Friday, April 8, 2022

[SOLVED] Bash script to run a detached loop that sequentially starts backgound processes

Issue

I am trying to run a series of tests on a remote Linux server to which I am connecting via ssh.

  • I don't want to have to stay logged in the ssh session during the runs -> nohup(?)
  • I don't want to have to keep checking if one run is done -> for loop(?)
  • Because of licensing issues, I can only run a single testing process at a time -> sequential
  • I want to keep working while the test set is being processed -> background

Here's what I tried:

#!/usr/bin/env bash
# Assembling a list of commands to be executed sequentially
TESTRUNS="";
for i in `ls ../testSet/*`;
do 
  MSG="running test problem ${i##*/}";
  RUN="mySequentialCommand $i > results/${i##*/} 2> /dev/null;";
  TESTRUNS=$TESTRUNS"echo $MSG; $RUN"; 
done
#run commands with nohup to be able to log out of ssh session
nohup eval $TESTRUNS &

But it looks like nohup doesn't fare too well with eval. Any thoughts?


Solution

You could take a look at screen, an alternative for nohup with additional features. I will replace your testscript with while [ 1 ]; do printf "."; sleep 5; done for testing the screen solution.
The commands screen -ls are optional, just showing what is going on.

prompt> screen -ls
No Sockets found in /var/run/uscreens/S-notroot.
prompt> screen
prompt> screen -ls
prompt> while [ 1 ]; do printf "."; sleep 5; done
# You don't get a prompt. Use "CTRL-a d" to detach from your current screen
prompt> screen -ls
# do some work
# connect to screen with batch running
prompt> screen -r
# Press ^C to terminate the batch (script printing dots)
prompt> screen -ls
prompt> exit
prompt> screen -ls

Google for screenrc to see how you can customize the interface.

You can change your script into something like

#!/usr/bin/env bash
# Assembling a list of commands to be executed sequentially
for i in ../testSet/*; do
do 
  echo "Running test problem ${i##*/}"
  mySequentialCommand $i > results/${i##*/} 2> /dev/null 
done

Above script can be started with nohup scriptname & when you do not use screen or simple scriptname inside the screen.



Answered By - Walter A
Answer Checked By - Gilberto Lyons (WPSolving Admin)
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