The outsider must know the port number and the password to use SSH, as well as the knock sequence required to open that port and enable the password.

外面的用户必须知道使用SSH所需的端口号和密码，还必须知道打开端口并启用密码所需的敲门序列。

youdao

Several handsome doors, which were always open and upon which opportunity tended to knock, lead to the restored Capitol's interior.

几个很漂亮的门总是开着，机会常来敲它们。 门后面是国会议厅的内部。

youdao

Oh! it is Green,' I said, recollecting myself--`only Green,' and I went on, intending to send somebody else to open it; but the knock was repeated: not loud, and still importunately.

“啊，那是格林，”我说，镇定着自己--“就是格林，”我仍然向前走，打算叫别人来开门；可是门又敲起来：声音不大，仍然很急促。

youdao

Greg would have known how to knock everything open, grab the goodies.

NEWYORKER: Deniers

But Anthony's scoring displays raised a question about whether his teammates would have enough of a rhythm to knock down open shots once the postseason began.

WSJ: Of Course the Celtics Fought Back

His inability to knock down open shots was hurting the team's offense, because opponents eventually began just leaving him open, playing the odds that he would miss without a defender contesting him.

WSJ: Jason Kidd, New York Knicks: Jason Kidd Retires