Linux – How to create several screen sessions on startup in Linux

bootcrongnu-screenlinuxUbuntu

Firstly, what's the best way to execute commands on startup, cron? Can I use su in a shell script to switch between different users, if so how?

How do I create several detached screen sessions on startup? screen -A -m -d -S test ./script.sh seems like it should work but using it in a script started by cron doesn't show any screen sessions running after booting.

It looks like the screen session is closed after the command finishes executing, can I keep it open so I can see the output?

Thanks!

Best Answer

To run a command when the system boots, schedule it for @reboot in cron. See man 5 crontab for details. This means your crontab line should look like

@reboot screen -m ...

Don't use su for that, put the command in the crontab of the user who should run the command. That way, the user can manage the commands without root's intervention. (But if you wanted to run a command as a system user without letting that system user change the command for security reasons, somethnig like su -c /path/to/command www-data in /etc/rc.local would be better.)

Screen closes a window when its command finishes and terminates the session when its last window is closed. If you want to see the script's output after it's finished, run another command after it to wait for input. For example, to leave the window open until you press Enter in it:

screen sh -c './script.sh; read'

Remember that screen only keeps a finite number of history lines. Unless script.sh sometimes requires interaction, you would be better served by redirecting its output to a file. If it does require interaction, you can use screen's log command to send output to a file (and then it's not a problem if the screen session terminates when it doesn't require input).

Related Solutions

Gnu screen automation

You can put your commands in a file, e.g., myscreenrc, like this:

screen command1
screen command2
screen command3

and then execute screen with the -c option followed by the name of that file, e.g.,

screen -c myscreenrc

UPDATE

in reponse to the updated question. The commands I used for testing were screen vim foo and screen vim bar, so I didn't see the screen-closing problem. The following solves the screen-closing problem, but it seems a bit of a kludge.

screen bash -c 'ls foo; exec bash -i'
screen bash -c 'ls bar; exec bash -i'

ls was just a convenient command for testing this problem.

UPDATE #2

Another approach would be to start the command from the shell's rc file rather than from screen's rc file. It requires another file for each command, though. For example, to run top in a screen window such that quitting top will return you to a bash prompt in that same window, create a file, call it runtop, that contains the following:

. ~/.bashrc
top

Then put this line in the file we're calling screenrc:

screen bash --rcfile ~/runtop -i

and start screen as

screen -c screenrc

Linux – How to launch multiple screen sessions from a single bash script

I ended up taking this question to StackOverflow, where Brian Gerard answered the question. The {0..5} loop syntax is bash (3.x+) specific. By default, my system was setup to run some other shell from /bin/sh, so I changed my sharp-bang to #!/bin/bash and my problem was solved!

Best Answer

Related Solutions

Gnu screen automation

Linux – How to launch multiple screen sessions from a single bash script

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