man: mention that drop-in files are merged in alphanumeric order

This addresses the request in https://github.com/systemd/systemd/issues/19467#issuecomment-829332877.

4 files changed, 20 insertions, 17 deletions

diff --git a/man/systemd.link.xml b/man/systemd.link.xml
index 34b56df937..4650b8f852 100644
--- a/man/systemd.link.xml
+++ b/man/systemd.link.xml
@@ -47,9 +47,9 @@
 
     <para>Along with the link file <filename>foo.link</filename>, a "drop-in" directory
     <filename>foo.link.d/</filename> may exist. All files with the suffix <literal>.conf</literal>
-    from this directory will be parsed after the file itself is parsed. This is useful to alter or add
-    configuration settings, without having to modify the main configuration file. Each drop-in file
-    must have appropriate section headers.</para>
+    from this directory will be merged in the alphanumeric order and parsed after the main file itself
+    has been parsed. This is useful to alter or add configuration settings, without having to modify
+    the main configuration file. Each drop-in file must have appropriate section headers.</para>
 
     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
diff --git a/man/systemd.netdev.xml b/man/systemd.netdev.xml
index d93ee8bb30..11442f2b82 100644
--- a/man/systemd.netdev.xml
+++ b/man/systemd.netdev.xml
@@ -52,9 +52,9 @@
 
     <para>Along with the netdev file <filename>foo.netdev</filename>, a "drop-in" directory
     <filename>foo.netdev.d/</filename> may exist. All files with the suffix <literal>.conf</literal>
-    from this directory will be parsed after the file itself is parsed. This is useful to alter or
-    add configuration settings, without having to modify the main configuration file. Each drop-in
-    file must have appropriate section headers.</para>
+    from this directory will be merged in the alphanumeric order and parsed after the main file itself
+    has been parsed. This is useful to alter or add configuration settings, without having to modify
+    the main configuration file. Each drop-in file must have appropriate section headers.</para>
 
     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index 64bd036e0c..beddcbe617 100644
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -51,9 +51,10 @@
 
     <para>Along with the network file <filename>foo.network</filename>, a "drop-in" directory
     <filename>foo.network.d/</filename> may exist. All files with the suffix
-    <literal>.conf</literal> from this directory will be parsed after the file itself is
-    parsed. This is useful to alter or add configuration settings, without having to modify the main
-    configuration file. Each drop-in file must have appropriate section headers.</para>
+    <literal>.conf</literal> from this directory will be merged in the alphanumeric order and parsed
+    after the main file itself has been parsed. This is useful to alter or add configuration settings,
+    without having to modify the main configuration file. Each drop-in file must have appropriate
+    section headers.</para>
 
     <para>In addition to <filename>/etc/systemd/network</filename>, drop-in <literal>.d</literal>
     directories can be placed in <filename>/usr/lib/systemd/network</filename> or
diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index b7a5ec0362..913cad05b4 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -184,14 +184,16 @@
     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 
     <para>Along with a unit file <filename>foo.service</filename>, a "drop-in" directory
-    <filename>foo.service.d/</filename> may exist. All files with the suffix <literal>.conf</literal> from this
-    directory will be parsed after the unit file itself is parsed. This is useful to alter or add configuration
-    settings for a unit, without having to modify unit files. Drop-in files must contain appropriate section
-    headers. For instantiated units, this logic will first look for the instance <literal>.d/</literal> subdirectory
-    (e.g. <literal>foo@bar.service.d/</literal>) and read its <literal>.conf</literal> files, followed by the template
-    <literal>.d/</literal> subdirectory (e.g. <literal>foo@.service.d/</literal>) and the <literal>.conf</literal>
-    files there. Moreover for unit names containing dashes (<literal>-</literal>), the set of directories generated by
-    repeatedly truncating the unit name after all dashes is searched too. Specifically, for a unit name
+    <filename>foo.service.d/</filename> may exist. All files with the suffix
+    <literal>.conf</literal> from this directory will be merged in the alphanumeric order and parsed
+    after the main unit file itself has been parsed. This is useful to alter or add configuration
+    settings for a unit, without having to modify unit files. Each drop-in file must contain appropriate
+    section headers. For instantiated units, this logic will first look for the instance
+    <literal>.d/</literal> subdirectory (e.g. <literal>foo@bar.service.d/</literal>) and read its
+    <literal>.conf</literal> files, followed by the template <literal>.d/</literal> subdirectory (e.g.
+    <literal>foo@.service.d/</literal>) and the <literal>.conf</literal> files there. Moreover for unit
+    names containing dashes (<literal>-</literal>), the set of directories generated by repeatedly
+    truncating the unit name after all dashes is searched too. Specifically, for a unit name
     <filename>foo-bar-baz.service</filename> not only the regular drop-in directory
     <filename>foo-bar-baz.service.d/</filename> is searched but also both <filename>foo-bar-.service.d/</filename> and
     <filename>foo-.service.d/</filename>. This is useful for defining common drop-ins for a set of related units, whose