]>
Commit | Line | Data |
---|---|---|
7a87fb61 LP |
1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> | |
5 | ||
6 | <refentry id="systemd-sysext" | |
7 | xmlns:xi="http://www.w3.org/2001/XInclude"> | |
8 | ||
9 | <refentryinfo> | |
10 | <title>systemd-sysext</title> | |
11 | <productname>systemd</productname> | |
12 | </refentryinfo> | |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>systemd-sysext</refentrytitle> | |
16 | <manvolnum>8</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>systemd-sysext</refname> | |
21 | <refname>systemd-sysext.service</refname> | |
1f4f1666 | 22 | <refname>systemd-confext</refname> |
23 | <refname>systemd-confext.service</refname> | |
7a87fb61 LP |
24 | <refpurpose>Activates System Extension Images</refpurpose> |
25 | </refnamediv> | |
26 | ||
27 | <refsynopsisdiv> | |
28 | <cmdsynopsis> | |
29 | <command>systemd-sysext</command> | |
30 | <arg choice="opt" rep="repeat">OPTIONS</arg> | |
782e41ab | 31 | <arg choice="plain">COMMAND</arg> |
7a87fb61 LP |
32 | </cmdsynopsis> |
33 | ||
34 | <para><literallayout><filename>systemd-sysext.service</filename></literallayout></para> | |
35 | ||
1f4f1666 | 36 | <cmdsynopsis> |
37 | <command>systemd-confext</command> | |
38 | <arg choice="opt" rep="repeat">OPTIONS</arg> | |
39 | <arg choice="plain">COMMAND</arg> | |
40 | </cmdsynopsis> | |
41 | ||
42 | <para><literallayout><filename>systemd-confext.service</filename></literallayout></para> | |
43 | ||
7a87fb61 LP |
44 | </refsynopsisdiv> |
45 | ||
46 | <refsect1> | |
47 | <title>Description</title> | |
48 | ||
49 | <para><command>systemd-sysext</command> activates/deactivates system extension images. System extension | |
50 | images may – dynamically at runtime — extend the <filename>/usr/</filename> and | |
51 | <filename>/opt/</filename> directory hierarchies with additional files. This is particularly useful on | |
52 | immutable system images where a <filename>/usr/</filename> and/or <filename>/opt/</filename> hierarchy | |
53 | residing on a read-only file system shall be extended temporarily at runtime without making any | |
54 | persistent modifications.</para> | |
55 | ||
56 | <para>System extension images should contain files and directories similar in fashion to regular | |
57 | operating system tree. When one or more system extension images are activated, their | |
58 | <filename>/usr/</filename> and <filename>/opt/</filename> hierarchies are combined via | |
59 | <literal>overlayfs</literal> with the same hierarchies of the host OS, and the host | |
be0d27ee | 60 | <filename>/usr/</filename> and <filename>/opt/</filename> overmounted with it ("merging"). When they are |
7a87fb61 LP |
61 | deactivated, the mount point is disassembled — again revealing the unmodified original host version of |
62 | the hierarchy ("unmerging"). Merging thus makes the extension's resources suddenly appear below the | |
63 | <filename>/usr/</filename> and <filename>/opt/</filename> hierarchies as if they were included in the | |
64 | base OS image itself. Unmerging makes them disappear again, leaving in place only the files that were | |
65 | shipped with the base OS image itself.</para> | |
66 | ||
67 | <para>Files and directories contained in the extension images outside of the <filename>/usr/</filename> | |
68 | and <filename>/opt/</filename> hierarchies are <emphasis>not</emphasis> merged, and hence have no effect | |
60bb6caa LB |
69 | when included in a system extension image. In particular, files in the <filename>/etc/</filename> and |
70 | <filename>/var/</filename> included in a system extension image will <emphasis>not</emphasis> appear in | |
71 | the respective hierarchies after activation.</para> | |
7a87fb61 LP |
72 | |
73 | <para>System extension images are strictly read-only, and the host <filename>/usr/</filename> and | |
74 | <filename>/opt/</filename> hierarchies become read-only too while they are activated.</para> | |
75 | ||
76 | <para>System extensions are supposed to be purely additive, i.e. they are supposed to include only files | |
77 | that do not exist in the underlying basic OS image. However, the underlying mechanism (overlayfs) also | |
566e4b3a | 78 | allows overlaying or removing files, but it is recommended not to make use of this.</para> |
