Job Control in Linux

How to Put a "Running Job" in the Background.

Linux is a multitasking operating system. Which means that you can run multiple jobs at the same time. Suppose you are logged in to a terminal which does not have X server running. And you're running a job at the terminal prompt, which is taking a very long time to complete. You want to put the job in the background. This is how you do it.

Press "CTRL - z" which temporarily suspends the job. Now run the command :

$ jobs

This will list all the jobs along with a job number. Now to resume a particular job in the background, do the following:

$ bg %jobnumber

in our case it will be

$ bg %1

To bring the job back to the foreground again, do :

$ fg %jobnumber

which in our case is

$ fg %1

Need to kill all jobs ?

Suppose you're using several suspended vi sessions and you just want everything to exit. This is achieved by running the following command:

$ kill -9 `jobs -p`

The "jobs -p" gives the process number of each job, and the "kill -9" kills everything. Sometimes "kill -9" is excessive and you should issue a "kill -15" that allows jobs to clean-up.

Sometimes you need to list the process id along with job information. For instance, here's process id with the listing.

$ jobs -pl

How to lower or raise the priority of a job
You use the 'renice' command for changing the priority of a running job. For example :

$ nice -n +15 find . -ctime 2 -type f -exec ls {} \; > last48hours
[Ctrl+z]
$ bg

Above we execute a 'find' command with a priority of 15. Then we suspended the job with a ctrl+z . Then, the job was run in the background by using the command 'bg'. Now, if you want to change the priority of the job to a lower value, you just 'renice' it as follows:

First get the process ID of the job.

$ jobs -pl
[1]+ 29388 Running

Now lower its priority.

$ renice +30 -p 29388
29388: old priority 15, new priority 19

The range of priority goes from -20 (highest priority) to +19 (lowest priority). You can lower the priority of your program but you cannot increase the priority unless you are root.