Linux

Linux
Basics Commands Filesystem Interaction (Continued) Processes 101 Shell Operators System Automation Online gernerators for crontab[1][2] Formating options for crontab Permissions [-rwxrwxrwx] Common Directories (root directories) Passwd and Shaddow

Basics

Commands

• echo [OPTION]... <YourText> -> prints out what comes after it

• whoami [OPTION]... -> prints out ur username

• ls [OPTION]... [FILE]... -> listing

• cd <PathToDirectory> -> change directory

• cat [OPTION]... <Filename> -> concatenate (list what is written in a file)

• pwd -> print working directory

• Ctr + L or clear -> clear terminal

• find [OPTION]... [FILE]... -> to find

• wc [OPTION]... [FILE]... -> prints how many newline (new entries), word, and byte counts are in [FILE]...

• grep [OPTION]... <PATTERNS> [FILE...] -> to find any entries in [FILE...]

• ssh [OPTION]... <username>@<IP-address> [command]... -> to connect with another computer via ssh

• man [OPTION]... <PROGRAMM> -> to get a manual for the use of the specified programm

• su [OPTION]... [username] -> “switch” between users

• wget [OPTION]... <URL>... -> allows us to download files from the web

• scp <Source> <username>@<IP-address>:<DESTINATION> -> [Secure copy] Copy files & directories from your current system to a remote system via SSH

• scp <username>@<IP-address>:<Source> <DESTINATION> -> [Secure copy] Copy files & directories from a remote system to your current system via SSH

• python3 -m http.server [OPTION]... -> turns your computer into a quick and easy web server

Filesystem Interaction (Continued)

• touch [OPTION]... <Filename> -> Create file

• mkdir [OPTION]... <DIRECTORY> -> [make directory] Create a folder

• cp [OPTION]... <SOURCE>... <DIRECTORY | DEST> -> [copy] Copy a file or folder

• mv [OPTION]... <SOURCE>... <DIRECTORY | DEST> -> [move] Move a file or folder

• rm [OPTION]... <Filename>... -> [remove] Remove a file or folder

• file [OPTION]... <Filename>... -> Determine the type of a file

Processes 101

• ps [OPTION]... -> provides a list of running processes from our users session

• ps aux [OPTION]... -> processes run by other users and those that don’t run from a session

• top [OPTION]... -> real-time statistics about the processes running on your system

• fg _[1][2] <JOB_SPEC> -> bring a background process back into use on the terminal

kill [OPTION] <PID> [...] -> send signals that terminate processes
-<signal> Description SIGTERM Kill the process, but allow it to do some cleanup tasks beforehand SIGKILL Kill the process - doesn’t do any cleanup after the fact SIGSTOP Stop/suspend a process

systemctl [OPTION...] <COMMAND> <SERVICE...> -> interact with systemd: system and service manager
<COMMAND> Description start Start/activate one or more services specified stop Stop/deactivate one or more services specified enable Enable one or more services or service instances [start service on the boot-up] disable Disables one or more services [stop the start of service on the boot-up]

Shell Operators

Symbol / Operator	Description
&	This operator allows you to run commands in the background of your terminal.
&&	This operator allows you to combine multiple commands together in one line of your terminal.
>	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.
>>	This operator does the same function of the > operator but appends the output rather than replacing (meaning nothing is overwritten).

• Ctrl + Z -> to background a process. (effective way of “pausing” the execution of a script or command)

System Automation

crontab -e
-> to edit the crontabs [specialfies]
Online Generators Crontab Generator Cron Guru
Formating options for crontab [@reboot] OR [MIN HOUR DOM MON DOW] CMD Value Options Description @reboot ---------- Execute after [re-] booting MIN * or [0-59] What minute to execute at HOUR * or [0-23] What hour to execute at DOM * or [0-31] What day of the month to execute at MON * or [1-12] or [JAN-DEC] What month of the year to execute at DOW * or [0-6] or [SUN-SAT] or [7] What day of the week to execute at CMD <command>... Actual command that will be executed Example: @reboot echo "Welcome back!" OR 0 */12 * * * echo "Hi" -> Only executed every 12 hours

Permissions [-rwxrwxrwx]

-	rwx	rwx	rwx
Filetype:   - d l file directory symbolic link	read, write and execute -> permissions for file owner	read, write and execute -> permissions for group owner(s) of the file	read, write and execute -> permissions for all other users

• ln -s <SourceFile> <LinkName> -> create symbolic soft links

Common Directories (root directories)

Directorie	Description
/etc	The /etc directory (short for etcetera) is a commonplace location to store system files that are used by your operating system.
/var	The /var directory (short for variable data) stores data that is frequently accessed or written by services or applications running on the system
/root	The /root directory is actually just the home for the “root” system user.
/temp	The /tmp directory (short for “temporary”) is volatile and is used to store data that is only needed to be accessed once or twice. [What’s useful for us in pentesting is that any user can write to this folder by default.]

• “passwd” and “shadow” files -> (special for Linux, located in the /etc directory) shows how your system stores the passwords for each user in encrypted formatting ( old:sha512 | new:yescrypt ).
• crack password hash with “John the Ripper“_[3][4] using the command john --format=crypt <filename>

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