Background Jobs and I/O Jobs being executed in the background will stop if they attempt to read input from your terminal. If you tried to interactively remove $PUBDIR/junk in the background, this is what would happen: $ rm i $PUBDIR/junk & [2] +Stopped (tty input) rm i $PUBDIR/junk & The job is stopped because it needs to prompt you for input. The rm i job is brought back into the foreground with the fg command and its prompt is displayed: $ fg %2 rm i $PUBDIR/junk rm: remove /usr/spool/uucppublic/junk? y By default, jobs send their output to your terminal, even while running in the background. Here, the find command sends its output to the terminal, even though it is running in the background: $ find / name core print & [2] 1453 $ /usr/lbin/core /home/anatole/bin/core That can be annoying, especially if you are in the middle of something else. To avoid this problem, redirect the output of background jobs to a file. Make sure to be careful with the redirection. If you don't redirect standard error, error messages will go to your terminal and not to the output file. Let's kill the find job, then restart it and send the output to c.out: $ kill %2 [2] + Terminated find / name core print>c.out & $ find / name core print >c.out & [2] 1453 $ jobs [2] ?Runningfind / name core print & [1] Runningsleep 1000 & We can work on something else until we get the completion message. [2] +Done find / name core print>c.out & Table 5.1. Job Control Commands| bg | put the current stopped job in the background | | bg %n | put the stopped job n in the background | | fg | move the current background job into the foreground | | fg %n | move background job n into the foreground | | jobs | display the status of all jobs | | jobs l | display the status of all jobs along with their process ids | | jobs p | display the process ids of all jobs | | kill %n | kill job n | | kill l | list all valid signal names | | kill ?/span>signal %n | send the specified signal to job n | | set m, set o monitor | enable job control; execute background jobs in a separate process group, and report the exit status of background jobs | | stty tostop | prevent background jobs from generating output | | stty tostop | allow background jobs to generate output (default) | | wait | wait for all background jobs to complete | | wait %n | wait for background job n to complete | | Ctl-z | stop the current job |
There are other ways to deal with job output. Jobs being executed in the background are prevented from generating output by setting stty tostop. Let's run the find job again with the tostop option enabled: $ stty tostop $ find / name core print & [2] 1460 Now when the job has some output, we get this message: [1] + Stopped(tty output) find / name core print & The only way to see the find output is to bring the job back into the foreground. $ fg /usr/lbin/core /home/anatole/bin/core The stty tostop command can be put into your profile file so that background job output is by default disabled. The nohup command can also be used to direct output from background jobs. It causes standard output and standard error to be automatically sent to nohup.out, or whatever file you give it. One added benefit: the nohup command will keep jobs running, even if you log out. Here we run the find job again using nohup. First we need to enable background job output: $ stty tostop $ nohup find / name core print & [2] 1469 $ wait Sending output to 'nohup.out' [2] + Done nohup find / name core print & The find job output is in nohup.out: $ cat nohup.out /usr/lbin/core /home/anatole/bin/core | 
