Linux Commands Cheat Sheet :)

Grep

grep "pattern" filename // search for the particular pattern
grep -n "pattern" filename // show along with page number
grep -e "pattern1" -e "pattern2" filename //Search for multiple patterns

Killall

It is used to stop all processes that match a given name

killall process_name

ps

It is used to list all the active processes in the current terminal

ps
ps aux 
(a - show all processes)
(u - display user)
(x - show processes not attached to the terminal)

Top

This command provides a real-time, interactive view of system processes, including CPU and memory usage.

top

Ping utility

It is a basic tool used to test network connectivity. It helps to check if your computer can reach another computer over the internet.

Round-trip time: Time it takes for data to travel from source to the destination and back

When you use the ping command, your computer sends a small data packet called an "ICMP echo request" to the target address. The target then sends back a response called an "ICMP echo reply."

ping [url]

Third party ping applications: fping

What is the Default Gateway?

It is the IP address of a router or network device that your computer uses to communicate with other devices outside your local network. In other words, it's the address that your computer sends traffic to when it needs to access resources beyond its own subnet.

This means that any network traffic that needs to go beyond your local subnet (e.g., to the internet) will be sent to 172.22.8.1, which is likely the IP address of your router or gateway device.

If your computer wants to access a website, it sends the request to the default gateway (172.22.8.1), which then forwards the request to the internet. The gateway also handles incoming traffic from the internet and directs it back to your computer.

File Transfer Protocol

1. Connect to FTP server It is used to connect to the FTP server from a terminal or command prompt.

ftp [url]

FTP Client

Ex. FileZilla

Network Mapper (nmap)

It is a network scanning tool used for discovering hosts and services on a computer network. It’s widely used for security auditing, network inventory, and identifying network issues.

nmap -sT target_ip //scan open TCP ports
nmap -sU target_ip //scan open UDP ports 
nmap -A target_ip //agressive scan

// Report
Lists all open ports
PORT    STATE SERVICE
21/tcp  open  ftp
80/tcp  open  http
110/tcp open  pop3
135/tcp open  msrpc
143/tcp open  imap
443/tcp open  https

ifconfig(Similar to ipconfig of windows)

This command gives you the details about network interface cards(NIC)

ifconfig

Symbolic Link (Symlink)

A symbolic link (or symlink) is a type of file that serves as a reference to another file or directory. It's essentially a shortcut or alias that points to the target file or directory.

ln -s [TARGET] [LINK_NAME]

Remove orca

sudo apt remove orca

Directory management

mkdir directory //create a folder
rmdir directory //delete a folder

Package management

apt-get install package-name
apt-get remove package-name
apt-get purge package-name
apt-get update
apt-get upgrade //upgrades all installed packages to the latest versions

Single Dash (-): Used for single-letter options. Example: -h for help. Double Dash (--): Used for word options. Example: --help for detailed help.

Create a New File:

cat > filename

Type your content and Press Ctrl + D to save and exit.

Granting Permissions

Each file and directory must be allocated a particular level of permission for the different identities using it. The three levels of permission are listed hereunder: r - (Read permission) This grants permission only to open and view a file. w - (Write permission) This allows users to view and edit a file. x - (Execute permission) This will enable users to execute a file (This does not guarantee viewing or editing it).

Changing Permissions We can use the Linux command chmod to change the permissions.

rwxrwxrwx
rwx for the owner: 7 (rwx)
rwx for the group: 7 (rwx)
rwx for others: 7 (rwx)

Read (r) = 4 (binary 100) Write (w) = 2 (binary 010) Execute (x) = 1 (binary 001)

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