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System Information & Management

man

Option	Description	Example
man <command>	Display the manual page for a command.	man ls

ps

Option	Description	Example
-e	Show all processes.	ps -e
-f	Show full-format listing.	ps -ef
-u <user>	Show processes for a specific user.	ps -u username

top

Option	Description	Example
-d <seconds>	Delay between updates in seconds.	top -d 5
-n <count>	Number of iterations to display.	top -n 1

df

Option	Description	Example
-h	Human-readable output (e.g., MB, GB).	df -h
-T	Show file system type.	df -T

mount

Option	Description	Example
<device> <mount_point>	Mount a device to a directory.	mount /dev/sda1 /mnt
-t <type>	Specify file system type.	mount -t ext4 /dev/sda1 /mnt

ifconfig

Option	Description	Example
-a	Show all interfaces.	ifconfig -a
eth0	Display specific interface details.	ifconfig eth0

traceroute

Option	Description	Example
-n	Show IP addresses instead of domain names.	traceroute -n google.com
-m <max>	Limit the number of hops.	traceroute -m 10 google.com

service

Option	Description	Example
start	Start a service.	service apache2 start
stop	Stop a service.	service apache2 stop
status	Check the status of a service.	service apache2 status

ssh

Option	Description	Example
<user>@<host>	SSH into a remote machine.	ssh username@host
-p <port>	Specify a port number.	ssh -p 2222 username@host

ufw

Option	Description	Example
enable	Enable the firewall.	ufw enable
disable	Disable the firewall.	ufw disable
allow <port>	Allow traffic on a specific port.	ufw allow 80

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File Management & Text Processing

sort

Option	Description	Example
-r	Sort in reverse order.	sort -r file.txt
-n	Sort numerically.	sort -n file.txt

export

Option	Description	Example
VAR=value	Set an environment variable.	export PATH=/usr/local/bin:$PATH
-p	Print all exported variables.	export -p

alias

Option	Description	Example
<name>=<command>	Create an alias for a command.	alias ll='ls -l'
-p	Display all defined aliases.	alias -p

whereis

Option	Description	Example
<command>	Locate binary, source, and man pages.	whereis ls

whatis

Option	Description	Example
<command>	Show a brief description of a command.	whatis ls

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Process & System Control

kill

Option	Description	Example
<PID>	Kill a process by its PID.	kill 1234
-9	Force kill a process (SIGKILL).	kill -9 1234

killall

Option	Description	Example
<name>	Kill all processes by name.	killall firefox
-9	Force kill all processes (SIGKILL).	killall -9 firefox

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Network & Downloading

wget

Option	Description	Example
-O	Specify output file name.	wget -O file.html http://example.com
-r	Download recursively.	wget -r http://example.com
-c	Resume a previous download.	wget -c http://example.com/file

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