You need to boot into single user mode. In MkLinux, hit "s" instead of
enter at the bootloader dialog (the one with the countdown).
 
In linux-pmac, you can set the boot-file to " /vmlinux 1" in the Boot Options
program or type "nvsetenv boot-file " /vmlinux 1"" as root.

When you do boot single user mode, you'll probably find the root filesystem
mounted read-only.
 
    mount -o remount,rw /
    mount /usr
 
The remount should remount it so you can edit things; the mount /usr is
for people who have a separate /usr filesystem.
 
jonh@cs.dartmouth.edu