Can linux change file permissions?

Linux can change the permissions of files. In Linux, you can use the chmod command to modify file permissions. The syntax is "chmod [-cfvR] [--help] [--version] mode file..."; chmod will change the permissions of each given file according to the mode value. File mode bits, the mode value can be a symbolic mode representation of the change to be made, or an octal number representing the bit pattern of the new mode bits.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

File permissions are very important for a system, and each file has access permissions set for different users. So, can the access permissions of files be manually modified?

In Linux, you can use the chmod command to modify file permissions. Let’s take a look at the chmod command.

1. Introduction to chmod command

Linux chmod (full English spelling: change mode) command is a command that controls user permissions on files.

chmod changes the file mode bits of each given file according to mode, which can be a symbolic mode representation of the change to be made, or an octal number representing the bit pattern of the new mode bits.

The format of the symbol pattern is [ugoa…][±=][perms…][…], where perms is zero or more letters in the set rwxXst, or the set ugo a single letter in . Multiple symbol patterns can be given, separated by commas.

The combination of the letters ugoa controls which users' access to the file will be changed: the user who owns the file (u), other users in the file group (g), other users not in the file group (o) Or all users (A).

If none of these are given, the effect is as if a was given, but the bits set in umask are not affected. chmod never changes the permissions of a symbolic link; the chmod system call cannot change its permissions.

2. Introduction to permissions

The file calling permissions of Linux/Unix are divided into three levels: file owner (Owner), user group (Group), other users ( Other Users).

 Only the file owner and superuser can modify the permissions of a file or directory. You can use absolute mode (octal number mode) and symbolic mode to specify file permissions.

##Permission symbolNameDescriptionrReadSet as read permissionwWriteSet to write permissionxExecute permissionSet to executable permissionXSpecial execution permissionsOnly when the file is a directory file, or other types of users have executable permissions, the file permissions are set to executablessetuid/gidWhen the file is executed, set the setuid or setgid permissions of the file according to the user type specified by the who parametertPaste bitSet the paste bit. Only the super user can set this bit, and only the file owner u can use this bit

3. Usage examples

1. Get command help information

[root@s141 ~]# chmod --help

2. View command version

[root@s141 ~]# chmod --version
 chmod (GNU coreutils) 8.22
 Copyright © 2013 Free Software Foundation, Inc.
 License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html.
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law.
 Written by David MacKenzie and Jim Meyering.

3. Add file execution permissions to all users

4. Cancel the execution permissions of other users

5. Use octal values ​​to set permissions as a whole

[root@s141 ~]# chmod 751 1.txt

6. Set directory and file permissions recursively

[root@s141 ~]# chmod -R 760 /home/test

7. Display detailed information about permission modification

[root@s141 ~]# chmod -Rv 760 /home/test
 mode of ‘/home/test’ retained as 0760 (rwxrw----)
 mode of ‘/home/test/.bash_logout’ retained as 0760 (rwxrw----)
 mode of ‘/home/test/.bash_profile’ retained as 0760 (rwxrw----)
 mode of ‘/home/test/.bashrc’ retained as 0760 (rwxrw----)
 mode of ‘/home/test/1’ retained as 0760 (rwxrw----)
 mode of ‘/home/test/2’ retained as 0760 (rwxrw----)

8. Display only when permissions are changed

9. Use symbols to set permissions

[root@s141 ~]# chmod o=r,u=rwx,g=rx 1.txt

10. Set permissions for the directory

4. Usage syntax and parameter description

1. Usage syntax

chmod [-cfvR] [--help] [--version] mode file...

Usage 1: chmod permission file

Usage two: chmod parameter permission file

2. Parameter description

Parameters	Parameter description
-c	The change action will only be displayed if the file permissions have indeed been changed
-f	Do not display an error message if the file permissions cannot be changed
-v	Display the details of permission changes
-R	Make the same permission changes to all files and subdirectories in the current directory (that is, change them one by one recursively)
–help	Show auxiliary instructions
--version	Show version

3. Operator description

Operator	Description
	Add permissions for the specified user type
-	Remove permissions for the specified user type Permissions
=	Set the settings for the specified user permissions, that is, reset all permissions of the user type

4. User symbol

who	User type	Description
u	user	File owner
g	group	File owner’s group
o	others	All other users
a	all	The user used is equivalent to ugo

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