(RHCSA) Manage Users and Groups

This is part of the independent and unofficial RHCSA Exam Study Guide series providing free 🤑 resources to prepare for the exam.

This post covers the objectives under the section:

“MANAGE USERS AND GROUPS”

It contains two main parts:

• Resources: with links to learn and practice for each objective.
• Cheatsheet: containing some examples of commands and actions performed in each objective (when applied).

📚 Resources:

• 📌 Introduction to Linux Users and Groups

• 📌 RHCSA v8 Practice Session: Manage users and groups

CREATE, DELETE, AND MODIFY LOCAL USER ACCOUNTS

• 📌 Chapter 7. Getting started with managing user accounts

• 📌 Understanding the /etc/passwd File

• 📌 How to create modify and delete users account on Linux

• 📌 A Complete Guide to Usage of ‘usermod’ command – 15 Practical Examples with Screenshots

• 📌 Linux sysadmin basics: User account management with UIDs and GIDs

• 📌 How to manage users and groups in Linux

• 📌 3 basic Linux user management commands every sysadmin should know

CHANGE PASSWORDS AND ADJUST PASSWORD AGING FOR LOCAL USER ACCOUNTS

• 📌 Managing Linux users with the passwd command

• 📌 Forcing Linux system password changes with the chage command

• 📌 How to Manage User Password Expiration and Aging in Linux

CREATE, DELETE, AND MODIFY LOCAL GROUPS AND GROUP MEMBERSHIPS

• 📌 Managing local group accounts in Linux

• 📌 Understanding /etc/group file

• 📌 3 basic Linux group management commands every sysadmin should know

• 📌 Chapter 22. Editing user groups using the command line

CONFIGURE SUPERUSER ACCESS

• 📌 Linux command line basics: sudo

• 📌 Exploring the differences between sudo and su commands in Linux

• 📌 RHEL 8 / CentOS 8 add user to sudoers

• 📌 How To Find All Sudo Users In Linux

• 📌 Chapter 23. Managing sudo access

📑 Cheatsheet:

CREATE, DELETE, AND MODIFY LOCAL USER ACCOUNTS

• last ➡ show a listing of last logged in users.

• lastb ➡ show a listing of last unsuccessful log in/outs.

• lastlog ➡ reports the most recent login of all users of a given user.

• who ➡ show who is logged in.

• w ➡ show who is logged in and what they are doing.

• id ➡ print real and effective user and group IDs.

• getent passwd | grep usr1 ➡ display usr1 definitions from /etc/passwd file.

• usermod -G -a db user99 ➡ add db group as a suplementary group to user99 account.

• usermod -u 1010 user99 ➡ change user’s UID.

• usermod -d /home/user-99-new -m user99 ➡ change user’s home directory.

• useradd -s /sbin/nologin user99 ➡ create user99 account with the disability of logging in.

• userdel -r user45 ➡ remove user and it’s home directory and mail spool.

CHANGE PASSWORDS AND ADJUST PASSWORD AGING FOR LOCAL USER ACCOUNTS

• passwd user1 ➡ change user’s password.

• chage -l usr1 ➡ display account aging information.

• chage -m 1 -M 90 usr1 ➡ set minimum and maximum days before password change for usr1.

• chage -d 2021-12-15 usr1 ➡ set the date of last password change.

• chage -W 10 -I 4 usr1 ➡ usr1 passwd will warn 10 days prior to password expiration, and is set to lock the user 4 days after expiration.

• passwd -x 30 -n 4 -w 10 user1 ➡ user 1 password expires in 30 days, cannot change at least 4 days, starts warning 10 days prior to expiration.

• usermod -e 2021-12-20 user1, chage -E 2022-12-15 user1 ➡ set password expiration date.

• passwd -S user1 ➡ report password status (expiration, etc).

• usermod -L user1, passwd -l user1 ➡ lock user1 account (verify the lock at /etc/shadow file, there must be !! prepending the password hash).

• Edit PASS_MAX_DAYS 30 in /etc/login.defs file ➡ set default password expiration limit to 30 days for the whole system.

CREATE, DELETE, AND MODIFY LOCAL GROUPS AND GROUP MEMBERSHIPS

• groups ➡ print the groups a user is in.

• getent group | grep db ➡ display db group definitions from /etc/group file.

• groupadd mkt ➡ create mkt group.

• gpasswd -d user1 db ➡ removes user1 from db group.

• groupmod -g 10400 mkt ➡ change group’s GID.

• groupmod -n newmkt mkt ➡ change group’s name.

• groupdel mkt ➡ delete mkt group.

CONFIGURE SUPERUSER ACCESS

• visudo ➡ edit the /etc/sudoers file.

• su -l user40 ➡ login as user40.

• user1 ALL=(ALL) NOPASSWD: ALL ➡ on sudoers file gives full root access to the system without prompting for password.

• usermod -aG wheel user99 ➡ add user99 to whell group which has extended privileges.

• sudo -l -U usr1 ➡ verify if user has sudo privileges.

Next:

(RHCSA) Manage Security

…or back to Red Hat Certified System Administrator (RHCSA) Exam Study Guide

Useful links & references:

• Red Hat Enterprise Linux Documentation

• Enable Sysadmin (a blog from Red Hat)

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