Linux chmod Command Guide

The chmod command is used to change the permissions of files or directories. It is a commonly used command in Linux systems to control the access permissions of files or directories, such as read, write, and execute permissions.

Command format:

chmod [选项]... 模式 文件...

Common options include:

1. -c: Display the permission modification results for each file.
2. -f: Do not display error messages.
3. -v: Display the permission changes for each file, including those that have not been modified.

The mode is a three-digit octal number used to specify the permissions of a file. Each digit represents a different permission: read (r), write (w), and execute (x), with corresponding values of 4, 2, and 1. By combining these three permissions, different permission values can be obtained.

For example:

1. Mode 777 allows the owner, group, and other users to have read, write, and execute permissions for the file.
2. The mode of 755 means the owner of the file has read, write, and execute permissions, while the group and other users only have read and execute permissions.

In addition to using three-digit octal numbers to specify permissions, you can also use symbolic notation to set permissions. The format for symbolic notation is [ugoa]*([-+=]([rwxXst]*|[ugo]))+, where:

1. “u denotes the owner of the file.”
2. “g” indicates the group ownership of the file.
3. “O signifies other users.”
4. “a represents all users.”
5. “+” indicates adding permission.
6. – Indicate removal of permissions.
7. = Indicates establishing permissions.

For example:

1. Adding execute permission to the owner of the file is denoted by u+x.
2. go-w is used to remove write permissions for the group and other users on a file.

In addition to changing permissions, the chmod command can also be used to modify the owner and group of a file. You can change the owner of a file with the chown option and change the group with the chgrp option.

In conclusion, the chmod command is a very useful command in Linux systems that can be used to modify file permissions, owner, and group.