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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.
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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> <command>systemd-nspawn</command>
101 may be used to boot full Linux-based operating systems
102 in a container.</para>
104 <para>Use a tool like
105 <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
106 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
108 <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
109 to set up an OS directory tree suitable as file system
110 hierarchy for <command>systemd-nspawn</command>
113 <para>Note that <command>systemd-nspawn</command> will
114 mount file systems private to the container to
115 <filename>/dev</filename>,
116 <filename>/run</filename> and similar. These will
117 not be visible outside of the container, and their
118 contents will be lost when the container exits.</para>
120 <para>Note that running two
121 <command>systemd-nspawn</command> containers from the
122 same directory tree will not make processes in them
123 see each other. The PID namespace separation of the
124 two containers is complete and the containers will
125 share very few runtime objects except for the
126 underlying file system. Use
127 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
128 <command>login</command> command to request an
129 additional login prompt in a running container.</para>
131 <para><command>systemd-nspawn</command> implements the
133 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
134 Interface</ulink> specification.</para>
136 <para>As a safety check
137 <command>systemd-nspawn</command> will verify the
138 existence of <filename>/etc/os-release</filename> in
139 the container tree before starting the container (see
140 <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>). It
141 might be necessary to add this file to the container
142 tree manually if the OS of the container is too old to
143 contain this file out-of-the-box.</para>
147 <title>Options</title>
149 <para>If option <option>-b</option> is specified, the
150 arguments are used as arguments for the init
151 binary. Otherwise, <replaceable>COMMAND</replaceable>
152 specifies the program to launch in the container, and
153 the remaining arguments are used as arguments for this
154 program. If <option>-b</option> is not used and no
155 arguments are specifed, a shell is launched in the
158 <para>The following options are understood:</para>
162 <term><option>-h</option></term>
163 <term><option>--help</option></term>
165 <listitem><para>Prints a short help
166 text and exits.</para></listitem>
170 <term><option>--version</option></term>
172 <listitem><para>Prints a version string
173 and exits.</para></listitem>
177 <term><option>-D</option></term>
178 <term><option>--directory=</option></term>
180 <listitem><para>Directory to use as
181 file system root for the namespace
182 container. If omitted, the current
184 used.</para></listitem>
188 <term><option>-b</option></term>
189 <term><option>--boot</option></term>
191 <listitem><para>Automatically search
192 for an init binary and invoke it
193 instead of a shell or a user supplied
194 program. If this option is used,
195 arguments specified on the command
196 line are used as arguments for the
197 init binary. This option may not be
199 <option>--share-system</option>.
204 <term><option>-u</option></term>
205 <term><option>--user=</option></term>
207 <listitem><para>Run the command
208 under specified user, create home
209 directory and cd into it. As rest
210 of systemd-nspawn, this is not
211 the security feature and limits
212 against accidental changes only.
217 <term><option>-M</option></term>
218 <term><option>--machine=</option></term>
220 <listitem><para>Sets the machine name
221 for this container. This name may be
222 used to identify this container on the
223 host, and is used to initialize the
224 container's hostname (which the
225 container can choose to override,
226 however). If not specified, the last
227 component of the root directory of the
228 container is used.</para></listitem>
232 <term><option>--slice=</option></term>
234 <listitem><para>Make the container
235 part of the specified slice, instead
237 <filename>machine.slice</filename>.</para>
242 <term><option>-Z</option></term>
243 <term><option>--selinux-context=</option></term>
245 <listitem><para>Sets the SELinux
246 security context to be used to label
247 processes in the container.</para>
252 <term><option>-L</option></term>
253 <term><option>--selinux-apifs-context=</option></term>
255 <listitem><para>Sets the SELinux security
256 context to be used to label files in
257 the virtual API file systems in the
263 <term><option>--uuid=</option></term>
265 <listitem><para>Set the specified UUID
266 for the container. The init system
268 <filename>/etc/machine-id</filename>
269 from this if this file is not set yet.
