Red Hat RHCSA RHEL 10 with Exam Labs - Pearson Cert Prep

Module 1: Performing Basic System Management Tasks

Lesson 1: Understanding RHEL

Lesson 2: Installing RHEL

Module 2: Basic Tasks

Introduction to working with linux and the command line.

Lesson 3: Using the Command Line

Learning objectives:

• Working with Bash shell
• GNOME graphical environment
• Virtual terminals
• Basic linux commands
• Cockpit

3.1 Working with the Bash Shell

• Shell is how a user interfaces with the operating system - bash is the default
• Can also have a graphical shell - from within you can run bash
• Bash has many features that making working with it easier
  • Tab completion
  • History
  • Variables to store settings
  • Scripts to automate tasks
• User must authenticate before gaining access to a shell

3.2 Exploring the GNOME Graphical Environment

• Button in upper right opens frequently used and search, plus show all apps
• Mr. Beep Boop says to go to power settings and disable screensaver because this is a VM and he says typing a password is annoying.
• Terminal window, we have our shell prompt - student@rhcsa1. You can type commands here! wow!
• Best use case for graphical env is to open multiple terminals simultaneously

3.3 Using Virtual Terminals

• Terminal is the environment that runs a shell - in graphical environment you can have multiple on one screen
• In the text-based environment you need virtual terminals using Ctrl[-Alt]-Fn key sequences
• who or w will show you who is active on which terminals
• chvt can change between virtual terminals

3.4 Starting with Linux Commands

• Commands are used with arguments or options which can further specify the use of the command or modify behavior
• You can usually use --help to get a basic overview of the command and its usage
• If the help output is too long, we can pipe the output to less — ls --help | less which is a pager. Then you can use arrow keys or press space to page
• Linux commands are case sensitive

3.5 Using Cockpit

• Cockpit is a web based interface for working with our rhel system - runs on port 9090.
• Not recommended for most of rhcsa, but become familiar with it.
• Overview of things like storage, resource usage, etc.

Lab

• Log into the graphical interface using default account
• Open a terminal and type who to find out which users are active
• Use the command who --help to get a usage overview

Lesson 4: Using Essential Tools

Learning objectives

• Using man
• Finding the right man page
• Using Lightspeed to get help
• Using an editor
• Understanding and exploring vim

4.1 Using Man

• No Internet access during RHCSA Exam - so man is your best bet
• man pages often have examples
• You can search for text using a /
• Fixed sections
  • 1 - executable programs or shell commands
  • 5 - file formats and conventions
  • 8 - system administration commands
  • learn more with man man

4.2 Finding the right man page

• All man pages are indexed in the mandb
• man -k to search the mandb based on a keyword
• Use grep to filter the results

4.3 Using Lightspeed to Get Help

• Useless on RHCSA exam because we have no Internet access
• Integrated AI in RHEL 10
• Must have a registered system
• dnf install command-line-assistant
• AI Slop

4.4 Using an Editor

• Most linux config is done by editing text files
• Common options on Linux include nano and vim

4.5 Understanding vim

• vi → vim
• vim has different modes - command is the default
• Insert mode to enter text

4.6 Exploring vim

• Honestly this is boring to me because I use vim all day every day. My dude covered
  • esc to get to command mode
  • i to enter insert mode, or o or a to open newline/append
  • :wq write and quit
  • dd to delete the current line

Lab

• Locate the man page that shows how to set a password
• Use the man page for useradd to create a user with name anna
• Set the password for user anna to password
• Use vim to create a file with the name users, make sure it contains alex, alexander, linda, and belinda on separate lines

Lesson 5: Understanding the Bash Shell

Learning Objectives

• I/O Redirection and pipine
• History
• Using keyboard shortcuts
• Introduction shell expansion
• Escaping special characters
• Variables
• Aliases
• Tuning the environment using startup files

5.1 Using I/O Redirection and Piping

• STDIN, STDERR, STDOUT to work with command input and output
  • > is for redirecting output to a file
  • >> will append instead of replacing a file
  • 2> will send STDERR to a file or /dev/null 2> /dev/null
  • < Redirecting to STDIN
• When piping, STDOUT of first command is used as STDIN for second command
  • ps auxf | grep -i ssh

