In Unix you can run "jobs", suspend them, run them in the background, or bring them to the foreground.
The commands for this are:
This command will list all of the active jobs. Some switches you may like to try include:
bg <JOB_SPEC> moves the job into the background.
Note : if the job is currently in the foreground you will first have to suspend it using Ctrl-z (SIGTSTP)
Note : To start an application in the background append & to the end of your command.
fg <JOB_SPEC> moves the stopped or backgrounded job into the foreground.
kill %<JOB_SPEC> sends a signal to a job.
Note : you can use use kill -l to list the possible signals you could send.
We can also specify the start or part of the job command.
For example: If a job command consisted of ping www.google.co.nz, then these commands are valid.
These will work as long as you don't supply an ambiguous job_spec. Notice that, only kill requires the % so that it knows we are providing it with a JOB_SPEC rather than a process id.
Internally each command line (job) gets it's own ProcessGroup assigned to it by the shell when it creates the job using setsid(2). While the command is running in the foreground it recieves any signals from the tty layer (such as SIGTSTP, SIGINT, SIGQUIT, SIGHUP etc).
If you press ^Z the ProcessGroup gets sent a SIGTSTP. If the process(es) ignore the SIGTSTP, this is converted by the kernel into a SIGSTOP. When a process recieves a SIGSTOP it's parent (the shell) will get notified (via a SIGCHLD), and will mark that job as being "Stopped".
When the shell recieves a SIGHUP (presumably from the terminal going away), then it will send a SIGHUP to each job. If a job is also "Stopped" then the shell will also send it a SIGCONT. Depending on your shell, exiting the shell with ^D, "exit", "logout","exit 0" etc may or may not cause jobs to recieve the SIGHUP.
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