恢復ubuntu環境變量的示例：
在終端輸入ls命令后，顯示如下結果:
root@wei:/etc# ls
Command 'ls' is available in '/bin/ls'
The command could not be located because '/bin' is not included in the PATH environment variable.
ls: command not found
解決方法：
直接在終端輸入以下命令即可。
export PATH=/usr/bin:/bin
