Cron

Install

On Linux (Compute Engine)

https://www.digitalocean.com/community/tutorials/how-to-use-cron-to-automate-tasks-ubuntu-1804

Open a terminal window and enter each command individually, press enter after each.

sudo apt update

sudo apt install cron

sudo systemctl enable cron

Time Zone

The time zone of your VM needs to be changed to ensure that the cron jobs are exectuted at the correct local time.

https://stackoverflow.com/questions/23924072/google-compute-engine-instances-timezone-changed-to-utc-automatically

From this page, go root user

sudo -s

and use

dpkg-reconfigure tzdata

This will bring up a GUI which will guide you to change your timezone information

Afterwards, confirm the date/time by typing date. I am not sure if needed but the Compute Engine Region & Zone was changed to one in the same local time zone and the VM was restarted. This is from the Settings section for the VM in Compute Engine.

Script Files

Create .sh file

Create a file to contain the GAM command. Nano (https://www.nano-editor.org/) is a builtin text editor, so the terminal screen will change.

sudo nano <File Name>.sh

Then add

#! /bin/bash

/path/to/GAM/folder/<Your GAM Command Here>

Example

#! /bin/bash

/home/user_name/bin/gamadv-xtd3/gam crosqueries "status:active" print cros todrive

The commands in nano to save the file are

CTRL + x (to exit the file) > Y (to confirm saving the changes) > Enter (to confirm file name)

Make Executable

sudo chmod +x <File Name>.sh

Test

Make sure the script file is working.

./<File Name>.sh

Cron

Edit

Edit the file that controls all the cron jobs

crontab -e

Add

For example to run nightly at 1am. The /path/to/script/ is where the .sh file is stored, not the GAM location.

0 1 * * * /path/to/script/<File Name>.sh

Or, to run on the 4th day of every month. This example will run the script at 3.45am on the 4th day of every month.

45 3 4 * * /path/to/script/<File Name>.sh

Example

0 1 * * * * /home/user_name/scripts/update.sh

This website, https://crontab.guru/, has useful examples and an expression checker for creating the cron timing.

Backup

crontab -l > /path/to/backup/crontab.bak

Resources