I want to run "screen" on a debian linode server, starting up over a ssh terminal window. I'd like a shell script to start and detach a screen, so that a process can continue when I log off. I'd also like the logging file screenlog.0 to be produced, so that there's a record if the process crashes.
But there's a problem in getting the log file to write. Locally, on a mac terminal window,
% screen -dm -L sh -c 'echo hello'
works fine, "hello" gets written to screenlog.0. But the same command issued in a ssh window to the server executes, but nothing gets written.
However, if in that window I go into screen,
% screen -L
and then do some stuff, the activity is written to screenlog.0 (on the server).
What am I missing?
It turns out that the screen() command can have problems. The above command sends no output to screenlog.0 under 'Debian GNU/Linux 9 (stretch)' , while 'Ubuntu 14.04.1 LTS' writes the odd message, "error: could not start server! try running as root!", to screenlog.0, even when running as root. 'Linux Mint 18.1' and MacOSX run correctly.
I was advised to use the venerable unix command "nohup" to solve my problem of detaching a process and logging its output, even when you close the ssh connection. Ordinarily, when you close a terminal window, the signal SIGHUP is sent to any processes that were started there. But
% nohup myprog > logfile.txt &
works perfectly. Old way, good way.
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This question already has answers here:
How to make a program continue to run after log out from ssh? [duplicate]
(6 answers)
Closed 3 years ago.
I need to run a Perl script for several days processing something. On a linux Centos server, from the SSH terminal I run this command:
nohup perl script.cgi 2>&1 &
This runs the script in the background and writes the output to nohup.out.
The problem when I close the SSH terminal or even my internet connection disconnects the script terminates.
I need to keep this command running in the background on the server after I close
the SSH terminal.
You can use Terminal multiplexer tools like screen, byobu or tmux.
I personally use screen. so install it on remote server via sudo apt-get install screen.
ssh into server
open screen session by screen -S sessionname
Now run your command (background/foreground both works)
now detach to your session by command ctrl+a then press d.
Now shut your pc and enjoy
now come back ssh into server then use command screen -x sessionname to reconnect the detached session.
Hurray! script is still running.
you can either use screen or run the command using supervisor in linux systems.
you can install screen using sudo apt install screen
then use following command to run it.
screen -S test_command
nohup perl script.cgi 2>&1 &
Then press ctrl+a and ctrl+d to leave that session running for whatever amount of time required until your server reboots.
If you want to stop the command use screen -x test_command, then ctrl+c and use ctrl+a and ctrl+d to close screen or ctrl+a and ctrl+d to leave the screen session as it is.
The only way I was able to run the command and exit the shell and keep the command running is using the "at" tool to schedule the job like this using the full script path:
echo "perl /home/username/www/script.cgi" | at now + 1 minute
I have a java program that starts a TCP/IP game server.
I have an angular application that speaks with an express node.js server to start/stop the game server.
When the button start is clicked the following operation is performed in the nodejs server:
shell.exec('/web/starter.sh');
And this is my script:
:set fileformat=unix
#!/bin/sh
screen -RD server -X quit;
screen -dmS server;
cd ~/cadesim-monomer;
java -jar CadeServerEngine.jar;
It works, it starts the server. But whenever I click start again, it doesn't restart the server as it should. It should kill the screen and restart?
What did I do wrong?
The issue is that the server commands aren't running inside the detached screen session. They are running after both of the screen commands.
To run a command in detached screen session for this example would need to use:
screen -dmS server sh -c "cd ~/cadesim-monomer; java -jar CadeServerEngine.jar"
Or you can put the server and its setup in its own shell file and that file would have a similar appearance to a daemontools run script. And then you would have a command like:
screen -dmS server ./server.sh
Also the shebang line should be the first line in the file. The script just happens to work because the shell is the default interpreter. It produces the error line 1: :set: command not found. The VIM mode setting should occur in a comment on the second line.
I am using SSH to start a background process on a remote server. This is what I have at the moment:
ssh remote_user#server.com "nohup process &"
This works, in that the process does start. But the SSH session itself does not end until I hit Ctr-C.
When I hit Ctr-C, the remote process continues to run in the background.
I would like to place the ssh command in a script that I can run locally, so I would like the ssh session to exit automatically once the remote process has started.
