Managing Users

The Saigon CTT
Managing Users
The Saigon CTT



Objectives
Objectives



Define the requirements for user accounts

Explain group and group accounts

Construct configuration files (group, passwd,
shadow)

Demonstrate adding users

Describe modifying user details

Explain user passwords

Demonstrate deleting users
The Saigon CTT



New User Requirements
New User Requirements


When adding a new user, you need be familiar with files :
passwd, shadow, group, gshadow under /etc directory

/etc/passwd contains information of all users : Login
name, User ID, Group ID, Descriptive name, Home
directory, Login shell

/etc/shadow stores parameters to control account
access: user’s password hash and password aging
information

/etc/group contains information about user’s groups

/etc/gshadow stores group’s password hash,…(rarely
used)
The Saigon CTT



Preparing Groups
Preparing Groups

Carefully constructed groups are very useful to
users who are all working in the same department
or project

Groups not only allow for a second level of
access control but also allow the members in
group to share files in secured environment


Each line in /etc/group file correspond to a group

Commands to modify groups: groupadd,
groupmod, groupdel
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


The /etc/passwd
The /etc/passwd

Each line in this file correspond to a user,
has the following form :
name:password:UID:GID:comment:home directory:shell
# more /etc/passwd
root:x:0:0:Super User:/root:/bin/bash
henry:x:101:101:Thiery Henry:/home/henry:/bin/ksh
...
The Saigon CTT



Allocating User IDs
Allocating User IDs

All Linux system come with several
administrator users pre-configured, are
intended to perform certain administrative
work. They are typically assigned UID less

than 100: root, bin, daemon, sys, adm, lp, …

System with administration tools allocate
UIDs automatically, greater than 100 in
general
The Saigon CTT



Adding Users
Adding Users

The useradd utility is recommended for administering
users. It creates the required record in /etc/passwd
and /etc/shadow

A list of options can be used with useradd to override
defaults:
-u UID
Specify new user ID (default: next available number)
-g GID
Specify default (primary) group ( default other group )
-c comment
Description of user ( default: blank )
-d directory
Define home directory ( default /home/username )
-m
Make home directory
-k skel_dir
Skeleton directory ( default /etc/skel )

-s shell
Specify login shell ( default /bin/bash )