units: express Conflict in syslog.socket instead of emergency.service

sourcejedi · sourcejedi · commit 950d8fcdd9aa · 2017-09-29T17:34:55.000+01:00
Note this commit only changes how the code is expressed; it does not change the existence of any dependency. The `Conflicts=` was added in 3136ec9, "Stop syslog.socket when entering emergency mode". The discussion in the issue adamlaska#266 raised concerns that this might be needed for other units, but failed to point out why syslog.socket is special. The reason is that syslog.socket has DefaultDepedencies=no, so it does not get Requires=sysinit.target like other socket units do. But syslog.service does require sysinit.target, among other things. We don't have many socket, path, or timer units with DefaultDependencies=no, and I don't think any of the triggered services have such additional hard dependencies as syslog.service does. It is much less confusing if we keep this `Conflicts=` in the same file as the `DefaultDependencies=no` which made it necessary.
diff --git a/units/emergency.service.in b/units/emergency.service.in
@@ -11,7 +11,6 @@ Documentation=man:sulogin(8)
 DefaultDependencies=no
 Conflicts=shutdown.target
 Conflicts=rescue.service
-Conflicts=syslog.socket
 Before=shutdown.target
 
 [Service]
diff --git a/units/syslog.socket b/units/syslog.socket
@@ -10,10 +10,14 @@ Description=Syslog Socket
 Documentation=man:systemd.special(7)
 Documentation=https://www.freedesktop.org/wiki/Software/systemd/syslog
 DefaultDependencies=no
-Before=sockets.target shutdown.target
+Before=sockets.target
 
 # Don't allow logging until the very end
 Conflicts=shutdown.target
+Before=shutdown.target
+
+# Don't try to activate syslog.service if sysinit.target has failed.
+Conflicts=emergency.service
 
 [Socket]
 ListenDatagram=/run/systemd/journal/syslog
