Linux Cheat Sheet For Beginners

#linux #ubuntu #tutorial #security

If you're not using the terminal, Linux commands may appear scary at first by once you start using them you will understand them very easily On a Linux system, there are numerous commands for executing operations and procedures.

Having a list of commands on hand is useful whether you are new to Linux or an experienced user.

File Permission commands

Command	Description
ls-l	to show file type and access permission
r	read permission
w	write permission
x	execute permission
-=	no permission
Chown user	For changing the ownership of a file/directory
Chown user:group filename	change the user as well as group for a file or directory

Hardware commands

Command	Description
dmesg	Displays bootup messages
cat /proc/cpuinfo	Displays more information about CPU e.g model, model name, cores, vendor id
cat /proc/meminfo	Displays more information about hardware memory e.g. Total and Free memory
lshw	Displays information about system's hardware configuration
lsblk	Displays block devices related information
free -m	Displays free and used memory in the system (-m flag indicates memory in MB)
lspci -tv	Displays PCI devices in a tree-like diagram
lsusb -tv	Displays USB devices in a tree-like diagram
dmidecode	Displays hardware information from the BIOS
hdparm -i /dev/xda	Displays information about disk data
hdparm -tT /dev/xda <:code>	Conducts a read speed test on device xda
badblocks -s /dev/xda	Tests for unreadable blocks on disk

Basic Linux commands

Command	Description
ls	Lists all files and directories in the present working directory
ls-R	Lists files in sub-directories as well
ls-a	Lists hidden files as well
ls-al	Lists files and directories with detailed information like permissions,size, owner, etc.
cd or cd ~	Navigate to HOME directory
cd ..	Move one level up
cd	To change to a particular directory
cd /	Move to the root directory
cat > filename	Creates a new file
cat filename	Displays the file content
cat file1 file2 > file3	Joins two files (file1, file2) and stores the output in a new file (file3)
mv file "new file path"	Moves the files to the new location
mv filename new_file_name	Renames the file to a new filename
sudo	Allows regular users to run programs with the security privileges of the superuser or root
rm filename	Deletes a file
man	Gives help information on a command
history	Gives a list of all past commands typed in the current terminal session
clear	Clears the terminal
mkdir directoryname	Creates a new directory in the present working directory or a at the specified path
rmdir	Deletes a directory
mv	Renames a directory
pr -x	Divides the file into x columns
pr -h	Assigns a header to the file
pr -n	Denotes the file with Line Numbers
lp -nc , lpr c	Prints "c" copies of the File
lp-d lp-P	Specifies name of the printer
apt-get	Command used to install and update packages
mail -s 'subject' -c 'cc-address' -b 'bcc-address' 'to-address'	Command to send email
mail -s "Subject" to-address < Filename	Command to send email with attachment

Environment Variables command

Command	Description
echo $VARIABLE	To display value of a variable
env	Displays all environment variables
VARIABLE_NAME= variable_value	Create a new variable
Unset	Remove a variable
export Variable=value	To set value of an environment variable

User management commands of linux

Command	Description
sudo adduser username	To add a new user to your current Linux machine
sudo userdel -r 'username'	deluser removes a user from a specific group.
finger	Gives information on all logged in user
finger username	Gives information of a particular user

Network command

Command	Description
SSH username@ip-address or hostname	login into a remote Linux machine using SSH
Ping hostname="" or =""	To ping and Analyzing network and host connections
dir	Display files in the current directory of a remote computer
cd "dirname"	change directory to "dirname" on a remote computer
put file	upload 'file' from local to remote computer
get file	Download 'file' from remote to local computer
ip addr show	Displays IP addresses and all the network interfaces
ip address add 192.168.0.1/24 dev eth0	Assigns IP address 192.168.0.1 to interface eth0
ifconfig	Displays IP addresses of all network interfaces
ping host	ping command sends an ICMP echo request to establish a connection to server / PC
whois domain	Retrieves more information about a domain name
dig domain	Retrieves DNS information about the domain
dig -x host	Performs reverse lookup on a domain
host google.com	Performs an IP lookup for the domain name
hostname -i	Displays local IP address
wget file_name	Downloads a file from an online source
netstat -pnltu	Displays all active listening ports
quit	Logout

Process command

Command	Description
bg	To send a process to the background
fg	To run a stopped process in the foreground
top	Details on all Active Processes
ps	Give the status of processes running for a user
ps PID	Gives the status of a particular process
pidof	Gives the Process ID (PID) of a process
kill PID	Kills a process
nice	Starts a process with a given priority
renice	Changes priority of an already running process
df	Gives free hard disk space on your system
free	Gives free RAM on your system

System Information

Command	Description
time	It is a utility that measures the time taken by a program to execute.
/proc	The files under /proc displays system information.
dmseg	This command is used to print the contents of the bootup messages displayed by the kernel. This is particularly useful in debugging issues.
df	Displays the information about the space on the mounted file-systems.
who	Displays information about the logged in users including their login time.
w	This command displays who are logged in into the system and the processes they are running.
users	This command prints the name of the currently logged in users.
last	This command displays the time of the logged-out users. This also displays the information when the computer was rebooted.
lastlog	Displays a list of the users and the time/day of their login.
whoami	It tells the username of the logged in user.
free	Displays memory status. (Total, Used, Free, cached, Swap)
uptime \| w	It displays how long the computer has been up and running. Additionally, it displays the number of users and the processor load.
uname	It is used to display system information such as OS type, kernel version, etc.
xargs	This command is used to run a command as many times as required.
date	It is used to display the system. It can also be used to set the date/time.
cal	This command displays the calendar of the current month.
acpi	This command is used to display the battery status and other ACPI(Advanced Configuration and Power Information) related information.
acpi_available	This command is used to test if the ACPI subsystem is available.
aptitude

VI Editing Commands

Command	Description
i	Insert at cursor (goes into insert mode)
a	Write after cursor (goes into insert mode)
A	Write at the end of line (goes into insert mode)
ESC	Terminate insert mode
u	Undo last change
U	Undo all changes to the entire line
o	Open a new line (goes into insert mode)
dd	Delete line
3dd	Delete 3 lines
D	Delete contents of line after the cursor
C	Delete contents of a line after the cursor and insert new text. Press ESC key to end insertion.
dw	Delete word
4dw	Delete 4 words
cw	Change word
x	Delete character at the cursor
r	Replace character
R	Overwrite characters from cursor onward
s	Substitute one character under cursor continue to insert
S	Substitute entire line and begin to insert at the beginning of the line
~	Change case of individual character