the socket path for ceph plugin needs to be updated for ceph 5 (pacific) based clusters.

The socket path in collectd.conf for ceph version until < pacific (ceph 5) was :

<Plugin ceph>
  LongRunAvgLatency false
  ConvertSpecialMetricTypes true
  <Daemon "mon.controller-0">
    SocketPath "/var/run/ceph/ceph-mon.controller-0.asok"
  </Daemon>
</Plugin>

However, this path does not exist anymore.
It is now behind the cluster fsid.

So, it should rather be updated to:

<Plugin ceph>
  LongRunAvgLatency false
  ConvertSpecialMetricTypes true
  <Daemon "mon.controller-0">
    SocketPath "/var/run/ceph/<cluster-fsid>ceph-mon.controller-0.asok"
  </Daemon>
</Plugin>