Managing Local Linux Users and Groups

Overview

Goal	To manage local linux users and groups and administer local password policies
Objectives	Explain the role of users and groups on a Linux system and how they are understood by the computer. Run commands as the superuser to administer a Linux system. Create, modify, lock, and delete locally defined user accounts. Create, modify, and delete locally defined group accounts. Lock accounts manually or by setting a password-aging policy in the shadow password file.
Sections	users and groups (and practice) Gaining Superuser Access (and Practice) Managing Local User Accounts (and Practice) Managing Local Group Accounts (and Practice) Managing User Passwords (and Practice)
Lab	Managing Local Linux User and Groups

 

Part 1: Users and Groups

Question: What is a User?

Every process (running program) on the system runs as a particular user. Every file is owned by a pariticular user. Access to files and directories are restricted by user. The user associated with a running process determines the files and directories accessible to that process.

 

 

[elewei@localhost Desktop]$id

The id command is used to show information about the current logged-in user.

 

[elewei@localhost Desktop]$ls -l /tmp

View the user associated with a file or directory. The third column shows the username

 

[elewei@localhost Desktop]$ps au

To view the process information, use the ps command. The default is to show only processes in the current shell. Add the a option to view all processes with a terminal.

To view the user associated with process, include the u option. 

 

The mapping of names to numbers is defined in databases of account information. By default, systems use a simple "flat file" the /etc/passwd file, to store information about local users.

username

password

UID

GID

GECOS:

/home/dir:

shell

 

username: is a mapping of a UID to a name for the benefit of human users.

password: historically, passwords were kept in an ecrypted format. Today, they are stored in a separate file called /etc/shadow.

UID: is a number that identifies the user at the most fundamental level.

GID: the user's primary group ID number.

GECOS: is arbitrary text, which usually includes the user's real name.

/home/dir: is the location of the user's personal data and configuratoin files.

shell: a program that runs as the user logs in. For a regualr user, this is normally the program that provides the user's command line prompt.

 

Question: What is a group?

Like users, groups have a name and a number (GID). Local groups are defined in /etc/group.