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Controlling core files (Linux)
Author: TonyLawrence
Date: Mon Mar 14 13:53:36 2005
Subject: Controlling core files (Linux)
If you don't want core files at all, set "ulimit -c 0" in your startup files. That's the default on many systems; in /etc/profile you may find
ulimit -S -c 0 > /dev/null 2>&1
If you DO want core files, you need to reset that in your own .bash_profile:
ulimit -c 50000
would allow core files but limit them to 50,000 bytes.
You have more control of core files in /proc/sys/kernel/
For example, you can do eliminate the tagged on pid by
echo "0" > /proc/sys/kernel/core_uses_pid
Core files will then just be named "core". People do things like that so that a user can choose to put a non-writable file named "core" in directories where they don't want to generate core dumps. That could be a directory (mkdir core) or a file (touch core;chmod 000 core). I've seen it suggested that a symlink named core would redirect the dump to wherever it pointed, but I found that didn't work.
But perhaps more interesting is that you can do:
mkdir /tmp/corefiles
chmod 777 /tmp/corefiles
echo "/tmp/corefiles/core" > /proc/sys/kernel/core_pattern
All corefiles then get tossed to /tmp/corefiles (don't change core_uses_pid if you do this).
Test this with a simple script:
# script that dumps core
kill -s SIGSEGV $$
But wait, there's more (if your kernel is new enough). From "man proc":
/proc/sys/kernel/core_pattern
This file (new in Linux 2.5) provides finer control over the
form of a core filename than the obsolete
/proc/sys/kernel/core_uses_pid file described below. The name
for a core file is controlled by defining a template in
/proc/sys/kernel/core_pattern. The template can contain %
specifiers which are substituted by the following values when
a core file is created:
%% A single % character
%p PID of dumped process
%u real UID of dumped process
%g real GID of dumped process
%s number of signal causing dump
%t time of dump (secs since 0:00h, 1 Jan 1970)
%h hostname (same as the 'nodename'
returned by uname(2))
%e executable filename
A single % at the end of the template is dropped from the core
filename, as is the combination of a % followed by any character
other than those listed above. All other characters in the
template become a literal part of the core filename. The maximum
size of the resulting core filename is 64 bytes. The default
value in this file is "core". For backward compatibility, if
/proc/sys/kernel/core_pattern does not include "%p" and
/proc/sys/kernel/core_uses_pid is non-zero, then .PID will be
appended to the core filename.
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Sat Feb 9 06:57:20 2008: Subject: anonymous
This topic was really helpful to know about core files in linux/unix. Appreciated!!
Mon Jun 23 16:11:03 2008: Subject: Great article anonymous
http://www.724care.com
Ultimate guide. It does take some time to figure out why there are no core files on ubuntu. apport is not set correctly by default to handle core files in server installations. This write up is really getting to the bottom of it.
Mon Dec 8 22:18:25 2008: Subject: anonymous
I found this page via Google, and just wanted to say that I found it really useful - no need for further research. First click, and satisfied - awesome! thanks!
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