From LXF Wiki
A Shell command that allows the user to change file permissions for a given file/directory (they are treated the same in Unix/Linux systems). It is exceptionally powerful and allows you to change read/write permissions for the following 3 categories. Owner of the file. Group owner of the file. Other potential users of the file.
chmod 777 anygiven.filedirname
Would allow anyone in the three groups to be able to access your files. It is equivalent to writing
chmod a=rwx anygiven.filedirname
chmod 700 anygiven.filedirname
Would allow the Owner of the file rwx permissions but no-one else.
Test it on a file, individual rwx values can be set purely by changing the values 0-7 for each group. You can see read/write permissions within a file for all ownership permissions by typing
ls anygiven.filedirname -g
Flags and Options