1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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6 This file is part of systemd.
8 Copyright 2010 Lennart Poettering
10 systemd is free software; you can redistribute it and/or modify it
11 under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or
13 (at your option) any later version.
15 systemd is distributed in the hope that it will be useful, but
16 WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 Lesser General Public License for more details.
20 You should have received a copy of the GNU Lesser General Public License
21 along with systemd; If not, see <http://www.gnu.org/licenses/>.
24 <refentry id="systemd-nspawn">
27 <title>systemd-nspawn</title>
28 <productname>systemd</productname>
32 <contrib>Developer</contrib>
33 <firstname>Lennart</firstname>
34 <surname>Poettering</surname>
35 <email>lennart@poettering.net</email>
41 <refentrytitle>systemd-nspawn</refentrytitle>
42 <manvolnum>1</manvolnum>
46 <refname>systemd-nspawn</refname>
47 <refpurpose>Spawn a namespace container for debugging, testing and building</refpurpose>
52 <command>systemd-nspawn</command>
53 <arg choice="opt" rep="repeat">OPTIONS</arg>
54 <arg choice="opt"><replaceable>COMMAND</replaceable>
55 <arg choice="opt" rep="repeat">ARGS</arg>
59 <command>systemd-nspawn</command>
60 <arg choice="plain">-b</arg>
61 <arg choice="opt" rep="repeat">OPTIONS</arg>
62 <arg choice="opt" rep="repeat">ARGS</arg>
67 <title>Description</title>
69 <para><command>systemd-nspawn</command> may be used to
70 run a command or OS in a light-weight namespace
71 container. In many ways it is similar to
72 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
73 but more powerful since it fully virtualizes the file
74 system hierarchy, as well as the process tree, the
75 various IPC subsystems and the host and domain
78 <para><command>systemd-nspawn</command> limits access
79 to various kernel interfaces in the container to
80 read-only, such as <filename>/sys</filename>,
81 <filename>/proc/sys</filename> or
82 <filename>/sys/fs/selinux</filename>. Network
83 interfaces and the system clock may not be changed
84 from within the container. Device nodes may not be
85 created. The host system cannot be rebooted and kernel
86 modules may not be loaded from within the
89 <para>Note that even though these security precautions
90 are taken <command>systemd-nspawn</command> is not
91 suitable for secure container setups. Many of the
92 security features may be circumvented and are hence
93 primarily useful to avoid accidental changes to the
94 host system from the container. The intended use of
95 this program is debugging and testing as well as
96 building of packages, distributions and software
97 involved with boot and systems management.</para>
100 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
101 <command>systemd-nspawn</command> may be used to boot
102 full Linux-based operating systems in a
105 <para>Use a tool like
106 <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
107 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>
109 <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
110 to set up an OS directory tree suitable as file system
111 hierarchy for <command>systemd-nspawn</command>
114 <para>Note that <command>systemd-nspawn</command> will
115 mount file systems private to the container to
116 <filename>/dev</filename>,
117 <filename>/run</filename> and similar. These will
118 not be visible outside of the container, and their
119 contents will be lost when the container exits.</para>
121 <para>Note that running two
122 <command>systemd-nspawn</command> containers from the
123 same directory tree will not make processes in them
124 see each other. The PID namespace separation of the
125 two containers is complete and the containers will
126 share very few runtime objects except for the
127 underlying file system. It is however possible to
128 enter an existing container, see
129 <link linkend='example-nsenter'>Example 4</link> below.
132 <para><command>systemd-nspawn</command> implements the
134 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
135 Interface</ulink> specification.</para>
139 <title>Options</title>
141 <para>If option <option>-b</option> is specified, the
142 arguments are used as arguments for the init
143 binary. Otherwise, <replaceable>COMMAND</replaceable>
144 specifies the program to launch in the container, and
145 the remaining arguments are used as arguments for this
146 program. If <option>-b</option> is not used and no
147 arguments are specifed, a shell is launched in the
150 <para>The following options are understood:</para>
154 <term><option>-h</option></term>
155 <term><option>--help</option></term>
157 <listitem><para>Prints a short help
158 text and exits.</para></listitem>
162 <term><option>--version</option></term>
164 <listitem><para>Prints a version string
165 and exits.</para></listitem>
169 <term><option>-D</option></term>
170 <term><option>--directory=</option></term>
172 <listitem><para>Directory to use as
173 file system root for the namespace
174 container. If omitted the current
176 used.</para></listitem>
180 <term><option>-b</option></term>
181 <term><option>--boot</option></term>
183 <listitem><para>Automatically search
184 for an init binary and invoke it
185 instead of a shell or a user supplied
186 program. If this option is used, arguments
187 specified on the command line are used
188 as arguments for the init binary.
193 <term><option>-u</option></term>
194 <term><option>--user=</option></term>
196 <listitem><para>Run the command
197 under specified user, create home
198 directory and cd into it. As rest
199 of systemd-nspawn, this is not
200 the security feature and limits
201 against accidental changes only.
206 <term><option>--uuid=</option></term>
208 <listitem><para>Set the specified uuid
209 for the container. The init system
211 <filename>/etc/machine-id</filename>
212 from this if this file is not set yet.
