start gdb using a pid
There are two ways.
From the command line, include the pid as an argument after the executable name:
gdb /path/to/prog PIDFrom within gdb, you can use the attach command:
gdb /path/to/proggdb> attach PIDWhile the specifying on the command line is more concise, there is a slight risk that if you have a core file that has a name that is the same as the pid (i.e. for pid 2345, the core file would have to be named "2345") then gdb will open the core file. Admittedly, the chance of this happening is minuscule.