MOTD on AWS linux instances

MOTD (message of the day) is that greeting message that appears on your screen every time you log into a linux system. On a AWS linux instance it looks like:

Last login: Wed Jun  6 18:02:10 2018 from 000.000.000.000

       __|  __|_  )
        _|    (     /   Amazon Linux AMI
     ___|\___|___|

https://aws.amazon.com/amazon-linux-ami/2015.03-release-notes/
8 package(s) needed for security, out of 35 available
Run "sudo yum update" to apply all updates.
Amazon Linux version 2018.03 is available.

This message is located in the file /etc/motd (which is actually a symlink to /var/lib/update-motd/motd) but that's not the right place to edit in case you want to change it. That's because the message is dynamically generated by running /usr/sbin/update-motd on a cronjob (/etc/cron.d/update-motd). If you edit the /etc/motd file it will be overwritten when this job executes.

To change the MOTD on you AWS linux instance simply add a new script to /etc/update-motd.d/. The scripts will be executed in alphabetical order (hence the number prefix to make it easy to set the order) and the final MOTD will be the sum of the output of all the scripts.