lastb 命令的输出结果中的 ssh:notty 的意思

“ Notty”一词仅表示“ no tty”，大致翻译为“ no terminal”。 当您本地登录到任何Linux计算机时，终端将始终在进程列表中显示为“ tty”。 如果通过SFTP建立了连接，或者您正在使用SCP复制文件，那么它将显示为tty（notty）。

以下是参考资料：

Who or what is root@notty?

If you’re looking through WHM’s process manager and you see root@notty mentioned as one of the processes, don’t be alarmed. It’s perfectly normal and it’s definitely not some hacker called ‘Notty’ who has suddenly got root permissions. Be honest, you’re here because you thought that 😉
You may also have seen sshd: root@notty in the output of ps aux too.

Why notty?

The term ‘notty’ just represents ‘no tty’ which roughly translates as meaning ‘no terminal’. When you login locally to any Linux machine the terminal will always appear in the process list as ‘tty’. If a connection is made via SFTP or you are copying files with SCP (as I did here on a test server prior to bringing up the screenshot above) then it will show as no tty (notty).

Where does TTY come from?

Many years ago, user terminals that were connected to computers were clunky and noisy Electro-mechanical Teleprinters also known as Teletypewriters. They took the latter phrase and chopped some characters out to get the TTY abbreviation:
TeleTYpewriter = TTY
Since then, TTY has been used as the shortened name for a text-only console.

参考资料

• Who or what is root@notty?
• https://www.putorius.net/explaination-of-sshnotty-rootnotty-or.html
• 拒绝ssh远程暴力破解
• 修改云服务器远程默认端口