man: add a new page with a general description of common syntax

We have a common parser, but for the user it might be
completely unobvious that the same general rules apply
to all those files. Let's add a page about the basic syntax
so that the more specific pages don't have to repeat those
details.

10 files changed, 142 insertions, 40 deletions

diff --git a/man/journal-remote.conf.xml b/man/journal-remote.conf.xml
index b21d38c5b8..24ade09023 100644
--- a/man/journal-remote.conf.xml
+++ b/man/journal-remote.conf.xml
@@ -48,7 +48,10 @@
     <title>Description</title>
 
     <para>These files configure various parameters of
-    <citerefentry><refentrytitle>systemd-journal-remote.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
+    <citerefentry><refentrytitle>systemd-journal-remote.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+    See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />
diff --git a/man/journal-upload.conf.xml b/man/journal-upload.conf.xml
index 846031d237..8e241370db 100644
--- a/man/journal-upload.conf.xml
+++ b/man/journal-upload.conf.xml
@@ -48,7 +48,10 @@
     <title>Description</title>
 
     <para>These files configure various parameters of
-    <citerefentry><refentrytitle>systemd-journal-upload.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
+    <citerefentry><refentrytitle>systemd-journal-upload.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+    See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />
diff --git a/man/journald.conf.xml b/man/journald.conf.xml
index a4ae1af170..96422a3a2f 100644
--- a/man/journald.conf.xml
+++ b/man/journald.conf.xml
@@ -47,9 +47,11 @@
   <refsect1>
     <title>Description</title>
 
-    <para>These files configure various parameters of the systemd
-    journal service,
-    <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
+    <para>These files configure various parameters of the systemd journal service,
+    <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+    See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
 
   </refsect1>
 
diff --git a/man/logind.conf.xml b/man/logind.conf.xml
index 6118aa5e3d..9e21c0b218 100644
--- a/man/logind.conf.xml
+++ b/man/logind.conf.xml
@@ -50,10 +50,10 @@
   <refsect1>
     <title>Description</title>
 
-    <para>These files configure various parameters of the systemd
-    login manager,
-    <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
-    </para>
+    <para>These files configure various parameters of the systemd login manager,
+    <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>. See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />
diff --git a/man/rules/meson.build b/man/rules/meson.build
index 173ed8f976..9b57f10cc0 100644
--- a/man/rules/meson.build
+++ b/man/rules/meson.build
@@ -699,6 +699,7 @@ manpages = [
  ['systemd.socket', '5', [], ''],
  ['systemd.special', '7', [], ''],
  ['systemd.swap', '5', [], ''],
+ ['systemd.syntax', '7', [], ''],
  ['systemd.target', '5', [], ''],
  ['systemd.time', '7', [], ''],
  ['systemd.timer', '5', [], ''],
diff --git a/man/systemd-sleep.conf.xml b/man/systemd-sleep.conf.xml
index 3652c2066b..84e52d3bd8 100644
--- a/man/systemd-sleep.conf.xml
+++ b/man/systemd-sleep.conf.xml
@@ -109,7 +109,10 @@
     <citerefentry><refentrytitle>systemd-sleep</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     when
     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    attempts to suspend or hibernate the machine.</para>
+    attempts to suspend or hibernate the machine.
+    See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />
diff --git a/man/systemd-system.conf.xml b/man/systemd-system.conf.xml
index b31eb11f8c..36bd4aaee5 100644
--- a/man/systemd-system.conf.xml
+++ b/man/systemd-system.conf.xml
@@ -63,7 +63,9 @@
     <filename>user.conf</filename> and the files in
     <filename>user.conf.d</filename> directories. These configuration
     files contain a few settings controlling basic manager
-    operations.</para>
+    operations. See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />
diff --git a/man/systemd.syntax.xml b/man/systemd.syntax.xml
new file mode 100644
index 0000000000..bafe817a9b
--- /dev/null
+++ b/man/systemd.syntax.xml
@@ -0,0 +1,107 @@
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
+<!ENTITY % entities SYSTEM "custom-entities.ent" >
+%entities;
+]>
+
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
+
+<refentry id="systemd.syntax">
+
+  <refentryinfo>
+    <title>systemd.syntax</title>
+    <productname>systemd</productname>
+
+    <authorgroup>
+      <author>
+        <contrib>A. U. Thor</contrib>
+        <firstname>Zbigniew</firstname>
+        <surname>Jędrzejewski-Szmek</surname>
+        <email>zbyszek@in.waw.pl</email>
+      </author>
+    </authorgroup>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>systemd.syntax</refentrytitle>
+    <manvolnum>7</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>systemd.syntax</refname>
+    <refpurpose>General syntax of systemd configuration files</refpurpose>
+  </refnamediv>
+
+  <refsect1>
+    <title>Introduction</title>
+
+    <para>This page describes the basic principles of configuration files used by
+    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    and related programs for:
+    <itemizedlist>
+      <listitem><para>systemd unit files, see
+      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry></para></listitem>
+
+      <listitem><para>daemon config files, see
+      <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      </para></listitem>
+    </itemizedlist>
+    </para>
+
+    <para>The syntax is inspired by
+    <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
+    <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
+    <filename>.ini</filename> files.
+    </para>
+
+    <para>Each file is a plain text file divided into sections, with configuration entries in the
+    style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
+    Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
+    ignored, which may be used for commenting.</para>
+
+    <para>Lines ending in a backslash are concatenated with the following line while reading and the
+    backslash is replaced by a space character. This may be used to wrap long lines. The limit on
+    line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
+    use multiple directives, variable substitution, or other mechanism as appropriate for the given
+    file type.</para>
+
+    <example><programlisting>[Section A]
+KeyOne=value 1
+KeyTwo=value 2
+
+# a comment
+
+[Section B]
+Setting="something" "some thing" "…"
+KeyTwo=value 2 \
+       value 2 continued
+</programlisting></example>
+
+    <para>Various settings are allowed to be specified more than once, in which case the
+    interpretation depends on the setting. Often, multiple settings form a list, and setting to an
+    empty value "resets", which means that previous assignments are ignored. When this is allowed,
+    it is mentioned in the description of the setting. Note that using multiple assignments to the
+    same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
+    file format.</para>
+  </refsect1>
+
+</refentry>
diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 2baf9d17e8..5ea615d998 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -83,18 +83,13 @@
   <refsect1>
     <title>Description</title>
 
