Detect if specific node.js script is running from bash

Question

Read as: Detect (if specific node.js script is running) from bash .

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I have a server that runs a specific node.js script on certain actions and certain cron intervals.

The script might take a few hours to finish, but is not supposed to run more than once at the same time.

Is there a way in sh or bash to detect if the specific script is already running?

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process

Simply running (if) pidof node won't work, because there might be other unrelated node scripts running.

pidfile

The closest half solution I can think of is touch /tmp/nodescript.lock and only run the script if it does not exist. But apparently /tmp doesn't (always) get cleaned on a server crash/reboot.

secret option number 3

Perhaps there's some other simple way I'm not aware of. Maybe I can give a process some kind of static identifier, which is gone when the process is. Any ideas?

Answer 1

When you invoke a script with nodejs, it appears in the process list such as:

user       773 68.5  7.5 701904 77448 pts/0    Rl+  09:49   0:01 nodejs scriptname.js

So you could simply check ps for its existence with a simple bash script:

#!/bin/bash

NAME="scriptname.js" # nodejs script's name here
RUN=`pgrep -f $NAME`

if [ "$RUN" == "" ]; then
 echo "Script is not running"
else
 echo "Script is running"
fi

Adjust it up to your needs and put into cron.

Answer 2

I recommend you to use a robust lock mechanism like this :

#!/bin/bash

exec 9>/path/to/lock/file
if ! flock -n 9  ; then
   echo "another instance of $0 is running";
   exit 1
fi

node arg1 arg2 arg3...

Now, only one instance of a node script can be run at once

Answer 3

I came across the same problem and I ended up with a completely NodeJS based solution.

I used this awesome module named ps-node .

You can look up if a specific process is already running before you fire up your code.

ps.lookup({
    command: 'node',
    arguments: 'your-script.js',
},
function(err, resultList){
    if (err) {
        throw new Error(err);
    }
    // check if the same process already running:
    if (resultList.length > 1){
        console.log('This script is already running.');
    }
    else{
        console.log('Do something!');
    }
});