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1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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8   Copyright 2010 Lennart Poettering
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23
24 <refentry id="systemd-nspawn">
25
26         <refentryinfo>
27                 <title>systemd-nspawn</title>
28                 <productname>systemd</productname>
29
30                 <authorgroup>
31                         <author>
32                                 <contrib>Developer</contrib>
33                                 <firstname>Lennart</firstname>
34                                 <surname>Poettering</surname>
35                                 <email>lennart@poettering.net</email>
36                         </author>
37                 </authorgroup>
38         </refentryinfo>
39
40         <refmeta>
41                 <refentrytitle>systemd-nspawn</refentrytitle>
42                 <manvolnum>1</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>systemd-nspawn</refname>
47                 <refpurpose>Spawn a namespace container for debugging, testing and building</refpurpose>
48         </refnamediv>
49
50         <refsynopsisdiv>
51                 <cmdsynopsis>
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>
56                         </arg>
57                 </cmdsynopsis>
58                 <cmdsynopsis>
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>
63                 </cmdsynopsis>
64         </refsynopsisdiv>
65
66         <refsect1>
67                 <title>Description</title>
68
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
76                 name.</para>
77
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
87                 container.</para>
88
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>
98
99                 <para>In contrast to
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>
103
104                 <para>Use a tool like
105                 <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
106                 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
107                 or
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>
111                 containers.</para>
112
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>
119
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. It is however possible to
127                 enter an existing container, see
128                 <link linkend='example-nsenter'>Example 4</link> below.
129                 </para>
130
131                 <para><command>systemd-nspawn</command> implements the
132                 <ulink
133                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
134                 Interface</ulink> specification.</para>
135
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>
144         </refsect1>
145
146         <refsect1>
147                 <title>Incompatibility with Auditing</title>
148
149                 <para>Note that the kernel auditing subsystem is
150                 currently broken when used together with
151                 containers. We hence recommend turning it off entirely
152                 by booting with <literal>audit=0</literal> on the
153                 kernel command line, or by turning it off at kernel
154                 build time. If auditing is enabled in the kernel,
155                 operating systems booted in an nspawn container might
156                 refuse log-in attempts.</para>
157         </refsect1>
158
159         <refsect1>
160                 <title>Options</title>
161
162                 <para>If option <option>-b</option> is specified, the
163                 arguments are used as arguments for the init
164                 binary. Otherwise, <replaceable>COMMAND</replaceable>
165                 specifies the program to launch in the container, and
166                 the remaining arguments are used as arguments for this
167                 program. If <option>-b</option> is not used and no
168                 arguments are specifed, a shell is launched in the
169                 container.</para>
170
171                 <para>The following options are understood:</para>
172
173                 <variablelist>
174                         <varlistentry>
175                                 <term><option>-h</option></term>
176                                 <term><option>--help</option></term>
177
178                                 <listitem><para>Prints a short help
179                                 text and exits.</para></listitem>
180                         </varlistentry>
181
182                         <varlistentry>
183                                 <term><option>--version</option></term>
184
185                                 <listitem><para>Prints a version string
186                                 and exits.</para></listitem>
187                         </varlistentry>
188
189                         <varlistentry>
190                                 <term><option>-D</option></term>
191                                 <term><option>--directory=</option></term>
192
193                                 <listitem><para>Directory to use as
194                                 file system root for the namespace
195                                 container. If omitted, the current
196                                 directory will be
197                                 used.</para></listitem>
198                         </varlistentry>
199
200                         <varlistentry>
201                                 <term><option>-b</option></term>
202                                 <term><option>--boot</option></term>
203
204                                 <listitem><para>Automatically search
205                                 for an init binary and invoke it
206                                 instead of a shell or a user supplied
207                                 program. If this option is used, arguments
208                                 specified on the command line are used
209                                 as arguments for the init binary.