7a87fb61 LP |
79 | |
80 | <para>System extension images may be provided in the following formats:</para> | |
81 | ||
82 | <orderedlist> | |
83 | <listitem><para>Plain directories or btrfs subvolumes containing the OS tree</para></listitem> | |
84 | <listitem><para>Disk images with a GPT disk label, following the <ulink | |
db811444 | 85 | url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink></para></listitem> |
09e917ea LP |
86 | <listitem><para>Disk images lacking a partition table, with a naked Linux file system (e.g. erofs, |
87 | squashfs or ext4)</para></listitem> | |
7a87fb61 LP |
88 | </orderedlist> |
89 | ||
90 | <para>These image formats are the same ones that | |
91 | <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
01ae74c8 | 92 | supports via its <option>--directory=</option>/<option>--image=</option> switches and those that the |
7a87fb61 LP |
93 | service manager supports via <option>RootDirectory=</option>/<option>RootImage=</option>. Similar to |
94 | them they may optionally carry Verity authentication information.</para> | |
95 | ||
0d6e0ade | 96 | <para>System extensions are searched for in the directories |
de862276 LB |
97 | <filename>/etc/extensions/</filename>, <filename>/run/extensions/</filename> and |
98 | <filename>/var/lib/extensions/</filename>. The first two listed directories are not suitable for | |
7a87fb61 LP |
99 | carrying large binary images, however are still useful for carrying symlinks to them. The primary place |
100 | for installing system extensions is <filename>/var/lib/extensions/</filename>. Any directories found in | |
0d6e0ade | 101 | these search directories are considered directory based extension images; any files with the |
9ea81191 LP |
102 | <filename>.raw</filename> suffix are considered disk image based extension images. When invoked in the |
103 | initrd, the additional directory <filename>/.extra/sysext/</filename> is included in the directories that | |
104 | are searched for extension images. Note however, that by default a tighter image policy applies to images | |
105 | found there, though, see below. This directory is populated by | |
106 | <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> with | |
107 | extension images found in the system's EFI System Partition.</para> | |
7a87fb61 LP |
108 | |
109 | <para>During boot OS extension images are activated automatically, if the | |
110 | <filename>systemd-sysext.service</filename> is enabled. Note that this service runs only after the | |
6a15846d | 111 | underlying file systems where system extensions may be located have been mounted. This means they are not |
7a87fb61 LP |
112 | suitable for shipping resources that are processed by subsystems running in earliest boot. Specifically, |
113 | OS extension images are not suitable for shipping system services or | |
114 | <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
8b9f0921 ZJS |
115 | definitions. See the <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable Services Documentation</ulink> |
116 | for a simple mechanism for shipping system services in disk images, in a similar fashion to OS | |
117 | extensions. Note the different isolation on these two mechanisms: while system extension directly extend | |
118 | the underlying OS image with additional files that appear in a way very similar to as if they were | |
119 | shipped in the OS image itself and thus imply no security isolation, portable services imply service | |
120 | level sandboxing in one way or another. The <filename>systemd-sysext.service</filename> service is | |
121 | guaranteed to finish start-up before <filename>basic.target</filename> is reached; i.e. at the time | |
122 | regular services initialize (those which do not use <varname>DefaultDependencies=no</varname>), the files | |
123 | and directories system extensions provide are available in <filename>/usr/</filename> and | |
124 | <filename>/opt/</filename> and may be accessed.</para> | |
7a87fb61 LP |
125 | |
126 | <para>Note that there is no concept of enabling/disabling installed system extension images: all | |
1abe15fe KL |
127 | installed extension images are automatically activated at boot. However, you can place an empty directory |
