To renice every process owned by a user,
To renice every process owned by a user, use the -u flag. For example, to make my processes more important than anyone else’s, I could enter this command: ………………………………………………………………………………………. # renice -5 -u mwlucas 1000: old priority 0, new priority -5 # ………………………………………………………………………………………. The 1000 is my user ID number on this system. Again, presumably I have a very good reason for doing this besides a need for personal power.[5] NoteRenicing, rescheduling, and process management don’t create additional CPU time, they simply rearrange the CPU time you do have. If you cannot reschedule processes, and you cannot satisfactorily renice things to tune the way the system behaves, you really do need faster or additional hardware. Some systems have an extra motherboard slot for an additional CPU, which is a quick and inexpensive way to boost performance when the system is CPU-bound. If you have multiple CPUs, definitely take a look at the discussion of SMP in Chapter 11. [2]Some users actually try to use up system resources by starting programs. This is called a forkbomb. These users are like script kiddies, but not as educated. [3]Sluggy Freelance (http://www.sluggy.com/) and Help Desk (http://www.ubersoft.net/), if anyone cares. [4]This might be one of the few circumstances where common sense won out in naming UNIX commands. [5]Being a selfish person doesn’t qualify as a good reason. Or so I’ve been told. When Swap Goes Bad I said earlier that using swap space isn’t bad in and of itself because swap space is used as virtual memory. (In other words, memory space on the hard drive is being used in the same way as RAM.) Swap space is much slower than chip memory, but it does work in a pinch, and many programs don’t need to have everything in RAM in order for them to run. If programs spend 80 percent of their time in 20 percent of their code, then 80 percent of their bulk can be put into swap space without seriously impacting performance. Many sysadmins use the term swapping generically, lumping two different activities (paging and swapping) together without understanding the crucial difference between them. Paging When you read about virtual memory, you’ll see references to pages. A page is simply a section of memory, 4KB on x86 hardware under FreeBSD. (Different platforms have different page sizes.) Data moves between real and virtual memory in units of pages. Paging happens when a portion of a running program is moved onto swap. This process can actually improve performance on a heavily loaded system because unused bits can be stored on disk until they’re needed. 414
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