274 <term><option>--private-network</option></term>
276 <listitem><para>Turn off networking in
277 the container. This makes all network
278 interfaces unavailable in the
279 container, with the exception of the
280 loopback device.</para></listitem>
284 <term><option>--network-interface=</option></term>
286 <listitem><para>Assign the specified
287 network interface to the
288 container. This will move the
289 specified interface from the calling
290 namespace and place it in the
291 container. When the container
292 terminates it is moved back to the
293 host namespace.</para></listitem>
297 <term><option>--read-only</option></term>
299 <listitem><para>Mount the root file
300 system read-only for the
301 container.</para></listitem>
305 <term><option>--capability=</option></term>
307 <listitem><para>List one or more
308 additional capabilities to grant the
309 container. Takes a comma-separated
310 list of capability names, see
311 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
312 for more information. Note that the
313 following capabilities will be granted
314 in any way: CAP_CHOWN,
315 CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
316 CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
319 CAP_NET_BIND_SERVICE,
320 CAP_NET_BROADCAST, CAP_NET_RAW,
321 CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP,
322 CAP_SETUID, CAP_SYS_ADMIN,
323 CAP_SYS_CHROOT, CAP_SYS_NICE,
324 CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
325 CAP_SYS_RESOURCE, CAP_SYS_BOOT,
326 CAP_AUDIT_WRITE, CAP_AUDIT_CONTROL. If
328 <literal>all</literal> is passed all
330 retained.</para></listitem>
334 <term><option>--drop-capability=</option></term>
336 <listitem><para>Specify one or more
337 additional capabilities to drop for
338 the container. This allows running the
339 container with fewer capabilities than
340 the default (see above).</para></listitem>
344 <term><option>--link-journal=</option></term>
346 <listitem><para>Control whether the
347 container's journal shall be made
348 visible to the host system. If enabled,
349 allows viewing the container's journal
350 files from the host (but not vice
352 <literal>no</literal>,
353 <literal>host</literal>,
354 <literal>guest</literal>,
355 <literal>auto</literal>. If
356 <literal>no</literal>, the journal is
357 not linked. If <literal>host</literal>,
358 the journal files are stored on the
359 host file system (beneath
360 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
361 and the subdirectory is bind-mounted
362 into the container at the same
363 location. If <literal>guest</literal>,
364 the journal files are stored on the
365 guest file system (beneath
366 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
367 and the subdirectory is symlinked into the host
368 at the same location. If
369 <literal>auto</literal> (the default),
370 and the right subdirectory of
371 <filename>/var/log/journal</filename>
372 exists, it will be bind mounted
373 into the container. If the
374 subdirectory does not exist, no
375 linking is performed. Effectively,
376 booting a container once with
377 <literal>guest</literal> or
378 <literal>host</literal> will link the
379 journal persistently if further on
380 the default of <literal>auto</literal>
381 is used.</para></listitem>
385 <term><option>-j</option></term>
387 <listitem><para>Equivalent to
388 <option>--link-journal=guest</option>.</para></listitem>
392 <term><option>--bind=</option></term>
393 <term><option>--bind-ro=</option></term>
395 <listitem><para>Bind mount a file or
396 directory from the host into the
397 container. Either takes a path
398 argument -- in which case the
399 specified path will be mounted from
400 the host to the same path in the
401 container --, or a colon-separated
402 pair of paths -- in which case the
403 first specified path is the source in
404 the host, and the second path is the
405 destination in the container. The
406 <option>--bind-ro=</option> option
407 creates read-only bind
408 mount.</para></listitem>
412 <term><option>--setenv=</option></term>
414 <listitem><para>Specifies an
415 environment variable assignment to
416 pass to the init process in the
417 container, in the format
418 <literal>NAME=VALUE</literal>. This
419 may be used to override the default
420 variables or to set additional
421 variables. This parameter may be used
422 more than once.</para></listitem>
426 <term><option>-q</option></term>
427 <term><option>--quiet</option></term>
429 <listitem><para>Turns off any status
430 output by the tool itself. When this
431 switch is used, then the only output
432 by nspawn will be the console output
