Suppress SSH banner when executing ad-hoc commands.

The system administrator can configure the SSH banner to display a custom message before user authentication.

$ ssh frontend.example.org 
Unauthorized access to this machine is prohibited

Last login: Mon Dec  7 21:12:31 2020 from 10.0.2.2
[milosz@frontend ~]$

This means that it will be sent even when executing the ad-hoc command.

$ ssh frontend.example.org date
Unauthorized access to this machine is prohibited

Mon Dec  7 21:18:37 UTC 2020

The solution is to use quiet mode as it will suppress most warning and diagnostic messages.

$ ssh -q frontend.example.org date
Mon Dec  7 21:32:41 UTC 2020

Alternatively, use LogLevel option.

$ ssh -o LogLevel=quiet frontend.example.org date
Mon Dec  7 21:39:25 UTC 2020