Simple Linux Command Line notes: chmod

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• Parameters
• Description
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Modify file permissions

Chmod [Options]Who operator permission file-list(Symbol Mode)

Chmod [Options]Mode file-list(Absolute Mode)

 

Parameters

File-list YesChmodThe name or directory path of the file to be modified.

 

Description

In Linux, there are two methods to change permissions:

First, use the symbolic mode. For example, chmod A + X file. Here, a represents all users, + represents adding permissions, and X represents executing permissions.

Type 2: Use absolute mode, for example, chmod 777 file, to add readable and writable executable permissions to all users. The three values correspond to three user types respectively.

 

Symbol Mode

WhoUser Type

Who	User Type	Meaning
U	User	File owner
G	Other	Group associated with the file
O	Other	All other users
A	All	Equivalent to Ugo, all users

 

 

 

 

 

 

OperatorOperator

Operator	Meaning
+	Add permissions for the specified user type
-	Deletes a permission for a specified user type.
=	Set or reset permissions for a specified user type

 

 

 

 

 

 

PermissionMode

permission	meaning	meaning of the file	meaning of directories
r	set read permission	you can view the file content	you can list contents in a directory
W	set write permission	you can modify the file content	you can create or delete files in the directory
x	set the execution permission	Executable File	you can enter the directory

 

 

 

 

We can see from the above why R and X are often set together in the directory permission.

Because you must enter the directory to read the content

 

Absolute Mode

Typical examples of absolute Mode

Model	Meaning
777	All users have read, write, and execute permissions on files.
755	The file owner has the read, write, and execute permissions on the file. group users and other users must have the read and execute permissions on the file.
711	The file owner has read, write, and execution permissions on the file. group users and other users have execution permissions on the file.
644	The file owner can read and write files. group users and other users can read files.
640	The file owner can read and write files. group users can read files. Other users cannot access files.

 

 

 

 

 

 

 

Option

-C: display the modification process information

-F force Modify permissions

-R: recursively modify directory permissions

-V: displays the modified information.

 

Example Chmod U + x

$Ls-L temp-RW-r --1Siu0January10 13:50TEMP $ChmodU +X temp $Ls-L temp-Rwxr -- r --1Siu0January10 13:50Temp
 

List the file details. You can see that-RW-r -- excludes the first digit. Each three digits in the end represent a user type, and-indicates no setting.

Add the execution permission to the file owner.

 

Chmod ug + x

$Ls-L temp-Rwxr -- r --1Siu0January10 13:50TEMP $ChmodUg =Rwx TEMP $Ls-L temp-Rwxrwxr --1Siu0January10 13:50Temp
 

Add execution permissions to the file owner and group users

 

Chmod g-x

$Ls-L temp-Rwxrwxr --1Siu0January10 13:50TEMP $ChmodG-X temp $Ls-L temp-Rwxrw-r --1Siu0January10 13:50Temp
 

Group users minus execution Permissions

 

Chmod 777

$Ls-L temp-Rwxrw-r --1Siu0January10 13:50TEMP $Chmod 777TEMP $Ls-L temp-Rwxrwxrwx1Siu0January10 13:50Temp
 

Add readable and writable executable permissions to all users

 

Chmod 755

$Ls-L temp-Rwxrwxrwx1Siu0January10 13:50TEMP $Chmod 755TEMP $Ls-L temp-Rwxr-XR-x1Siu0January10 13:50Temp
 

Add read, write, and execution permissions to the owner, and add read and execution permissions to group users and other users.

 

Chmod-RV 755

$Ls-L total usage4Drwxr-XR-x2Siu4096January10 13:57 Dir$Chmod-RV755 Dir"Dir"The permission mode of is 0755 (rwxr-XR-x)
 

Recursively add permissions to folders and display the permission adding information

 

Tips

1. the folder must have the execution permission before it can be read and written.

2. In addition to the above basic user permissions, there are settings such as setuid, setgid, and sticky bit, which are somewhat advanced. Here are concise notes