While some may think I’m daft, I have a legitimate reason for wanting to crash mysqld. However first we need to find a way to crash it.
Great thanks to Alan K, Mark L, Harrison and Hartmut on #mysql-dev for several suggestions and a config option I was unaware of. My investigation even lead to a documentation bug logged as #51739.
My first thought was to find a known bug and if necessary install the correct version to test that. A good one was suggested, Bug #48508 which fails on several versions that I will use to demonstrate with, however the simplest way is to issue kill -11
By default, no core file will be produced which is what I’m seeking but with the right options this is possible. First, the user running mysqld probably has a core file limit size of 0.
$ ulimit -c 0
You can fix this with with ulimit or you can specify this in the [mysqld_safe] section with core-file-size=unlimited
$ ulimit -c unlimited $ ulimit -c unlimited
The option I was not aware of is you also have to also specify core-file in your my.cnf
I also for my CentOS 5.4 installation ran the following kernel commands, but this may be unnecessary.
sudo /sbin/sysctl -w kernel.core_pattern="core" sudo /sbin/sysctl -w fs.suid_dumpable= 1
It is now easy to produce a core file.
$ bin/mysqld_safe & $ killall -11 mysqld $ bin/mysqld_safe: line 137: 2656 Segmentation fault (core dumped) ... 100304 16:46:43 mysqld_safe Number of processes running now: 0 100304 16:46:43 mysqld_safe mysqld restarted $ find . -name "core*" ./data/core.99999
NOTE: Do no run killall on a multi-instance server. I use this syntax here only for simplicity in presentation. It is best to run ps and kill the appropriate pid.
On a side note, I also tried to produce a core on Mac OS X without success. I’d still like to document that way, so if anybody can assist please ping me.