[mythtv-users] Backend Crashes / Status Monitoring

David myth at dgreaves.com
Wed Mar 23 14:38:11 UTC 2005


There's a bit of a writeup at 
http://www.mythtv.info/moin.cgi/StatusMonitoringHowTo


dave at theansells.com wrote:

>David,
>
>    Thanks.
>  So as I understand it create a new line in /etc/inittab, simple as that.
>  
>
yes - that could work.
However, it's not the best way to do it - the backend may start before 
mysql - or your frontend may start before the backend does.
For this reason...

>  What confused me was the various other scripts in other directories,
>/etc/rc.d/rc3.d , etc which claim to start mythbackend.
>
...the rc3.d and rc5.d scripts are numbered to start in a certain order 
to ensure that mysql starts before the backend which starts before the 
frontend etc.

>  As I now
>understand it these got created when I did  "chkconfig mythbackend on"
>command to autostart the backend.
>  
>
yes

>  Presumably this means I need to "chkconfig mythbackend off" to get rid
>of these when I edit the inittab file? yes?
>  
>
it's one approach - but using a monitor like monit or daemontools is 
better as this lets things start up normally and then just re-starts 
them if they die.
Now *that* you can start from the inittab (as I said earlier).
There is actually a slight gotcha (I don't know if this applies to 
daemontools too) : if the monitor is started *before* the backend 
service is fully up and running then it can detect a failure and kill 
and restart the backend needlessly. For this reason I've submitted a 
patch to the Debian monit maintainer that helps fix this.

>   Sorry, being a bit slow, but I never seem to get the whole picure from
>the man pages.
>  
>
's OK

As long as people do read them, think and *then* ask questions I don't 
mind at all ;)

So if I were you I'd leave the chkconfig stuff set to 'on' and pick one 
of monit or daemontools.
Then follow the instructions at the wiki.
Don't do init to start until you can do an /etc/init.d/mythbackend stop
and have it restart

David

>cheers,
>Dave
>
>  
>
>>well,
>>  man init
>>and
>>  man inittab
>>are good :)
>>
>>You say:
>>
>>    
>>
>>>    My /etc/inittab file calls up a script   (
>>>/etc/rc.d/rc3.d/S86mythbackend )  to start the backend.
>>>      
>>>
>>surely that's not on a line by itself?
>>My reading of the manpage suggests that that would be an error...
>>
>>
>>You would just edit the file, and add the line I mention below pretty
>>much anywhere.
>>
>>David
>>PS, notice it has respawn in the line itself - that's what I meant...
>>Let me know if you have problems.
>>
>>Dave Ansell wrote:
>>
>>    
>>
>>>David,
>>>
>>>    Sorry, but I am not that familiar with the workings of inittab.
>>>    My /etc/inittab file calls up a script   (
>>>/etc/rc.d/rc3.d/S86mythbackend )  to start the backend.
>>>    Where exactly do I put the respawn option?
>>>
>>>
>>>      
>>>
>>>>Fair question :)
>>>>
>>>>The answer is 'init' via 'inittab'
>>>>
>>>>use the respawn option and it will...
>>>>
>>>>moni:235:respawn:/usr/sbin/monit
>>>>
>>>>(however make sure you get the config right first!)
>>>>
>>>>If init crashes then you've got problems...
>>>>
>>>>
>>>>David
>>>>
>>>>
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>>>      
>>>
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>>    
>>
>
>
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