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CompTIA® Linux+ Certification, Powered by LPI, Student Manual by Axzo Press

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42 CompTIA Linux+ Certification, Powered by LPI
Topic A: Users and groups
This topic covers the following CompTIA exam objectives for Linux+ [Powered by
LPI] Certification, LX0-101 and LX0-102 exams.
# Objective
103.2 Process text streams using filters
The following is a partial list of the used files, terms, and utilities:
tail
105.1 Customize and use the shell environment
Maintain skeleton directories for new user accounts
The following is a partial list of the used files, terms, and utilities:
/etc/profile
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
~/.bash_logout
107.1 Manage user and group accounts and related system files
Add, modify and remove users and groups
Manage user/group info in password/group databases
Create and manage special purpose and limited accounts
The following is a partial list of the used files, terms, and utilities:
/etc/passwd
/etc/shadow
/etc/group
/etc/skel
chage
groupadd
groupdel
groupmod
passwd
useradd
userdel
usermod
110.1 Perform security administration tasks
Set or change user passwords and password aging information
Basic sudo configuration and usage
The following is a partial list of the used files, terms, and utilities:
passwd
chage
sudo
/etc/sudoers
su
usermod
110.2 Setup host security
Awareness of shadow passwords and how they work
The following is a partial list of the used files, terms, and utilities:
/etc/passwd
/etc/shadow
System administration 43
User security
Explanation Linux is a multi-user system, meaning more than one person can use the same
computer. Networking is built in to the very core of the operating system. For this
reason, user identification and authorization are critical functions. Linux performs these
functions via user and group accounts.
You can determine the name of the currently logged-on user account by using the
whoami command. It simply prints the username to the screen. Alternatively, you can
use the
id command; it prints your user ID, group ID, and the list of groups you belong
to.
User accounts
Every user account defined on a system is represented by a line in the /etc/passwd file.
Each user entry (line) contains nine fields, separated by colons. Exhibit 4-1 illustrates a
sample /etc/passwd file.
Exhibit 4-1: An example /etc/passwd file
The fields of the /etc/passwd file are:
User name
Encrypted password or reference to the /etc/shadow file
User ID
Group ID of the user’s primary group
GECOS description, typically left blank
Home directory
Shell (for example, /bin/bash to load the bash shell)
Internally, Linux works with the user id, also called the uid, not the name.

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