A while back, I had to set up a system for a former client of my previous employer (my previous employer had no Linux help, you see, while the former client had new Linux machines to set up, so...). One of the things I did was get a banner going for them. It was an added bonus, and completely frivolous. I was up late one night and happened upon a DOD site with a cool banner, so I cabbaged parts of it, and knocked together this:
**WARNING**WARNING**WARNING**Feel free to use it if you want. Just save it to /etc/issue, make a symlink called /etc/issue.net which points to it, and then add a line in /etc/ssh/sshd_config which says Banner /etc/issue.net. HUP sshd. All done.
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