ssh login without welcome banner

Try ssh -q to supress the banner message

You should be able to silence this banner, and other diagnostic messages, by passing -q to SSH:

ssh -q user@remote_host

If you want to make -q permanent for all your SSH sessions, do:

echo "LogLevel QUIET" >> ~/.ssh/config

This will run command1 command2 and command3 on the remote_host.

ssh user@remote_host 'command1; command2; command3'

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What works here seems to depend on the operating system, SSH version, and the server-side configuration of sshd.

For connecting to a stock Ubuntu 18 server ssh -q didn't work for me, and neither did ssh -o LogLevel=error that is suggested elsewhere.

What did work is the comment posted under the question about creating a .hushlogin file in the remote user's home directory:

$ ssh myuser@myhost
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-55-generic x86_64)
<snip>
Last login: Thu Aug  1 14:04:26 2019 from 1.2.3.4
myuser@myhost$ touch .hushlogin
myuser@myhost$ exit

Then:

$ ssh myuser@myhost echo 'Test'
Test