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systemd/man/systemd-volatile-root.service.xml

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fstab-generator: add support for volatile boots This adds support for a new kernel command line option "systemd.volatile=" that provides the same functionality that systemd-nspawn's --volatile= switch provides, but for host systems (i.e. systems booting with a kernel). It takes the same parameter and has the same effect. In order to implement systemd.volatile=yes a new service systemd-volatile-root.service is introduced that only runs in the initrd and rearranges the root directory as needed to become a tmpfs instance. Note that systemd.volatile=state is implemented different: it simply generates a var.mount unit file that is part of the normal boot and has no effect on the initrd execution. The way this is implemented ensures that other explicit configuration for /var can always override the effect of these options. Specifically, the var.mount unit is generated in the "late" generator directory, so that it only is in effect if nothing else overrides it.
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<?xml version="1.0"?>
<!--*-nxml-*-->
man: use same header for all files The "include" files had type "book" for some raeason. I don't think this is meaningful. Let's just use the same everywhere. $ perl -i -0pe 's^..DOCTYPE (book|refentry) PUBLIC "-//OASIS//DTD DocBook XML V4.[25]//EN"\s+"http^<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"\n "http^gms' man/*.xml
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
license: LGPL-2.1+ -> LGPL-2.1-or-later
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
fstab-generator: add support for volatile boots This adds support for a new kernel command line option "systemd.volatile=" that provides the same functionality that systemd-nspawn's --volatile= switch provides, but for host systems (i.e. systems booting with a kernel). It takes the same parameter and has the same effect. In order to implement systemd.volatile=yes a new service systemd-volatile-root.service is introduced that only runs in the initrd and rearranges the root directory as needed to become a tmpfs instance. Note that systemd.volatile=state is implemented different: it simply generates a var.mount unit file that is part of the normal boot and has no effect on the initrd execution. The way this is implemented ensures that other explicit configuration for /var can always override the effect of these options. Specifically, the var.mount unit is generated in the "late" generator directory, so that it only is in effect if nothing else overrides it.
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<refentry id="systemd-volatile-root.service">
<refentryinfo>
<title>systemd-volatile-root.service</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-volatile-root.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-volatile-root.service</refname>
<refname>systemd-volatile-root</refname>
<refpurpose>Make the root file system volatile</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-volatile-root.service</filename></para>
<para><filename>/usr/lib/systemd/systemd-volatile-root</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-volatile-root.service</filename> is a service that replaces the root directory with a
volatile memory file system (<literal>tmpfs</literal>), mounting the original (non-volatile)
man: use trailing slash on directories in more places
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<filename>/usr/</filename> inside it read-only. This way, vendor data from <filename>/usr/</filename> is available as
usual, but all configuration data in <filename>/etc/</filename>, all state data in <filename>/var/</filename> and all
fstab-generator: add support for volatile boots This adds support for a new kernel command line option "systemd.volatile=" that provides the same functionality that systemd-nspawn's --volatile= switch provides, but for host systems (i.e. systems booting with a kernel). It takes the same parameter and has the same effect. In order to implement systemd.volatile=yes a new service systemd-volatile-root.service is introduced that only runs in the initrd and rearranges the root directory as needed to become a tmpfs instance. Note that systemd.volatile=state is implemented different: it simply generates a var.mount unit file that is part of the normal boot and has no effect on the initrd execution. The way this is implemented ensures that other explicit configuration for /var can always override the effect of these options. Specifically, the var.mount unit is generated in the "late" generator directory, so that it only is in effect if nothing else overrides it.
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other resources stored directly under the root directory are reset on boot and lost at shutdown, enabling fully
stateless systems.</para>
<para>This service is only enabled if full volatile mode is selected, for example by specifying
<literal>systemd.volatile=yes</literal> on the kernel command line. This service runs only in the initial RAM disk
("initrd"), before the system transitions to the host's root directory. Note that this service is not used if
<literal>systemd.volatile=state</literal> is used, as in that mode the root directory is non-volatile.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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