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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 that the container is

accessible 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>

<varlistentry>

<term><option>--keep-unit</option></term>

<listitem><para>Instead of creating a

transient scope unit to run the

container in, simply register the

service or scope unit

<command>systemd-nspawn</command> has

been invoked in in

<citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. This

has no effect if

<option>--register=no</option> is

used. This switch should be used if

<command>systemd-nspawn</command> is

invoked from within an a service unit,

and the service unit's sole purpose

is to run a single

<command>systemd-nspawn</command>

container. This option is not

available if run from a user

session.</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>