How to Change Permissions on Files and Directories in Linux

What are the permissions of a file or directory in Linux

three file permissions

• text read file content (r);
• write data to file(w);
• Execute file(x) as a command.

Three permissions for directories

• read the name of the file contained in the directory (r);
• write information to the directory (add and delete links to index points, w);
• Search a directory (can use the directory name as a pathname to access the files and subdirectories it contains, x).

chmod command parsing

chmod uses 3 numbers to express the user (the owner of the file or directory, usually the creator of the file), the user group (when a user creates a file, the group of the file is the group of the user) and permissions of other users, such as:

**chmod 777 /home/user ** Note: Only set the permissions of the /home/user directory to rwxrwxrwx

**chmod -R 777 /home/user ** Note: It means to set the permissions of the entire /home/user directory and its files and subdirectories to rwxrwxrwx

details as follows:

• Read----represented by the number 4;
• Write----represented by the number 2;
• Execute----represented by the number 1.

According to the rules, if you want to set the permissions of the /test directory to:

1. Readable and writable to the user: 4 (read) + 2 (write) = 6;
2. Readable and executable for user group: 4 (read) + 1 (execute) = 5;
3. Read only to other users: 4 (read);

So you can use the command: chmod 654 /test

Several common permission examples

• -rw------- (600) Only the owner has read and write permissions
• -rw-r--r-- (644) Read and write permissions only for owner, group and others only read permissions
• -rwx------ (700) Only the owner has read, write, and execute permissions
• -rwxr-xr-x (755) Only owner has read, write, execute permissions, group and others only have read and execute permissions
• -rwx--x--x (711) Only owner has read, write, execute permissions, group and others have execute permissions only
• -rw-rw-rw- (666) Everyone has read and write permissions
• -rwxrwxrwx (777) Everyone has read, write and execute permissions