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I have a running command that should take about 10 days. As the process is search files in all subdirectories and converting videos. To each video comand line found, the system changes the process number.

This is the line I'm running:

find . -exec ffmpeg -i {} -vf scale=1280:720 -vcodec libx264 -crf 30 -b:v 300000 {}_250.mp4 \;

How can I do to quit the SSH session and leave some current command line running normally?

I'm already on day 2 and my fear is that my connection will be interrupted simply and I lose all this time.

marked as duplicate by Thomas Dickey, Rui F Ribeiro, Raphael Ahrens, jimmij, Anthony Geoghegan Jan 14 '18 at 18:25

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  • You should probably have started the session with nohup? – Weijun Zhou Jan 13 '18 at 15:25
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    i normally run commands in background with & at the end of command then disown – user137124 Jan 13 '18 at 15:57
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    @ThomasDickey This is obviously not a duplicate as this question is about saving a running process and not about preparations to avoid the problem. – Hauke Laging Jan 13 '18 at 17:43
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With

netstat --inet --inet6 -lnp | grep :22

you can find the PID of the sshd process. And with

# pstree -p -n 1527
sshd(1527)─┬─sshd(32296)───bash(32298)───screen(32336)
           └─sshd(32723)───bash(32725)───find(32763)───sleep(323)

you can see the subprocesses.

If bash(32725) dies then it kills find(32763) with SIGHUP. This could be prevented by making find run in the background and using the shell builtin disown. But if sshd(32723) dies then the controlling terminal for all its child processes and their children goes away and thus the kernel kills them.

You can suspend shd(32723) and bash(32725). That way they cannot kill the find when e.g. the SSH connection is broken:

kill -stop 32723 32725

And next time be a bit cleverer in advance. There is hardly any reason not to use screen or tmux when you login over a network.

  • Okay, I think I got it. I can suspend shd(32723) and bash(32725) process. How do I return to this task run and log out safely? – Max Jan 13 '18 at 17:33
  • @Max With a non-responding sshd you do not log out at all. On the client side you can either kill the ssh process, wait for it to die on its own due to the non-responding server or have it break the session and exit by pressing <enter>, <~>, and <.> – Hauke Laging Jan 13 '18 at 17:40
  • Do you believe that the best then would be to start the whole process again? I'd rather do it now and lose only 2 days than on day 9 something happen and I have to repeat it all over again. Can you help me? What would my command line look like so I can get out of here and then return and continue seeing the whole process running? – Max Jan 13 '18 at 20:12
  • @Max I think you are on the safe side with kill -stop. But then you cannot "see" the process any more. This can work only if neither find nor any of the subprocesses try to read from or write to the terminal. So if you are sure there will be neither reads nor writes then use kill. If you are not then stop the process and use screen. Do you lose time at all when stopping? You can skip the files you already processed, can't you? Is it difficult to detect them? – Hauke Laging Jan 13 '18 at 20:18
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    +1 for (paraphrased) always use screen. Just make sure you're not on a systemd system with KillUserProcesses turned on! – Fox Jan 14 '18 at 18:06
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nohup find . -exec ffmpeg -i {} -vf scale=1280:720 -vcodec libx264 -crf 30 -b:v 300000 {}_250.mp4 \; &

You will get a warning on the first quit, but if you repeat the quit the program should keep running - unless it needs terminal input.

But I was too fast, overlooked the fact that your program is already running.

  • Well I could have posted this as an answer but I didn't because it seems that the command is already running without nohup ... – Weijun Zhou Jan 13 '18 at 16:09
  • He restarted anyhow, in which case he could have used nohup. – Gerard H. Pille Jan 13 '18 at 21:55

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