Cron jobs are a vital part of every sysadmins setup. Backups, log rotation, certificate renewal and whatnot.
I've mostly just relied on them working as they should until now, but with my recent Huginn + Matrix obsession I figured I should have some sort of notifications.

Crontab supports sending emails for your jobs, all you have to do is add MAILTO=youremail@example.com at the top. It defaults (on most distros) to sendmail, which I discovered was kind of a pain to set up. Instead I found these instructions for sSMTP.

I already had an account at Mailgun for an old app so I just had to add my domain. Mailgun recommends using a subdomain so in my case I went with mg.jonnev.se. I configured sSMTP with my Mailgun credentials following the guide above and it worked just fine!

Now getting emails for everything is kinda annoying so using Mailguns routes I forwarded all incoming emails for the address I setup in crontab to a webhook in Huginn. In the Mailgun examples you can see the JSON for a forwarded email.

I then added an EventFormattingAgent in Huginn with these attributes

{
  "instructions": {
    "message_html": "<b>{{bin.cmd}}</b><br>{{body-plain}}",
    "message": "{{bin.cmd}} {% line_break %} {{body-plain}}"
  },
  "matchers": [
    {
      "path": "{{subject}}",
      "regexp": ">\\s(?<cmd>.*)",
      "to": "bin"
    }
  ],
  "mode": "clean"
}

Matrix supports HTML formatting with a fallback for plain text. There should be a <pre> around the message_html above but Ghost wouldn't let me...

The result looks like this:

You could easily use this to send notifications to Slack, Pushover or any of the other services supported by Huginn. Or just an outbound webhook with PostAgent, which is what I use to post to my Matrix room.

Hint: To learn how to control the output of commands in cron I found this post helpful

Hint 2: To silence certbot (in the screenshot above) I'm now using this!