Display message before OpenSSH authentication using simple built-in mechanism.
Create file /etc/sshd/sshd_banner that will contain specific message or ASCII art.
Use Christopher Johnson’s ASCII Art Collection or ASCII Art Archive to get cool ASCII art.
..,co88oc.oo8888cc,..
o8o. ..,o8889689ooo888o"88888888oooc..
.88888 .o888896888".88888888o'?888888888889ooo....
a888P ..c6888969""..,"o888888888o.?8888888888"".ooo8888oo.
088P ..atc88889"".,oo8o.86888888888o 88988889",o888888888888.
888t ...coo688889"'.ooo88o88b.'86988988889 8688888'o8888896989^888o
888888888888"..ooo888968888888 "9o688888' "888988 8888868888'o88888
""G8889""'ooo888888888888889 .d8o9889""' "8688o."88888988"o888888o .
o8888'""""""""""' o8688" 88868. 888888.68988888"o8o.
88888o. "8888ooo. '8888. 88888.8898888o"888o.
"888888' "888888' '""8o"8888.8869888oo8888o .
. :.:::::::::::.: . . :.::::::::.: . . : ::.:."8888 "888888888888o
:..8888,. "88888888888.
.:o888.o8o. "866o9888o
:888.o8888. "88."89".
. 89 888888 "88":.
atc :. '8888o
. "8888..
888888o.
"888889,
. : :.:::::::.: :.
Update /etc/ssh/sshd_config configuration file to define Banner option.
[...] Banner /etc/sshd/sshd_banner [...]
Reload OpenSSH server.
$ sudo systemctl reload sshd
Verify that that your message is displayed as expected.
$ ssh debian.example.org -l milosz -i ~/.ssh/ext_milosz
..,co88oc.oo8888cc,..
o8o. ..,o8889689ooo888o"88888888oooc..
.88888 .o888896888".88888888o'?888888888889ooo....
a888P ..c6888969""..,"o888888888o.?8888888888"".ooo8888oo.
088P ..atc88889"".,oo8o.86888888888o 88988889",o888888888888.
888t ...coo688889"'.ooo88o88b.'86988988889 8688888'o8888896989^888o
888888888888"..ooo888968888888 "9o688888' "888988 8888868888'o88888
""G8889""'ooo888888888888889 .d8o9889""' "8688o."88888988"o888888o .
o8888'""""""""""' o8688" 88868. 888888.68988888"o8o.
88888o. "8888ooo. '8888. 88888.8898888o"888o.
"888888' "888888' '""8o"8888.8869888oo8888o .
. :.:::::::::::.: . . :.::::::::.: . . : ::.:."8888 "888888888888o
:..8888,. "88888888888.
.:o888.o8o. "866o9888o
:888.o8888. "88."89".
. 89 888888 "88":.
atc :. '8888o
. "8888..
888888o.
"888889,
. : :.:::::::.: :.
Enter passphrase for key '/home/milosz/.ssh/ext_milosz': ****************
Linux buster 4.19.0-4-amd64 #1 SMP Debian 4.19.28-2 (2019-03-15) x86_64
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Aug 25 18:19:24 2019 from 192.168.50.1
milosz@debian.example.org:~$
As you can see it does not affect standard motd (/etc/motd) and it is best to add additional lines before and after ASCII art.
