Core dump file is not generated

Question

Every time, my application crash a core dump file is not generated. I remember that few days ago, on another server it was generated. I'm running the app using screen in bash like this:

#!/bin/bash ulimit -c unlimited while true; do ./server; done 

As you can see I'm using ulimit -c unlimited which is important if I want to generate a core dump, but it still doesn't generate it, when I got an segmentation fault. How can I make it work?

Answer 1

This link contains a good checklist why core dumps are not generated:

• The core would have been larger than the current limit.
• You don't have the necessary permissions to dump core (directory and file). Notice that core dumps are placed in the dumping process' current directory which could be different from the parent process.
• Verify that the file system is writeable and have sufficient free space.
• If a sub directory named core exist in the working directory no core will be dumped.
• If a file named core already exist but has multiple hard links the kernel will not dump core.
• Verify the permissions on the executable, if the executable has the suid or sgid bit enabled core dumps will by default be disabled. The same will be the case if you have execute permissions but no read permissions on the file.
• Verify that the process has not changed working directory, core size limit, or dumpable flag.
• Some kernel versions cannot dump processes with shared address space (AKA threads). Newer kernel versions can dump such processes but will append the pid to the file name.
• The executable could be in a non-standard format not supporting core dumps. Each executable format must implement a core dump routine.
• The segmentation fault could actually be a kernel Oops, check the system logs for any Oops messages.
• The application called exit() instead of using the core dump handler.

Answer 2

Make sure your current directory (at the time of crash -- server may change directories) is writable. If the server calls setuid, the directory has to be writable by that user.

Also check /proc/sys/kernel/core_pattern. That may redirect core dumps to another directory, and that directory must be writable. More info here.