433 of the container OS itself.</para></listitem>
437 <term><option>--share-system</option></term>
439 <listitem><para>Allows the container
440 to share certain system facilities
441 with the host. More specifically, this
442 turns off PID namespacing, UTS
443 namespacing and IPC namespacing, and
444 thus allows the guest to see and
445 interact more easily with processes
446 outside of the container. Note that
447 using this option makes it impossible
448 to start up a full Operating System in
449 the container, as an init system
450 cannot operate in this mode. It is
451 only useful to run specific programs
452 or applications this way, without
453 involving an init system in the
454 container. This option implies
455 <option>--register=no</option>. This
456 option may not be combined with
457 <option>--boot</option>.</para></listitem>
461 <term><option>--register=</option></term>
463 <listitem><para>Controls whether the
464 container is registered with
465 <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
466 a boolean argument, defaults to
467 <literal>yes</literal>. This option
468 should be enabled when the container
469 runs a full Operating System (more
470 specifically: an init system), and is
471 useful to ensure that the container is
473 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
474 and shown by tools such as
475 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>. If
476 the container does not run an init
477 system it is recommended to set this
478 option to <literal>no</literal>. Note
479 that <option>--share-system</option>
481 <option>--register=no</option>.
486 <term><option>--keep-unit</option></term>
488 <listitem><para>Instead of creating a
489 transient scope unit to run the
490 container in, simply register the
491 service or scope unit
492 <command>systemd-nspawn</command> has
494 <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. This
496 <option>--register=no</option> is
497 used. This switch should be used if
498 <command>systemd-nspawn</command> is
499 invoked from within an a service unit,
500 and the service unit's sole purpose
502 <command>systemd-nspawn</command>
503 container. This option is not
504 available if run from a user
505 session.</para></listitem>
513 <title>Example 1</title>
515 <programlisting># yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
516 # systemd-nspawn -bD /srv/mycontainer</programlisting>
518 <para>This installs a minimal Fedora distribution into
519 the directory <filename noindex='true'>/srv/mycontainer/</filename> and
520 then boots an OS in a namespace container in
525 <title>Example 2</title>
527 <programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
528 # systemd-nspawn -D ~/debian-tree/</programlisting>
530 <para>This installs a minimal Debian unstable
531 distribution into the directory
532 <filename>~/debian-tree/</filename> and then spawns a
533 shell in a namespace container in it.</para>
537 <title>Example 3</title>
539 <programlisting># pacstrap -c -d ~/arch-tree/ base
540 # systemd-nspawn -bD ~/arch-tree/</programlisting>
542 <para>This installs a mimimal Arch Linux distribution into
543 the directory <filename>~/arch-tree/</filename> and then
544 boots an OS in a namespace container in it.</para>
548 <title>Example 4</title>
550 <programlisting># mv ~/arch-tree /var/lib/container/arch
551 # systemctl enable systemd-nspawn@arch.service
552 # systemctl start systemd-nspawn@arch.service</programlisting>
554 <para>This makes the Arch Linux container part of the
555 <filename>multi-user.target</filename> on the host.
560 <title>Example 5</title>
562 <programlisting># btrfs subvolume snapshot / /.tmp
563 # systemd-nspawn --private-network -D /.tmp -b</programlisting>
565 <para>This runs a copy of the host system in a
566 btrfs snapshot.</para>
570 <title>Example 6</title>
572 <programlisting># chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
573 # 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>
575 <para>This runs a container with SELinux sandbox security contexts.</para>
579 <title>Exit status</title>
581 <para>The exit code of the program executed in the
582 container is returned.</para>
586 <title>See Also</title>
588 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
589 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
590 <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
591 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
592 <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
593 <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
594 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>