LINUX NOTES

Getting Help

• --help -> Shows the instructions and flags of a command / program
• man -> manual pages

Command Line Interface (CLI) Navigation

• pwd -> print working dir (see which directory you are in)
• ls -> list (list anything in the directory)
• cd -> Change Directory (move to a directory)

Flags

• -l (long format)
• -a (Show hidden files)
• -s (Show size)
• -h (human readable)
  Example: user$ ls -lash

Helpful Commands

• echo -> outputs the result of something
• which -> Tells you what the path is to the program you are running (which ls)
• cat (Prints contents of a file to terminal)
• head (First 10 lines)
• head -n 50 (First 50 lines)
• tail -> outputs last 10 lines of a file
• !! -> runs last command you have used
• yes -> program that types y in terminal until (ctrl + c)
• test -> program that checks file types and compares values
• touch .hidden-file (touch makes a file, the dot makes the file hidden, need -a to view the file)
• less (Read a file, but not for file editing, using /hey lets you search for stuff)
• ps aux (programs running)

CLI Search

• ~ (tilda represents home directory)
• / (root directory)
• Use tab to find all programs with the name you give them
• ctr + r (reverse search, searchs using keyword for the command used)

Bash History

• ~/.bash_history (bash history of all commands written)
• Note: bash history is buffered and is only written after you log out

Signals

• CTRL + C (Sigint, signal interrupt)

• CTRL + D (SigQuit, signal quit)

• kill -l (List all possible kill commands)

• kill -9 (Sigkill stops a program without any clean up)

VIM Fundamentals

• i -> interactive mode
• :q (quit)
• :q! (force quit)
• :d (delete the line I am on)
• :d100 (delete line 100)
• yy Yank a line
• dd Delete a line
• p paste a line

Create and Move Files / Directories

• mkdir -> Create Directory

• mkdir -p (Make multiple folders at the same time)

• rm (removes a file)

• rm -r (remove directory)

• rm -rf (Force Deletion)

• cp (Copy to destination file)

• cp textfile.txt dest.txt

• mv (Re-name File or Folder)

Tape Archiver (TAR Files)

• tar (Create, Extract, and List Archive Contents)

• Create tar -cfz archive.tar.gz textfile1.txt textfile2.txt folder1

• Extract tar -xzf archive.tar.gz -C destination

Wild Cards and Replacements

• touch file{1,2,3,4}.txt (Use curly brace is a replacement)
• ls file-_ (Star _ finds all of something)
• ls file*.txt
• ls file?.txt (Question mark matches exactly one character)
• touch file{1..30}.txt``` (In a range)
• echo {a..z..5} (Spaces are every 5 indexes)
• \ (Escape Character)

Output Streams

• echo 'this is my text' 1> newfile.txt (Changes the output stream so that the echo'd text goes to a file)

• 1> (redirects the output stream)

• 1>> (appends the output stream)

• Note: 1 is standard output, 2 is standard error

• 2> (directs standard error message to something (file))

• cat nonexistent-file.txt 2> error.txt

Note: > directs both error and standard out to both
Note: If you want to direct standard error to the black hole of nothing use this command 2> /dev/null

Input Streams

• < (Takes from some input)
• cat < newfile.txt (Takes from input stream ie the file a gives it to cat)
• grep (Searches for something)
• grep "ls-error.txt" < ls.txt (Searches for the text in the text file ls.txt)

$ grep "ls-error.txt" < ls.txt 1> grep.txt 2> /dev/null

Pipes

• cat ls.txt | grep "ls-error.txt" (Connects cat with grep, the output of cat is going to grep)

• ps aux | grep "ps aux" (Taking ps-aux results and searching for a text using grep in the output)

• yes > /dev/null & (& means put process in the background, infinite running program running in the background)

• ps aux | grep "yes" (Searches for the program)

• kill -9 1224 (Kills the process via ID)

• yes | rm -i file*.txt (Pipes yes program into the program asking for yes or no answers)

Principle Of Least Power

Users

• whoami (user you are in)
• cat /etc/passwd (shows all users)

Super User

• sudo -s (Swap to super user)
• sudo (Temporarily switch to super user)

Create User

• sudo useradd brian (Makes user brian)
• sudo passwd brian (Set password)
• su brian (Switch to brian)

Groups and Permissions

• sudo usermod -aG sudo brian (Adds brian to the sudo group, now brian can use sudo)
• sudo usermod -aG ubuntu brian

Change Ownership Of a File / Folder

• sudo chown ubuntu:ubuntu textfile.txt

• sudo chown ubuntu:ubuntu /folder1

• sudo chmod u=rw,g=rw,o=rw hello.txt

• sudo chmod +x mynewprogram (Now everyone can execute the program)

Passwd File Format

• Username : Password : UserID : GroupID : User ID Info : Home Dir : Command/Shell
• oracle:x:1021:1020:Oracle user:/data/network/oracle/:/bin/bash

Using Enviroment

• printenv (shows all environmental variables)

• $USER (replaces with the environment variable)

• echo $USER

• /etc/environment (makes environment variables permanent)

• BASHRC (Runs at the beginning of every session)

• ~/.bashrc

• source ~/.bashrc (Runs .bashrc again)

