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Annotated edit history of JobControl version 7, including all changes. View license author blame.
Rev Author # Line
1 PerryLorier 1 In Unix you can run "jobs", suspend them, run them in the background, or bring them to the foreground.
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3 The commands for this are:
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4 BenStaz 5 !jobs
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7 This command will list all of the active jobs.
8 Some switches you may like to try include:
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10 *''jobs -r'' will display running jobs only.
11 *''jobs -s'' will display stopped jobs only.
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13 !bg
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15 ''bg <JOB_SPEC>'' moves the job into the background.
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6 BenStaz 17 Note : if the job is currently in the foreground you will first have to suspend it using ''Ctrl-z'' ([SIGTSTP])
4 BenStaz 18
19 Note : To start an application in the background append ''&'' to the end of your command.
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21 *ping www.gooogle.co.nz &
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23 !fg
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25 ''fg <JOB_SPEC>'' moves the stopped or backgrounded job into the foreground.
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28 !kill
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30 ''kill %<JOB_SPEC>'' sends a signal to a job.
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32 Note : you can use use ''kill -l'' to list the possible signals you could send.
3 BenStaz 33
34 !bg,fg and kill are not limited to jobids.
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36 We can also specify the start or part of the job command.
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38 For example: If a job command consisted of ''ping www.google.co.nz'', then these commands are valid.
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40 *kill %ping
41 *kill %?google
42 *fg ping
7 BenStaz 43 *bg ?goo
3 BenStaz 44
45 These will work as long as you don't supply an ambiguous job_spec.
4 BenStaz 46 Notice that, only kill requires the ''%'' so that it knows we are providing it with a JOB_SPEC rather than a process id.
7 BenStaz 47
1 PerryLorier 48
49 !!How this works
2 PerryLorier 50 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).
1 PerryLorier 51
52 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".
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2 PerryLorier 54 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.
1 PerryLorier 55
56 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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58 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].