I always run linux applications manually using the terminal during the development stage. This has helped me immensely as I could see all the messages that were printed on to the linux console. I also had the habit of forgetting to start the Java program once the linux machine reboots. Well how many of you have had that experience? Ohh yes, I forgot to mention that I will be using a compiled java program as an example executable file for this tutorial.
Though this is acceptable for a system that is under development, it is not suitable to run an executable program using a terminal in production environment. So I would go about setting up a cron job to check if the process is running and start it up if it is not, using a shell script. This tutorial will give you an understanding of how to check for a running processes and start the process if not running using a shell script in linux.
Please note that shell script is not the only way to check for a running process or to start a process.
The Shell Script:
So let's name the file testshellscript.sh
You can use any editor like vi to write shell script.
#!/bin/sh
This is the first line of the shell script. It tells the script which interpreter to refer to. Next let us check for the running process
PROCESSFILE='ExecutableFile.jar'
if ps ax | grep -v grep | grep $PROCESSFILE > /dev/null
I am assigning the jar file name to a variable named PROCESSFILE and then using the linux command ps to check if the process is running.
then
echo "$PROCESSFILE is running, everything is fine"
else
echo "$PROCESSFILE is not running"
#start the process
/usr/local/jdk/bin/java -jar /opt/$PROCESSFILE > /dev/null 2>&1 &
Fi
If there is a running process, we need not do anything to it. So I am simply echoing a message saying that the Java program is running. And if the Java program is not running, I will attempt to start the Java program. The logic of the conditional statement is as follows:
if process running
then
do nothing
else
start the process / java program
end if
As the example executable file is a jar file I am using bin\java to execute the file. This is almost the same command used in a linux terminal. Only difference is the use of full paths. Also all the outputs are directed to the null device which is a special file that discards all data written to it.
Here is the complete code...
#!/bin/sh
PROCESSFILE='ExecutableFile.jar'
if ps ax | grep -v grep | grep $PROCESSFILE > /dev/null
then
echo "$PROESSFILE is running, everything is fine"
else
echo "$PROCESSFILE is not running"
#start the process
/usr/local/jdk/bin/java -jar /opt/$PROCESSFILE > /dev/null 2>&1 &
Fi
