Ubuntu – Start a screen session and run a script without attaching to it

background-processbashgnu-screenscriptssession

I'm trying to write a script to:

Start a new screen session
Run some program or script within that new screen session
Detach from the screen session, while the program from step 2 may still be running in there. If the program from step 2 finishes, immediately or later, the screen session should remain running (detached).

I have been trying all sorts of combinations with screen -X program or screen -S somename followed by program followed by screen -D, combining with -d or -m options which I find in related questions and answers but nothing works.

The closest I could get was this:

screen -S MySessionName -d -m myprogram

This launches a new screen session in the backgroun, running myprogram.
Except as soon as myprogram finishes (sometimes instantly) the screen session terminates, whereas I want to keep it running.

Best Answer

Method 1

I created a demo setup you described here in my machine. I also faced the issue you reported. But adding a small line of script solved my issue.

I added the following line at the end of myprogram

exec $SHELL

After your script is finished, the Bash process will replace itself with a new invocation of itself.

Method 2

Or you can try the following method in which we start a detached screen first and send command to that screen using stuff

For this first you need to start a detached screen.

screen -dmS MySessionName

And then send the script to that screen.

screen -S MySessionName -p 0 -X stuff 'myprogram\n'

This also worked for me.

Related Solutions

Ubuntu – Run a program with GNU screen and immediately detach after

Did you really mean to put the \ at the end of the line? If not then try removing those - they escape the following character.

also, dropping the -X helps the setup work for me, for instance:

screen -S test -d -m -X touch /tmp/test

fails with No screen session found, however:

screen -S test -d -m touch /tmp/test

works fine. As such I suspect the following will work for you:

#!/bin/bash
screen -S test -d -m $HOME/folder/folder/.program
screen -S test2 -d -m $HOME/folder/folder/.program2

Remember, that if you run this at boot time, $HOME is not the same as after you log in as a specific user. If you need to run it as a certain user you'll need to use the likes of su to run it as that user, and specifying the full path will remove any ambiguity:

#!/bin/bash
screen -S test -d -m su - username /home/username/folder/folder/.program
screen -S test2 -d -m su - username /home/username/folder/folder/.program2

Or, you would call the entire script above as su - username /path/to/your/script.

Ubuntu – Reattaching to an existing screen session

There are two levels of "listings" involved here. First, you have the "window listing" within an individual session, which is what ctrl-A A is for, and second there is a "session listing" which is what you have pasted in your question and what can also be viewed with screen -ls.

You can customize the session names with the -S parameter, otherwise it uses your hostname (teamviggy), for example:

$ screen

(ctrl-A d to detach)

$ screen -S myprogramrunningunderscreen

(ctrl-A d to detach)

$ screen -ls

There are screens on:
    4964.myprogramrunningunderscreen    (05/31/2013 09:42:29 PM)    (Detached)
    4874.pts-1.creeper  (05/31/2013 09:39:12 PM)    (Detached)
2 Sockets in /var/run/screen/S-paul.

As a bonus, you can use an unambiguous abbreviation of the name you pass to -S later to reconnect:

screen -r myprog

(I am reconnected to the myprogramrunningunderscreen session)

Best Answer

Related Solutions

Ubuntu – Run a program with GNU screen and immediately detach after

Ubuntu – Reattaching to an existing screen session

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