1) System

uname Displays Operating system name

uname -r Displays kernel release information

uptime Displays how long the system has been running including load average

hostname Shows the system hostname

hostname -i Displays the IP address of the system

last reboot Shows system reboot history

date Displays current system date and time

timedatectl Query and change the System clock

cal Displays the current calendar month and day

w Displays currently logged in users in the system

whoami Displays who you are logged in as

tree Displays tree system of files

2) Hardware
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

lscpu Displays information about cpu and processing unit.

lsblk Displays block devices related information

free -m Displays free and used memory in the system (-m flag indicates memory in MB)

df -h Displays mounted spaces

lspci -tv Displays PCI devices in a tree-like diagram

dmidecode Displays hardware information from the BIOS

Fdisk -l To list partition tables.

ps To see all the running process

Kill -9 pid To kill that process

3) File Commands
touch filename To Create a file
mkdir directory-name To create a directory

ls -al Lists files - both regular & hidden files

rm filename Removes a file

rm -f filename Forcefully removes a file

rm -r directory-name Removes a directory recursively

rm -rf directory-name Removes a directory forcefully and recursively

cp file1 file2 Copies the contents of file1 to file2

cp -r dir1 dir2 Recursively Copies dir1 to dir2. dir2 is created if it does not exist

mv file1 file2 Renames file1 to file2

ln -s /path/to/filename link-
Creates a symbolic link to filename
name

touch filename Creates a new file

cat > filename Places standard input into a file

more filename Outputs the contents of a file

head filename Displays the first 10 lines of a file

tail filename Displays the last 10 lines of a file

gpg -c filename Encrypts a file

gpg -c filename.gpg Decrypts a file

wc Prints the number of bytes, words and lines in a file

xargs Executes commands from standard input

4) Users
id Displays the details of the active user e.g. uid, gid, and groups

last Shows the last logins in the system

who Shows who is logged in to the system

groupadd "admin" Adds the group 'admin'

adduser "Sam" Adds user Sam

userdel "Sam" Deletes user Sam

usermod Used for changing / modifying user information
6) File Permission
chmod octal filename Change file permissions of the file to octal

Example

Set rwx permissions to owner, group and everyone (everyone else

chmod 777 /data/test.c
who has access to the server)

chmod 755 /data/test.c Set rwx to the owner and r_x to group and everyone

chmod 766 /data/test.c Sets rwx for owner, rw for group and everyone

chown owner user-file Change ownership of the file

chown owner-user:owner-group
Change owner and group owner of the file
filename

chown owner-user:owner-group
Change owner and group owner of the directory
directory
7) Network
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 command sends an ICMP echo request to establish a

ping localhost
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 filename Downloads a file from an online source

netstat -r Displays Kernel IP routing table

8) Compression/Archives
tar -cf home.tar home<:code> Creates archive file called 'home.tar' from file 'home'
tar -xf files.tar Extract archive file 'files.tar'

tar -zcvf home.tar.gz source-folder Creates gzipped tar archive file from the source folder

gzip file Compression a file with .gz extension

9) Install Packages
rpm -i pkg_name.rpm Install an rpm package

rpm -e pkg_name Removes an rpm package

dnf install pkg_name Install package using dnf utility

11) Search
grep 'pattern' files Search for a given pattern in files

grep -r pattern dir Search recursively for a pattern in a given directory

locate file Find all instances of the file

find /home/ -name "index" Find file names that begin with 'index' in /home folder

find /home -size +10000k Find files greater than 10000k in the home folder
12) Disk Usage
df -h Displays free space on mounted systems

df -i Displays free inodes on filesystems

fdisk -l Shows disk partitions, sizes, and types

du -sh Displays disk usage in the current directory in a human-readable format

findmnt Displays target mount point for all filesystems

mount device-path mount-point Mount a device

13) Directory Traverse
cd .. Move up one level in the directory tree structure

cd ~ Change directory to $HOME directory

cd /test Change directory to /test directory