128 | named like the extension (no <filename>.raw</filename>) in <filename>/etc/extensions/</filename> to "mask" | |
129 | an extension with the same name in a system folder with lower precedence.</para> | |
7a87fb61 | 130 | |
60bb6caa LB |
131 | <para>A simple mechanism for version compatibility is enforced: a system extension image must carry a |
132 | <filename>/usr/lib/extension-release.d/extension-release.<replaceable>$name</replaceable></filename> | |
133 | file, which must match its image name, that is compared with the host <filename>os-release</filename> | |
ab4d43c5 KL |
134 | file: the contained <varname>ID=</varname> fields have to match unless <literal>_any</literal> is set |
135 | for the extension. If the extension <varname>ID=</varname> is not <literal>_any</literal>, the | |
136 | <varname>SYSEXT_LEVEL=</varname> field (if defined) has to match. If the latter is not defined, the | |
16c1ca0d KL |
137 | <varname>VERSION_ID=</varname> field has to match instead. If the extension defines the |
138 | <varname>ARCHITECTURE=</varname> field and the value is not <literal>_any</literal> it has to match the kernel's | |
139 | architecture reported by <citerefentry><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
140 | but the used architecture identifiers are the same as for <varname>ConditionArchitecture=</varname> | |
141 | described in <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. | |
142 | System extensions should not ship a <filename>/usr/lib/os-release</filename> file (as that would be merged | |
143 | into the host <filename>/usr/</filename> tree, overriding the host OS version data, which is not desirable). | |
144 | The <filename>extension-release</filename> file follows the same format and semantics, and carries the same | |
60bb6caa LB |
145 | content, as the <filename>os-release</filename> file of the OS, but it describes the resources carried |
146 | in the extension image.</para> | |
1f4f1666 | 147 | |
148 | <para>The <command>systemd-confext</command> concept follows the same principle as the | |
149 | <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
150 | functionality but instead of working on <filename>/usr</filename> and <filename>/opt</filename>, | |
151 | <command>confext</command> will extend only <filename>/etc</filename>. Files and directories contained | |
152 | in the confext images outside of the <filename>/etc/</filename> hierarchy are <emphasis>not</emphasis> | |
153 | merged, and hence have no effect when included in the image. Formats for these images are of the | |
154 | same as sysext images.</para> | |
155 | ||
156 | <para>Confexts are looked for in the directories <filename>/run/confexts/</filename>, | |
157 | <filename>/var/lib/confexts/</filename>, <filename>/usr/lib/confexts/</filename> and | |
158 | <filename>/usr/local/lib/confexts/</filename>. The first two listed directories are not suitable for | |
159 | carrying large binary images, however are still useful for carrying symlinks to them. The primary place | |
160 | for installing system extensions is <filename>/var/lib/confexts/</filename>. Any directories found in | |
161 | these search directories are considered directory based confext images, any files with the | |
162 | <filename>.raw</filename> suffix are considered disk image based confext images.</para> | |
163 | ||
164 | <para>Again, just like sysext images, the confext images will contain a | |
165 | <filename>/etc/extension-release.d/extension-release.<replaceable>$name</replaceable></filename> | |
166 | file, which must match the image name (with the usual escape hatch of xattr), and again with content | |
167 | being one or more of <varname>ID=</varname>, <varname>VERSION_ID=</varname>, and | |
168 | <varname>CONFEXT_LEVEL</varname>. Confext images will then be checked and matched against the | |
169 | base OS layer.</para> | |
7a87fb61 LP |
170 | </refsect1> |
171 | ||
172 | <refsect1> | |
173 | <title>Uses</title> | |
174 | ||
175 | <para>The primary use case for system images are immutable environments where debugging and development | |
be0d27ee ZJS |
176 | tools shall optionally be made available, but not included in the immutable base OS image itself (e.g. |
