Remove snapshot unit type

Snapshots were never useful or used for anything. Many systemd
developers that I spoke to at systemd.conf2015, didn't even know they
existed, so it is fairly safe to assume that this type can be deleted
without harm.

The fundamental problem with snapshots is that the state of the system
is dynamic, devices come and go, users log in and out, timers fire...
and restoring all units to some state from the past would "undo"
those changes, which isn't really possible.

Tested by creating a snapshot, running the new binary, and checking
that the transition did not cause errors, and the snapshot is gone,
and snapshots cannot be created anymore.

New systemctl says:
Unknown operation snapshot.
Old systemctl says:
Failed to create snapshot: Support for snapshots has been removed.

IgnoreOnSnaphost settings are warned about and ignored:
Support for option IgnoreOnSnapshot= has been removed and it is ignored

http://lists.freedesktop.org/archives/systemd-devel/2015-November/034872.html

4 files changed, 2 insertions, 144 deletions

diff --git a/man/systemctl.xml b/man/systemctl.xml
index 2fe24fd139..173c463d12 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -1342,46 +1342,6 @@ kobject-uevent 1 systemd-udevd-kernel.socket systemd-udevd.service
     </refsect2>
 
     <refsect2>
-      <title>Snapshot Commands</title>
-
-      <variablelist>
-        <varlistentry>
-          <term><command>snapshot <optional><replaceable>NAME</replaceable></optional></command></term>
-
-          <listitem>
-            <para>Create a snapshot. If a snapshot name is specified,
-            the new snapshot will be named after it. If none is
-            specified, an automatic snapshot name is generated. In
-            either case, the snapshot name used is printed to standard
-            output, unless <option>--quiet</option> is specified.
-            </para>
-
-            <para>A snapshot refers to a saved state of the systemd
-            manager. It is implemented itself as a unit that is
-            generated dynamically with this command and has dependencies
-            on all units active at the time. At a later time, the user
-            may return to this state by using the
-            <command>isolate</command> command on the snapshot unit.
-            </para>
-
-            <para>Snapshots are only useful for saving and restoring
-            which units are running or are stopped, they do not
-            save/restore any other state. Snapshots are dynamic and lost
-            on reboot.</para>
-          </listitem>
-        </varlistentry>
-        <varlistentry>
-          <term><command>delete <replaceable>PATTERN</replaceable>...</command></term>
-
-          <listitem>
-            <para>Remove a snapshot previously created with
-            <command>snapshot</command>.</para>
-          </listitem>
-        </varlistentry>
-      </variablelist>
-    </refsect2>
-
-    <refsect2>
       <title>Environment Commands</title>
 
       <variablelist>
diff --git a/man/systemd.snapshot.xml b/man/systemd.snapshot.xml
deleted file mode 100644
index 96069c324a..0000000000
--- a/man/systemd.snapshot.xml
+++ /dev/null
@@ -1,83 +0,0 @@
-<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
-  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
-  This file is part of systemd.
-
-  Copyright 2010 Lennart Poettering
-
-  systemd is free software; you can redistribute it and/or modify it
-  under the terms of the GNU Lesser General Public License as published by
-  the Free Software Foundation; either version 2.1 of the License, or
-  (at your option) any later version.
-
-  systemd is distributed in the hope that it will be useful, but
-  WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-  Lesser General Public License for more details.
-
-  You should have received a copy of the GNU Lesser General Public License
-  along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
-
-<refentry id="systemd.snapshot">
-  <refentryinfo>
-    <title>systemd.snapshot</title>
-    <productname>systemd</productname>
-
-    <authorgroup>
-      <author>
-        <contrib>Developer</contrib>
-        <firstname>Lennart</firstname>
-        <surname>Poettering</surname>
-        <email>lennart@poettering.net</email>
-      </author>
-    </authorgroup>
-  </refentryinfo>
-
-  <refmeta>
-    <refentrytitle>systemd.snapshot</refentrytitle>
-    <manvolnum>5</manvolnum>
-  </refmeta>
-
-  <refnamediv>
-    <refname>systemd.snapshot</refname>
-    <refpurpose>Snapshot unit configuration</refpurpose>
-  </refnamediv>
-
-  <refsynopsisdiv>
-    <para><filename><replaceable>snapshot</replaceable>.snapshot</filename></para>
-  </refsynopsisdiv>
-
-  <refsect1>
-    <title>Description</title>
-
-    <para>Snapshot units are not configured via unit configuration
-    files. Nonetheless they are named similar to filenames. A unit
-    whose name ends in <literal>.snapshot</literal> refers to a
-    dynamic snapshot of the systemd runtime state.</para>
-
-    <para>Snapshots are not configured on disk but created dynamically
-    via <command>systemctl snapshot</command> (see
-    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
-    for details) or an equivalent command. When created, they will
-    automatically get dependencies on the currently activated units.
-    They act as saved runtime state of the systemd manager. Later on,
-    the user may choose to return to the saved state via
-    <command>systemctl isolate</command>. They are useful to roll back
-    to a defined state after temporarily starting/stopping services or
-    similar.</para>
-  </refsect1>
-
-  <refsect1>
-      <title>See Also</title>
-      <para>
-        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
-        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
-        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
-        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
-      </para>
-  </refsect1>
-
-</refentry>
diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 5c74318fec..caba7ea69d 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -60,7 +60,6 @@
     <filename><replaceable>target</replaceable>.target</filename>,
     <filename><replaceable>path</replaceable>.path</filename>,
     <filename><replaceable>timer</replaceable>.timer</filename>,
-    <filename><replaceable>snapshot</replaceable>.snapshot</filename>,
     <filename><replaceable>slice</replaceable>.slice</filename>,
     <filename><replaceable>scope</replaceable>.scope</filename></para>
 
@@ -90,7 +89,7 @@
     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 temporary system state snapshot, a resource management slice or
+    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
@@ -115,8 +114,7 @@
     <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.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
-    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
     <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
     </para>
 
@@ -652,16 +650,6 @@
       </varlistentry>
 
       <varlistentry>
-        <term><varname>IgnoreOnSnapshot=</varname></term>
-
-        <listitem><para>Takes a boolean argument. If
-        <option>true</option>, this unit will not be included in
-        snapshots. Defaults to <option>true</option> for device and
-        snapshot units, <option>false</option> for the
-        others.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
         <term><varname>StopWhenUnneeded=</varname></term>
 
         <listitem><para>Takes a boolean argument. If
@@ -1431,7 +1419,6 @@ PrivateTmp=yes</programlisting>
       <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.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
diff --git a/man/systemd.xml b/man/systemd.xml
index 08ce99d0cc..6de18f8294 100644
--- a/man/systemd.xml
+++ b/man/systemd.xml
@@ -318,12 +318,6 @@
       boot-up. See
       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 
-      <listitem><para>Snapshot units can be used to temporarily save
-      the state of the set of systemd units, which later may be
-      restored by activating the saved snapshot unit. For more
-      information, see
-      <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
-
       <listitem><para>Timer units are useful for triggering activation
       of other units based on timers. You may find details in
       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>