core: optionally create LOGIN_PROCESS or USER_PROCESS utmp entries

When generating utmp/wtmp entries, optionally add both LOGIN_PROCESS and
INIT_PROCESS entries or even all three of LOGIN_PROCESS, INIT_PROCESS
and USER_PROCESS entries, instead of just a single INIT_PROCESS entry.

With this change systemd may be used to not only invoke a getty directly
in a SysV-compliant way but alternatively also a login(1) implementation
or even forego getty and login entirely, and invoke arbitrary shells in
a way that they appear in who(1) or w(1).

This is preparation for a later commit that adds a "machinectl shell"
operation to invoke a shell in a container, in a way that is compatible
with who(1) and w(1).

1 files changed, 38 insertions, 3 deletions

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 8fd75d274e..cb11199ad3 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -1,3 +1,4 @@
+<?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">
 
@@ -911,10 +912,16 @@
         <term><varname>UtmpIdentifier=</varname></term>
 
         <listitem><para>Takes a four character identifier string for
-        an utmp/wtmp entry for this service. This should only be set
-        for services such as <command>getty</command> implementations
+        an <citerefentry
+        project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        and wtmp entry for this service. This should only be
+        set for services such as <command>getty</command>
+        implementations (such as <citerefentry
+        project='die-net'><refentrytitle>agetty</refentrytitle><manvolnum>8</manvolnum></citerefentry>)
         where utmp/wtmp entries must be created and cleared before and
-        after execution. If the configured string is longer than four
+        after execution, or for services that shall be executed as if
+        they were run by a <command>getty</command> process (see
+        below). If the configured string is longer than four
         characters, it is truncated and the terminal four characters
         are used. This setting interprets %I style string
         replacements. This setting is unset by default, i.e. no
@@ -923,6 +930,34 @@
       </varlistentry>
 
       <varlistentry>
+         <term><varname>UtmpMode=</varname></term>
+
+         <listitem><para>Takes one of <literal>init</literal>,
+         <literal>login</literal> or <literal>user</literal>. If
+         <varname>UtmpIdentifier=</varname> is set, controls which
+         type of <citerefentry
+         project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>/wtmp
+         entries for this service are generated. This setting has no
+         effect unless <varname>UtmpIdentifier=</varname> is set
+         too. If <literal>init</literal> is set, only an
+         <constant>INIT_PROCESS</constant> entry is generated and the
+         invoked process must implement a <command>getty</command>
+         compatible utmp/wtmp logic. If <literal>login</literal> is
+         set, first an <constant>INIT_PROCESS</constant> entry,
+         followed by an <constant>LOGIN_PROCESS</constant> entry is
+         generated. In this case the invoked process must implement a
+         <citerefentry
+         project='die-net'><refentrytitle>login</refentrytitle><manvolnum>1</manvolnum></citerefentry>-compatible
+         utmp/wtmp logic. If <literal>user</literal> is set, first an
+         <constant>INIT_PROCESS</constant> entry, then a
+         <constant>LOGIN_PROCESS</constant> entry and finally an
+         <constant>USER_PROCESS</constant> entry is generated. In this
+         case the invoked process may be any process that is suitable
+         to be run as session leader. Defaults to
+         <literal>init</literal>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><varname>SELinuxContext=</varname></term>
 
         <listitem><para>Set the SELinux security context of the