secure keyboard entry is enabled because another app has turned it on.

当Iterm2的右上角突然显示一把钥匙图标时，说明有其它应用正在设定安全键盘输入，具体提示如下：

secure keyboard entry is enabled because another app has turned it on.

当出现这个提示时，整个Mac电脑的全部快捷键都会失效，而且无法查到是什么引起的。

iTerm > Secure Keyboard Entry
When this is enabled, the operating system will prevent other programs running on your computer from being able to see what you are typing. If you’re concerned that untrusted programs might try to steal your passwords, you can turn this on, but it may disable global hotkeys in other programs.

解决办法：
只要把所有应用逐一关闭，并观察iTerm2上的钥匙图标，关哪个应用时它消失了，就是哪个应用导致的。
目前知道会影响的是KeePass App，可以在console里查一下日志，但不好查。