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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">COMMAND</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. It is however possible to

enter an existing container, see

<link linkend='example-nsenter'>Example 4</link> below.

</para>

<para><command>systemd-nspawn</command> implements the

<ulink

url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container

Interface</ulink> specification.</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>-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.</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>--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>-C</option></term>

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

<listitem><para>Makes the container appear in

other hierarchies than 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>

<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>--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 doesn't 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>

</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>/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 id='example-nsenter'>

<title>Example 4</title>

<para>To enter the container, PID of one of the

processes sharing the new namespaces must be used.

<command>systemd-nspawn</command> prints the PID

(as viewed from the outside) of the launched process,

and it can be used to enter the container.</para>

<programlisting># nsenter -muinpt $PID</programlisting>

<para><citerefentry><refentrytitle>nsenter</refentrytitle><manvolnum>1</manvolnum></citerefentry>

is part of

<ulink url="https://github.com/karelzak/util-linux">util-linux</ulink>.

Kernel support for entering namespaces was added in

Linux 3.8.</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>unshare</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>

</para>

</refsect1>

</refentry>