A small number of signals which cause abnormal termination of a process also cause a record of the processs in-core state to be written to disk for later examination by one of the available debuggers. (See sigaction 2.) This memory image is written to a file named by default programname.core in the working directory; provided the terminated process had write permission in the directory, and provided the abnormality did not cause a system crash. (In this event, the decision to save the core file is arbitrary, see savecore 8.)
The maximum size of a core file is limited by setrlimit(2). Files which would be larger than the limit are not created.
The name of the file is controlled via the sysctl(8) variable kern.corefile. The contents of this variable describes a filename to store the core image to. This filename can be absolute, or relative (which will resolve to the current working directory of the program generating it). Any sequence of %N in this filename template will be replaced by the process name, %P by the processes PID, and %U by the UID. The name defaults to %N.core, yielding the traditional
By default, a process that changes user or group credentials whether real or effective will not create a corefile. This behaviour can be changed to generate a core dump by setting the sysctl(8) variable kern.sugid_coredump to 1.
In order to store all core images in per-user private areas under /var/coredumps, the following sysctl(8) command can be used:
sysctl kern.corefile= "/var/coredumps/%U/%N.core"
gdb(1), kgdb(1), setrlimit(2), sigaction(2), sysctl(8)