Linux Permissions Cheat Sheet

This cheat sheet focuses on the most common permission sets you’ll encounter when managing Linux systems, backups, and hypervisors.

Each permission has a value: Read (4), Write (2), and Execute (1).

Code	Meaning	Typical Use Case
777	`rwxrwxrwx`	Danger! Everyone can do everything. Avoid in production.
755	`rwxr-xr-x`	Standard for directories and executable scripts.
700	`rwx------`	Private directories or scripts only for the owner.
664	`rw-rw-r--`	Shared files where the group can also edit.
644	`rw-r--r--`	Standard for regular files (Config files, HTML).
600	`rw-------`	Sensitive files (SSH keys, backup credentials).
400	`r--------`	Read-only for owner; maximum security for keys.

Command	Action
`chown user file`	Change the owner of a file.
`chown user:group file`	Change both owner and group.
`chown -R user:group dir`	Recursive: Change owner/group for a folder and everything inside.

Command	Action
`chmod +x script.sh`	Make a script executable for everyone.
`chmod u+x script.sh`	Make a script executable for the owner only.
`chmod -R 755 /data`	Apply `755` to a directory and all its contents.
`chmod 444 config.ini`	Make a file read-only for everyone (even the owner).

When managing shared folders (like a common backup landing zone), you might want users to add files but prevent them from deleting each other’s work.

Command: chmod +t /shared_folder
Result: Only the file owner or root can delete or rename the files within that directory.