Redhat: Shadow

The Redhat Shadow Password Suite

Before security became an issue all users and passwords were stored in /etc/passwd and /etc/group files. But having the passwords stored in a reachable file is obviously not an option any more. The shadow password suite is designed to solve this problem. Sensitive data such as passwords have been moved to a file only accessible to the root user.

The Shadow password suite consists of four files. /etc/passwd and /etc/group are the files used origanally. Two files have been added to the suite: /etc/shadow and /etc/gshadow. The default values of the files are defined in /etc/login.defs

passwd

The passwd file contain teh basic information about every user on the system. Each user has seven columns of information.

AAAS_TEST:x:30587:30588::/home/AAAS_TEST:/bin/bash
tom_gds:x:30588:30589::/home/tom_gds:/bin/bash
manu_iitk:x:30589:30589::/home/manu_iitk:/bin/bash
jump_trading:x:30590:30590::/home/jump_trading:/bin/bash
saha_pec:x:30591:30591::/home/saha_pec:/bin/bash

Username	michael	The username used to log into the system
Password	x	The password of the user. An 'x' means the password in in the shadow file, an '*' means the account is disabled or the encrypted password.
User ID	500	numeric user ID - users IDs start at 500 by default
Group ID	500	numeric gorup ID - group IDs start at 500 by default. Redhat will create a group for every user which will normally have the same id as the user.
User Info	Michael H	any extra information
Home Directory	/home/michael	The users home direcotory, by default in /home/<username>
Login Shell	/bin/bash	The shell used by the user, by default this is bash

A service account is have the /bin/nologin sheell. This prevents anyone logging into the system as a service. If you see a service logged in it likely means that someone has broken into the system

group

Every user is assinged by default to a group with the same name, their private group. This group will only have that user as a member.

Each group is defined in the group file using four columns of information