Depends on the file system type. If you are using ext2 then use "resize2fs" see "man resize2fs". I am not sure but since ext2 and ext3 use the same format I believe it should work on ext3 as well. But check for more info on this first as I am not sure. I can do some digging on this if you can't find any info. If you run reiserfs then use "resize_reiserfs" and see "man resize_reiserfs".
Note, the above resizes the "file system". If you are wanting to enlarge the file system then you first must run "fdisk" and delete the existing partition, then recreate the partition at the same starting cylinder but make the ending cylinder beyond the old ending cylinder (requires enough contiguous free space after the partition you want to enlarge). Then you can enlarge your file system using the above utilities.
If you want to shrink the partition, first shrink the file system using the above utilities, then delete the partition and create a new partition on the same starting cylinder but put the ending cylinder at the end of your filesystem (or just beyond the end).
[ August 15, 2002: Message edited by: VoidMain ]