Is there a way to restart pm2 process using cron but only if it's not already running?

I want to restart my Node.Js app using PM2 through

pm2 restart app.js

using crontab but ONLY if the app is not already running (e.g. if my server crashed and restarted and pm2 didn't restart).

the command above restarts it anyway even if it's running.

How do I fix it?

UPDATE

I do not want my app to restart if it's already running. I want it to restart only if it's listed as "stopped" or if it is not running. Some suggestions offer to write a bash script, but what would it be? I tried the options below, but they either don't work or restart the app even if it's running.

Solution

The better way of doing it is use the pm2 startup command

http://pm2.keymetrics.io/docs/usage/startup/

To get the automatically-configured startup script for your machine you need to type this command:

# Detect available init system, generate configuration and enable startup system
pm2 startup

You can specify the platform you use by yourself if you want to (where platform can be either one of the cited above):

pm2 startup [ubuntu | ubuntu14 | ubuntu12 | centos | centos6 | arch | oracle | amazon | macos | darwin | freebsd | systemd | systemv | upstart | launchd | rcd | openrc]

The output of this command can be a recommendation of the line to copy/paste with all environment variables and options configured for you.

Example:

[PM2] You have to run this command as root. Execute the following command: sudo su -c "env PATH=$PATH:/home/unitech/.nvm/versions/node/v4.3/bin pm2 startup -u --hp

You simply have to copy/paste the line PM2 gives you and the startup script will be configured for your OS.

Once you run the sudo pm2 startup. It will create the systemctl service. You can check the status of the same using

systemctl status pm2-root

By default the service is not configure to restart automatically. You will run the below commands

sudo mkdir -p /etc/systemd/system/pm2-root.service.d

and then create a file name 10_auto_restart_pm2.conf with below content

[Service]
Restart=always
RestartSec=3

After that execute

systemctl daemon-reload
systemctl restart pm2-service

Now let's test the auto restart part

$ systemctl status pm2-root.service
● pm2-root.service - PM2 process manager
   Loaded: loaded (/etc/systemd/system/pm2-root.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/pm2-root.service.d
           └─10_auto_restart_pm2.conf
   Active: active (running) since Wed 2018-02-28 16:52:19 UTC; 11s ago
     Docs: https://pm2.keymetrics.io/
  Process: 5014 ExecStop=/usr/local/lib/node_modules/pm2/bin/pm2 kill (code=exited, status=0/SUCCESS)
  Process: 5022 ExecStart=/usr/local/lib/node_modules/pm2/bin/pm2 resurrect (code=exited, status=0/SUCCESS)
 Main PID: 5031 (PM2 v2.10.1: Go)
    Tasks: 9
   Memory: 24.3M
      CPU: 460ms
   CGroup: /system.slice/pm2-root.service
           └─5031 PM2 v2.10.1: God Daemon (/home/vagrant/.pm2)

Now we kill the process manually and wait for 3 seconds

$ kill -9 5031
$ sleep 3
$ systemctl status pm2-root.service
● pm2-root.service - PM2 process manager
   Loaded: loaded (/etc/systemd/system/pm2-root.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/pm2-root.service.d
           └─10_auto_restart_pm2.conf
   Active: active (running) since Wed 2018-02-28 16:52:55 UTC; 641ms ago
     Docs: https://pm2.keymetrics.io/
  Process: 5057 ExecStop=/usr/local/lib/node_modules/pm2/bin/pm2 kill (code=exited, status=0/SUCCESS)
  Process: 5081 ExecStart=/usr/local/lib/node_modules/pm2/bin/pm2 resurrect (code=exited, status=0/SUCCESS)
 Main PID: 5088 (PM2 v2.10.1: Go)
    Tasks: 9
   Memory: 24.3M
      CPU: 461ms
   CGroup: /system.slice/pm2-root.service
           └─5088 PM2 v2.10.1: God Daemon (/home/vagrant/.pm2)

As you can see the process/service was restarted automatically. No cron needed and it is how you should do it.