210                                 </para></listitem>
211                         </varlistentry>
212
213                         <varlistentry>
214                                 <term><option>-u</option></term>
215                                 <term><option>--user=</option></term>
216
217                                 <listitem><para>Run the command
218                                 under specified user, create home
219                                 directory and cd into it. As rest
220                                 of systemd-nspawn, this is not
221                                 the security feature and limits
222                                 against accidental changes only.
223                                 </para></listitem>
224                         </varlistentry>
225
226                         <varlistentry>
227                                 <term><option>-M</option></term>
228                                 <term><option>--machine=</option></term>
229
230                                 <listitem><para>Sets the machine name
231                                 for this container. This name may be
232                                 used to identify this container on the
233                                 host, and is used to initialize the
234                                 container's hostname (which the
235                                 container can choose to override,
236                                 however). If not specified, the last
237                                 component of the root directory of the
238                                 container is used.</para></listitem>
239                         </varlistentry>
240
241                         <varlistentry>
242                                 <term><option>--slice=</option></term>
243
244                                 <listitem><para>Make the container
245                                 part of the specified slice, instead
246                                 of the
247                                 <filename>machine.slice</filename>.</para>
248                                 </listitem>
249                         </varlistentry>
250
251                         <varlistentry>
252                                 <term><option>--uuid=</option></term>
253
254                                 <listitem><para>Set the specified UUID
255                                 for the container. The init system
256                                 will initialize
257                                 <filename>/etc/machine-id</filename>
258                                 from this if this file is not set yet.
259                                 </para></listitem>
260                         </varlistentry>
261
262                         <varlistentry>
263                                 <term><option>--private-network</option></term>
264
265                                 <listitem><para>Turn off networking in
266                                 the container. This makes all network
267                                 interfaces unavailable in the
268                                 container, with the exception of the
269                                 loopback device.</para></listitem>
270                         </varlistentry>
271
272                         <varlistentry>
273                                 <term><option>--read-only</option></term>
274
275                                 <listitem><para>Mount the root file
276                                 system read-only for the
277                                 container.</para></listitem>
278                         </varlistentry>
279
280                         <varlistentry>
281                                 <term><option>--capability=</option></term>
282
283                                 <listitem><para>List one or more
284                                 additional capabilities to grant the
285                                 container. Takes a comma-separated
286                                 list of capability names, see
287                                 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
288                                 for more information. Note that the
289                                 following capabilities will be granted
290                                 in any way: CAP_CHOWN,
291                                 CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
292                                 CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
293                                 CAP_KILL, CAP_LEASE,
294                                 CAP_LINUX_IMMUTABLE,
295                                 CAP_NET_BIND_SERVICE,
296                                 CAP_NET_BROADCAST, CAP_NET_RAW,
297                                 CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP,
298                                 CAP_SETUID, CAP_SYS_ADMIN,
299                                 CAP_SYS_CHROOT, CAP_SYS_NICE,
300                                 CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
301                                 CAP_SYS_RESOURCE, CAP_SYS_BOOT,
302                                 CAP_AUDIT_WRITE,
303                                 CAP_AUDIT_CONTROL.</para></listitem>
304                         </varlistentry>
305
306                         <varlistentry>
307                                 <term><option>--link-journal=</option></term>
308
309                                 <listitem><para>Control whether the
310                                 container's journal shall be made
311                                 visible to the host system. If enabled,
312                                 allows viewing the container's journal
313                                 files from the host (but not vice
314                                 versa). Takes one of
315                                 <literal>no</literal>,
316                                 <literal>host</literal>,
317                                 <literal>guest</literal>,
318                                 <literal>auto</literal>. If
319                                 <literal>no</literal>, the journal is
320                                 not linked. If <literal>host</literal>,
321                                 the journal files are stored on the
322                                 host file system (beneath
323                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
