ssh 连接到一半，想回到本地，可以 suspend ssh 会话。
输入 ~+<C-z> ，回到本地：
[email protected]B ~$:
[email protected]A ~$:
上面的 ~ 符号其实就是 -e 选项的默认参数：
Sets the escape character for sessions with a pty (default: `~'
) . The escape character is only recognized at the beginning of
a line. The escape character followed by a dot (`.') closes
the connection; followed by control-Z suspends the connection;
and followed by itself sends the escape character once. Setting
the character to “none'' disables any escapes and makes the
session fully transparent.