Notes: Linux Fundamentals Part 2 | THM

Remotely Execute Commands

Protocol: Secure Shell (SSH)

- connect/interact w/command line of remote Linux

- encrypted - using cryptography (encrypted - sent - unencrypted)

SSH Syntax

Needed

- IP Address to remote machine

- Credentials to a valid account on remote machine

Command

ssh 'username'@'IP Address'

Asked to trust the host: yes

Provide password for the user (pw won't be visible while typing)

Introduction to Flags and Switches

Most commands allow for arguments (have --help option which list all arguments, ex: ls --help (=man page)), identified by hyphen and certain keyword known as flags or switches

Flags and switches used to extend behaviour of commands

Argument '-a' used with command 'ls' will also list the hidden files: ls -a

The Man(ual) Page

- source of info for system commands and applications

- command: man COMMAND (ex: man ls)

Filesystem Interaction cont.

Commands

touch: create file

mkdir: create folder

cp: copy file/folder

mv: move file/folder

rm: remove file/folder

file: determine type of file

Creating Files and Folders

Create file: touch NAME_OF_FILE

Create folder: mkdir NAME_OF_FOLDER

Removing Files and Folders

Remove file: rm NAME_OF_FILE

Remove folder/directory: rm -R NAME_OF_FOLDER

Copying and Moving Files and Folders

Copy file/folder: cp NAME_OF_EXISTING_FILE NAME_OF_NEW_FILE

Move file/folder: mv LOCATION/NAME_OF_EXISTING_FILE LOCATION/NAME_OF_NEW_FILE (can also be used to rename file)

Determine File Type

Command: file NAME_OF_FILE

Permissions

Some users cannot access certain files/folders

List permissions of all files in current directory

Command: ls -lh

Output:

-rw-r--r-- 1 cmnatic cmnatic 0 Feb 19 10:37 file1

-rw-r--r-- 8 cmnatic cmnatic 0 Feb 19 10:37 file2

r: read

w: write

e: execute

Command to switch user

su USERNAME

(pw)

Start shell with more properties of the other user

su -l USERNAME

(pw)

(= drops into this user's home directory)

Difference between Users & Groups

Use root user permissions with 'sudo'

Common Directories

/etc

- root directory

- important

- store system files used by os

- sudoers: list of users/groups permission to run sudo or set of commands as root user

- passwd & shadow: how system store pw's for each user encrypted sha512

/var

- main root folder

- store data frequently accessed or written by services/applications

- containt log files (/var/log)

/root

- home directory for root system user

- /home/root

/tmp

- unique root directory

- volatile

- store data needed to be accessed once or twice (like memory on computer)

- content cleared out at restart

- any user can write to this folder by default (good place to store things during pentesting, like enumeration scripts)

(egne notater: sikkerhetstiltak: endre default!!)