Linux File Permissions

chmod, chown and the octal values behind read, write and execute

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How the numbers work

Each permission is a value: read = 4, write = 2, execute = 1. Add them together for each of owner, group and others.

Octal	Symbolic	Owner	Group	Others	Typical use
777	rwxrwxrwx	rwx	rwx	rwx	Full access (avoid for security)
755	rwxr-xr-x	rwx	r-x	r-x	Directories and executable scripts
644	rw-r--r--	rw-	r--	r--	Regular files
700	rwx------	rwx	---	---	Private scripts
600	rw-------	rw-	---	---	Private keys and config
400	r--------	r--	---	---	Read-only private key
750	rwxr-x---	rwx	r-x	---	Group-executable dirs
640	rw-r-----	rw-	r--	---	Group-readable files

chmod

chmod 755 script.sh              # set with octal
chmod u+x script.sh              # add execute for owner
chmod g-w file.txt               # remove write for group
chmod -R 755 /var/www            # recursive

chown and chgrp

chown user:group file.txt        # change owner and group
chown -R user:group /var/www     # recursive
chgrp group file.txt             # change group only

Special bits

chmod 4755 file    # setuid: run as the file owner
chmod 2755 dir     # setgid: inherit directory group
chmod 1777 dir     # sticky: only owners can delete (e.g. /tmp)