lightdm writing the same DEBUG message to /var/log/lightdm/lightdm.log

[Colin Ian King]

I was trying to figure out where excessive file system writes were
coming from on the ubuntu phone (to try to reduce flash writes and hence reduce power
consumption) and I spotted that /var/log/lightdm/lightdm.log is getting the same debug message written to every every 300 seconds:

tail -f /var/log/lightdm/lightdm.log
[+5109.66s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+5409.67s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+5709.66s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+6009.66s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+6309.64s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+6609.65s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+6909.67s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+7209.66s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+7509.66s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+7809.57s] DEBUG: User /org/freedesktop/Accounts/User32011 changed
[+8109.65s] DEBUG: User /org/freedesktop/Accounts/User32011 changed

while this isn't much of a message, it still is causing file system writes every 5 minutes for the same debug message. Is this necessary? The fact that it is the same message about the same account and that it occurs every 300 seconds make me wonder if we can cull this particular piece of repeated logging.

[Robert Ancell (robert-ancell)]

I'd like to find out what is changing on this user every 300s - this doesn't occur on desktop and there's nothing that I can see that should be frequently changed for a user. The debugging is useful, but can be removed if there is a legitimate reason for a user to change this frequently.

[Robert Ancell (robert-ancell)]

I think this might be the XHasMessages property that is being set, since the patch for that doesn't stop Changed from being emitted if the value has not changed. The other properties seem to correctly check if they are changed.

[Robert Ancell (robert-ancell)]

Hmm, not finding anything that sets this. Other candidates are XKeyboardLayouts, BackgroundFile and IconFile which also may emit Changed even if they are not.

I checked the properties of this user on a phone and confirm they are unchanged before and after this signal occurs.

[Robert Ancell (robert-ancell)]

Ah, it turns out there are a lot of extensions in /usr/share/accountsservice/interfaces/ that might be setting things. Thus there is no limit on how much information might be updated.

[Launchpad Janitor (janitor)]

This bug was fixed in the package lightdm - 1.12.1-0ubuntu1

---------------
lightdm (1.12.1-0ubuntu1) utopic; urgency=medium

  * New upstream release:
    - Fix crash when having configuration keys defined in multiple places
      (LP: #1377373)
    - Allow user switching in multi-seat until bug stopping greeter showing on
      logout is fixed
    - Disable log message when AccountsService users change (LP: #1376357)
 -- Robert Ancell <email address hidden> Thu, 09 Oct 2014 08:59:27 +1300