Linux File and Directory Permission Management Tutorial

This guide introduces the fundamentals of managing file and directory permissions on Linux systems.

Permission categories : read (r), write (w), execute (x) correspond to numeric values 4, 2, and 1 respectively; combinations form the familiar three‑digit mode (e.g., 644, 777).

Viewing permissions : use ls -l (or ll ) to list files. The first character indicates the type ( d for directory, - for regular file) followed by three groups of three characters representing user, group, and others permissions.

Permission string breakdown :

-rw- --- ---
First character: file or directory type
The next nine characters are divided into three groups of three:
1. User permissions – owner of the file
2. Group permissions – users belonging to the file's group
3. Others permissions – all other users

Adding permissions :

chmod 777 file → rwxrwxrwx (full access for everyone)

chmod 644 file → rw-r--r-- (owner read/write, group and others read‑only, the default mode)

Individual permission changes :

chmod u+x b.txt – add execute permission for the owner (user)

chmod g+x b.txt – add execute permission for the group

chmod o+x b.txt – add execute permission for others

Revoking permissions :

chmod 400 c.txt – set read‑only for the owner, no permissions for group/others

chmod u-r c.txt – remove read permission from the owner

Recursive permission changes : chmod -R a /path/to/dir applies the specified mode to all files and sub‑directories under a .