Unix Interview Questions and Answers

 

How do you change File Access Permissions in UNIX OS?

Every file has 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).



Example 1:



To change 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).



Example 2:



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



chmod(myfile,0744).

Posted by:Richards