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

1 files changed, 0 insertions, 83 deletions

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>