177 | <citerefentry project='man-pages'><refentrytitle>strace</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
178 | and | |
179 | <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
180 | shall be an optionally installable addition in order to make debugging/development easier). System | |
181 | extension images should not be misunderstood as a generic software packaging framework, as no dependency | |
182 | scheme is available: system extensions should carry all files they need themselves, except for those | |
183 | already shipped in the underlying host system image. Typically, system extension images are built at the | |
184 | same time as the base OS image — within the same build system.</para> | |
7a87fb61 LP |
185 | |
186 | <para>Another use case for the system extension concept is temporarily overriding OS supplied resources | |
187 | with newer ones, for example to install a locally compiled development version of some low-level | |
188 | component over the immutable OS image without doing a full OS rebuild or modifying the nominally | |
189 | immutable image. (e.g. "install" a locally built package with <command>DESTDIR=/var/lib/extensions/mytest | |
301265ea | 190 | make install && systemd-sysext refresh</command>, making it available in |
7a87fb61 LP |
191 | <filename>/usr/</filename> as if it was installed in the OS image itself.) This case works regardless if |
192 | the underlying host <filename>/usr/</filename> is managed as immutable disk image or is a traditional | |
193 | package manager controlled (i.e. writable) tree.</para> | |
1f4f1666 | 194 | |
195 | <para>For the confext case, the OSConfig project aims to perform runtime reconfiguration of OS services. | |
196 | Sometimes, there is a need to swap certain configuration parameter values or restart only a specific | |
197 | service without deployment of new code or a complete OS deployment. In other words, we want to be able | |
198 | to tie the most frequently configured options to runtime updateable flags that can be changed without a | |
199 | system reboot. This will help reduce servicing times when there is a need for changing the OS configuration.</para></refsect1> | |
7a87fb61 LP |
200 | |
201 | <refsect1> | |
202 | <title>Commands</title> | |
203 | ||
1f4f1666 | 204 | <para>The following commands are understood by both the sysext and confext concepts:</para> |
7a87fb61 LP |
205 | |
206 | <variablelist> | |
207 | <varlistentry> | |
301265ea LP |
208 | <term><option>status</option></term> |
209 | ||
210 | <listitem><para>When invoked without any command verb, or when <option>status</option> is specified | |
1f4f1666 | 211 | the current merge status is shown, separately (for both <filename>/usr/</filename> and |
212 | <filename>/opt/</filename> of sysext and for <filename>/etc/</filename> of confext).</para></listitem> | |
301265ea LP |
213 | </varlistentry> |
214 | ||
215 | <varlistentry> | |
216 | <term><option>merge</option></term> | |
7a87fb61 LP |
217 | <listitem><para>Merges all currently installed system extension images into |
218 | <filename>/usr/</filename> and <filename>/opt/</filename>, by overmounting these hierarchies with an | |
219 | <literal>overlayfs</literal> file system combining the underlying hierarchies with those included in | |
1f4f1666 | 220 | the extension images. This command will fail if the hierarchies are already merged. For confext, the merge |
221 | happens into the <filename>/etc/</filename> directory instead.</para></listitem> | |
7a87fb61 LP |
222 | </varlistentry> |
223 | ||
224 | <varlistentry> | |
301265ea | 225 | <term><option>unmerge</option></term> |
7a87fb61 | 226 | <listitem><para>Unmerges all currently installed system extension images from |
1f4f1666 | 227 | <filename>/usr/</filename> and <filename>/opt/</filename> for sysext and <filename>/etc/</filename>, |
228 | for confext, by unmounting the <literal>overlayfs</literal> file systems created by <option>merge</option> | |
7a87fb61 LP |
229 | prior.</para></listitem> |
230 | </varlistentry> | |
231 | ||
232 | <varlistentry> | |
301265ea LP |
233 | <term><option>refresh</option></term> |
234 | <listitem><para>A combination of <option>unmerge</option> and <option>merge</option>: if already | |
7a87fb61 LP |
