问题表现为许多命令无法使用，如图

lisa@lisa-VirtualBox:~$ 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

而且无法再次使用nano ~/.bashrc指令来修改出错部分

lisa@lisa-VirtualBox:~$ nano ~/.bashrc
Command 'nano' is available in '/bin/nano'
The command could not be located because '/bin' is not included in the PATH environment variable.
nano: command not found

解决办法:在/usr/bin目录下运行vi 指令来编辑根目录的.bashrc文件

lisa@lisa-VirtualBox:~$ cd /usr/bin
lisa@lisa-VirtualBox:/usr/bin$ vi ~/.bashrc

将错误的PTAH修改为PATH后,退出vi编辑器，使用source ~/.bashrc后，发现ls等指令仍然不能使用
此时需要切换到root用户，再使用source ~/.bashrc

切换到root用户后 使用source ~/.bashrc

lisa@lisa-VirtualBox:/usr/bin$ sudo -i
[sudo] password for lisa:
root@lisa-VirtualBox:~# source ~/.bashrc

再切换到正常用户，基本指令就可以使用了

root@lisa-VirtualBox:~# su lisa
lisa@lisa-VirtualBox:/root$ cd
lisa@lisa-VirtualBox:~$ ls
anaconda3                        aspera-connect-3.6.2.117442-linux-64_1.tar.gz  Desktop    Downloads                lisa@v  Pictures  Templates
Anaconda3-5.2.0-Linux-x86_64.sh  aspera-connect-3.6.2.117442-linux-64.sh        Documents  hisat2-2.1.0-source.zip  Music   Public    Videos
lisa@lisa-VirtualBox:~$