Every file has the following attributes:

• Owner's user ID ( 16 bit integer ).

• Owner's group ID ( 16 bit integer ).

• File access mode word

  'r w x -r w x- r w x' 

  (user permission-group permission-others permission)

  r-read, w-write, x-execute.

  To change the access mode, we use chmod(filename,mode).

  Code Practise 1:

  To change the mode of myfile to 'rw-rw-r--' (ie. read, write permission for user - read, write permission for group - only read permission for others)  we give the args as:

  chmod(myfile,0664) .

  Each operation is represented by discrete values 

  'r' is 4

  'w' is 2

  'x' is 1

  Therefore, for 'rw' the value is 6(4+2).

  Code Practise 2:

  To change the mode of myfile to 'rwxr--r--' we give the args as:

  chmod(myfile,0744).