235 | mounted the existing <literal>overlayfs</literal> instance is unmounted temporarily, and then |
236 | replaced by a new version. This command is useful after installing/removing system extension images, | |
237 | in order to update the <literal>overlayfs</literal> file system accordingly. If no system extensions | |
1f4f1666 | 238 | are installed when this command is executed, the equivalent of <option>unmerge</option> is executed, |
239 | without establishing any new <literal>overlayfs</literal> instance. | |
240 | Note that currently there's a brief moment where neither the old nor the new <literal>overlayfs</literal> | |
241 | file system is mounted. This implies that all resources supplied by a system extension will briefly | |
242 | disappear — even if it exists continuously during the refresh operation.</para></listitem> | |
7a87fb61 LP |
243 | </varlistentry> |
244 | ||
245 | <varlistentry> | |
301265ea | 246 | <term><option>list</option></term> |
7a87fb61 LP |
247 | |
248 | <listitem><para>A brief list of installed extension images is shown.</para></listitem> | |
249 | </varlistentry> | |
250 | ||
251 | <xi:include href="standard-options.xml" xpointer="help" /> | |
252 | <xi:include href="standard-options.xml" xpointer="version" /> | |
253 | </variablelist> | |
7a87fb61 LP |
254 | </refsect1> |
255 | ||
256 | <refsect1> | |
257 | <title>Options</title> | |
258 | ||
259 | <variablelist> | |
260 | <varlistentry> | |
261 | <term><option>--root=</option></term> | |
262 | ||
263 | <listitem><para>Operate relative to the specified root directory, i.e. establish the | |
264 | <literal>overlayfs</literal> mount not on the top-level host <filename>/usr/</filename> and | |
1f4f1666 | 265 | <filename>/opt/</filename> hierarchies for sysext or <filename>/etc/</filename> for confext, |
266 | but below some specified root directory.</para></listitem> | |
7a87fb61 LP |
267 | </varlistentry> |
268 | ||
301265ea LP |
269 | <varlistentry> |
270 | <term><option>--force</option></term> | |
271 | ||
272 | <listitem><para>When merging system extensions into <filename>/usr/</filename> and | |
1f4f1666 | 273 | <filename>/opt/</filename> for sysext and <filename>/etc/</filename> for confext, |
274 | ignore version incompatibilities, i.e. force merging regardless of | |
275 | whether the version information included in the images matches the host or not.</para></listitem> | |
301265ea LP |
276 | </varlistentry> |
277 | ||
9ea81191 LP |
278 | <varlistentry> |
279 | <term><option>--image-policy=<replaceable>policy</replaceable></option></term> | |
280 | ||
281 | <listitem><para>Takes an image policy string as argument, as per | |
282 | <citerefentry><refentrytitle>systemd.image-policy</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The | |
283 | policy is enforced when operating on system extension disk images. If not specified defaults to | |
284 | <literal>root=verity+signed+encrypted+unprotected+absent:usr=verity+signed+encrypted+unprotected+absent</literal>, | |
285 | i.e. only the root and <filename>/usr/</filename> file systems in the image are used. When run in the | |
286 | initrd and operating on a system extension image stored in the <filename>/.extra/sysext/</filename> | |
287 | directory a slightly stricter policy is used by default: | |
288 | <literal>root=signed+absent:usr=signed+absent</literal>, see above for details.</para></listitem> | |
289 | </varlistentry> | |
290 | ||
7a87fb61 | 291 | <xi:include href="standard-options.xml" xpointer="no-pager" /> |
16a36b56 | 292 | <xi:include href="standard-options.xml" xpointer="no-legend" /> |
8d0d1a30 | 293 | <xi:include href="standard-options.xml" xpointer="json" /> |
7a87fb61 LP |
294 | </variablelist> |
295 | </refsect1> | |
296 | ||
297 | <refsect1> | |
298 | <title>Exit status</title> | |
299 | ||
300 | <para>On success, 0 is returned.</para> | |
301 | </refsect1> | |
302 | ||
303 | <refsect1> | |
304 | <title>See Also</title> | |
305 | <para> | |
306 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
9ea81191 LP |
307 | <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
308 | <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
7a87fb61 LP |
309 | </para> |
310 | </refsect1> | |
311 | ||
312 | </refentry> |