UNIX for Dummies Questions & Answers

i read a book about this a couple of times and i still find it confusing.

they talking about when you increase a priority number, that decreases nice number. I really dont understand this.

I'm working on a solaris and linux red hat 7.2 system.

if anyone can explain this stuff to me in full depth and also tell me the situation it is most used in, I will certainly appreciate it.

(please explain it in plain english)

Let me help.


There are 2 commands nice and renice. First of all, nice is only used when you want to change the default priority level of the process that you are initiating. On all flavors of unix there is a default priority level for Users and for Root. I believe this can be modified, but I wouldn't mess with that. use renice instead.

Nice is used only at the time you kick off a script or a command from the command line to set the priority to something other than the default setting which is usually somewhere in the middle of the priority range. For some systems it is from +20 to -20. so the default could be around +10 for users and +-0 for Root.

Renice is only used when a process is running to change the priority level up or down.

Now, when you change the priority, A higher number is a lower priority. A lower number is a higher priority. Just think of the game of golf. lower is faster, better.

Hope this helps.

If a higher number is a lower priority and a lower number is a higher priority, then tell me, what are the steps in making only the important process run while the less important ones be runned when the most important ones are done running?

meaning, I want to make all important processes run before the less important onces. By the way, how do I word that?? do I say I want to increase the priority or decrease??

by the way, if anyone is going to help me hear, can you please tell me the steps you would go thru when working on a solaris and linux red hat 7.2 system. I would prefer the answer to deal with Linux


thanks in advance

In general only the root user can give a process a higher( lower number) priority. Users can only give a process a lower( higher number) priority.

NORMAL USERS ONLY
In general for normal users, they can use the nice command but probably wouldn't because they have the best priority they can get with the default priority they are assigned, usually around +10 or so. They can, however, use nice to give a process a lower ( higher number) priority, if it is something that can take its time to complete.


ROOT USER ONLY
For the nice command you can do something like this. It will give it the lowest priority possible. However, this can be dangerous if the process is CPU intensive. It could severly slow down your box! I would never go below -10, if your system priority goes from +20 to -20. Some OSs are different.

nice --20 /path/to/some/process


to change the nice value of this process.

renice -10 /path/to/some/process


Notice that I used 2 -- in the first example. The first dash is for the option. The second one is for the "sign" of the priority. You must give it a negative sign in order to increase the priority. REMEMBER, ONLY THE ROOT USER CAN INCREASE PRIORITY OF A PROCESS.

Read the man pages for more detail on this topic. man nice and man renice.