chmod -- change file modes or Access Control Lists
chmod [-fv] [-R [-H | -L | -P]] mode file …
chmod [-fv] [-R [-H | -L | -P]] [-a | +a | =a] ACE file …
chmod [-fhv] [-R [-H | -L | -P]] [-E] file …
chmod [-fhv] [-R [-H | -L | -P]] [-N] file ...
chmod 644 /home/looker/.ssh/id_rsa.pub