Pause a process and bring it back to foreground in a separate screen in Ubuntu

Question

A process put to sleep by issuing ^Z can be brought back to the foreground by listing the running jobs $ jobs and giving the job id to fg %id. But when I tried to list the jobs in a separate screen of the same terminal there was no results. How to achieve this ?

What I want is to start the same process without killing it in a separate screen of the same terminal.

Look into using the screen utility. This will allow you to share terminal sessions — Raman Sailopal, Jul 19 '18 at 08:22
Can you elaborate bit more what function in screen to use. ? — Gayan Kavirathne, Jul 19 '18 at 09:02

Kusalananda · Answer 1 · 2018-07-19T09:26:57.377

2

You can't. The handling of shell jobs (foreground and background processes) is done by each individual shell instance. You can't migrate a job from one interactive shell to another, not even within something like screen.

The terminal doesn't really have anything to do with this. It just runs the shell.

What you may do is to migrate a whole shell session with a terminal multiplexer, such as tmux or screen. A shell session within one of these may be moved to another terminal through detaching the screen or tmux session in one terminal and reattaching to it in another on the same machine.

With tmux this is done by first starting tmux, then starting your program inside of the tmux session. When the program is running, you may press prefixd (prefix is Ctrl+B by default) to detach the tmux session. In another terminal, you then give the command tmux attach to get the tmux session back. Detaching can also be done through the command tmux detach.

See the manuals for screen and tmux on your system.

edited Jul 19 '18 at 09:26

answered Jul 19 '18 at 08:25

Kusalananda

333,661

1

There is a funky way of recovering a background job in a different session, IIRC, I’ll try to find it... – Stephen Kitt Jul 19 '18 at 08:33
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@StephenKitt Using magic might always be possible, but would it be a better way than doing it with tmux/screen? – Kusalananda Jul 19 '18 at 08:34
@Kusalananda indeed it is. But think of a situation where the user accidentally starting a process and discover that he forgot to start it in a screen after a considerable amount of the resource and time is consumed by the process, as in perticularyly in my case. – Gayan Kavirathne Jul 19 '18 at 09:06
@StephenKitt Well, essentially you "just" need to attach std{in,out,err} of that process to a new subprocess spawned by your shell. If you have ptys allocated this is fairly simple. If it isn't, IIRC there is some dark ritual you can do with gdb, but I'd like to quote @Kusalananda "would it be a better way than doing it with tmux/screen?" – Bananguin Jul 19 '18 at 09:10
Dark gdb ritual howto slight variation, still dark socially acceptable dark ritual – Bananguin Jul 19 '18 at 09:14
@StephenKitt using reptyr? – muru Jul 19 '18 at 10:05
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And yes, I agree @Kusalananda, it’s better to start off in a terminal multiplexer of some sort. – Stephen Kitt Jul 19 '18 at 11:28

score 1 · Answer 2 · answered Jul 19 '18 at 09:23

The terminal is a viewer onto a process such as the shell. The terminal itself doesn't run any commands - that's the shell's purpose - but without the terminal you cannot interact with the shell or any program it runs.

Normally, when you close a terminal window it sends a signal to the shell to tell it to close down, which in turn kills any process you may have running there.

You can run a process under screen. What this does is create a "virtual terminal" for a shell to run in. Your "real" terminal window can attach to that screen session and control the virtual terminal that screen has provided. The net effect is that it feels perfectly normal BUT you can also detach from the virtual screen and let the shell continue running.

screen                     # Create a leader and a virtual terminal/screen running a shell
screen -ls                 # List sessions (attached/detached)
screen -r                  # Reattach to the single detached session
screen -r {identifier}     # Reattach to the named detached session
screen -md {command...}    # Make a new detached session running {command...}

Finally, Ctrl Ad detaches from the current session and Ctrl A? gets you the list of interactive commands.

Pause a process and bring it back to foreground in a separate screen in Ubuntu

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