一、 Escape Sequences

 Escape Sequences是SSH客户端的一个功能，用于在SSH会话中执行一些特定的操作，比如打开一个新的终端或者传输文件。

Use escape sequences to manage your client terminal session. Escape sequences are recognized only after a newline character. If you have just logged in, press Enter before you enter your first escape sequence. You can configure an alternate escape character using -eon the command line or EscapeChar in the configuration file.

The following escape sequences are available. These are shown with the default escape character, a tilde (~).

 ~. Terminates the connection.
~^Z Suspends ssh.
~# Lists active forwarded connections. Note: Forwarded connections are listed only when the ports are actually transmitting data.
~- Disables use of the escape character for the duration of the session.
~? Displays a list of available escape sequences.
~~ Sends the escape character to the host. (Type the escape character twice to send one escape character.)

~C Execute command mode, which you can use to request port forwarding. The options are:

 -L[bind_address:]port:host:hostport    Request local forward
-R[bind_address:]port:host:hostport    Request remote forward
-KL[bind_address:]port                 Cancel local forward
 -KR[bind_address:]port                 Cancel remote forward

 ~V Sends version information to stderr.
~s Sends connection information to stderr.
~r Initiates an immediate key exchange to establish new encryption and integrity keys.
~l Enters line mode. Keystrokes are stored to a buffer and output when you press Enter.
~B Sends a BREAK to the remote system.

二、配置文件/etc/ssh/sshd_config

配置文件中有一些关于SSH服务器的设置，例如端口、协议版本、认证方式等。在这个配置中，使用了UsePAM no来禁用PAM（Pluggable Authentication Modules）认证。PAM是用于管理应用程序的认证模块，它可以增强系统的安全性和灵活性，但在某些情况下可能导致一些命令或功能受限。