Displaying an alert message

What mechanism exists for displaying an alert message for critical system events? Yes, I know about “notify-send” and “xmessage”, but those are only available for programs running within the current GUI session. Don’t even bother mentioning “wall”, since that has been rendered useless now that terminal emulator sessions are no longer visible as separate logins and there is no certainty that any terminal sessions are running. I can’t find anything that works.

Where do you want the message to show up? On the login screen, which I’m not sure how to do? Emailed to the sysadmin, which you could do with the mail command? Something else?

echo is probably the simplest way to print a message but you have to know where you want it.

A popup window in the manner of either notify-send or xmessage would be satisfactory, though I would prefer that an alert sound were included. It seems odd that there is no way to do that.

Which still doesn’t answer the question of where you want this message to be displayed.

On the login screen? On your desktop when you first log in? On a terminal when you open one? Somewhere else?

On the desktop would be a nice start.

Parse whatever logfile you want to parse, when you find the output you’re looking for feed it to notify-send and you’re all set.

Yes, I can use “journalctl --follow” with suitable filters as a “pull” solution. I’m just very surprised that there isn’t a “push” method for notifications in the manner that “wall” used to be for terminal sessions.