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UNIX/Linux group and user management

Oracle Database Tips by Donald Burleson

Advanced Oracle Utilities: The Definitive Reference by Rampant TechPress is written by top Oracle database experts (Bert Scalzo, Donald Burleson, and Steve Callan).  The following is an excerpt from the book.

In UNIX, a user named oracle is generally created to become the owner of the Oracle software on the UNIX server.  In addition to the oracle user, other UNIX users may be created and granted access to certain oracle files on the server. First on the menu is how UNIX manages user IDs and groups. 


UNIX group management

Groups are defined in a file called /etc/group.  Each line of the /etc/group file contains group data separated by a colon ":". This file defines each group and contains the following values:


group name   :  group_nbr  : members of the group

root> cat /etc/group




Now see how user information is stored inside UNIX.

UNIX user management

UNIX users are controlled by a special file called /etc/passwd.  This file contains a series of strings separated by colons ":".  The values are:


username  :  password  :  user_nbr : group_nbr :  default shell

root> cat /etc/passwd



From the above listing, it can be determined that the oracle user has a encrypted password in /etc/shadow, that they are user 108, and they are in group 102.  The oracle user has /export/home/oracle for a home directory, and they are using the Korn shell as a default shell.  For some people, the John the Ripper tool, explained later, meets the definition of a utility. But for the purposes of this book, it definitely does not.

UNIX passwords on Oracle servers

UNIX passwords are extremely vulnerable to hacking.  Users can change their passwords by invoking the passwd command.  Note that the listing of /etc/passwd does not contain the encrypted passwords for the user IDs, and the password column is denoted with an "x".  This indicates that the system administrator is storing the passwords in another special file called /etc/shadow.


However, protecting passwords in a /etc/shadow file is not always enough to ensure security.  Several tools such as John the Ripper can be used to easily crack into these UNIX files, stealing access to the Oracle server and all database data.  To learn how to protect a UNIX password from hacking, see the UNIX password cracker at

Advanced Oracle Utilities: The Definitive Reference by Rampant TechPress is written by top Oracle database experts (Bert Scalzo,  Donald Burleson, and Steve Callan). 

Buy direct from the publisher and save 30%!



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