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wall "Hello, world!"

will send a message that looks like

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Broadcast message from root@localhost (pts/0) (Sat Feb  1 14:50:14 2024):

Hello world!

to every user currently logged in to the system.

When might this be relevant? When you’re working in a small team, by remoting into custom hardware, and constantly reflashing the device, to give everyone a heads up, for instance:

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wall "Device will be reflashed in 5 minutes" && sleep 300 && ./reflash.sh

I’m surprised it took me over a decade of toying with Linux to learn about wall. Nobody ever talks about it. There are almost certainly big frustrations people have with how it works, but when it’s just you, your buddy, and an SSH connection - it might be just what the doctor ordered.