man: briefly document permitted user/group name syntax for User=/Group= and syusers.d (#6321)

As discussed here:

https://lists.freedesktop.org/archives/systemd-devel/2017-July/039237.html

1 files changed, 16 insertions, 17 deletions

diff --git a/man/sysusers.d.xml b/man/sysusers.d.xml
index 18ee3800d6..f232d9906d 100644
--- a/man/sysusers.d.xml
+++ b/man/sysusers.d.xml
@@ -53,15 +53,11 @@
   <refsect1>
     <title>Description</title>
 
-    <para><command>systemd-sysusers</command> uses the files from
-    <filename>sysusers.d</filename> directory to create system users
-    and groups at package installation or boot time. This tool may be
-    used to allocate system users and groups only, it is not useful
-    for creating non-system users and groups, as it accesses
-    <filename>/etc/passwd</filename> and
-    <filename>/etc/group</filename> directly, bypassing any more
-    complex user databases, for example any database involving NIS or
-    LDAP.</para>
+    <para><command>systemd-sysusers</command> uses the files from <filename>sysusers.d</filename> directory to create
+    system users and groups at package installation or boot time. This tool may be used to allocate system users and
+    groups only, it is not useful for creating non-system (i.e. regular, "human") users and groups, as it accesses
+    <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly, bypassing any more complex user
+    databases, for example any database involving NIS or LDAP.</para>
   </refsect1>
 
   <refsect1>
@@ -83,6 +79,9 @@ g input - -
 m authd input
 u root 0 "Superuser" /root</programlisting>
 
+    <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
+    commenting.</para>
+
     <refsect2>
       <title>Type</title>
 
@@ -134,14 +133,14 @@ u root 0 "Superuser" /root</programlisting>
     <refsect2>
       <title>Name</title>
 
-      <para>The name field specifies the user or group name. It should
-      be shorter than 31 characters and avoid any non-ASCII
-      characters, and not begin with a numeric character. It is
-      strongly recommended to pick user and group names that are
-      unlikely to clash with normal users created by the
-      administrator. A good scheme to guarantee this is by prefixing
-      all system and group names with the underscore, and avoiding too
-      generic names.</para>
+      <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
+      A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
+      A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
+      user/group name must have at least one character, and at most 31.</para>
+
+      <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
+      created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
+      underscore, and avoiding too generic names.</para>
 
       <para>For <varname>m</varname> lines, this field should contain
       the user name to add to a group.</para>