-    <para>A unit configuration file encodes information about a
-    service, a socket, a device, a mount point, an automount point, a
-    swap file or partition, a start-up target, a watched file system
-    path, a timer controlled and supervised by
-    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
-    a resource management slice or
-    a group of externally created processes. The syntax is inspired by
-    <ulink
-    url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
-    Desktop Entry Specification</ulink> <filename>.desktop</filename>
-    files, which are in turn inspired by Microsoft Windows
-    <filename>.ini</filename> files.</para>
+    <para>A unit file is a plain text ini-style file that encodes information about a service, a
+    socket, a device, a mount point, an automount point, a swap file or partition, a start-up
+    target, a watched file system path, a timer controlled and supervised by
+    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, a
+    resource management slice or a group of externally created processes. See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
 
     <para>This man page lists the common configuration options of all
     the unit types. These options need to be configured in the [Unit]
@@ -117,15 +112,6 @@
     <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
     </para>
 
-    <para>Various settings are allowed to be specified more than once,
-    in which case the interpretation depends on the setting. Often,
-    multiple settings form a list, and setting to an empty value
-    "resets", which means that previous assignments are ignored. When
-    this is allowed, it is mentioned in the description of the
-    setting. Note that using multiple assignments to the same value
-    makes the unit file incompatible with parsers for the XDG
-    <filename>.desktop</filename> file format.</para>
-
     <para>Unit files are loaded from a set of paths determined during
     compilation, described in the next section.</para>
 
@@ -154,11 +140,6 @@
     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 
-    <para>Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
-    ignored. This may be used for commenting. Lines ending in a backslash are concatenated with the
-    following line while reading and the backslash is replaced by a space character. This may be
-    used to wrap long lines.</para>
-
     <para>Units can be aliased (have an alternative name), by creating a symlink from the new name
     to the existing name in one of the unit search paths. For example,
     <filename>systemd-networkd.service</filename> has the alias
diff --git a/man/timesyncd.conf.xml b/man/timesyncd.conf.xml
index c6dbb1ef4e..9292373bd9 100644
--- a/man/timesyncd.conf.xml
+++ b/man/timesyncd.conf.xml
@@ -47,9 +47,9 @@
   <refsect1>
     <title>Description</title>
 
-    <para>These configuration files control NTP network time
-    synchronization.</para>
-
+    <para>These configuration files control NTP network time synchronization. See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
   </refsect1>
 
   <xi:include href="standard-conf.xml" xpointer="main-conf" />