I'm writing a program and I need to know the install location of linux as well as root and boot partitions. I'm getting root and boot from /etc/mtab, but I can't find a good way to always determine where the os is installed. This recently caused me to wipe out one of my systems that was booting from a small partition on a windows drive and had the os installed on a separate disk. Also with the recent addition of /dev/mapper to the 2.6 kernel, it's making my life a little harder. Something that accomplishes the analog of the windows environment variables "windir" "SystemRoot" and "SystemDrive" would be what I'm looking for.

The distribution currently running is installed in /. It's always going to be /. What are you trying to do with this information?

if mtab or fstab says /boot is on /dev/hda1 and / is on /dev/hda3, then that's where they're always going to be.