324                                 and the subdirectory is bind-mounted
325                                 into the container at the same
326                                 location. If <literal>guest</literal>,
327                                 the journal files are stored on the
328                                 guest file system (beneath
329                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
330                                 and the subdirectory is symlinked into the host
331                                 at the same location. If
332                                 <literal>auto</literal> (the default),
333                                 and the right subdirectory of
334                                 <filename>/var/log/journal</filename>
335                                 exists, it will be bind mounted
336                                 into the container. If the
337                                 subdirectory does not exist, no
338                                 linking is performed. Effectively,
339                                 booting a container once with
340                                 <literal>guest</literal> or
341                                 <literal>host</literal> will link the
342                                 journal persistently if further on
343                                 the default of <literal>auto</literal>
344                                 is used.</para></listitem>
345                         </varlistentry>
346
347                         <varlistentry>
348                                 <term><option>-j</option></term>
349
350                                 <listitem><para>Equivalent to
351                                 <option>--link-journal=guest</option>.</para></listitem>
352                         </varlistentry>
353
354                         <varlistentry>
355                                 <term><option>--bind=</option></term>
356                                 <term><option>--bind-ro=</option></term>
357
358                                 <listitem><para>Bind mount a file or
359                                 directory from the host into the
360                                 container. Either takes a path
361                                 argument -- in which case the
362                                 specified path will be mounted from
363                                 the host to the same path in the
364                                 container --, or a colon-separated
365                                 pair of paths -- in which case the
366                                 first specified path is the source in
367                                 the host, and the second path is the
368                                 destination in the container. The
369                                 <option>--bind-ro=</option> option
370                                 creates read-only bind
371                                 mount.</para></listitem>
372                         </varlistentry>
373                 </variablelist>
374
375         </refsect1>
376
377         <refsect1>
378                 <title>Example 1</title>
379
380                 <programlisting># yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
381 # systemd-nspawn -bD /srv/mycontainer</programlisting>
382
383                 <para>This installs a minimal Fedora distribution into
384                 the directory <filename noindex='true'>/srv/mycontainer/</filename> and
385                 then boots an OS in a namespace container in
386                 it.</para>
387         </refsect1>
388
389         <refsect1>
390                 <title>Example 2</title>
391
392                 <programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
393 # systemd-nspawn -D ~/debian-tree/</programlisting>
394
395                 <para>This installs a minimal Debian unstable
396                 distribution into the directory
397                 <filename>~/debian-tree/</filename> and then spawns a
398                 shell in a namespace container in it.</para>
399         </refsect1>
400
401         <refsect1>
402                 <title>Example 3</title>
403
404                 <programlisting># pacstrap -c -d ~/arch-tree/ base
405 # systemd-nspawn -bD ~/arch-tree/</programlisting>
406
407                 <para>This installs a mimimal Arch Linux distribution into
408                 the directory <filename>~/arch-tree/</filename> and then
409                 boots an OS in a namespace container in it.</para>
410         </refsect1>
411
412         <refsect1 id='example-nsenter'>
413                 <title>Example 4</title>
414
415                 <para>To enter the container, PID of one of the
416                 processes sharing the new namespaces must be used.
417                 <command>systemd-nspawn</command> prints the PID
418                 (as viewed from the outside) of the launched process,
419                 and it can be used to enter the container.</para>
420
421                 <programlisting># nsenter -m -u -i -n -p -t $PID</programlisting>
422
423                 <para><citerefentry><refentrytitle>nsenter</refentrytitle><manvolnum>1</manvolnum></citerefentry>
424                 is part of
425                 <ulink url="https://github.com/karelzak/util-linux">util-linux</ulink>.
426                 Kernel support for entering namespaces was added in
427                 Linux 3.8.</para>
428         </refsect1>
429
430         <refsect1>
431                 <title>Exit status</title>
432
433                 <para>The exit code of the program executed in the
434                 container is returned.</para>
435         </refsect1>
436
437         <refsect1>
438                 <title>See Also</title>
439                 <para>
440                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
441                         <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
442                         <citerefentry><refentrytitle>unshare</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
443                         <citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
444                         <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
445                         <citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
446                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
447                 </para>
448         </refsect1>
449
450 </refentry>