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In Unix you can run "jobs", suspend them, run them in the background, or bring them to the foreground. The commands for this are: !jobs This command will list all of the active jobs. Some switches you may like to try include: *''jobs -r'' will display running jobs only. *''jobs -s'' will display stopped jobs only. !bg ''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. *ping www.gooogle.co.nz & !fg ''fg <JOB_SPEC>'' moves the stopped or backgrounded job into the foreground. !kill ''kill %<JOB_SPEC>'' sends a signal to a job. Note : you can use use ''kill -l'' to list the possible signals you could send. !bg,fg and kill are not limited to jobids. 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. *kill %ping *kill %?google *fg ping *bg ?goo 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. !!How this works 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 you type "fg" or "bg", then the process is started with a [SIGCONT], and in the case of fg, [tcsetpgrp(3)] is called to make that ProcessGroup the new foreground ProcessGroup. 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]. The disown builtin may be used to remove a process group from the shells list of jobs, so when the shell exits it doesn't send that process a [SIGHUP].
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