193

I have a running program on a SSH shell. I want to pause it and be able to unpause its execution when I come back.

One way I thought of doing that was to transfer its ownership to a screen shell, thus keeping it running in there.

Is there a different way to proceed?

Improve this question
3
  • 9
    See also Can I nohup/screen an already-started process? and Resume command running in dropped SSH session, which mention several ptrace-based solutions not (currently) mentioned here.
    – Gilles 'SO- stop being evil'
    Nov 15, 2010 at 22:47
  • 1
    From questions like unix.stackexchange.com/a/4039/13496 I'm hearing about retty and neercs. Hmmm... wonder if there's smth like a "screen here" layer before I run a process next time should I lose the top terminal in the future, that will make it easy to snap back in the stdin/out/err
    – Marcos
    Mar 8, 2012 at 15:00
  • The secondary/implicit issue in this question I can't fathom is...why did the shell choose to disown a suspended job when there is a newer/just launched one in background that doesn't even need/wait for stdin? This is the treatment I've gotten used to so don't know what went different here...
    – Marcos
    Mar 11, 2012 at 13:54

9 Answers 9

Reset to default
131

You can revoke “ownership” of the program from the shell with the disown built-in:

# press Ctrl+Z to suspend the program
bg
disown

However this only tells the shell not to send a SIGHUP signal to the program when the shell exits. The program will retain any connection it has with the terminal, usually as standard input, output and error streams. There is no way to reattach those to another terminal. (Screen works by emulating a terminal for each window, so the programs are attached to the screen window.)

It is possible to reattach the filedescriptors to a different file by attaching the program in a debugger (i.e. using ptrace) and making it call open, dup and close. There are a few tools that do this; this is a tricky process, and sometimes they will crash the process instead. The possibilities include (links collected from answers to How can I disown a running process and associate it to a new screen shell? and Can I nohup/screen an already-started process?):

Improve this answer
6
  • disown removes the process from the job-control list.
    – ctrl-alt-delor
    Apr 15, 2015 at 14:39
  • 4
    Why not disown -h?
    – Cees Timmerman
    Jun 17, 2015 at 15:18
  • @CeesTimmerman That leaves the job in the shell's job table, but what's the advantage of that?
    – Gilles 'SO- stop being evil'
    Jun 17, 2015 at 15:20
  • @Gilles: so you can still fg or kill it, and see if it ends on its own.
    – Peter Cordes
    Aug 11, 2015 at 20:47
  • 1
    @dma_k In this example, you'd only need to move grep's output.
    – Gilles 'SO- stop being evil'
    Oct 18, 2015 at 12:02
85

Using GNU screen is your best bet.

Start screen running when you first login - I run screen -D -R, run your command, and either disconnect or suspend it with CTRL-Z and then disconnect from screen by pressing CTRL-A then D.

When you login to the machine again, reconnect by running screen -D -R. You will be in the same shell as before. You can run jobs to see the suspended process if you did so, and run %1 (or the respective job #) to foreground it again.

Improve this answer
4
  • 52
    I think this doesn't answer the question. The question begins with "I have a program running". This answer assumes it's not running yet…
    – Anko
    Apr 16, 2015 at 9:25
  • 2
    yes he clearly wrote he wants to get it into a screen session :-)
    – Florian Heigl
    Oct 8, 2019 at 17:12
  • This doesn't answer the question, or at least it doesn't answer this question which is linked: unix.stackexchange.com/questions/171250/…
    – user3728501
    Jun 11, 2020 at 19:26
  • This answer is great, as you need some preparation, if you want to it right, at least the next time
    – PythoNic
    Jan 4, 2022 at 12:40
76

To move a process between terminals or to reattach a disowned, you can use e.g. reptyr.

Improve this answer
5
  • 2
    Yeah that saved it, thanks! I read the author's website how it works better than similar or older tools eg. for ncurses programs.
    – Marcos
    Mar 8, 2012 at 15:19
  • 8
    This is awesome; it should solve a friend's predicament of constantly losing her work by running it straight in ssh and then needing to get on a train. "Oops, forgot to use screen. Again."
    – Adam Katz
    Jan 16, 2015 at 5:13
  • 3
    +1 Although the accepted screen answer is of course ideal, it doesn't actually answer the question, which specifically requests a way to move a currently running process to screen or the like. Also see this answer: serverfault.com/a/284795
    – toxefa
    Apr 18, 2015 at 21:15
  • 2
    Absolute live saver. Allowed me to re-attach to running apt dist-upgrade that was sitting on waiting for user confirmation.
    – andig
    Feb 10, 2019 at 12:24
  • Can be installed using APT on Debian based distros: sudo apt install reptyr.
    – Qumber
    Jul 9, 2020 at 10:46
27

My favorite solution is using tmux, you could detach the session, and re-attach it in another terminal.

When you detached from previous session, you can safely close the terminal; later use tmux attach to get back to the session, even if you logged out.

Improve this answer
2
  • 1
    you also can share your session with ur friend and use multiple windows and panes and so much more! love it ^_^
    – igor
    Sep 24, 2013 at 8:03
  • example of using please?
    – Vitaly Zdanevich
    Feb 20, 2016 at 0:55
24

There's also a small utility called retty that lets you reattach running programs to another terminal.

Improve this answer
20

I don't use it regularly, but neercs claims to support this. It's a screen-like program with miscellaneous fancy features like better pane management, but the main thing it offers is the ability to import a process into a pane

Improve this answer
2
  • 2
    Interesting. It does play dirty (ptrace), but it doesn't just manipulate the file descriptors, it forks the process. It's able to grab find /, but crashed an interactive bash.
    – Gilles 'SO- stop being evil'
    Nov 13, 2010 at 22:20
  • @Gilles I can't remember how it went when I tried, but it doesn't have a great reputation, I'm told it fails pretty regularly
    – Michael Mrozek
    Nov 13, 2010 at 22:25
13

If you just want to pause it and restart afterwards, you can use kill with STOP or CONT signal.

At first find out the processes PID with

$ ps aux

Then send the signals to that PID listed to the process

$ kill -STOP <PID>

$ kill -CONT <PID>
Improve this answer
11

"injcode" from ThomasHabets seems to be exactly the thing I need:

https://github.com/ThomasHabets/injcode

The injcode program allows arbitrary code to be injected into a running process, whether or not you knew beforehand and were running screen or tmux

From the README:

Example 1: move irssi from one terminal to another

Maybe move it into a screen.

First start irssi in one terminal.

Run injcode in another terminal: $ injcode -m retty

Irssi should now be moved to the second terminal, including having a new controlling terminal.

Improve this answer
4

This worked for me:

  1. bg the process
  2. jobs -l find process number
  3. tmux start shell window manager
  4. reptyr -L PROCESSNUMBER

reptyr's -L was necessary to get this to work:

-L Like '-l', but also redirect the child's stdio to the slave.

because of this error:

$ reptyr 30622

[-] Unable to open the tty in the child.
Unable to attach to pid 30622: Permission denied

And with -L

$ reptyr -L 30622
Opened a new pty: /dev/pts/4
Improve this answer
1
  • How do we resume the suspended thread in the current terminal?
    – Oron Port
    Dec 18, 2022 at 17:39

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .