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1 | <?xml version="1.0"?> |
2 | <!--*-nxml-*--> | |
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3 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
4 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
0307f791 | 5 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
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6 | <refentry id="systemd-fstab-generator"> |
7 | ||
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8 | <refentryinfo> |
9 | <title>systemd-fstab-generator</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>systemd-fstab-generator</refentrytitle> | |
15 | <manvolnum>8</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>systemd-fstab-generator</refname> | |
20 | <refpurpose>Unit generator for /etc/fstab</refpurpose> | |
21 | </refnamediv> | |
22 | ||
23 | <refsynopsisdiv> | |
12b42c76 | 24 | <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator</filename></para> |
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25 | </refsynopsisdiv> |
26 | ||
27 | <refsect1> | |
28 | <title>Description</title> | |
29 | ||
30 | <para><filename>systemd-fstab-generator</filename> is a generator | |
31 | that translates <filename>/etc/fstab</filename> (see | |
3ba3a79d | 32 | <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
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33 | for details) into native systemd units early at boot and when |
34 | configuration of the system manager is reloaded. This will | |
35 | instantiate mount and swap units as necessary.</para> | |
36 | ||
37 | <para>The <varname>passno</varname> field is treated like a simple | |
38 | boolean, and the ordering information is discarded. However, if | |
39 | the root file system is checked, it is checked before all the | |
40 | other file systems.</para> | |
41 | ||
42 | <para>See | |
43 | <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
44 | and | |
45 | <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
46 | for more information about special <filename>/etc/fstab</filename> | |
47 | mount options this generator understands.</para> | |
48 | ||
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49 | <para>One special topic is handling of symbolic links. Historical init |
50 | implementations supported symlinks in <filename>/etc/fstab</filename>. | |
51 | Because mount units will refuse mounts where the target is a symbolic link, | |
52 | this generator will resolve any symlinks as far as possible when processing | |
53 | <filename>/etc/fstab</filename> in order to enhance backwards compatibility. | |
54 | If a symlink target does not exist at the time that this generator runs, it | |
55 | is assumed that the symlink target is the final target of the mount.</para> | |
56 | ||
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57 | <para><filename>systemd-fstab-generator</filename> implements |
58 | <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> | |
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59 | </refsect1> |
60 | ||
61 | <refsect1> | |
62 | <title>Kernel Command Line</title> | |
63 | ||
64 | <para><filename>systemd-fstab-generator</filename> understands the | |
65 | following kernel command line parameters:</para> | |
66 | ||
67 | <variablelist class='kernel-commandline-options'> | |
68 | ||
69 | <varlistentry> | |
70 | <term><varname>fstab=</varname></term> | |
71 | <term><varname>rd.fstab=</varname></term> | |
72 | ||
73 | <listitem><para>Takes a boolean argument. Defaults to | |
74 | <literal>yes</literal>. If <literal>no</literal>, causes the | |
91214a37 | 75 | generator to ignore any mounts or swap devices configured in |
798d3a52 | 76 | <filename>/etc/fstab</filename>. <varname>rd.fstab=</varname> |
91214a37 | 77 | is honored only by the initial RAM disk (initrd) while |
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78 | <varname>fstab=</varname> is honored by both the main system |
79 | and the initrd.</para></listitem> | |
80 | </varlistentry> | |
91214a37 | 81 | |
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82 | <varlistentry> |
83 | <term><varname>root=</varname></term> | |
84 | ||
85 | <listitem><para>Takes the root filesystem to mount in the | |
86 | initrd. <varname>root=</varname> is honored by the | |
87 | initrd.</para></listitem> | |
88 | </varlistentry> | |
91214a37 | 89 | |
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90 | <varlistentry> |
91 | <term><varname>rootfstype=</varname></term> | |
92 | ||
93 | <listitem><para>Takes the root filesystem type that will be | |
94 | passed to the mount command. <varname>rootfstype=</varname> is | |
95 | honored by the initrd.</para></listitem> | |
96 | </varlistentry> | |
91214a37 | 97 | |
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98 | <varlistentry> |
99 | <term><varname>rootflags=</varname></term> | |
100 | ||
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101 | <listitem><para>Takes the root filesystem mount options to use. <varname>rootflags=</varname> is |
102 | honored by the initrd.</para> | |
103 | ||
104 | <para>Note that unlike most kernel command line options this setting does not override settings made | |
105 | in configuration files (specifically: the mount option string in | |
106 | <filename>/etc/fstab</filename>). See | |
107 | <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem> | |
798d3a52 | 108 | </varlistentry> |
91214a37 | 109 | |
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110 | <varlistentry> |
111 | <term><varname>mount.usr=</varname></term> | |
112 | ||
113 | <listitem><para>Takes the <filename>/usr</filename> filesystem | |
114 | to be mounted by the initrd. If | |
115 | <varname>mount.usrfstype=</varname> or | |
116 | <varname>mount.usrflags=</varname> is set, then | |
117 | <varname>mount.usr=</varname> will default to the value set in | |
118 | <varname>root=</varname>.</para> | |
119 | ||
b938cb90 | 120 | <para>Otherwise, this parameter defaults to the |
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121 | <filename>/usr</filename> entry found in |
122 | <filename>/etc/fstab</filename> on the root filesystem.</para> | |
