How can I save the coredump (vmcore) onto the hard disk when I get a system OOPS or a kernel panic on Red Hat Enterprise Linux 4

Make sure diskdump package is installed and service is running. Now take a dump using Alt-SysRq-C or "echo c > /proc/sysrq-trigger".

After completing the dump, a vmcore file will be created during the next reboot sequence, and saved in a directory of the name format:

/var/crash/127.0.0.1-

The vmcore file's format is same as that created by the netdump facility, so you can use the crash command to analyze it.