5.2 Exploring History

• Recently used commands can be viewed by typing history
• Also kept in ~/.bash_history
• HISTSIZE and HISTFILESIZE vars used to define number of entries kept
• Up arrow key to scroll backwards through history
• CTRL-R reverse search to find a pattern in history
• !nn repeats based on history from its number
• !a repeats the last command that starts with the letter a
• history -w syncs from memory to history file
• history -c clears the history
• history -d nn removes line nn from current history

5.3 Using Keyboard Shortcuts

• CTRL-c quits the current interactive process
• CTRL-d sends an end-of-file character to current interactive process
• CTRL-a moves to beginning of line
• CTRL-e moves to the end of the line
• CTRL-l clear screen
• CTRL-u remove current line

5.4 Introducing Shell Expansion

• Globbing, such as ls *
• or ls a?*
• Brace expansion - touch file{1..9}
• Tilde expansion - cd ~
• Command sub: ls -l $(which ls)
• Var sub: echo $PATH

5.5 Escaping Special Characters

• In expansion, special characters are interpreted by the shell, such as $ - but sometimes you need to type that.
• Double quotes suppress globbing and shell expansion
• Single quotes take away special meaning of chars
• \ escapes just the next character

5.6 Applying Variables

• In scripting, separate site specific data from generic code
• env will show current values in environment
• [export] key=value
  • export means valid in this shell and sub shells
• To make vars persistent, put them in bash startup files

5.7 Using alias

• Use to define custom commands - type alias to see all that are already set
• Define your own with alias key=value

5.8 Tuning the Bash Environment

• /etc/profile is the generic bash startup file for a login shell
• /etc/bashrc processed while opening any shell
• ~/.bash_profile for user specific settings
• ~/.bashrc is user specific /etc/bashrc
• To source a file is to include it in your current shell - immediately

Lab

• Managing Bash configuration
  • Set a var color to the value red and ensure this setting is available every time your current user account logs in (in .bash_profile export color=‘red’)
  • Also create an alias that runs the command ls -ltr while executing the dir command (in ~/.bashrc alias dir=‘ls -ltr’)
  • Ensure that the Bash history file can grow to a maximum size of 2500 entries (edit .bash_profile, export HISTFILESIZE=2500)

Module 3: Performing Basic System Management Tasks

Lesson 6: Using Essential File Management Tools

6.1 Exploring the Filesystem Hierarchy

• Directories are standardized per FHS, maintained by the Linux Foundation man hier
• Starting point of filesystem is the root directory
• Different devices may be integrated using mounts
• Distributions can deviate from FHS
• /usr/bin, /usr/sbin “program files”
• /etc for configuration
• /var for dynamically created files, including logs
• /boot includes kernel and other requirements for starting system
• /dev device interface files

6.2 Using Essential File Management Commands

• ls
• mkdir
• cp
• mv
• rmdir
• rm

6.3 Finding Files

• which looks for binaries in $PATH
• locate uses a database, but requires updatedb to update said database
• find is the most flexible - find files based on many criteria
  • -type f (files), -type d (dirs)
  • -size +100M
  • -exec examples
  • find /etc/ -name '*' -type f | xargs grep "127.0.0.1"

6.4 Mounting Filesystems

• To access a device, it must be connected to a directory - known as mounting
• Different types of data may live on different devices for multiple reasons
  • security
  • management
  • mount options
• mount /dev/sdb1 /mnt example of the mount command
• mount to show all mount points, findmnt gives more details
• lsblk to give an overview of real devices and their mountpoints

6.5 Using Links

• Pointer to a file in a different location - kind of like a shortcut. There are hard and symbolic links (soft links)
• inode contains all the properties of a file - every file has one - inode references block
  • multiple names per inode is what a hard link is - must exist on the same device
  • Cannot hard link a directory
• Gain some flexibility with a symlink - instead of pointing to an inode, it points to a name
  • When creating a symlink, use full path so that if you copy it it does not become invalid

6.6 Archiving Files

• tar is the tape archiver (old!)
• By default, tar does not compress data
  • But we can add it with -z, -j, -J

6.7 Working with Compression

• Wide range of compression solutions for Linux - used independently or as a part of the tar command
• gzip(-z)
• bzip2(-j)
• xz(-J)

Lab

• Use tar to create a compressed archive of all files in /etc and /opt in your homedir
• Create a symlink to the archive in /tmp
• Remove archive - now what?

