This author used to have a custom-made backup system that would update an extra copy of the $HOME directory on an external drive each night. That was a simple combo of Cron and a custom-tailoured Bash script, which contained the notification solution: the script collected all details in a log and then sent it via Postfix to a Gmail account.
That was fully functional, rock-solid, but there was always the feeling that there could be a more elegant solution of being notified of a backup attempt. If you agree then take a look at Ntfy, a great way of pushing custom messages right to your Android phone (iOS support isn’t here yet, but it’s being worked on). It’s blazingly fast, easy to set up and totally free. You’ll need to install the Ntfy Android app via Google Play or F-Droid, create a ‘topic’ (random text string), and that’s about it. Check to see how it works with $ curl -d “Hello World!” ntfy.sh/topic_nameWait, but where’s the actual Hotpick? As you can see, we’ve just used the public Ntfy.shserver for pushing our test hello message. If you don’t need to transfer any sensitive information via Ntfy, then it’s fine to stay with that public server. However, it’s much better to host your own. The Ntfy documentation explains how to get a self-hosted Ntfy server up and running via installing traditional Linux packages, or going with a Docker image (alternatively, consult ntfy.sh/docs/developto build the server part from sources). Having your own Ntfy server instance under your control is always a good idea. On the phone part you’ll need to check the ‘Use another server’ mark in the subscription dialog and then provide your Ntfy server address. The rest should work just the same way as if using the public server.