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, 2 insertions, 15 deletions

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>,