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When a process receives certain signals it will exit and dump core.  This is the state of the process when the signal arrived.  A debugger such as gdb can be used to examine this corefile.
A corefile can be called "core", "program.core" or even be configured to be written to a certain location (in [[FreeBSD]]).

The kernel also can dump core upon a panic or when instructed to do so.  It saves the corefile to swap which is then transferred upon the next boot to /var/crash, it's a good idea to have the /var filesystem big enough to accomodate the size of the physical memory of the system.


== Signals that cause a process to dump core ==

     SIGQUIT     create core image   quit program
     SIGILL      create core image   illegal instruction
     SIGTRAP     create core image   trace trap
     SIGABRT     create core image   abort(3) call (formerly SIGIOT)
     SIGEMT      create core image   emulate instruction executed
     SIGFPE      create core image   floating-point exception
     SIGBUS      create core image   bus error
     SIGSEGV     create core image   segmentation violation
     SIGSYS      create core image   system call given invalid argument