Under Linux is divided into two kinds of users:
1. superuser (root)
2. ordinary user
Supervisor: can do anything under the linux system, not limited by
normal users: You can not do anything in Linux, only do limited things
switch between the two user permissions command: su [username]
Linux privilege management
1. file visitors are divided into:
1) the owner of the files and directories: u-user
owner 2) files and directories where the user group: group G-
2) others: O-others
2. access permissions and file type 
file types:
D: folder
-: normal file
L: soft link
B: block device file
P: pipe file
c: character device file
s: socket file
access
permissions 1. read read have read the contents of the documents, browse the directory information
2. write write with modified contents of the file, the right to delete or move files within a directory
3. perform execute enforceable document, enter the directory permissions
file permissions and Linux represent binary, octal notation