Lesson 7: Managing Text Files

7.1 Exploring Common Text Tools

• more was the original file pager - less came along to bring some more advanced features and is the commonly used pager today
• Use head or tail to see only a given number of lines in a text file (default, 10 lines)
  • tail -f to follow and show new output as it appears
• cat dumps the file contents to screen - can show all non printable characters using -A.
• tac is reverse of cat - why? idk.
• cut can filter output
• sort will sort output of previous command
• tr for translate - lowercase, uppercase, etc.

7.2 Using grep

• Excellent to find text in files or output - ps auxf | grep ssh
• okay it’s grep

7.3 Applying Regular Expressions

• pattern used by grep and other tools
• Always put regex between single quotes because of shell interpretation issues
• Globbing is not the same as regex
• man 7 regex
• grep -E for extended regex

7.4 Awk

• Text processing utility that can perform actions on selectors - a few use cases today, a bit antiquated.

7.5 Sed

• sed is the stream editor - from 70s!
• Used to search and transform text

Lab

• Use head and tail to display the fifth line of the file /etc/passwd (head -5 /etc/passwd | tail -1)
• Use sed to display the fifth line of the file /etc/passwd (sed -n 5p /etc/passwd)
• Use awk in a pipe to filter the last column of the results of ps aux (ps aux | awk ‘{print $NF}’
• Use grep to show all lines from all files in /etc that have lines that contain the text ‘root’ (grep -r “root” /etc)
• Use grep to show all lines from all files in /etc that have exactly 3 characters (grep -r ($…^) /etc)
• Use grep to find all files that contain the string alex, but make sure alexander is not inclued in the result (grep ‘alex\b’ users)

Lesson 8: Using root Privileges

8.1 Understanding the root user

• user account with UID 0 exists to perform admin tasks - called root by default
• root user operates in kernel space so it has unlimited access to all parts of the system
• While installing RHEL 10, root user can be activated or not - for security we often do not set a password for this user and use another administrative user
• To activate the root user we simply have to set a password
• Additional measures are possible to restrict root user access to a system
  • Avoid working as root, use an administrative user instead with sudo privileges
  • Restrict root login for ssh

8.2 Switching User with su

• Two ways to work as the root user, one is more modern
  • su command is used to switch user account from a shell - specifically su - which will load environment of the target user (best practice)
  • Using su - root is bad practice
  • Use sudo -i instead so you don’t need the root password

8.3 Performing Administrator Tasks with sudo

• Behind sudo is sophisticated configuration to limite what users can do with sudo - maintained in /etc/sudoers
• Use visudo while editing sudoers file to prevent errors from breaking system
• Basic use of sudo is sudo <command> - only works if allowed in /etc/sudoers
• To open a root shell, sudo -i
• While using shell metacharacters, sudo needs a special approach

8.4 Managing sudo configuration

• configuration is managed through /etc/sudoers - do not edit directly, only use visudo
  • Can also use drop in files in /etc/sudoers.d to avoid files being ovewritten during package updates
• Users that are a member of the group wheel get full sudo access by default
  • Thanks to %wheel ALL=(ALL) ALL
  • To add a user to the wheel group, usermod -a -G wheel <user>
  • Do not enable %wheel ALL=(ALL) NOPASSWD: ALL as this provides full root access without any password. DANGEROUS
• Add access for specific tasks lisa ALL=/sbin/useradd, /usr/bin/passwd
• You can add specific args to further limit access %users ALL=/bin/mount /dev/sdb, /bin/umount /dev/sdb

8.5 Using ssh to login remotely

• By default, all RHEL servers are running a secure shell server (sshd)
  • Verify using systemctl status sshd
• Firewall rule is also enabled by default for port 22/tcp
• Root access is often denied or restricted to pubkey authentication only
• scp is part of ssh and is used to copy files securely

Lab

• Use useradd linda to create a user linda
• Create sudo config to allow linda to perform useradd, usermod, userdel and change passwords, but not the root password
• Ensure that the user only needs to enter a password for sudo every 60 minutes

Lesson 9: Managing Users and Groups

Lesson 10: Securing Files with Permissions

Lesson 11: Managing Network Configuration