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I noticed in my system monitor app, on the "Processes" tab, that one can change the 'priority' of a certain program. What specifically would this do? (I'm new)

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This explains how priorities work. "Very high", "High", "Normal", "Low" and "Very Low" represent nice values -20, -5, 0, 5 and 19. – Salem May 5 '12 at 20:24
up vote 3 down vote accepted

An app running with higher priority gets more access to cpu time as compared to an app running with low priority. This is primarily used to keep an app (like the Arista transcoder) from eating all of the cpu time and slowing the system to a crawl, OR, for allowing one app to suck up as much CPU as it can regardless of the consequences.

It is not possible by default to raise the priority of running apps. This includes after you have lowered the priority. However if you wish to do so you simply need to add the following to /etc/security/limits.conf :

USER             -       nice            -20

Replacing USER with your username and then rebooting the machine.

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Can you raise the priority of an app at all by default? Because I changed 'compiz' to low, but if I try to raise it back to normal, I get a permission denied message. – Jiskya May 5 '12 at 21:06
You cannot set it above Normal priority or raise a previously lowered priority without adding the line I noted in an edit to my answer to /etc/security/limits.conf , and then rebooting. Sorry, I edited the answer to clarify. – Mark Paskal May 5 '12 at 21:08

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