chmod permissions explained

Common permissions

• 755 rwxr-xr-x Folders and scripts on web servers: you change them, everyone else can open folders and run scripts. The default for directories on most hosts.
• 644 rw-r--r-- Normal files on web servers: PHP files, HTML, CSS, JavaScript and images. You change them, everyone can read them.
• 777 rwxrwxrwx Nothing on a live server. Everyone (every account and every process) can read, change and run it. Fix permission errors with the right owner and 755/775 instead.
• 775 rwxrwxr-x Folders shared with your group, for example Laravel's storage/ and bootstrap/cache/ when the web server runs in your group.
• 600 rw------- Private files: SSH keys, .env, credentials. Only the owner can read and change them (SSH refuses keys that are more open).
• 700 rwx------ Private folders such as ~/.ssh and your own scripts: only you can open, change or run them.
• 664 rw-rw-r-- Files you and your group both edit, for example uploads and logs written by the web server user in your group.
• 400 r-------- Read-only private files, such as an AWS .pem key: only the owner can read them.
• 444 r--r--r-- Read-only files everyone can read, such as a locked wp-config.php or a generated file you don't want edited.
• 750 rwxr-x--- Folders and scripts only your group should reach, for example deploy scripts shared with a deploy user.
• 640 rw-r----- Config files the web server group must read but others must not, for example a .env file read by the www-data group.
• 660 rw-rw---- Files shared with your group that others must not read, such as a group-readable database socket or log.
• 770 rwxrwx--- Private shared folders: owner and group work in them, everyone else is locked out.
• 744 rwxr--r-- Scripts only you run, while others can still read them.
• 711 rwx--x--x Home or parent folders others must pass through (to reach public_html) without listing what is inside.
• 666 rw-rw-rw- Files everyone may change, such as /dev/null. On a website, use 664 or 644 instead.
• 766 rwxrw-rw- Rarely right: everyone can change the file but only the owner can run it. Usually a sign that 664 or 644 was meant.
• 555 r-xr-xr-x Read-only folders and scripts that everyone can open or run but nobody changes.
• 500 r-x------ Read-only private folders or scripts: only the owner can read or run them, and nobody can change them.
• 440 r--r----- Read-only files for the owner and group, such as /etc/sudoers.