Free disk space by making holes in files
zum reads a files list on the command line and attempts to perforate these files. Perforation means, that series of `0' bytes are replaced by lseek(2)s, thus giving the file system a chance of not allocating real disk space for those bytes.
find . -type f -print0 | xargs -0 zum
If you zum under /boot, where your kernel image lives, your system will become unbootable unless you run lilo again.