Increasing filesystem space

Now, i know a ufs file system can be increased using mkfs but hwo do I take space from a file system and add it to another file system? at my job here, that seems to be possible because I see request on it almost every day.

what is the exact command to do this and does the system need to be down or only processes writting to the desired directory ought to be killed to complete this procedure??

i dont think its possable useing the default commands. at least on aix and solaris. outside of completely removing the exhisting fs and recreateing it.

i think you can do something like that with veritas.

your topic should actually read "DEcreasing FS space"