systemd: Add explicit Before=ceph.target

The PartOf= and WantedBy= directives in the various systemd
unit files and targets create the following logical hierarchy:

- ceph.target
  - ceph-fuse.target
    - ceph-fuse@.service
  - ceph-mds.target
    - ceph-mds@.service
  - ceph-mgr.target
    - ceph-mgr@.service
  - ceph-mon.target
    - ceph-mon@.service
  - ceph-osd.target
    - ceph-osd@.service
  - ceph-radosgw.target
    - ceph-radosgw@.service
  - ceph-rbd-mirror.target
    - ceph-rbd-mirror@.service

Additionally, the ceph-{fuse,mds,mon,osd,radosgw,rbd-mirror}
targets have WantedBy=multi-user.target.  This gives the
following behaviour:

- `systemctl {start,stop,restart}` of any target will restart
  all dependent services (e.g.: `systemctl restart ceph.target`
  will restart all services; `systemctl restart ceph-mon.target`
  will restart all the mons, and so forth).
- `systemctl {enable,disable}` for the second level targets
  (ceph-mon.target etc.) will cause depenent services to come
  up on boot, or not (of course the individual services can
  be enabled or disabled as well - for a service to start
  on boot, both the service and its target must be enabled;
  disabling either will cause the service to be disabled).
- `systemctl {enable,disable} ceph.target` has no effect on
  whether or not services come up at boot; if the second level
  targets and services are enabled, they'll start regardless of
  whether ceph.target is enabled.  This is due to the second
  level targets all having WantedBy=multi-user.target.
- The OSDs will always start regardless of ceph-osd.target
  (unless they are explicitly masked), thanks to udev magic.

So far, so good.  Except, several users have encountered
services not starting with the following error:

  Failed to start ceph-osd@5.service: Transaction order is
  cyclic. See system logs for details.

I've not been able to reproduce this myself in such a way as to
cause OSDs to fail to start, but I *have* managed to get systemd
into that same confused state, as follows:

- Disable ceph.target, ceph-mon.target, ceph-osd.target,
  ceph-mon@$(hostname).service and all ceph-osd instances.
- Re-enable all of the above.

At this point, everything is fine, but if I then subseqently
disable ceph.target, *then* try `systemctl restart ceph.target`,
I get "Failed to restart ceph.target: Transaction order is cyclic.
See system logs for details."

Explicitly adding Before=ceph.target to each second level target
prevents systemd from becoming confused in this situation.

Signed-off-by: Tim Serong <tserong@suse.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/systemd/ceph-mgr.target b/systemd/ceph-mgr.target
index 72be8e8e9eb..f25e494b1d3 100644
--- a/systemd/ceph-mgr.target
+++ b/systemd/ceph-mgr.target
@@ -1,5 +1,6 @@
 [Unit]
 Description=ceph target allowing to start/stop all ceph-mgr@.service instances at once
 PartOf=ceph.target
+Before=ceph.target
 [Install]
 WantedBy=multi-user.target ceph.target