list of controllers.

</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>

</variablelist>

</refsect1>

<refsect1>

<title>Example 1</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 2</title>

<programlisting># mock --init

# systemd-nspawn -D /var/lib/mock/fedora-rawhide-x86_64/root/ /sbin/init systemd.log_level=debug</programlisting>

<para>This installs a minimal Fedora distribution into

a subdirectory of <filename>/var/lib/mock/</filename>

and then boots an OS in a namespace container in it,

with systemd as init system, configured for debug

logging.</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>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>