123 | ||
124 | <para><varname>mount.usr=</varname> is honored by the initrd. | |
125 | </para></listitem> | |
126 | </varlistentry> | |
91214a37 | 127 | |
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128 | <varlistentry> |
129 | <term><varname>mount.usrfstype=</varname></term> | |
130 | ||
131 | <listitem><para>Takes the <filename>/usr</filename> filesystem | |
132 | type that will be passed to the mount command. If | |
133 | <varname>mount.usr=</varname> or | |
134 | <varname>mount.usrflags=</varname> is set, then | |
135 | <varname>mount.usrfstype=</varname> will default to the value | |
136 | set in <varname>rootfstype=</varname>.</para> | |
137 | ||
b938cb90 | 138 | <para>Otherwise, this value will be read from the |
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139 | <filename>/usr</filename> entry in |
140 | <filename>/etc/fstab</filename> on the root filesystem.</para> | |
141 | ||
142 | <para><varname>mount.usrfstype=</varname> is honored by the | |
143 | initrd.</para></listitem> | |
144 | </varlistentry> | |
91214a37 | 145 | |
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146 | <varlistentry> |
147 | <term><varname>mount.usrflags=</varname></term> | |
148 | ||
149 | <listitem><para>Takes the <filename>/usr</filename> filesystem | |
150 | mount options to use. If <varname>mount.usr=</varname> or | |
151 | <varname>mount.usrfstype=</varname> is set, then | |
ff9b60f3 | 152 | <varname>mount.usrflags=</varname> will default to the value |
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153 | set in <varname>rootflags=</varname>.</para> |
154 | ||
b938cb90 | 155 | <para>Otherwise, this value will be read from the |
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156 | <filename>/usr</filename> entry in |
157 | <filename>/etc/fstab</filename> on the root filesystem.</para> | |
158 | ||
159 | <para><varname>mount.usrflags=</varname> is honored by the | |
160 | initrd.</para></listitem> | |
161 | </varlistentry> | |
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162 | |
163 | <varlistentry> | |
164 | <term><varname>systemd.volatile=</varname></term> | |
165 | ||
166 | <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the | |
167 | special value <option>state</option>.</para> | |
168 | ||
169 | <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in | |
170 | normal mode.</para> | |
171 | ||
172 | <para>If true the generator ensures | |
173 | <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
174 | is run as part of the initial RAM disk ("initrd"). This service changes the mount table before transitioning to | |
175 | the host system, so that a volatile memory file system (<literal>tmpfs</literal>) is used as root directory, | |
176 | with only <filename>/usr</filename> mounted into it from the configured root file system, in read-only | |
177 | mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and | |
178 | lost at shutdown, as <filename>/etc</filename> and <filename>/var</filename> will be served from the (initially | |
179 | unpopulated) volatile memory file system.</para> | |
180 | ||
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181 | <para>If set to <option>state</option> the generator will leave the root directory mount point unaltered, |
182 | however will mount a <literal>tmpfs</literal> file system to <filename>/var</filename>. In this mode the normal | |
183 | system configuration (i.e. the contents of <literal>/etc</literal>) is in effect (and may be modified during | |
184 | system runtime), however the system state (i.e. the contents of <literal>/var</literal>) is reset at boot and | |
185 | lost at shutdown.</para> | |
186 | ||
187 | <para>If this setting is set to <literal>overlay</literal> the root file system is set up as | |
188 | <literal>overlayfs</literal> mount combining the read-only root directory with a writable | |
189 | <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified | |
190 | nonetheless with all changes being lost at reboot.</para> | |
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191 | |
192 | <para>Note that in none of these modes the root directory, <filename>/etc</filename>, <filename>/var</filename> | |
193 | or any other resources stored in the root file system are physically removed. It's thus safe to boot a system | |
194 | that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para> | |
195 | ||
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196 | <para>Note that with the exception of <literal>overlay</literal> mode, enabling this setting will only work |
197 | correctly on operating systems that can boot up with only <filename>/usr</filename> mounted, and are able to | |
198 | automatically populate <filename>/etc</filename>, and also <filename>/var</filename> in case of | |
199 | <literal>systemd.volatile=yes</literal>.</para></listitem> | |
91214a37 | 200 | </varlistentry> |
567a5307 | 201 | |
202 | <varlistentry> | |
203 | <term><varname>systemd.swap</varname></term> | |
204 | ||
205 | <listitem><para>Takes a boolean argument or enables the option if specified | |
206 | without an argument. If disabled, causes the generator to ignore | |
207 | any swap devices configured in <filename>/etc/fstab</filename>. | |
208 | Defaults to enabled.</para></listitem> | |
209 | </varlistentry> | |
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210 | </variablelist> |
211 | </refsect1> | |
212 | ||
213 | <refsect1> | |
214 | <title>See Also</title> | |
215 | <para> | |
216 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
3ba3a79d | 217 | <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
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218 | <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
219 | <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
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220 | <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
221 | <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
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222 | </para> |
223 | </refsect1> | |
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224 | |
225 | </refentry> |