[mythtv-users] Watch TV - Then nothing

Sam Varshavchik mrsam at courier-mta.com
Tue Mar 28 03:40:28 UTC 2006

jborn at charter.net writes:

> 2006-03-27 22:04:22.021 Image size. dispxoff 0, dispyoff: 0, dispwoff: 0, disphoff: 0
> 2006-03-27 22:04:22.021 Image size. imgx 0, imgy: 0, imgw: 480, imgh: 480
> 2006-03-27 22:04:22.023 waiting for prebuffer... 0
> Segmentation fault
> Thanks again for all the help,

The following are some general suggestions to help you collect more useful 
debugging data.  These are general diagnostic hints, and are not really 
mythtv-specific.  You did not mention your platform, I'm assuming you're on 

* If you built mythtv manually, rebuild mythtv with the debugging symbols 
included.  For the mythtv-specific configure script, pass the extra options 
"--extra-cflags=-g --extra-cxxflags=-g".  You'll need to extract the source 
tarball into a new directory, run configure with these options (and any 
others you've previously used) and rebuild with those flags, and reinstall.

* Before trying to watch TV, open another terminal window, use the 'ps -l 
-T' command to obtain the pid of the running mythfrontend process.  If 
mythfrontend uses threads (I don't know, haven't checked), you'll see 
mythfrontend listed more than once.

Run  "strace -F -o mythfrontend.log -s 512 -p [PID]", substituting the 
numerical process id of the mythfrontend in place of [PID].  If you show 
more than one mythfrontend threads, run strace in the background, or in 
multiple terminal windows, once for each process using the process id 
obtained from the "SPID" column, and using a different filename in each 
strace command, instead of "mythfrontend.log".

It will be very useful to see the last dozen, or so, lines in the 
mythfrontend.log file(s).

The following will only work if you've built mythtv with debugging symbols, 
as mentioned earlier.  If not -- if you've installed someone else's 
pre-built package -- this is not going to work:

* Before starting mythfrontend, run "ulimit -c unlimited".  After it 
crashes, you should have a "core" file in the current directory. Hopefully.  
If not, you're out of luck.  If you do, run the command "gdb <mythfrontend> 
core", and specify the FULL path to the mythfrontend program as the first 
argument, ex: "gdb /usr/bin/mythfrontend core".

When gdb starts, hit "enter" until the gdb> prompt comes up.  Type "where", 
and save the output of this command.

Finally, get the attention of someone who's familiar with the code, and ask 
them to look at your mythfrontend.log file(s) and the output of the "where" 
command from gdb.  This should help them narrow down the cause of your 

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