Module Linux essentials - Module 14: Managing users and groups

Module Linux essentials - Module 14 introduce managing users and groups. After studying this chapter students should be able to: Creating users and groups, understanding user and group commands, creating user IDs.

Module 14 Managing Users and Groups

Exam Objective 5.2 Creating Users and Groups

Objective Summary

Working with Groups

Creating a Group

creating or modifying a group, you can verify the changes by viewing the /etc/group file or

running the getent command.

The groupadd Command

groupadd -g 506 research

command will automatically provide a GID for the new group.

Group ID Considerations

where you expect to create user IDs if your

system uses UPG.

system use.

that will be less than the lowest standard UID.

Group Naming Considerations

either an underscore (_) or a lower-case

alphabetic character (a-z).

distributions, but using more than 16 can be

problematic as some distributions may not

accept more than 16.

characters can be alphanumeric, dash (-) and underscore(_).

that were associated with that group will no

longer be associated with that group.

Deleting a Group

Working with Users

The /etc/default/useradd File

define default settings when creating user

accounts.

the useradd -D command.

The /etc/default/useradd File

user's new home directory will be created

the password expires that the account is disabled

SHELL /bin/bash The SHELL setting indicates the default shell for

user's when they login to the system

SKEL /etc/skel The contents of this directory are copies into the

new user's home directory and the new user is given ownership of these files

CREATE_MAIL_SPO

OL yes A "mail spool" is a file where incoming email is placed ".

The /etc/login.defs File

default settings when creating user accounts.

viewing the contents of this file.

editing the file directly.

The /etc/login.defs File

MAIL_DIR /var/mail/spool The directory in which the user's mail spool file will be created.

PASS_MAX_DAYS 99999 The maximum number of days that a user can continue to use

the same password

PASS_MIN_DAYS 0 The shortest time that a user are required to keep a password.

PASS_MIN_LEN 5 This indicates the minimum number of characters that a

password must contain

PASS_WARN_AGE 7 This is the default for the warning field

UID_MIN 500 The UID_MIN determines the first UID that will be assigned to

an ordinary user

UID_MAX 60000 The UID_MAX determines the highest possible UID that will be

assigned to an ordinary user

GID _MIN 500 The GID _MIN determines the first GID that will be assigned to

an ordinary group.

GID _MAX 60000 The GID_MAX determines the highest possible GID that will be

assigned to a regular group

CREATE_HOME yes The value of this determines whether or not a new directory

will be created for the user, when their account is created.

UMASK 077 Determines what the default permissions will be for the user's

home directory

Working with Account

Information

Advantages to Individuals

having Separate Accounts

access to files or services

grant the ability to specify individuals to permit execution of select administrative commands

and rights associated with it allowing for

greater management flexibility

Account Considerations

values you want to set for the following:

The useradd Command

create new users Example:

useradd -u 1000 -c 'Jane Doe' jane

(/var/spool/mail/jane) and user’s home

Password Security

Picking a Password

as to make them hard to remember.

reset their passwords.

passwd command with no argument.

chage Command

Using the chage Command

user.

Short option Long option Description

-l list List the account aging information

-d LAST_DAY lastday LAST_DAY Set the date of the last password change to

LAST_DAY -E

EXPIRE_DATE expiredate EXPIRE_DATE Set account to expire on EXPIRE_DATE

-h help Show the help for chage

-I INACTIVE inactive INACTIVE Set account to permit login for INACTIVE days

after password expires -m MIN_DAYS mindays MIN_DAYS Set the minimum number of days before

password can be changed to MIN_DAYS -M MAX_DAYS maxdays MAX_DAYS Set the maximum number of days before a

password should be changed to MAX_DAYS -W

WARN_DAYS warndays WARN_DAYS Set the number of days before a password expires to start displaying a warning to

WARN_DAYS

Modifying a User Account

Modify a User

the account.

determine if a user is currently logged in to the system.

The usermod Command

Option Description

-e

Removing a User

Delete a User

account.

of the files owned by the user.

directory and the user’s mail spool are deleted.