chmod Permissions Cheat Sheet

Change file and directory permissions with symbolic and numeric modes for secure Linux access control.

What this cheat sheet is for

This chmod permissions reference helps you complete common developer tasks quickly and avoid repeated trial-and-error when working under deadlines.

When you need a reliable command or pattern during debugging and incident response.
When you are implementing a feature and want a known-good syntax example immediately.
When onboarding teammates and documenting repeatable workflows for daily use.
When reviewing pull requests and verifying that command usage follows best practices.

chmod 640 config.env

Example:

chmod 600 ~/.ssh/id_rsa

chmod 755 deploy.sh

Example:

chmod 700 ./scripts

chmod u+x backup.sh

Example:

chmod g-w report.txt

chmod u=rw,g=r,o= file.txt

Example:

chmod a+r docs.md

chmod -R 755 public

Example:

chmod -R u+rwX,g+rX,o-rwx project

ls -l

Example:

stat -c "%a %n" *

Using chmod -R 777 is insecure and should be avoided on real systems.
Numeric modes differ for files and directories; execute bit on dirs means traversal.
Changing permissions without checking ownership can still leave access denied errors.

Last updated: February 2026