Is there a way to make this happen?
The "-f" option to ssh tells ssh to run the remote command in the background and to return immediately. E.g.,
ssh -f user#host "echo foo; sleep 5; echo bar"
If you type the above, you will get your shell prompt back immediately, you will then see "foo" output. Five seconds later you will then see "bar" output. In the meantime, you could have been using the shell.
When using nohup, make sure you also redirect stdin, stdout and stderr:
ssh user#server 'DISPLAY=:0 nohup xeyes < /dev/null > std.out 2> std.err &'
In this way you will be completely detached from the remote process. Be carefull with using ssh -f user#host... since that will only put the ssh process in the background on the calling side. You can verify this by running a ps -aux | grep ssh on the calling machine and this will show you that the ssh call is still active, but just put in the background.
In my example above I use DISPLAY=:0 since xeyes is an X11 program and I want it started on the remote machine.
You could use screen to run your process on this screen, detach from screen Ctrl-a :detach and exit your current session without problem. Then you can reconnect to SSH and attach to this screen again to continue with your task or check if is finished.
Or you can send the command to an already running screen. Your local script should look like this:
ssh remote_user#server.com
screen -dmS new_screen sh
screen -S new_screen -p 0 -X stuff $'nohup process \n'
exit
For more info see this tutorial
Well this question is almost 10 years old, but I recently had to launch a very long script (taking several hours to complete) on a remote server and I found a way using the crontab.
If can edit your user's crontab on the remote server, connect with ssh to the server, edit the crontab and add an entry that will start your script the next minute. Let's say it's 15h03. Add this line :
4 15 * * * /path/to/your/script.sh
save your crontab, wait a minute for the script to be launched. Then edit again your crontab to remove this entry.
You can then safely exit ssh, even shut down your computer while the script is running.
I'm connecting to my ubuntu server using ssh. I start an encoding program using a command. However, it seems that when my ssh session closes (because I started it on a laptop which went to sleep). Is there a way to avoid this (of course preventing my laptop from sleeping is not a permanent solution).
Run your command with nohup or use screen
nohup is better when your program generate some loging output because it's forward to file and then you can check it, but with screen you can detach ssh session and when you log again you can restore your work-space. For encoding I'll use nohup. It is easier and you probably run it in background, so you really don't need detaching
Screen is the best for you.
screen -S some_name
than run it. Detach it with: ctrl+a d
Next time, attach it with:
screen -rd some_name
You can have more runnning screens. To show the list of them:
screen -ls
Install "screen" on your ubuntu server, that way you can start any program in your session, disconnect the output of the program from your current session and exit.
Later when you connect again to your server, you can restore the program which will continue running and see its progress.
I've searched, googled, sat in IRC for a week and even talked to a friend who is devoutly aligned with linux but I haven't yet received a solid answer.
I have written a shell script that runs as soon as I log into my non-root user and runs basically just does "./myprogram &" without quotation. When I exit shh my program times out and I am unable to connect to it until I log back in. How can I keep my program running after I exit SSH of my non-root user?
I am curious if this has to be done on the program level or what? My apologizes if this does not belong here, I am not sure where it goes to be perfectly honest.
Beside using nohup, you can run your program in terminal multiplexer like screen or tmux. With them, you can reattach to sessions, which is for example quite helpful if you need to run terminal-based interactive programs or long time running scripts over a unstable ssh connections.
boybu is a nice enhancement of screen.
Try nohup: http://linux.die.net/man/1/nohup
Likely your program receives a SIGHUP signal when you exit your ssh session.
There's two signals that can cause your program to die after your ssh session ends: SIGHUP and SIGPIPE.
SIGHUP will be sent to your program because the parent process (ssh) has died. You can get around this either by using the program nohup (i.e. nohup ./myprogram &) or by using the shell builtin disown (./myprogram& disown)
SIGPIPE will be sent to your program if it tries to write to stdout or stderr after the ssh session has been disconnected. To get around this, redirect them to a file or /dev/null, i.e. nohup ./myprogram >/dev/null 2>/dev/null &
You might also want to use the batch (or at) command, in addition to the other answers (nohup, screen, ...). And ssh has a -f option which might interest you.