[mythtv-users] Backend crashes, sometimes with memory faults

Michael T. Dean mtdean at thirdcontact.com
Tue Dec 23 14:18:01 UTC 2008

On 12/23/2008 05:19 AM, Kenan Ezal wrote:
> I recently built a new 64-bit dual-core myth master backend and frontend
> box. The hardware for my old box was getting a little unreliable and
> difficult to replace. While the old system (Fedora 6, Myth 0.20, 32-bit,
> Intel Monterrey 1700 MHz) was very stable (except for the motherboard
> dying on me recently), the new system has a serious problem that I've
> been trying to (unsuccessfully) diagnose for about a month: Basically,
> the backend dies without warning, sometimes taking out the frontend with
> it. Although I can't prove it, it seems to be related to deletes and
> maybe even mysql/mythconverg. However, there is sometimes a delay
> involved.
> My system information is:
> Linux MythTV2 #1 SMP Thu Nov 13 20:29:07 EST 2008
> x86_64 x86_64 x86_64 GNU/Linux
> Dual core CPU E2180 @ 2.00GHz with 3.9GiB
> My video partition is a RAID 5 with an ext3 filesystem.
> I know that people have reported problems deleting with ext3, but with
> my old machine, which had slower hard drives, ext3 was the only
> filesystem that I did NOT have any problems with. Other filesystems
> would often crash my entire system. The current problem seems to be
> limited to mythtv -- at least the system doesn't crash.
> The new machine does have SATA drives so I'm considering changing to
> another filesystem, however, I thought I would see if anyone else can
> think of something else that might going on before I commit to such a
> move.
> One thing that I thought could be the problem related to the message
> almost always found in mythbackend.log just before a crash:
> GetRecordBasename found no entry
> I've gone through and manually tried to clean
> mythconverg.recorded/.recordedprogram and hoped that would solve the
> problem. I didn't help, but I'm not sure if I was successful in finding
> the reason for the above message. I did find at least one entry that did
> not have a matching file. But as far as I could tell, all database
> entries matched my video directory contents after my spring cleaning. Is
> there a way to check this with higher confidence? (I've also used
> mysqlcheck without success -- everything seems OK). Maybe I need to
> revisit this...
> The only other solid clue I have is that sometimes I get a memory faults
> (both mythfrontend and mythbackend, but mostly mythbackend). 
> Otherwise, my observation is that there is a higher probability of a
> crash if I've just deleted one or more recordings. I know there is a
> "slow delete" feature (that I used to be able to control with 0.20), but
> I'm not sure if it could case a delayed crash due to deletes.
> Anyway I'm providing a couple of samples of my mythbackend.log and
> mythfrontend.log in the hopes that someone will have a eureka moment. In
> one case I also caught a mythfrontend memory corruption. All memory
> faults/corruptions appear to have mysql libraries involved. 
> I appreciate you reading even this far!
> There are more but I will spare you.
> I have saved all these logs if anyone thinks they might be of some use.
> Thanks again.

My first guess--assuming no hardware problems, such as bad 
memory/overheating (I had a mobo where the chipset would overheat, 
causing similar issues)/too-aggressive-overclock) would be a problem 
with the installation.  I'd recommend removing /all/ of myth 
(mythtv--including mythbackend, mythfrontend, mythfilldatabase, 
etc.--and mythplugins at least).  Do a backup first, too.  ( 
http://www.mythtv.org/wiki/index.php/Database_Backup_and_Restore )  
Then, once you've removed everything using your package manager, make 
sure nothing is left (i.e. check for and remove files from 
/usr/{,local/}lib/{libmyth,mythtv} and /usr/{,local/}include/mythtv ).  
Then, re-install (and restore the database, if necessary).

If that doesn't help, we'd need a full backtrace to find out why things 
are segfaulting.  http://mythtv.org/docs/mythtv-HOWTO-22.html#ss22.2  
Note, though, that Fedora and Ubuntu both have packages that contain all 
the debug symbols, so there's no need to rebuild mythtv--just 
(temporarily) install the proper debug packages.  Talk to someone who 
uses your distro to find out how.


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