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nspawn: spawn shell under specified --user
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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">
4
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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 <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">COMMAND</arg> <arg choice="opt" rep="repeat">ARGS</arg></command>
53                 </cmdsynopsis>
54         </refsynopsisdiv>
55
56         <refsect1>
57                 <title>Description</title>
58
59                 <para><command>systemd-nspawn</command> may be used to
60                 run a command or OS in a light-weight namespace
61                 container. In many ways it is similar to
62                 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
63                 but more powerful since it fully virtualizes the file
64                 system hierarchy, as well as the process tree, the
65                 various IPC subsystems and the host and domain
66                 name.</para>
67
68                 <para><command>systemd-nspawn</command> limits access
69                 to various kernel interfaces in the container to
70                 read-only, such as <filename>/sys</filename>,
71                 <filename>/proc/sys</filename> or
72                 <filename>/selinux</filename>. Network interfaces and
73                 the system clock may not be changed from within the
74                 container. Device nodes may not be created. The host
75                 system cannot be rebooted and kernel modules may not
76                 be loaded from within the container.</para>
77
78                 <para>Note that even though these security precautions
79                 are taken <command>systemd-nspawn</command> is not
80                 suitable for secure container setups. Many of the
81                 security features may be circumvented and are hence
82                 primarily useful to avoid accidental changes to the
83                 host system from the container. The intended use of
84                 this program is debugging and testing as well as
85                 building of packages, distributions and software
86                 involved with boot and systems management.</para>
87
88                 <para>In contrast to
89                 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
90                 <command>systemd-nspawn</command> may be used to boot
91                 full Linux-based operating systems in a
92                 container.</para>
93
94                 <para>Use a tool like
95                 <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry> or <citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</manvolnum></citerefentry>
96                 to set up an OS directory tree suitable as file system
97                 hierarchy for <command>systemd-nspawn</command> containers.</para>
98
99                 <para>Note that <command>systemd-nspawn</command> will
100                 mount file systems private to the container to
101                 <filename>/dev</filename>,
102                 <filename>/run</filename> and similar. These will
103                 not be visible outside of the container, and their
104                 contents will be lost when the container exits.</para>
105
106                 <para>Note that running two
107                 <command>systemd-nspawn</command> containers from the
108                 same directory tree will not make processes in them
109                 see each other. The PID namespace separation of the
110                 two containers is complete and the containers will
111                 share very few runtime objects except for the
112                 underlying file system.</para>
113         </refsect1>
114
115         <refsect1>
116                 <title>Options</title>
117
118                 <para>If no arguments are passed the container is set
119                 up and a shell started in it, otherwise the passed
120                 command and arguments are executed in it. The
121                 following options are understood:</para>
122
123                 <variablelist>
124                         <varlistentry>
125                                 <term><option>--help</option></term>
126
127                                 <listitem><para>Prints a short help
128                                 text and exits.</para></listitem>
129                         </varlistentry>
130
131                         <varlistentry>
132                                 <term><option>--directory=</option></term>
133                                 <term><option>--D</option></term>
134
135                                 <listitem><para>Directory to use as
136                                 file system root for the namespace
137                                 container. If omitted the current
138                                 directory will be
139                                 used.</para></listitem>
140                         </varlistentry>
141
142                         <varlistentry>
143                                 <term><option>--user=</option></term>
144                                 <term><option>--u</option></term>
145
146                                 <listitem><para>Run the command
147                                 under specified user, create home
148                                 directory and cd into it. As rest
149                                 of systemd-nspawn, this is not
150                                 the security feature and limits
151                                 against accidental changes only.
152                                 </para></listitem>
153                         </varlistentry>
154
155                 </variablelist>
156
157         </refsect1>
158
159         <refsect1>
160                 <title>Example 1</title>
161
162                 <programlisting># debootstrap --arch=amd64 unstable debian-tree/
163 # systemd-nspawn -D debian-tree/</programlisting>
164
165                 <para>This installs a minimal Debian unstable
166                 distribution into the directory
167                 <filename>debian-tree/</filename> and then spawns a
168                 shell in a namespace container in it.</para>
169
170         </refsect1>
171
172         <refsect1>
173                 <title>Example 2</title>
174
175                 <programlisting># mock --init
176 # systemd-nspawn -D /var/lib/mock/fedora-rawhide-x86_64/root/ /bin/systemd systemd.log_level=debug</programlisting>
177
178                 <para>This installs a minimal Fedora distribution into
179                 a subdirectory of <filename>/var/lib/mock/</filename>
180                 and then boots an OS in a namespace container in it,
181                 with systemd as init system, configured for debug
182                 logging.</para>
183
184         </refsect1>
185
186         <refsect1>
187                 <title>Exit status</title>
188
189                 <para>The exit code of the program executed in the
190                 container is returned.</para>
191         </refsect1>
192
193         <refsect1>
194                 <title>See Also</title>
195                 <para>
196                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
197                         <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
198                         <citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>
199                         <citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</manvolnum></citerefentry>
200                 </para>
201         </refsect1>
202
203 </refentry>