[mythtv-users] backend crashes

Bruce Taber b.taber at comcast.net
Wed Jan 31 22:20:19 UTC 2007

On Wed, 2007-01-31 at 22:03 +0000, junk wrote:
> Hi,
> My backend seems to be going through periods where it repeatedly dies 
> and I'm not sure how to determine the cause of it. Sometimes it'll run 
> fine for a day or two and I can make a number of scheduled recordings 
> and/or watch live-tv, other times it'll die on me without warning, 
> sometimes several times an hour. I don't get much indication in the log 
> beyond seeing 'Starting up as the master server.' as it restarts after 
> (presumably) crashing.
> Firstly, is there any way to force it print a backtrace when it dies? 
> It's running as a service started by init - does anyone know how to edit 
> the Gentoo /etc/init.d/mythbackend script to start it under gdb safely 
> and generate a backtrace on a fatal signal without requiring any user 
> input (so when it suddently dies at 3AM, I don't need to be there to 
> watch it!)
> Secondly, can anyone hazard a guess at possible causes?
> Things that might be relevant:
>   - I'm running a single tuner dvb setup on a vanilla kernel
>   - my dvb reception is poor but backend crashes don't seem particularly 
> correlated with periods of particularly poor reception/bursts of errors 
> in the received MPEG2 stream - sometimes I can record hours of 
> programming with masses of reported errors in the stream and visible 
> glitches, other times the back end will die repeatedly with no reported 
> errors in received stream.
>   - I've tried messing with PCI latencies, but put them back to defaults 
> when it didn't seem to help
>   - I have mythcommflag running sometimes, I suspect it might be 
> contributing to the problem - is this possible?
>   - All my filesystems are XFS, so autoexpire delete storm is not a 
> likely cause?

Check into the usage of XFS further. There is a noted problem with XFS,
LVM, and sizes of partition > something. I don't know what that
something is. I was having these types of problems and worse. The worse
was that my system would unexpectedly hang completely. Couldn't ssh it
and couldn't see the console. I finally set it up so the console
wouldn't blank and caught some error messages. Sure enough XFS was
peppered all around in the messages.
My one video partition was XFS. That was cleared of all recordings and
files and reformatted to EXT3. All of the crashes, hangs, and mysterious
behavior has been eliminated.

>   - Machine has loads of memory (2GB) and 1.8GHz A64 CPU (in 32bit mode) 
> - I doubt it's overloaded recording one dvb stream
>   - Single ATA disk has bus to itself and DMA is definitely enabled
>   - CPU, northbridge, memory and disk are all cool and I don't believe 
> the hardware is flakey (it's previously been running quite heavy Linux 
> loads without any odd behavior before being repurposed as my MythTV box)
> Any suggestions gratefully received, thanks
> -- jeek
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