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chmod Permissions Guía rápida

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.
  • Make scripts executable quickly.
  • Lock down config files containing secrets.
  • Set shared directory permissions for team collaboration.

Numeric chmod modes

Set owner read/write, group read, others none

chmod 640 config.env

Example:

chmod 600 ~/.ssh/id_rsa

Make script executable

chmod 755 deploy.sh

Example:

chmod 700 ./scripts

Symbolic chmod modes

Add execute permission for owner

chmod u+x backup.sh

Example:

chmod g-w report.txt

Apply multiple symbolic rules

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

Example:

chmod a+r docs.md

Recursive and directory-safe usage

Apply recursively to directory

chmod -R 755 public

Example:

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

Check permission bits

ls -l

Example:

stat -c "%a %n" *

Common mistakes / Errores comunes

  • 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.

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Last updated: February 2026