If you ^Z from a process, it gets "stopped". How do you switch back in?

Question

I accidentally "stopped" my telnet process. Now I can neither "switch back" into it, nor can I kill it (it won't respond to kill 92929, where 92929 is the processid.)

So, my question is, if you have a stopped process on linux command line, how do you switch back into it, or kill it, without having to resort to kill -9?

Solution 1

The easiest way is to run fg to bring it to the foreground:

$ help fg
fg: fg [job_spec]
    Move job to the foreground.

    Place the job identified by JOB_SPEC in the foreground, making it the
    current job.  If JOB_SPEC is not present, the shell's notion of the
    current job is used.

    Exit Status:
    Status of command placed in foreground, or failure if an error occurs.

Alternatively, you can run bg to have it continue in the background:

$ help bg
bg: bg [job_spec ...]
    Move jobs to the background.

    Place the jobs identified by each JOB_SPEC in the background, as if they
    had been started with `&'.  If JOB_SPEC is not present, the shell's notion
    of the current job is used.

    Exit Status:
    Returns success unless job control is not enabled or an error occurs.

If you have just hit Ctrl Z, then to bring the job back just run fg with no arguments.

Solution 2

You can use jobs to list the suspended process. Take the example. Start with a process:

$ sleep 3000  

Then you suspend the process:

^Z
[1]+  Stopped                 sleep 3000

You can list the process:

$ jobs
[1]+  Stopped                 sleep 3000

and bring it back to the foreground:

$ fg %1
sleep 3000

The %1 corresponds to the [1] listed with the jobs command.

Solution 3

You should be able to re-start a suspended process by using the kill command to send the process the CONTINUE signal, from the command-line, thus:

kill -CONT 92929

Comments

[bobobobo]

Thanks!! I suppose this is the eq of Alt+Tab. Do you know what happened as soon as I did fg telnet though. It said Terminated, presumably b/c of my previous kill cmd.

[terdon]

@bobobobo presumably, yes. Anyway, the fg does not need any arguments. If you have just hit ^Z, run fg in the same terminal and it will bring back the 1st job.

[bahamat]

This will cause it to resume operation, but not to be brought to the foreground.

[Geeb]

@bahamat Yes, quite true. One would still need to fg inside the original terminal. I like to -STOP and -CONT gui programs to save resources, but they are effectively running in the background anyway.

[Timo]

In case of sleep it will kill the process which is not what you want..;)

[SR_]

Maybe not the correct answer, but a very useful one ! I have a script that opens several terminals in order to execute several commands concurrently. When I press ctrl-z on a terminal where a shell was launched to execute a command given as a parameter, it will stop the command. jobs then shows an empty list. I don't understand why the list is empty, but this kill -CONT is the only solution I know in this case to resume the stopped process.