RE: collecting data from a coring process

[Paul Marquess <Paul dot Marquess at owmobility dot com>]

From: Dmitry Samersoff [mailto:dms@samersoff.net] 

> Paul,
> 
> >> 1) Why not dump the information that you are looking for into a file 
> >> in the process signal handler ?
> >
> > Would love to, but I have no idea what state the process is in once 
> > the SEGV has been triggered.
> 
> If you use altstack and avoid malloc you can dump bunch of information from the signal handler more or less safely.
> 
> e.g.
> 
> http://hg.openjdk.java.net/jdk9/hs/hotspot/file/tip/src/share/vm/utilities/vmError.cpp

Thanks, will take a look at that. When you say "more or less safely", I'm reading that as saying there will be issues with it.  :-)

I know we've had problems with signal handlers causing problems, thus my preference to find a way to have the signal handler code do as little as possible and get all the data collection handled at arm's length by gdb.  

> >>> My first thought was to add a script in 
> >>> /proc/sys/kernel/core_pattern to catch the process as it is coring. 
> >>> Then I get gdb to attach to the PID of the process that is about to 
> >>> core. Unfortunately, when I tried that, gdb gives me this error
> 
> One of possible solution is:
> 
> 1. Change /proc/sys/kernel/core_pattern to have all coredumps from your app in a separate directory, something like /var/dumps/%e/core.%p
> 
> 2. Have a cron job that looks over this directory and run gdb <exe image name> <core_name> < gdb_script > core.%p.out on demand.

That is exactly what I'm doing at the moment. Trouble is I soon will not allow a core file to be written -- the process is reaching a size where I cannot allow it to be out of action for the amount of time it takes to write that to disk. 

Paul

P.S. Sorry for the delay in following up. Had no internet access for about 10 days.