systemd/man/localtime.xml
Luca BRUNO 3d909037e3 man/localtime: document default timezone
This explicitly documents the default `UTC` timezone which is used
by systemd and (other softwares) when `/etc/localtime` is not present.

Ref: https://github.com/systemd/systemd/blob/v247/src/basic/time-util.c#L1460-L1469
2020-12-21 12:39:18 +00:00

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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="localtime">
<refentryinfo>
<title>localtime</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>localtime</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>localtime</refname>
<refpurpose>Local timezone configuration file</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/localtime</filename> -&gt; <filename>../usr/share/zoneinfo/…</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The <filename>/etc/localtime</filename> file configures the
system-wide timezone of the local system that is used by
applications for presentation to the user. It should be an
absolute or relative symbolic link pointing to
<filename>/usr/share/zoneinfo/</filename>, followed by a timezone
identifier such as <literal>Europe/Berlin</literal> or
<literal>Etc/UTC</literal>. The resulting link should lead to the
corresponding binary
<citerefentry project='man-pages'><refentrytitle>tzfile</refentrytitle><manvolnum>5</manvolnum></citerefentry>
timezone data for the configured timezone.</para>
<para>Because the timezone identifier is extracted from the
symlink target name of <filename>/etc/localtime</filename>, this
file may not be a normal file or hardlink.</para>
<para>If <filename>/etc/localtime</filename> is missing, the
default <literal>UTC</literal> timezone is used.</para>
<para>The timezone may be overridden for individual programs by
using the <varname>$TZ</varname> environment variable. See
<citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
<para>You may use
<citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
to change the settings of this file from the command line during
runtime. Use
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
to initialize the time zone on mounted (but not booted) system
images.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>tzset</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>localtime</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>timedatectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-timedated.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>