Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

If I run a process as root on an out-of-the-box fedora machine, is there any reason for a process to not be able to use up ~80% of the cpu?

share|improve this question

migrated from Dec 25 '09 at 0:06

This question came from our site for professional and enthusiast programmers.

Not that I'm aware of. Can you be more specific about why you think this is the case? – Peter Rowell Dec 25 '09 at 0:02
This question is far more suited for ServerFault. – Dav Dec 25 '09 at 0:02
If it's a multicore machine, it can use no more than 100% of one core. So, on a 4-core machine it will be limited to 25% CPU. – Artelius Dec 25 '09 at 0:04
up vote 4 down vote accepted

There are several reasons why a process might not use up all of the CPU. A process may have a limitation on how much CPU it uses, such as a loop that sleeps every once in a while in order to avoid using too much CPU or battery. Or a process may be I/O bound; that is, it needs to do I/O frequently (disk I/O, network I/O, or swapping in lots of memory). A process may also be niced to be lower priority and take up less CPU when another process needs it.

share|improve this answer

See the ulimit command

share|improve this answer

Any process can use 100% CPU. Even on a multicore machine - it could spawn threads or child processes which are run on the other cores. Generally if the process is using 100% CPU, it is because it is CPU bound and must do so to complete its work. There is nothing wrong with this, unless the app is written inefficiently.

You may want to look at renice if you want the process to share the CPU more nicely with other processes.

(Hope the link is OK by you, mgb.)

share|improve this answer
Upvoted for the mention of renice. – TrueDuality Dec 25 '09 at 7:06

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.