In my previous post I briefly mentioned debugging a php process with gdb. In this post I am going to describe the steps and required tools to successfully get insights/stacktrace from a running PHP process.
First thing first, make sure you have install php5-dbg package. In this example I am using an Ubuntu box.
$ dpkg-query -l | grep php5-dbg
If not found install it first
$ sudo apt-get install php5-dbg
We also need a .gdbinit file. Get it from here according to php version.
Now it's time to start gdb with the php process.
$ sudo gdb -p PID
At the point gdb will pause the program, you need to type continue inside the gdb shell.
> cont
Wait for a while and then press Ctrl+C to get back to gdb shell.
Now source the .gdbinit, I put it into my home directory.
> source ~/.gdbinit
Type zbacktrace to see actual backtrace from the underlying php program.
> zbacktrace
After getting the stacktrace detach the program from gdb and then quit, if you dont detach the program, gdb will kill it when you quit gdb.
> detach
> q
You can check other commands available in the .gdbinit file.
This helped me today to get actual stacktrace of the php program instead of php interpreter calls that I got with bt command.
gdb is really an awesome sauce!
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