I have been able to use 'nice' and 'renice' to set priorities of processes but I run into a few weird problems with 'renice'. When I start an application without 'nice' I get the default priority of 0 and when I manually set the priority using 'nice' it works fine. BUT when a process is already running (with either the default priority or the newly set one) I can't only renice to the current priority and lower. I get a permission denied if I try to go higher. I think this example will make it clear:

prompt> ./myscript1 &
prompt> nice 10 ./myscript2 &

Now if I want to change the first scripts priority to a lower one (like the second one) I can successfully do this: (for the sake of the example lets say the priority of myscript1 is 24106)

prompt> renice 10 24106
24106: old priority 0, new priority 10

And that works fine, so both are running at the lower priority of 10.
Now if I want to put them back to 0 or anything higher than 10 it always says permission denied:

prompt>renice 5 24106
renice: 24106: setpriority: Permission denied

But I can successfully set them to (the same or) lower priorities:

prompt>renice 10 24106
24106: old priority 10, new priority 10
prompt>renice 11 24106
24106: old priority 10, new priority 11
prompt>renice 10 24106
renice: 24106: setpriority: Permission denied

But then I am just getting stuck at lower priorities since now that I have dropped to 11 in the above example I can't get back up higher...

I did a quick play at the command line myself, and it would appear that regular users cannot 'unnice' their own processes. I knew that reg users couldn't negative nice anything, but it seems odd that they cannot bring the priority back to the default of '0'.

Try as root and you can set them lower (higher?) again...

Well I can use root to do anything on my own systems, but if I had root access on the system in question I wouldn't worry about nice'ing anything as I wouldn't be nice. But it isn't my system so I don't have root... I too just thought it was odd that I coulded renice my processes (as long as I stayed over 0). There must be a reson for that though...

I read both the man and info page for nice and renice and saw no mention of this behavior.

That is what prompted my question, I too read them and then was puzzled why I kept having the aforementioned problem. (so I guess the question still stands)

Sorry man, I'm as flabbergasted as you

nice/renice are part of coreutils, which is distributed by the FSF, maybe that is your next place to look if you really want to get to the bottom of this.

This is from a UNIX man page on renice....



So once you've lowered the priority of a process, your screwed. Of course I'm assuming that nobody has re-written renice for Linux and we're all just using the UNIX version

Good call. I read that paragraph paying close attention to "Users other than the privileged user may only alter the priority of processes they own" and selectively ignoring "and can only monotonically increase their "nice value""

<shrug>