By default logging into dd-wrt via ssh the pre-login sshd banner looks like this:
DD-WRT v3.0-r42054 std (c) 2020 NewMedia-NET GmbH
Release: 01/21/20
Board: Dlink-DIR880L
I wanted to remove this as my router is public-facing, and it might not be the best practice to expose your system info from a security stand-point.
Solution[1]
stopservice sshd && echo -e "Your message here\n" > /tmp/loginprompt && startservice sshd
This one-liner is fairly self-explanatory: it stops sshd and overwrite /tmp/loginprompt with your desired message, and before starting sshd again.
$ ssh root@10.0.0.100
Your message here
==========================================================
___ ___ _ _____ ______ ____ ___
/ _ \/ _ \___| | /| / / _ \/_ __/ _ __|_ / / _ \
/ // / // /___/ |/ |/ / , _/ / / | |/ //_ <_/ // /
/____/____/ |__/|__/_/|_| /_/ |___/____(_)___/
DD-WRT v3.0
http://www.dd-wrt.com
==========================================================
BusyBox v1.31.1 (2020-01-21 11:19:55 +04) built-in shell (ash)
root@ddwrt:~#
Persisting it for reboots
To make this permanent, under Administration > Commands > Save Startup, save it as a Start Up script.
DO NOT execute the one-liner in ssh
Executing the one-liner drops the ssh connection immediately, before the startservice sshd part is executed. I learnt this the hard way and locked myself out of my router while I was remote because of this.