What are the linux permissions?

There are four types of Linux permissions: 1. Read permission, which is the permission to read the contents of the file; 2. Write permission, which is the permission to write data to the file; 3. Executable permission; 4. Special permission .

#The operating environment of this tutorial: linux5.9.8 system, Dell G3 computer.

There are three identities for accessing files/directories in Linux:

• u: The owner of the file

• g: The group to which the file belongs

• o: Other users

For each identity, there are four more permissions

• r: Read permission (read)

  For files, it is the permission to read its contents. For directories, it is impossible to view the contents in the directory. Content (ls failed)
  

• w: Write permission (write)

  Write permission: For files, data can be written to the file, for directories It is said that the files in the directory cannot be deleted
  

• x: Executable permission (execute)

  cannot be used for executable files (you can see the color have changed), the directory cannot be entered (cd fails)
  

• #s: Special permissions

Linux permissions Representation method

#When it comes to permissions, then we must talk about users under Linux!

There are only two types of Linux users: ordinary users, and super users

• Super users: have all the permissions under this system and can do anything you want. Without any restrictions

• Ordinary users: only have some permissions, and the things they can do are also limited (but usually we can use sudo to perform things that require root permissions, but root is required. Password)

Change permissions in numerical form

chmod 755 test.sh

Convert 755 into character form, which is rwxr -xr-x, which means that the owner of the file, the group to which it belongs, and other users can read and run the test.sh file, but only the owner can write to the file, which means that other people have no rights to modify test. .sh file.

(Of course root users do not have this restriction, whoever wants to change can do it. This is also an experience that reflects the supreme power of the root account!)

Change files in character form Permissions

chmod +x test.sh

The mathematical form can change the four permissions of all three identities of the file at one time, while the character form is more flexible and can be set individually for a certain permission of a certain identity. , for example, the above command is to grant execution permissions to all three identities. You can also set them separately:

chmod u+x test.sh　　只给拥有者加上可执行权限
chmod g+x test.sh　　只给群组身份加上可执行权限
chmod o+x test.sh　　只给其他人身份加上可执行权限

The above three commands combined are equivalent to the above command, which is given to all identities. All enable executable permissions. You can also operate as follows:

chmod a+x test.sh

The a here represents all 3 identities!

If you want to remove a certain permission of a certain identity, you only need to change it to -, for example, to remove the executable permissions of other people's identities:

chmod o-x test.sh

Related recommendations: " Linux video tutorial》

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