- Command, options and parameters
2.1. What is the format of the
command Command (Command) Options (options) (there can be more than one) Arguments (there can be more than one)
$ is ordinary user
~ is home directory
# is an administrator user
2.1 The command entered under ls 1.ls
-a hide files
2.ls -l view file attributes
3.ls / -l or ls -l / view attributes of files or folders under the root
2.2 Command input in CD
CD or home directory cd ~ 
cd .. back one level 
cd ../ .. Back on two 
cd / Back root 
cd ../d quick access to the same layer as the folder
e.g. : Create a folder a in the home directory, then create a folder b, d in the a folder, create a folder c in the b folder, 
step into the c folder, 
step into the d folder
2.2. Enter root in two modes
1. Entering sudo su in ordinary users does not change the path 
2. Entering su in ordinary users-root returns to root's home directory 
3.sudo -i
