Core Dump is is not working

Question

When I run programs with segfaults I get an error message Segmentation fault: 11. For some reason, I'm not getting the (core dumped) message. I tried running the shell command ulimit -c unlimited, but I still get the same error and it doesn't say core dumped. I'm new to GDB so I tried it with a simple program:

/* coredump.c */
#include <stdio.h>
int main (void) {
  int *point = NULL;
  *point = 0;
  return 0;
}

But when I compile using:

gcc coredump.c -g -o coredump

And run it, it still says segfault: 11

Is it still creating a core dump somewhere I don't know about? I want to be able to use gdb coredump core.

possible duplicate of [How to enable full coredumps on OS X?](http://stackoverflow.com/questions/2207233/how-to-enable-full-coredumps-on-os-x) — John Carter, Aug 18 '12 at 23:42

score 2 · Answer 1 · edited May 23 '17 at 12:27

2

Look at this link:

How to generate a core dump in Linux when a process gets a segmentation fault?

Options include:

ulimit -c unlimited (default = 0: no core files generated)
the directory for the dump must be writable. By default this is the current directory of the process, but that may be changed by setting /proc/sys/kernel/core_pattern.
in some conditions, the kernel value in /proc/sys/fs/suid_dumpable may prevent the core to be generated.
"man core" for other options
find / -name core -print 2> /dev/null to search your filesystem for core files

I presume you're running Linux, and I presume you're executing the .exe in a directory where you have write permissions.

So my top two guesses would be 1) "ulimit -c unlimited" isn't getting set, or is being overridden, or 2) the core files are being generated, but going "somewhere else".

The above suggestions should help. Please post back what you find!

edited May 23 '17 at 12:27

Community

1
1

answered Aug 18 '12 at 17:06

paulsm4

114,292
17
138
190

Thanks for the link! I am using OSX, and when i checked the man page for core, it said that dumps are disabled by default under Darwin/Max OS X to re-enable core dumps, a privelaged user must edit **/etc/launchd.conf**, but I don't see that file under /etc..? – DanMoore Aug 18 '12 at 18:12
2

@DanMoore - Check out these links: [setting-environment-variables-in-os-x](http://stackoverflow.com/questions/135688/), https://developer.apple.com/library/mac/#technotes/tn2004/tn2124.html, [how-to-enable-full-coredumps-on-os-x](http://stackoverflow.com/questions/2207233/). Note that `/etc/launchd.conf` might not exist. Just create one, per the example in one of the replies the first link. – paulsm4 Aug 18 '12 at 18:49
It worked! I checked out the first link you sent me. i created a new config file in /etc, wrote the line **limit core unlimited**, rebooted my mac, and now all my segfault error messages say (core dumped)! The core file itself can be found in /cores. Thanks!! – DanMoore Aug 18 '12 at 19:18
@DanMoore - Cool: thank you for the good word! Please mark this reply "accepted" if it worked. – paulsm4 Aug 18 '12 at 21:39

score 1 · Answer 2 · edited May 23 '17 at 12:20

If you're running the program that crashes from the shell, then you should follow the guidelines in Apple's Tech Note TN2124, which I found out about in in the answer to SO2207233.

There are a few key points:

You need to set ulimit -c unlimited in bash (same effect, different command in tcsh).
You need to set the permissions on the /cores directory so that you can create files in it. The default permissions are 1775; you need 1777. The 1 indicates the sticky bit is set.
The core dumps are then created in /cores suffixed with a PID (/cores/core.5312, for example).

If you want programs launched graphically to dump core when they crash, then you need to create /etc/launchd.conf if it does not already exist, and add a line limit core unlimited to the file. Again, see the information in the Tech Note for more details.

Watch it; core dumps are huge! Consider this not very complicated or big program:

#include <stdio.h>
int main(void)
{
    int *i = 0;
    int j = 0;
    printf("i = %d, j = %d, i / j = %d\n", *i, j, *i / j);
    return 0;
}

The core dump from this is nearly 360 MB.

that's really interesting. Why is that core dump so big? – Steven Lu Aug 19 '12 at 16:18 — Steven Lu, Aug 19 '12 at 16:18

score 0 · Answer 3 · edited Dec 06 '12 at 07:06

0

Sometimes core files are not store in current directory and may follow a different naming rule

sysctl -a | grep kern.core

may give hints to where your core files are stored

edited Dec 06 '12 at 07:06

philant

34,748
11
69
112

answered Aug 18 '12 at 17:07

Stephane Rouberol

4,286
19
18

nothing happens when i type that command into bash :( thanks though The current directory has no core files and i looked into the /cores directory from the root and theres nothing there either. – DanMoore Aug 18 '12 at 17:45
grep kernel.core /etc/sysctl.conf ? – Stephane Rouberol Aug 18 '12 at 21:31

score 0 · Answer 4 · answered Aug 18 '12 at 17:07

0

Using gcc, if you add the flags:

gcc -g -dH

you should be able to generate a core dump

The -g flag produces some debugging information to use with gdb, and the -dH flag produces a core dump when there is an error

answered Aug 18 '12 at 17:07

smang

1,187
10
23

i compiled using **gcc -g -dH coredump.c**, but when I ran the a.out, no core dump message appeared :( thanks though – DanMoore Aug 18 '12 at 17:46
The message may not appear, but was there a file named coredump.dSYM, or something similar – smang Aug 18 '12 at 17:48

Core Dump is is not working

4 Answers4