217 <term><option>-C</option></term>
218 <term><option>--controllers=</option></term>
220 <listitem><para>Makes the container appear in
221 other hierarchies than the name=systemd:/ one.
222 Takes a comma-separated list of controllers.
227 <term><option>--private-network</option></term>
229 <listitem><para>Turn off networking in
230 the container. This makes all network
231 interfaces unavailable in the
232 container, with the exception of the
233 loopback device.</para></listitem>
237 <term><option>--read-only</option></term>
239 <listitem><para>Mount the root file
240 system read only for the
241 container.</para></listitem>
245 <term><option>--capability=</option></term>
247 <listitem><para>List one or more
248 additional capabilities to grant the
249 container. Takes a comma separated
250 list of capability names, see
251 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
252 for more information. Note that the
253 following capabilities will be granted
254 in any way: CAP_CHOWN,
255 CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
256 CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
259 CAP_NET_BIND_SERVICE,
260 CAP_NET_BROADCAST, CAP_NET_RAW,
261 CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP,
262 CAP_SETUID, CAP_SYS_ADMIN,
263 CAP_SYS_CHROOT, CAP_SYS_NICE,
264 CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
265 CAP_SYS_RESOURCE, CAP_SYS_BOOT,
267 CAP_AUDIT_CONTROL.</para></listitem>
271 <term><option>--link-journal=</option></term>
273 <listitem><para>Control whether the
274 container's journal shall be made
275 visible to the host system. If enabled
276 allows viewing the container's journal
277 files from the host (but not vice
279 <literal>no</literal>,
280 <literal>host</literal>,
281 <literal>guest</literal>,
282 <literal>auto</literal>. If
283 <literal>no</literal>, the journal is
284 not linked. If <literal>host</literal>,
285 the journal files are stored on the
286 host file system (beneath
287 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
288 and the subdirectory is bind-mounted
289 into the container at the same
290 location. If <literal>guest</literal>,
291 the journal files are stored on the
292 guest file system (beneath
293 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
294 and the subdirectory is symlinked into the host
295 at the same location. If
296 <literal>auto</literal> (the default),
297 and the right subdirectory of
298 <filename>/var/log/journal</filename>
299 exists, it will be bind mounted
300 into the container. If the
301 subdirectory doesn't exist, no
302 linking is performed. Effectively,
303 booting a container once with
304 <literal>guest</literal> or
305 <literal>host</literal> will link the
306 journal persistently if further on
307 the default of <literal>auto</literal>
308 is used.</para></listitem>
312 <term><option>-j</option></term>
314 <listitem><para>Equivalent to
315 <option>--link-journal=guest</option>.</para></listitem>
319 <term><option>--bind=</option></term>
320 <term><option>--bind-ro=</option></term>
322 <listitem><para>Bind mount a file or
323 directory from the host into the
324 container. Either takes a path
325 argument -- in which case the
326 specified path will be mounted from
327 the host to the same path in the
328 container --, or a colon-separated
329 pair of paths -- in which case the
330 first specified path is the source in
331 the host, and the second path is the
332 destination in the container. The
333 <option>--bind-ro=</option> option
334 creates read-only bind
335 mount.</para></listitem>
342 <title>Example 1</title>
344 <programlisting># yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
345 # systemd-nspawn -bD /srv/mycontainer</programlisting>
347 <para>This installs a minimal Fedora distribution into
348 the directory <filename>/srv/mycontainer/</filename> and
349 then boots an OS in a namespace container in
354 <title>Example 2</title>
356 <programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
357 # systemd-nspawn -D ~/debian-tree/</programlisting>
359 <para>This installs a minimal Debian unstable
360 distribution into the directory
361 <filename>~/debian-tree/</filename> and then spawns a
362 shell in a namespace container in it.</para>
366 <title>Example 3</title>
368 <programlisting># pacstrap -c -d ~/arch-tree/ base
369 # systemd-nspawn -bD ~/arch-tree/</programlisting>
371 <para>This installs a mimimal Arch Linux distribution into
372 the directory <filename>~/arch-tree/</filename> and then
373 boots an OS in a namespace container in it.</para>
376 <refsect1 id='example-nsenter'>
377 <title>Example 4</title>
379 <para>To enter the container, PID of one of the
380 processes sharing the new namespaces must be used.
381 <command>systemd-nspawn</command> prints the PID
382 (as viewed from the outside) of the launched process,
383 and it can be used to enter the container.</para>
385 <programlisting># nsenter -muinpt $PID</programlisting>
387 <para><citerefentry><refentrytitle>nsenter</refentrytitle><manvolnum>1</manvolnum></citerefentry>
389 <ulink url="https://github.com/karelzak/util-linux">util-linux</ulink>.
390 Kernel support for entering namespaces was added in
395 <title>Exit status</title>
397 <para>The exit code of the program executed in the
398 container is returned.</para>
402 <title>See Also</title>
404 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
405 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
406 <citerefentry><refentrytitle>unshare</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
407 <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
408 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
409 <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>