Linux fundamentals tryhackme

Question 1

echo

Answer 1

Output any text that we provide

Question 2

whoami

Answer 2

Find out what user we’re currently logged in as!

Question 3

ls

Answer 3

listing

Question 4

cd

Answer 4

Change Directory

Question 5

cat

Answer 5

concatenate

Question 6

pwd

Answer 6

print working directory

Question 7

find

Answer 7

search for files in a directory hierarchy

Question 8

grep

Answer 8

Grep, short for “global regular expression print”, isa command used for searching and matching text patterns in files contained in the regular expressions.

Question 9

&

Answer 9

This operator allows you to run commands in the background of your terminal.

Question 10

&&

Answer 10

This operator allows you to combine multiple commands together in one line of your terminal.

Question 11

>

Answer 11

This operator is a redirector - meaning that we can take the output from a command (such as using cat to output a file) and direct it elsewhere.

Question 12

> >

Answer 12

This operator does the same function of the > operator but appends the output rather than replacing (meaning nothing is overwritten).

Question 13

What is SSH and how does it work

Answer 13

Secure Shell or SSH simply is a protocol between devices in an encrypted form. Using cryptography, any input we send in a human-readable format is encrypted for travelling over a network – where it is then unencrypted once it reaches the remote machine,

SSH allows us to remotely execute commands on another device remotely.
Any data sent between the devices is encrypted when it is sent over a network such as the Internet

Question 14

–help

Answer 14

This option is, in fact, a formatted output of what is called the man page (short for manual), which contains documentation for Linux commands and applications.

Question 15

–help

Answer 15

This option is, in fact, a formatted output of what is called the man page (short for manual), which contains documentation for Linux commands and applications.

Question 16

man

Answer 16

The manual pages are a great source of information for both system commands and applications available on both a Linux machine, which is accessible on the machine itself and online.

Question 17

man

Answer 17

The manual pages are a great source of information for both system commands and applications available on both a Linux machine, which is accessible on the machine itself and online.

Question 18

touch

Answer 18

Create file

Question 19

mkdir

Answer 19

Create a folder

Question 20

cp

Answer 20

Copy a file or folder

Question 21

mv

Answer 21

Move a file or folder

Question 22

rm

Answer 22

Remove a file or folder

Question 23

file

Answer 23

Determine the type of a file

Question 24

What is the difference between Users & Groups

Answer 24

The great thing about Linux is that permissions can be so granular, that whilst a user technically owns a file, if the permissions have been set, then a group of users can also have either the same or a different set of permissions to the exact same file without affecting the file owner itself.

Let’s put this into a real-world context; the system user that runs a web server must have permissions to read and write files for an effective web application. However, companies such as web hosting companies will have to want to allow their customers to upload their own files for their website without being the webserver system user – compromising the security of every other customer.

Question 25

How do you switch users?

Answer 25

Switching between users on a Linux install is easy work thanks to the su command. Unless you are the root user (or using root permissions through sudo), then you are required to know two things to facilitate this transition of user accounts:

The user we wish to switch to
The user’s password
The su command takes a couple of switches that may be of relevance to you. For example, executing a command once you log in or specifying a specific shell to use. I encourage you to read the man page for su to find out more. However, I will cover the -l or –login switch.

Question 26

what is /tmp

Answer 26

This is a unique root directory found on a Linux install. Short for “temporary”, the /tmp directory is volatile and is used to store data that is only needed to be accessed once or twice. Similar to the memory on your computer, once the computer is restarted, the contents of this folder are cleared out.

What’s useful for us in pentesting is that any user can write to this folder by default. Meaning once we have access to a machine, it serves as a good place to store things like our enumeration scripts.

Question 27

what is /etc

Answer 27

This root directory is one of the most important root directories on your system. The etc folder (short for etcetera) is a commonplace location to store system files that are used by your operating system.

For example, the sudoers file highlighted in the screenshot below contains a list of the users & groups that have permission to run sudo or a set of commands as the root user.

Also highlighted below are the “passwd” and “shadow” files. These two files are special for Linux as they show how your system stores the passwords for each user in encrypted formatting called sha512.

Question 28

what is /var

Answer 28

The “/var” directory, with “var” being short for variable data, is one of the main root folders found on a Linux install. This folder stores data that is frequently accessed or written by services or applications running on the system. For example, log files from running services and applications are written here (/var/log), or other data that is not necessarily associated with a specific user (i.e., databases and the like).

Question 29

what is /root

Answer 29

Unlike the /home directory, the /root folder is actually the home for the “root” system user. There isn’t anything more to this folder other than just understanding that this is the home directory for the “root” user. But, it is worth a mention as the logical presumption is that this user would have their data in a directory such as “/home/root” by default.

Question 30

What is Nano

Answer 30

It is easy to get started with Nano! To create or edit a file using nano, we simply use nano filename – replacing “filename” with the name of the file you wish to edit.
Once we press enter to execute the command, nano will launch! Where we can just begin to start entering or modifying our text. You can navigate each line using the “up” and “down” arrow keys or start a new line using the “Enter” key on your keyboard.
Nano has a few features that are easy to remember & covers the most general things you would want out of a text editor, including:
Searching for text
Copying and Pasting
Jumping to a line number
Finding out what line number you are on
You can use these features of nano by pressing the “Ctrl” key (which is represented as an ^ on Linux) and a corresponding letter. For example, to exit, we would want to press “Ctrl” and “X” to exit Nano.

Question 31

how can you use wget in linux

Answer 31

open python3 -m python.server

then in a new terminal use

wget http”//”ipaddress”:port/directory/filename

Question 32

how do you use scp

Answer 32

this is used with the following syntax
import file with,
scp filename_for_import user@ipaddress:/filepath/filename
export file with
scp remoteuser@ipaddress:/filepath/remotename.txt ourfilename.txt

Question 33

what does kill “PID” do?

Answer 33

This terminates a proccess

Question 34

what does killterm do

Answer 34

Kill the process, but allow it to do some cleanup tasks beforehand

Question 35

what does sigkill do

Answer 35

Kill the process - doesn’t do any cleanup after the fact

Question 36

what does sigstop do

Answer 36

Stop/suspend a process

Question 37

what does systemctl do

Answer 37

Enter the use of systemctl – this command allows us to interact with the systemd process/daemon. Continuing on with our example, systemctl is an easy to use command that takes the following formatting: systemctl [option] [service]
For example, to tell apache to start up, we’ll use systemctl start apache2. Seems simple enough, right? Same with if we wanted to stop apache, we’d just replace the [option] with stop (instead of start like we provided)
We can do four options with systemctl:
Start
Stop
Enable
Disable

Question 38

how do you push the current process which is running in the foreground to the background?

Answer 38

CTRL + Z