Linux File Permissions Cheat Sheet

Understanding File Permissions

Each file and directory in Linux has permissions assigned to three categories:

• Owner (u): The user who owns the file.
• Group (g): The group associated with the file.
• Others (o): Everyone else.

Permissions are represented as:

r - Read | w - Write | x - Execute

Example: -rwxr--r--

Breakdown: The owner has read (r), write (w), and execute (x) permissions, the group has only read (r), and others have only read (r).

Changing Permissions with chmod

chmod 755 filename - Sets read, write, and execute for owner, and read & execute for group and others.

chmod u+x filename - Adds execute (x) permission to the owner.

chmod g-w filename - Removes write (w) permission from the group.

chmod o+r filename - Adds read (r) permission for others.

chmod a+x filename - Adds execute (x) permission for everyone.

Changing Ownership with chown

chown user:group filename - Changes file owner and group.

chown user filename - Changes only the owner of the file.

chown :group filename - Changes only the group of the file.

chown -R user:group directory/ - Recursively changes ownership for all files in a directory.

Special Permissions

chmod 4755 filename - Set user ID (SUID), allowing execution as the file owner.

chmod 2755 filename - Set group ID (SGID), making files inherit the group of the parent directory.

chmod 1755 directory - Sticky bit, preventing others from deleting files they don't own.