Master Linux File Permissions: chown, chmod, and Permission Bits Explained

Linux is a multi‑user operating system where each user has distinct privileges. To protect system security, Linux defines separate access rights for different users on the same file or directory.

The two primary commands for modifying file ownership and permissions are chown (change owner) and chmod (change mode).

Use ls -l or ll to view a file’s attributes, including its type and permission bits. The first character indicates the file type (d for directory, - for regular file, l for symbolic link, etc.). The next nine characters are three groups of rwx representing read, write, and execute permissions for owner, group, and others.

Permission bits can be expressed numerically: r=4, w=2, x=1. The sum of each group yields a three‑digit number such as 770 (owner = 7, group = 7, others = 0). The symbolic form chmod u=rwx,g=rx,o=r filename sets the same permissions.

Changing ownership is done with chown (e.g., chown bin install.log) or chown root:root install.log. Changing the owning group uses chgrp, optionally with -R for recursive changes.

Examples:

# ls -l

drwxr-xr-x 2 root root 4096 Dec 14 2012 bin
...
# chown bin install.log
# chmod 777 .bashrc
# chmod u=rwx,g=rx,o=r test1

Images illustrate the permission string layout and the mapping of characters to numeric values.