Keep a script on remote machine running (nohup?)

Shell Programming and Scripting
1

Hi,

I'm using expect to ssh into remote machine (i know its not the best practice), and run script "script.sh".

This "script.sh" checks whether an other process (some another script) is running and if not, it runs it as some other user.

#!/bin/bash

/usr/bin/expect << EOD
        set timeout 2
        spawn ssh "$user@$host"
        sleep 2
        expect "*assword:"
        send "$passwd\r"
	
        expect ">"
	send "/home/$user/script.sh\r"
        sleep 2
        expect ">"
        send "exit\r"
EOD

Heres the "script.sh"

#!/bin/bash
        if [ -z "$(pgrep some_process)" ]; then
		echo "some_process not running.. Starting.."
        	echo "passwd" | su - user
        	nohup ./some_process &
		echo "PS : $(ps ax | grep some process)"
                echo "passwd_of_original_user" | su - original_user
		echo "PS : $(ps ax | grep some process)" #some_process is already not running at this line
        else
 		echo "Some_process already running.."
        fi

Now the problem is that the "some_process" should run continuously, yet at the second check of running processes (the line with a comment in code) it is already not running.

From what I googled, the "nohup" command should keep it running even after logging out of the system, but apparently it doesn't.

I dont know what I'm doing wrong, any help will be appreciated

2

What does "some process" do? Is it short lived by definition? Any error msgs? Does your grep work correctly (the "_" is missing in the search pattern)? Why do you change from pgrep to grep ? I think by switching to and fro between users you're closing your shell/script...

3

Some_process isnt short lived. It runs continuously until user tells it to stop.

The greps are working correctly (the first one displays the process, I've obviously changed the code to be easier to read for people here, so missing "_" is not a real problem).

As for closing my shell/script - from what I understand that's exactly what

nohup

is for - keep the process running even after logout, user change, shell close, yet somehow it seems to be not working

4

Is it really required to have 2 passwords, 1 for each user, hardcoded in the script, that is stored remotely?

AFAIU: expect is to make it easy to the user to TYPE the password which then is passed to 'whatever'.
Why is it even required to change the user?

Further, i'd change:

nohup ./some_process &
echo "PS : $(ps ax | grep some process)"

to

nohup ./some_process &
PID=$!
echo "PS : $(ps ax | grep $PID)"

or even just

nohup ./some_process &
PID=$!
ps $PID|grep -v PID

My 2 cents, hth

5

I don't think the below is the correct way to run some_process as user

		echo "some_process not running.. Starting.."
        	echo "passwd" | su - user
        	nohup ./some_process &
		echo "PS : $(ps ax | grep some process)"
                echo "passwd_of_original_user" | su - original_user
		echo "PS : $(ps ax | grep some process)" #some_process is already not running at this line

Instead try something like this:

		echo "some_process not running.. Starting.."
        	echo "passwd" | su - user -c "nohup ./some_process &"
		echo "PS : $(ps ax | grep some process)" #some_process is already not running at this line

However su on many systems will also refuse to accept passwords from a pipe issuing an error like standard in must be a tty .

sudo is usually a better choice in this situation, as the requiretty constraint can be relaxed for some_process or user .
If as I suspect you have little admin control over host you may be forced to run another expect script to get some_process running as user

1 Like
6

Thanks Chubler, that code is indeed the correct way as I just checked

echo "passwd" | su - user -c "nohup ./some_process &"

Although I couldnt check it on the original "some_process" today, it seemed to click with "some_another_process" :wink: I sure hope it'll also work for the original one or I'll get sad