help: bash script to start a process and stop it (not another instance)

[frafu]

Hello,

I want to write a script that starts a process and later kills it again. In other words, I call a script to start the process; later I call it again to stop the process.

How can I make sure to kill the process that I started and not another instance of that process?

I thought about getting the pid of the started process and storing it into a file. When the script is called again, it reads the file to get the pid of the process to kill.

Or is there a better standard way to do it and that does not involve creating a file?

Thanks in advance.

[duff]

You've got the right idea. That's what all those *.pid files in /var/run are for.

[frafu]

Thanks for the confirmation.

I did not know about the /var/run directory. But the process that I am starting is not listed in that directory. Is it because it is a program written in python?

Francesco

[Mr. C.]

It won't be there unless you put it there. Your program needs to get its own PID, and create a file in /var/run so that it can later interrogate that file. The file is up to you to create.

If you want only one instance of your program running, your program should refuse to run when another instance is running. There are various techniques for doing this.

If you want multiple instances to run, you'll have to specify to your start/stop script the PID or some unique instance ID you create and use.

MrC

[frafu]

Thanks for your reply.

In fact, there might be other instances of the program I am starting; but later, I want to kill the instance that I created.

Could you please tell me how I can get the pid of the instance of the program that I started from a script? I tried the following in the script, but it did not work:

myProgramInstance=`/usr/bin/program&`

Could you also tell me how to start the program so that the script can end, but program keeps on running? The & after the programcall does not seem to work.

Thanks in advance for any additional help.

Francesco

[cwaldbieser]

Thanks for your reply.

In fact, there might be other instances of the program I am starting; but later, I want to kill the instance that I created.

Could you please tell me how I can get the pid of the instance of the program that I started from a script? I tried the following in the script, but it did not work:

myProgramInstance=`/usr/bin/program&`

Could you also tell me how to start the program so that the script can end, but program keeps on running? The & after the programcall does not seem to work.

Thanks in advance for any additional help.

Francesco

The variable "$!" has the PID of the last background process you started. So:

#!/bin/bash

PROGRAM=/path/to/myprog
$PROGRAM &
PID=$!
echo $PID > /path/to/pid/file.pid

The pid of the background process is now stored in "/path/to/pid/file.pid". You can later retrieve the PID from this file and kill your process.

The only complication is that if you allow multiple instances of your program to run, you need a way to save all the PIDs in different files and then determine which process you actually mean to kill.

You might want to explain how you plan on running your program a second time decides to kill a particular process. It seems to me, that without more information (e.g. the sessions are named by the user, only one instance per user) it would be hard to do this.

[frafu]

@ cwaldbieser

Thanks for your help. In fact, it is the script that starts the command and that kills it.

In order to know what instance of the program to kill, I also add the display number to the filename. But I don't manage to get the pidfile written.

 
#!/bin/sh

fixPartOfFilename="onboard-at-gdmlogin-display-"
displayPartOfFilename=$DISPLAY
extensionOfFilename=".pid"
pathOfFile="/tmp/"

filenameWithPath=$pathOfFile$fixPartOfFilename$displayPartOfFilename$extensionOfFilename

PROGRAM="/usr/bin/onboard --size 400x150 -x 10 -y 10"
$PROGRAM &
PID=$!
echo $PID > $filenameWithPath

Could anybody please tell me where the mistake is?
Why does it not create the file?
I suppose that it is only a problem of syntax.

Thanks in advance.

Francesco

[Mr. C.]

It might be creating the file, but not with a name you are expecting. Try instead:

echo $PID > "$filenameWithPath"

If this doesn't help, echo the output of each variable as a debugging aid.

I'd also suggest for readability, reducing to something like:

basedir="/tmp/"
pidfile="$basedir/onboard-at-gdmlogin-display-${DISPLAY}.pid"

...

echo $PID > "$pidfile"

MrC

[frafu]

Thanks, it works now.

However, there remains one detail: the name of the pidfile ends with a "?" when using the command ls, and "^M", when I do a tab for the autocompletion.

Could anybody please tell me how I can get rid of the question mark character at the end of the name?

I am using the following to create the filename:

 
basedir="/tmp"
pidfile="$basedir/onboard-at-gdmlogin-display-${DISPLAY}.pid"

Thanks

Francesco

[Mr. C.]

I'm not following you. Are you saying your script is incorrectly adding the ? character at the end of the file name ? The script you showed earlier would not be doing that.

Please show your completed script, and the output of ls.

MrC