5 reasons to want a core dump!

There are several reasons to want to make the kernel dump core – the central one being there is some kernel or hardware based problem which continues to occur. What happens during a kernel panic (when properly configured) is that the kernel itself “dumps core” and the core can be used after reboot for analysis.

So here are some reasons:

  • Intermittent kernel reboots
  • Hard drive “lockups” (constant access, system frozen)
  • Apparent hardware failures
  • Speed problems in the kernel
  • Kernel panic debugging

All except the last depend on a user (administrator) generated kernel panic with associated kernel dump. Of course, this is hard on filesystems, though Linux at least has the option of performing a “sync” from the same location as the user generated panic.

Most UNIX operating systems have the capability for the administrator to generate a kernel-based core dump. Linux users must have a kernel that supports the Magic SysReq key. Solaris on SPARC is set to go; Solaris on Intel processors requires booting the Solaris kernel with the kmdb kernel module loaded (through parameters and settings in the boot loader).

Applications will also generate core dumps, and a lot of the core dump analysis tools used for applications and the methods used can be useful in analyzing kernel dumps as well. BEA has an excellent (multi-platform) description of creating and analyzing core dumps – even though it is oriented towards their Tuxedo product, it seems still useful.

Sun has an excellent article, Core Dump Management on the Solaris OS, that covers both application core dumps and system kernel core dumps written by Adam Zhang at Sun.

For HP-UX, there isn’t as much on crash dump analysis, though the whitepaper Debugging Core Files using HP WDB (PDF) may be useful.

I don’t know AIX (nor z/OS) that well myself, but there are some free RedBooks that include core dump analysis as part of the book. There is z/OS Diagnostic Data Collection and Analysis for z/OS (if you just happen to have a mainframe in house) and Problem Solving and Troubleshooting in AIX 5L for AIX.

Likely I’ll be covering some of these tools in depth.  For most versions of UNIX and Linux, there are man pages for core(5).  Some systems offer the commands gcore and savecore as well.  As always, the FreeBSD man pages web page covers HP-UX (HP-UX 11.22), Solaris (Solaris 9), and Red Hat (Red Hat Linux 9) and others as well as FreeBSD. Unfortunately, it appears that other Linux and UNIX versions are not being updated (for whatever reason – space?).

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