kernel panic - any ideas?

I am working with a Compaq server that appears to be in good working order
but it has kernel paniced after a reboot. This is the message:

begins kjournald
EXT3-fs: mounted filesystem with ordered data mode
pivotroot: pivot_root (/sysroot, /sysroot/initrd) failed 2
Free unused kernel memory 440k
Kernel panic: no init found, try passing init=option to kernel

Does anyone know what the pivotroot does? I am probably just going to
rebuild the machine, but I wanted to know if anyone has seen a panic like
this in case it happens in the future.

Thanks,

Brian