Ubuntu16.04.4 The command could not be located
修改过系统配置文件 /etc/environment ，修改参数要是不正确，会导致所有命令失效错误，重启登陆系统的时候，就会显示如下的错误信息：
Command 'ls' is available in '/bin/ls'
The command could not be located because '/bin' is not included in the PATH envi ronment variable.
ls: command not found
Command 'lesspipe' is available in the following places
* /bin/lesspipe
* /usr/bin/lesspipe
The command could not be located because '/usr/bin:/bin' is not included in the PATH environment variable.
lesspipe: command not found
Command 'dircolors' is available in '/usr/bin/dircolors'
The command could not be located because '/usr/bin' is not included in the PATH environment variable.
dircolors: command not found
Command 'ls' is available in '/bin/ls'
The command could not be located because '/bin' is not included in the PATH envi ronment variable.
ls: command not found
zslswrmz@ubuntu:~$
zslswrmz@ubuntu:~$ sudo
Command 'sudo' is available in '/usr/bin/sudo'
The command could not be located because '/usr/bin' is not included in the PATH environment variable.
sudo: command not found
zslswrmz@ubuntu:~$ sudo su
Command 'sudo' is available in '/usr/bin/sudo'
The command could not be located because '/usr/bin' is not included in the PATH environment variable.
sudo: command not found
zslswrmz@ubuntu:~$ ls -lh
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
zslswrmz@ubuntu:~$
zslswrmz@ubuntu:~$
执行任何指令，都会报错，看到这样的错误，其实不用担心，那要如何解决呢？
之前修改过系统配置文件，肯定是配置有问题，意思是：找不到命令，因为 '/usr/bin:/bin' 没有被包含在环境变量PATH中， 这就是问题产生的原因。
Linux有PATH 通过PATH变量指定命令存放的位置， 所以正常情况下，使用 echo $PATH 查看环境变量PATH的内容如下：
~$ echo $PATH
/home/zslswrmz/bin:/home/scm/.local/bin:$JAVA_HOME/bin:$PATH
zslswrmz@ubuntu:~$
由于配置系统 PATH 错误，我在使用指令时系统不能正常到存放指令的目录中去寻找，因此会提示：Command not found。
很人性化的是，系统会提示我们要使用的指令存放的正确位置，比如使用 sudo 时提示的：Command 'sudo' is available in '/usr/bin/sudo'。sudo 命令是存放在'/usr/bin/'目录下的。
所以只能人工指定它们的绝对路径了。sudo 和 vim 都是存放在'/usr/bin/'目录下的，所以 sudo 和 vim 的绝对路径分别是：/usr/bin/sudo /usr/bin/vim ，现在明白了吗？那就快快动手把之前修改错误的配置文件重新修改好，重启系统就OK了。
~$
zslswrmz@ubuntu:~$ /usr/bin/sudo /usr/bin/vim /etc/environment
[sudo] password for scm:
zslswrmz@ubuntu:~$
修改好重启系统，就能正常使用指令了，不会再报任何错了。