Changing file attributes

chmod command is used to the change a file's permissions. Only the user who
owns the file can change the permissions of a file (the root user can also do it).
chmod [-R] operation files
chmod 777      add rwx permission for owner,group&others [numeric method]
chmod u+rwx g-w    add rwx permission to owner& remove w of group of file [symbolic]
chmod -R a-x /tmp        turn off x permissions,for all users,for all files in the /tmp.