core -- memory image file format
A small number of signals which cause abnormal termination of a process
also cause a record of the process's 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 FreeBSD behaviour.
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.
The core file consists of the u. area, whose size (in pages) is defined
by the UPAGES manifest in the <sys/param.h> file. The u. area starts
with a user structure as given in <sys/user.h>. The remainder of the
core file consists of the data pages followed by the stack pages of the
process image. The amount of data space image in the core file is given
(in pages) by the variable u_dsize in the u. area. The amount of stack
image in the core file is given (in pages) by the variable u_ssize in the
u. area. The size of a ``page'' is given by the constant PAGE_SIZE (also
In order to store all core images in per-user private areas under
/var/coredumps, the following sysctl(8) command can be used:
gdb(1), kgdb(1), setrlimit(2), sigaction(2), sysctl(8)
A core file format appeared in Version 6 AT&T UNIX.
FreeBSD 5.2.1 January 9, 2002 FreeBSD 5.2.1 [ Back ]