#762731 lightdm: issues strange error message when requested to start but is non-default dm

Package:
lightdm
Source:
lightdm
Description:
simple display manager
Submitter:
Yann Dirson
Date:
2014-09-24 20:12:05 UTC
Severity:
normal
#762731#5
Date:
2014-09-24 19:17:01 UTC
From:
To:
kdm is the default dm here, and I just switched from systemd.  When
hunting various dm issues, I found that asking lightdm to start
results in the following unexpected error (it does start as expected
when set to be the default, however).  It should surely check the
default dm settings, like eg. xdm does, and does not even attempt to
start.

# service lightdm start
Job for lightdm.service failed. See 'systemctl status lightdm.service' and 'journalctl -xn' for details.
# systemctl status lightdm.service
lightdm.service - Light Display Manager
   Loaded: loaded (/lib/systemd/system/lightdm.service; enabled)
   Active: failed (Result: start-limit) since mer. 2014-09-24 21:13:26 CEST; 1min 55s ago
     Docs: man:lightdm(1)
  Process: 8079 ExecStartPre=/bin/sh -c [ "$(cat /etc/X11/default-display-manager 2>/dev/null)" = "/usr/sbin/lightdm" ] (code=exited, status=1/FAILURE)
 Main PID: 7122 (code=exited, status=0/SUCCESS)

sept. 24 21:13:25 home systemd[1]: Failed to start Light Display Manager.
sept. 24 21:13:25 home systemd[1]: Unit lightdm.service entered failed state.
sept. 24 21:13:26 home systemd[1]: lightdm.service holdoff time over, scheduling restart.
sept. 24 21:13:26 home systemd[1]: Stopping Light Display Manager...
sept. 24 21:13:26 home systemd[1]: Starting Light Display Manager...
sept. 24 21:13:26 home systemd[1]: lightdm.service start request repeated too quickly, refusing to start.
sept. 24 21:13:26 home systemd[1]: Failed to start Light Display Manager.
sept. 24 21:13:26 home systemd[1]: Unit lightdm.service entered failed state.
#762731#10
Date:
2014-09-24 19:24:59 UTC
From:
To:

Well, that's exactly what it's doing…
#762731#15
Date:
2014-09-24 19:44:27 UTC
From:
To:
I'm not sure if you're saying that it does check the dm settings.  If
it's the case, then it looks like it causes the service start to error
out, causing systemd to retry to launch it, whereas it is a perfectly
legal situation for a dm to be disabled.  In that case, it is a change
from what we've been used to, and I'm not sure to see the advantages
of doing so.

I tried to lookup any policy information about display managers, but
could not find any.  That makes me even more curious about how the
collaboration among maintainers of dm packages is organized.

The only mildly-official page that is mildly relevant to how an admin
can deal with dm's (that I could find) is
https://wiki.debian.org/DisplayManager, and it does not say anything
on that matter either.
#762731#20
Date:
2014-09-24 19:47:47 UTC
From:
To:
Well, the same thing happens with sysvrc, the init.d script checks for
the default display manager and errors out if it's not the selected one.

See #733220
#762731#25
Date:
2014-09-24 20:08:21 UTC
From:
To:
AFAICT, it really looks like it just does "exit 0", as do other DMs.

You mean, bugreports are the only collaboration ?

I would have thought that eg. the debconf stuff that has to be shared
(duplicated ?) in the various DM packages, could come from a central
package (a debhelper tool ?), around which some sort of DM policy
would live ?