Posts tagged multitasking

bash multitasking
posted on 2014-05-04 17:50:46

When working in the shell under linux and having started a long-running process, which blocks the shell (and you working in it), gives you some options:

  • wait until process is finished, you land at the prompt, you can work on (NO!)
  • open a new shell window, which is no problem when working under a graphical window manager (MAYBE...)
  • use bash's multitasking capabilities (YES!)


First the shortcuts:

Ctrl-C kills the process currently in the foreground.
Ctrl-Z "suspends"/pauses the process currently running in the foreground and puts it into background.
Ctrl-Y suspend job the next time it asks for user input.

The last two differ in such a way, as suspending via Ctrl-Z may swallow pending shell output, whereas Ctrl-Y will not.

Now the commands:

$ jobs              # list all background processes
$ fg                # start marked process in foreground (see '+' on `jobs` list)
$ bg                # start marked process in background (see '+' on `jobs` list)
$ fg %x             # start process with id 'x' in foreground
$ %n                # alias for fg %n
$ bg %x             # start process with id 'x' in background
$ %n &              # alias for bg %n
$ kill %x           # kill process with id 'x'
$ <processname> &   # '&' will start a process and let it run in background

Example usage: (demonstrated via bash's sleep, which just waits for the specified time in seconds)

[sjas@lorelei ~]% sleep 100
[1]  + 7848 suspended  sleep 100

[sjas@lorelei ~]% sleep 200
[2]  + 10920 suspended  sleep 200

[sjas@lorelei ~]% sleep 300
[3]  + 3676 suspended  sleep 300

[sjas@lorelei ~]% sleep 400
[4]  + 10012 suspended  sleep 400

[sjas@lorelei ~]% jobs
[1]    suspended  sleep 100
[2]    suspended  sleep 200
[3]  - suspended  sleep 300
[4]  + suspended  sleep 400

[sjas@lorelei ~]% bg
[4]    10012 continued  sleep 400

[sjas@lorelei ~]% jobs
[1]    suspended  sleep 100
[2]  - suspended  sleep 200
[3]  + suspended  sleep 300
[4]    running    sleep 400

[sjas@lorelei ~]% kill %1
[1]    7848 terminated  sleep 100

[sjas@lorelei ~]% jobs
[2]  - suspended  sleep 200
[3]  + suspended  sleep 300
[4]    running    sleep 400

[sjas@lorelei ~]% fg
[3]    3676 continued  sleep 300

[sjas@lorelei ~]% jobs
[2]  - suspended  sleep 200
[3]  + suspended  sleep 300
[4]    running    sleep 400

[sjas@lorelei ~]%

There is also disown for removing jobs from the list of jobs and other actions. In case of interest man bash and search for disown.

Have fun.

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