Two instances of node started on linux - linux

Question

I have a node.js server app which is being started twice for some reason. I have a cronjob that runs every minute, checking for a node main.js process and if not found, starting it. The cron looks like this:
* * * * * ~/startmain.sh >> startmain.log 2>&1
And the startmain.sh file looks like this:
if ps -ef | grep -v grep | grep "node main.js" > /dev/null
then
echo "`date` Server is running."
else
echo "`date` Server is not running! Starting..."
sudo node main.js > main.log
fi
The log file storing the output of startmain.js shows this:
Fri Aug 8 19:22:00 UTC 2014 Server is running.
Fri Aug 8 19:23:00 UTC 2014 Server is running.
Fri Aug 8 19:24:00 UTC 2014 Server is not running! Starting...
Fri Aug 8 19:25:00 UTC 2014 Server is running.
Fri Aug 8 19:26:00 UTC 2014 Server is running.
Fri Aug 8 19:27:00 UTC 2014 Server is running.
That is what I expect, but when I look at processes, it seems that two are running. One under sudo and one without. Check out the top two processes:
$ ps -ef | grep node
root 99240 99232 0 19:24:01 ? 0:01 node main.js
root 99232 5664 0 19:24:01 ? 0:00 sudo node main.js
admin 2777 87580 0 19:37:41 pts/1 0:00 grep node
Indeed, when I look at the application logs, I see startup entries happening in duplicate. To kill these processes, I have to use sudo, even for the process that does not start with sudo. When I kill one of these, the other one dies too.
Any idea why I am kicking off two processes?

Answer 1

First, you are starting your node main.js application with sudo in the script startmain.sh. According to sudo man page:
When sudo runs a command, it calls fork(2), sets up the execution environment as described above, and calls the execve system call in the child process. The main sudo process waits until the command has completed, then passes the command's exit status to the security policy's close method and exits.
So, in your case the process with name sudo node main.js is the sudo command itself and the process node main.js is the node.js app. You can easily verify this - run ps auxfw and you will see that the sudo node main.js process is the parent process for node main.js.
Another way to verify this is to run lsof -p [process id] and see that the txt part for the process sudo node main.js states /usr/bin/sudo while the txt part of the process node main.js will display the path to your node binary.
The bottom line is that you should not worry that your node.js app starts twice.