System Processes

• ps (process status)

• CTRL + Z (Stops the process)

• bg 1 (Continues running the job in the background)

• fg 1 (Puts job in the foreground)

• jobs (Shows you what jobs are running)

• jobs -l (Shows PID of the jobs, so you are able to kill them)

Operators (&&, ||)

• touch status.txt && date >> status.txt && uptime >> status.txt

• Means: Run touch and if it works run date, append to status.txt and if that works run uptime and append to status.txt

• && Both commands including the first must return successfully

• || One of the commands must return successfully (if both return successful it does not work)

Network and Internet

Making a VM

• multipass launch --name secondary
• multipass shell secondary

Adding a User to the VM

• sudo useradd -s /bin/bash -m -g ubuntu brian
• sudo passwd brian

SSH

• Create Public and Private Key

• ssh-keygen -t rsa

• Secondary PC

• make folder called .ssh and make file called authorized_keys

• save key on secondary pc in the authorized_keys file

• chmod the directory 700

• chmod 600 keyfile

• ifconfig (gives ip of the secondary pc)

• Primary PC

• ssh brian@192.168.64.5

SFTP

• sftp brian@192.168.64.3

• lpwd (local pwd)

• lls (local list)

• sftp> put status.txt (Sends file from local to secondary)

• sftp> put file-to-put.txt putted-file.txt (sends and renames on secondary pc)

• sftp> get status.txt (to get a file from the secondary PC)

WGET (Download something Online, HTTP Request)

wget https://raw.githubusercontent.com/btholt/bash2048.sh

CURL (Download something Online)

curl https://raw.github/2048.sh > game.sh

• Start API Server

• python3 -m http.server 8000 --bind 0.0.0.0

• In Browser go to (192.168.64.2:8000 to visit the server)

curl http://192.168.64.2:8000/
curl -o res2.txt http://192.168.64.2:8000/output.txt

curl -X POST http://192.168.64.2:8000/
curl -d "this is the post body" PUT http://192.168.64.2:8000/
curl -X DELETE "anything" http://192.168.64.2:8000/
curl -b "name=brian"

Package Managment & APT COMMANDS (Advanced Packaging Tools)

• Note: dpkg (debian)
• apt install (newer tool)
• apt search nodejs (search a tool)
• sudo apt autoremove
• apt update (Updates a package that already exists)
• apt upgrade (Update gets a new version of the registry [list of packages])
• apt full-upgrade (runs autoremove and upgrade)

Snaps

• runs on multiple linux distros

• Safer, sandboxed and cannot break out of home folder

• Automatically updates

• sudo snap install lolcat

• sudo snap install --channel=14/stable --classic node

Shell Scripts

Writing Scripts

• vi genfiles.sh

DESTINATION=~/temp                                 (This is a variable)
FILE_PREFIX=file

mkdir -p $DESTINATION                              (-p means create or dont create based on if the file exists or not)
cd $DESTINATION
touch file{1..10}.txt
touch ${FILE_PREFIX}{1..10}.txt
echo done

• source genfiles.sh
• . genfiles.sh
• ./genfiles.sh

Hashbang

• At the top of the file. This denotes how to run the file, file no longer needs the .sh extension
• #! /bin/bash

Path and Variables

• Path shows where linux searches for programs from left to right

• $PATH

• If we make a bash script and we want linux to automatically recognize it as a program, we need to add the directory the script is in to the $PATH.

• In .bashrc Add

export PATH=~/folder_with_scripts:$PATH

• Now folder with sctipts will be the first thing linux looks through for scripts you have written

Command Line Arguments

• In the bash file, you want to use $number

• $1 (first argument being provided)

• $2 (second argument being provided)

User Input from Bash Script

• use the read keyword for user input
• read -p "enter a file prefix: " FILE_PREFIX

Conditionals

if [ -z $DESTINATION ]; then                                                       (-z means if string is empty)
    echo "no path provided, defaulting to ~/temp"
    DESTINATION=temp
fi

• CHECK IF FILE EXISTS
• test -e ~output.txt && echo is true

Else If Statements

if [ $1 -gt 10]; then
    echo "greater than 10"
elif [ $1 -lt 10]; then
    echo "less than 10"
else
    echo "equals 10"
fi

Case Statements

case $1 in
    "smile"
        echo"I am happy"
            ;;
    "sad"
        echo"I am sad"
            ;;
    "laugh"
        echo ":D"
            ;;
    echo "I don't know that one yet!"
        ;;
esac

Loops and Arrays

friends=(Kyle Marc jem "brian holt" Sarah)            (Array declare)
echo my second friend is ${friends[1]}

#FOR LOOP
for friends in ${friends[]}
do
     echo friend: $friend
done

echo "I have ${#friends[*]} friends"         (length of the array)

#WHILE LOOP
while [ $VAR1 -ne $VAR2 ]
do
    read -p "your guess: " $VAR2
done
echo "you got var 1"

Automation and Customization

Cron

• runs tasks on a schedule (daily, weekly, hourly)

• file put in cron folder must be executable file chmod +x

• /etc/cron.

• crontab -e

• echo -e "this is how you make color \e[32mgreen]"