After upgrading from RedHat 6.1, the system would not boot into runlevel 3.
Tons of error messages were spewed to the console during various parts of
the init process about the root fs being read only. Further investigation
revealed that rc.sysinit no longer existed, and had been moved to
rc.sysinit.rpmsave. The contents of that file indicated that it was my old
6.1 rc.sysinit, which I had made some small customizations to (I don't know
if that would cause this problem).

Copying the file to rc.sysinit allowed the system to remount the root fs
read-write at the next boot, but the following error was still reported
when starting each service: " "/etc/init.d/functions: No such file or
directory". /etc/init.d was not a symlink to /etc/rc.d/init.d, but rather a
directory containing only the file "cups" (I had installed cups 1.1.4 prior
to the upgrade). Replacing it with a symlink allowed the system to boot
properly.

The system is an i686 SMP.