Open Stack

Background
----------

Oslo Guru Meditation (error) Reports (GMR)[*] are a useful debugging
mechanism that allows one to capture the current state of a Nova
process/executable (e.g. `nova-compute`, `nova-api`, etc).

The way to generate the error report is to supply the 'User-defined
signal', SIGUSR1, when killing a Nova process.  E.g.

    $ kill -USR1 `pgrep nova-compute`

which results in GMR being printed to your standard error ('stderr')
stream, wherever it ends up being redirected to (e.g. to a corresponding
Nova process-specific log file, otherwise, on systemd-enabled systems,
to its journal).


Change in Mitaka (and above)
----------------------------

>From the upcoming Mitaka release onwards, the default expected UNIX
signal to generate GMR has been changed[1] from USR1 to USR2 (another
User-defined singal), because the USR1 is reserved by Apache 'mod_wsgi'
for its own purpose.

So, to generate GMR, from Mitaka release:

    $ kill -USR2 `pgrep nova-compute`

A corresponding Nova documentation change[2] has been submitted to
reflect this new reality.


[1] https://review.openstack.org/#/c/223133/ -- guru_meditation_report:
    Use SIGUSR2 instead of SIGUSR1 
[2] https://review.openstack.org/#/c/227779/ -- doc: gmr: Update
    instructions to generate GMR error reports


[*] References
--------------

Related reading:

- http://docs.openstack.org/developer/nova/gmr.html
- http://docs.openstack.org/developer/oslo.reports/usage.html
- https://wiki.openstack.org/wiki/GuruMeditationReport
- https://www.berrange.com/posts/2015/02/19/nova-and-its-use-of-olso-incubator-guru-meditation-reports/

-- 
/kashyap