Nuances of running Node.js script from linux cron

General outline

There is a script that should run on some schedule.

The script is type of run-once-then-shutdown.

Script is pretty simple, here are some of the core components:

• dotenv for environment variables
• pino for logging
• firebase-admin for some db logic

Script logic

1. Initialize env
2. Do some db stuff
3. Shut down
4. Repeat when cron will invoke script again

Crontab

1 0 * * * /path/to/node /path/to/script.js >> /path/to/log 2>&1

>> /path/to/log 2>&1 will say cron to write any output from script to a file

What can go wrong?

No MTA installed, discarding output

This record can be found in /var/log/syslog right after our cron job.

It is the signal that we probably have an error in our script.

Make sure that you specified the outputs for cron job.

I mean >> /path/to/log 2>&1.

The “path” argument must be of type string. Received undefined

It happens when our code relies on paths, that are specified in .env file:

• path to firebase creds
• path to logs
• etc.

To make sure dotenv loads .env file correctly we need to specify it in .config method.

In my case env initialization was in app-root/lib/config.js, and env file was in app-root folder.

This worked for me:

require('dotenv').config({path: __dirname + '../.env'})

See https://github.com/motdotla/dotenv#path

Recommendations

Consider of using absolute paths in .env file

Also keep in mind that path.resolve() method uses process.cwd() as a base path. To be sure everything is fine it would be a good idea to use __dirname variable as a base, so path.resolve(__dirname, '../') can be better than simply path.resolve('..')