Shell commands
	Terminal emulators
	date command
	cal command
	whoami command
	id command
	pwd command
	cd command
	. directory and .. directory
	ls command
	mkdir command
	rm command
	Copying a file using cp command
	Renaming or moving a file
	tree command
	wc command
	less command
	echo command
	Redirecting the command output
	Using > to redirect output to a file
	Moving around in the command line
	man pages
	Counting files in a directory
	Editing longer commands
File system
	FHS
Useful commands
	Creating soft link to a file
	Creating hard links
	Extracting a tar file
	Creating a tar file
	Vim editor
	:q to exit vim
	Open a new file or edit an existing file
	Different modes of vim
	:w to save a file
	:q! to quit without saving
	Becoming root user
	Using sudo command
	!! trick
	Setting up hostname
	Environment variables
	Setting up environment variable values
	locate command
	Finding date/time in different timezones
	Bash history
	Sort files by size
Curl! For all your web needs
	Viewing a file
	Downloading the file
	Download with the same name
	Making a POST request using curl
	Following redirection
	Example: To view github’s pull request patch
	Viewing more details about the transfer
	Making multiple requests at once
	Inspecting HTTP headers
	Adding new HTTP headers
	Curl video/talk
	Curl book
Users and Groups
	Finding the owner of file
	/etc/passwd file
	Details about groups
	wheel group
	Becoming superuser
	Adding a new user
	Changing user passwords
	Modifying existing user details
	Deleting a user
	Adding a new group
	Adding new group to an user
File permissions
	chmod command
	PATH variable
	~/.bash_profile file
	.bashrc file
	/etc/profile file
	which command
	Use which command to see how $PATH variable works
	she-bang or sha-bang in executable files
Processes in Linux
	How to view all running processes?
	How to find a particular process?
	How to kill/stop a particular process?
	Finding out list of open files
	Signals
	top command
	Load average
	htop tool
	More about Linux processes
	/proc directory
	/proc/cpuinfo
	/proc/cmdline
	/proc/meminfo
	/proc/uptime
	/proc/sys/ & sysctl command
	Enabling IP forward with sysctl
Linux Services
	What is a service?
	What is a daemon?
	What is the init system?
	Units in systemd
	.service units in systemd
	How to find all the systemd units in the system?
	Working with a particular service
	Enabling or disabling a service
	Shutdown or reboot the system using systemctl
	journalctl
	Finding the logs of a service
	To view only the last N entries
	Continuous stream of logs
	Listing of previous boots
	Time-based log viewing
	Total size of the journal logs
	Writing your own service file
Securing a service using systemd
	Installing verybad service
	Vulnerabilities in the application
	Directory traversal vulnerability/ LFI
	Arbitary file write vulnerability
	Remote code execution (RCE) vulnerability
	Remove access to system’s tmp directory
	Protecting home dirctories
	Fixing directory paths
	DynamicUser
	Allowed Executables
	What is next?
Package management
	dnf command
	Searching for a package
	Finding more information about a package
	Installing a package
	To list the available updates
	To list all security updates
	Update the packages via dnf
	Find out the services & applications need restart after update in Fedora/CentOS/RHEL
	Automatic updates in dnf systems
	apt command
	apt update
	Installing a package via apt
	apt-cache search
	Listing upgrades
	Upgrading packages
	Figuring out which services/processes need restart after package upgrade in Debian
	Listing available security updates in Debian systems
	Unattended upgrades in Debian systems
SELinux
	SELinux Modes
	getenforce
	setenforce
	Labels/Contexts
	Checking contexts of files/directories or processes
	SELinux booleans
File system mounting
	Connecting USB drives to your system
	Mounting a device
	Unmounting
	Encrypting drives with LUKS (for only Linux)
	Encrypting drives for any OS using Veracrypt
Networking commands
	Finding the IP address
	Finding ARP table
	ping command
	Short note about DNS
	/etc/hosts
	/etc/resolv.conf
	systemd-resolved controlled name resolution
	resolvectl command
	host command
	dig command
	ss command
	traceroute command
	tracepath command
	Remote login to a computer using ssh tool
	ssh key generation
	ssh-copy-id
	Stop and disable the sshd service
	Disable password based login for ssh
	How to find active (open) network connections from your computer?
	To know about ports
Linux Firewall
	Installation
	Tables, chains and rules
	filter table
	nat table
	iptables command
	View the existing rules
	Appending rules to INPUT chain
	Flushing all rules
	Example of a series of rules
	Delete a rule based on rule number
	Delete a rule directly
	Saving the rules
	A blog post from Major Hayden
	Debugging firewall rules
Random things
	xclip to copy from terminal
	w command
	How long is the system running?
	Finding CPU time of a command
	dmesg command
	Setting up cron jobs
	Finding out details about previous logins or system reboots
Whats next?
Workbook
	How to use this workbook?
	copy paste
	Find your user id
	Creating softlinks
	Basic vim usage
	Adding a new user
	Deleting an existing user
	Finding the IP address of dgplug.org
	Change the local timezone of the system
	Add sudo access to an user
Advanced section
Containers
Team
Indices and tables
Index