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I want to execute a script, start.sh on a remote server which runs this:

nohup node server.js &

Naively, I call SSH like this:

ssh myserver <<EOF
./start.sh &
EOF

This starts the script, but leaves the session connected. I want to follow this step with other commands in a script, so that's no good.

How can I SSH to the remote machine, launch a nohup command into the background, then disconnect? I suppose I could put the SSH process itself into the background, but that doesn't seem right.

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5 Answers 5

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50

You have already found the right way, here document.

NOTE: you can put the ssh (client) into background by placing a & at the end, but you will not see the output. If you really want to do this, redirect the stdout/stderr to a file in case you need to check the response from the remote host.

Basically you can do it in either way:

Directly run the command{,s}

ssh user@host "nohup command1 > /dev/null 2>&1 &; nohup command2; command3"

OR

ssh user@host "$(nohup command1 > /dev/null 2>&1 &) && nohup command2 >> /path/to/log 2>&1 &"

NOTE: && requires the first command to return 0 before executing the second

Use Here document

ssh user@host << EOF
nohup command1 > /dev/null 2>&1 &
nohup command2 >> /path/to/command2.log 2>&1 &
......
EOF

The above 3 options should work for you.

In addition, take a look at the answer here: https://askubuntu.com/a/348921/70270

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10
  • Thanks - so the bit I was missing was really the > /dev/null.
    – Steve Bennett
    Sep 24, 2013 at 0:04
  • Not really, > /dev/null 2>&1 is to discard any stdout/stderr output by redirecting to the black hole lol
    – Terry Wang
    Sep 24, 2013 at 0:18
  • 5
    Note that I would suggest using >> instead of just > to write to log files. Otherwise, you'll only get the errors from the very last run.
    – Alexis Wilke
    Sep 24, 2013 at 0:24
  • Is it correct that if I simply start a command as nohup command2 >> /path/to/command2.log 2>&1 & in a terminal and then close the terminal that the process is lost?
    – Luke
    Apr 7, 2014 at 11:00
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    @TerryWang the second example will not work with ampersand followed by double ampersand, see unix.stackexchange.com/q/67006/86716
    – tsionyx
    Dec 9, 2016 at 14:18
17 
ssh node "nohup sleep 10 &"

is not running in daemon mode, keeping your ssh session connected. Ssh session will return in 10 seconds, despite you used nohup.

Reason is that remote stdout and stderr still connected to your session. It keeps ssh session alive, nohup does not help.

This:

ssh node "nohup sleep 10 1>/dev/null 2>/dev/null &"

returns immediately. It does start remote process with nohup and exits ssh session immediately.

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5
  • This was exactly our problem. We only had a 1>file.log. The ssh on the one machine was stuck. The process on the 'node' machine was running. When we added a 2>&1 just before the closing &, that let the ssh disconnect.
    – Lee Meador
    May 22, 2019 at 22:11
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    This answer explains the key issue: that you need to redirect both stdout and stderr otherwise SSH will kill the command.
    – Davor Cubranic
    Mar 19, 2020 at 3:06
  • Thank you for clarifying the actual problem: the need to redirect stdout & stderr.
    – Sebastiaan
    Oct 20, 2020 at 9:24
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    Just as an even further clarification, nohup isn't even needed when redirecting the stdout and stderr.
    – fullStackChris
    Aug 11, 2021 at 11:58
  • Note: If you run the above but ssh with the -t option (Force pseudo-terminal allocation) then SSH immediately terminates but the remote command never gets started properly. I omitted -t and it then worked. SSH connects passwordless, starts command on the remote (on my NAS it starts a long wget --continue download), quickly thereafter SSH terminates, but the command on the remote (wget on NAS) continued until the download had finished. I checked this as I later connected by SSH interactively and the download there was completed. Tested several times. Worked all times. Thanks!
    – porg
    Dec 24, 2022 at 0:15
9

Why not just tmux or screen and be done with it? For example:

$ tmux new -s SessionNameHere
$ nohup /path/to/your/script.sh

This is practical if it's something that will continuously loop or take a while to finish. You can disconnect from the session and it will remain active.

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1
  • 4
    Doesn't really fit what I'm asking for, which is a single command that can be run on my laptop, which will connect, fork a command, then disconnect.
    – Steve Bennett
    Nov 13, 2014 at 22:24
5

Shorter form:

ssh host "(command 1; command 2; ...) &>/dev/null &"

It appears, that bash itself performs detaching from terminal, so no nohup needed. I run Ubuntu 14.04 x86_64, bash 4.3.11.

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3
  • 2
    This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. - From Review
    – David Foerster
    Feb 28, 2016 at 9:34
  • This doesn't seem to work. nohup; just outputs a complaint about missing arguments.
    – Steve Bennett
    Feb 29, 2016 at 4:32
  • @DavidFoerster, no Idea why, if command 1; command 2; ... represents script OP want to run. OP can also use special case of this answer: ssh myserver ./start.sh &>/dev/null &
    – Alek_A
    Feb 29, 2016 at 10:31
1

And last but not least, remember not to allocate a tty for your session.
If you do that, it will not work.

So if you got any -t or -tt or -ttt and so on in your command. Thats the reason why it is not working for you.

So instead of

ssh -tt host "(command 1; command 2; ...) &>/dev/null &"

Use

ssh host "(command 1; command 2; ...) &>/dev/null &"
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