02-14-2011
Let the process produce a core file
There are two ways you can deal with this problem.
The first, and most obvious one, is to run the program under the debugger (e.g.: dbx). When it crashes, you'll get the debugger's prompt and you can explore the location and causes of the crash.
Since running under the debugger may change the behavior of the program, you may want to let it run normally. If the program crashes due to certain signals (e.g.: SIGSEGV - indicating accessing a bad address, such as address 0), it can produce a core file, at least under Unix variants, including Linux. You can then use the debugger to look at the state of the program at the time of the crash and analyze the reason for the crash.
For example, if the name of the program is prog, then
use: dbx prog core
to explore the state of the program at the time of the crash.
The core file is not always produced even when the program crashes due to a signal such as SIGSEGV. The reason is that there is a limit on the size of the core file. Often, this limit is 0. You can change this limit to "unlimited" and then the core file will be produced when the need arises.
The command to change the core file size limit is shell dependent.
For example, under bash I am using: ulimit -c unlimited
under tcsh, I use: limit coredumpsize unlimited
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CORE(5) BSD File Formats Manual CORE(5)
NAME
core -- memory image file format
SYNOPSIS
#include <sys/param.h>
DESCRIPTION
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
core.pid, where pid is the process ID of the process, in the /cores directory, provided the terminated process had write permission in the
directory, and the directory existed.
The maximum size of a core file is limited by setrlimit(2). Files which would be larger than the limit are not created.
The core file consists of the Mach-O(5) header as described in the <mach-o/loader.h> file. The remainder of the core file consists of vari-
ous sections described in the Mach-O(5) header.
NOTE
Core dumps are disabled by default under Darwin/Mac OS X. To re-enable core dumps, a privileged user must do one of the following
* Edit /etc/launchd.conf or $HOME/.launchd.conf and add a line specifying the limit limit core unlimited
* A privileged user can also enable cores with launchctl limit core unlimited
* A privileged user can also enable core files by using ulimit(1) or limit(1) depending upon the shell.
SEE ALSO
gdb(1), setrlimit(2), sigaction(2), Mach-O(5), launchd.conf(5), launchd.plist(5), sysctl(8)
HISTORY
A core file format appeared in Version 6 AT&T UNIX.
BSD
June 26, 2008 BSD