File permission management

1. file type

Linux Think everything is a document .

  Ordinary documents “-”

Directory file “d” （directory）

Pipeline files “p” （piping）

Link to the file “l” （link）

Device file （ Block device “b”（block）, Character device “c”（char））

Socket file “s” （socket）

Explain what it means ？

Pipeline files ： A means of interprocess communication

Link to the file ： Soft link （ Character link ） And hard links , Soft links can be considered windows Next shortcut

Device file ： Block device ： A device that can read a certain length from any position ： For example, disk ,U disc ,TF Cards and so on

Device file ： Character device ： Only one byte per byte can be read , Can't read randomly , For example, mouse , Keyboard and so on.

Socket file ： A way of network communication

2. How to check the type of a file ？ 

Go to the specified directory , adopt ls -l To check ：

  The first character looks at the file type , such as a.out, The first character is ‘-’, For ordinary documents .

3. File permissions

Divide every three  

rwx What do they stand for ？

 r Read permission value ：4

w Write permissions value ：2

x Executive authority value ：1    For ordinary files, it represents execution permission , For catalog files , Delegates have access to

- No authority value ：0

4. There are two ways to modify permissions ： Text setting method and number setting method  

 4.1 Text setting

chmod Command to modify permissions

u：user Access rights of the owner （ The owner ）

g：group Access rights of the group （ People in the same group as the owner ）

o：other Other people's access

a：all All the people

+： Add permissions

- ： Remove authority

=： Indicates direct assignment permission

Be careful ： If you want to give it to the owner at the same time , Generic group , Others modify permissions , Separate them with commas

First, show the permissions of the current file ：

 

  to main2 Modify the permissions of this executable file , Remove the execution permission of the owner , The order is as follows ：

  Subtract the execution command from the execution permission of the owner x,u-x. Want to give it to the owner at the same time , Generic group , Others modify permissions , Separate them with commas .

 4.2 Number setting method

r：read value 4（100）

w：write value 2 （010）

x：execute value 1 （001）

Through the command chmod xxx filename Make changes ,x Is greater than or equal to 0 Less than or equal to 7.

0 ： No authority

1：--x（001）

2：-w- （010）

3：-wx（011）

4：r--（100）

5：r-x（101）

6：rw-（110）

7：rwx（111）

Examples are as follows ： From the above file permissions at the beginning , For my convenience, I put the pictures here .

to a.txt The master permission of this file plus the command of execution permission ：

chmod 764 a.txt

rw- The value of is 6,x The value of is 1, We add x After permission rwx The value of is 7, Membership group and other permissions remain unchanged .