Linux File Permissions Cheat Sheet

1. **Quick Reference**

| Command | Description |

| --- | --- |

| chmod | Change file permissions |

| chown | Change file owner |

| chgrp | Change file group |

| ls -l | List file permissions |

2. **Syntax**

The basic syntax for chmod is:

chmod [permissions] [file]

* [permissions] is a three-digit number representing the permissions for the owner, group, and others, respectively.

* [file] is the file or directory you want to modify.

Example:

chmod 755 /path/to/file

This sets the permissions to rwx for the owner, r-x for the group, and r-x for others.

3. **Common Patterns**

* Set execute permission for owner, group, and others:

chmod 755 /path/to/file

* Set read and write permission for owner, and read permission for group and others:

chmod 644 /path/to/file

* Set read, write, and execute permission for owner, and read and execute permission for group and others:

chmod 755 /path/to/directory

* Recursively set permissions for a directory and its contents:

chmod -R 755 /path/to/directory

4. **Gotchas**

* Inconsistent permissions: If you don't set consistent permissions across your files and directories, you may encounter issues with access control.

* Overly permissive permissions: Setting permissions to 777 can be a security risk, as it allows anyone to read, write, and execute the file.

* Using chmod with symbolic links: When using chmod with symbolic links, the permissions are changed on the target file, not the link itself.

5. **Related Commands**

* stat: Displays detailed information about a file, including its permissions.

* getfacl: Displays the access control list (ACL) of a file or directory.

* setfacl: Sets the ACL of a file or directory.

* umask: Sets the default permissions for new files and directories.

Example use cases:

* Use stat to check the permissions of a file: stat /path/to/file

* Use getfacl to check the ACL of a file: getfacl /path/to/file

* Use setfacl to set the ACL of a file: setfacl -m u:user:rwx /path/to/file