Introduction to Linux

Linux

Open source operating system

Windows and OS X are mainly used on Desktops

Used not only on personal computers, but web servers, electronics

Android is a variation of Linux (they removed some stuff and customized it for mobile)

●      Tired of privacy issues in Windows/OS X?

●      Learn to manage web servers or build electronics/robots?

Different “versions” of Linux, one of the most popular is Ubuntu

1.    Download Ubuntu

2.    Install VMware Player for Windows 64-bit

a.    Remove all USB drives from computer

3.    If you are installing on other computer, burn ISO to DVD

4.    Create a new virtual machine

a.    Select ISO

                    i.     Ubuntu

                   ii.     bucky

                 iii.     bacon123

b.    Store virtual disk into a single file

c.     Customize Hardware > Memory: 2-4 GB (2048 MB)

                                           i.        too much will take away from your host OS

5.    Finish & Play

Ctrl+Altto switch to main OS

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Basic architecture of Linux

Bottom layer is hardware

●      1’s and 0’s

Next layer is the kernel

●      Core operating system

●      Software that tells hardware directly what to do

Top layer are Applications or user processes

●      Programs that you use and make

●      Browser, games, Text editor…

●      When making programs, you don’t need to tell CPU how to work

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Kernel decides which app is allowed to use the CPU at any time

Manages memory for each app

Computer with a single core CPU, it can appear several apps are running at the same time

What’s actually happening is each app uses CPU for small amount of time, process pauses, and then another one does

CPU can switch between processes so fast they appear to be running simultaneously by humans

Kernel manages all of these operations (also for multi-core CPU’s)

Kernel also gives each app it’s own chunk of memory

That way, programs don’t mess with each other when running

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Basic Commands

Shell window (or Terminal) is a program where you can type commands

Search computer > Terminal > Open

Right Click > Lock to Launcher

Right click > Profile > Profile Preferences

Cursor shape > I-beam

 

You can also right click and unlock things you don’t want

name@host:path$

●      Make a file called Story on the Desktop

●      Add some text in it

Display current working directory

➔   pwd

Display the contents of a file

➔   cat Desktop/Story

 

List all contents in directory (and detailed list)

-a shows dot files (hidden files) usually used as configuration files

➔   ls

➔  ls -l

➔  ls -a

➔   ls -la

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Navigating

Move directories (parent, child, home)

➔  cd ..

➔  cd Other

➔   cd

Create and delete directories

➔  mkdir Other

➔  mkdir Tuna

➔   rmdir Tuna

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Working with Files

Create a file. If it already exists, doesn’t change it

➔   touch Story

➔   touch Bacon

Delete (remove) a file

➔   rm Bacon

Copy a file

➔   cp Story Story2

Move a file

➔   mv Story2 Other/Story2

You can also rename a file using

➔   mv Story Tuna

Display content

➔   echo hey now

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Other Commands

Search - print lines from Story that include the word bacon

➔   grep bacon Story

See the difference between two files

➔   diff file1 file2

To change password

➔   passwd

You can use variables to store info

➔  NAME=Bucky

➔   echo $NAME

Clear terminal, all data is still stored

➔   clear

➔   echo $NAME

Learn more about a commands

➔   info echo

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Shell Tips

You can use the up arrow to cycle through previous commands

Editors

When working on servers or over a network, you don’t have GUI text editors

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You can send the results of a command using

➔   ls > Crap

Will overwrite it if it already exists

➔   pwd > Crap

To append

➔   pwd >> Crap

For a list of programs (processes) running

➔   ps

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Permissions

File permissions

➔   ls -l

r = readable

w = writable

x = executable

First is user permissions (who owns the file)

Second is permissions for group members (more on groups later)

Last are permissions for anyone (global)

To change permissions

chmod options permissions filename

Give group permission to read the file (to remove use - instead of +)

➔   chmod g+r Tuna

Set permissions for:

●      u - user

●      g - group members

●      o - other people (from the outside world)

chmod u=rwx,g=rx,o=r myfile

Easier format

➔   chmod 754 filename

Here the digits 7, 5, and 4 each individually represent the permissions for the user, group, and others, in that order.

●      4 stands for "read"

●      2 stands for "write"

●      1 stands for "execute"

●      0 stands for "no permission”

7 is the combination of permissions 4+2+1 (read, write, and execute)

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Compress files

➔   gzip Crap

Decompress them

➔   gunzip Crap.gz

For multiple files

tar cvf archive.tar file1 file2

➔   tar cvf Sample.tar Story Crap

●      c = create mode

●      v = displays output in terminal (leave it out if you don’t want to display file names)

●      f = file options (argument after this must be file name of tar)

To extract files

➔   tar xvf Sample.tar

x = extract mode

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Linux Directory Overview

●      Click “Files” icon on launcher bar

●      Choose “Computer” on left

Verify Checksum

●      Download file

●      Navigate to that directory in Terminal

●    algorithm filename

○   md5sum ubuntu-11.10-dvd-i386.iso

○   sha1sum ubuntu-14.04-server-amd64.iso

●      Compare this against the official checksum (look at this from different computers)

○   sha256sum ubuntu-14.04-server-amd64.iso | grep c7bf55250ca7a7ad897fd219af6ef3d4768be54fb3e2537abb3da8f7f4ed8913

○      red means they are the same

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●      Make new profiles

●      Change background transparency

Compress files

➔  gzip Crap

Decompress them

➔  gunzip Crap.gz

For multiple files

tar cvf archive.tar file1 file2

➔   tar cvf Sample.tar Story Crap

●      c = create mode

●      v = displays output in terminal (leave it out if you don’t want to display file names)

●      f = file options (argument after this must be file name of tar)

To extract files

➔  tar xvf Sample.tar

x = extract mode

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Installing Stuff

apt - Advanced Package Tool (Linux built in software installer)

sudo apt-get update

java -version

sudo apt-get install default-jre

When you download something

●      Download from internet

●      Extract file

# Navigate to bin and run shell script

cd

cd pycharm-xxx/bin

bash pycharm.sh

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Users

●      A user is anyone who uses the computer

●      Most users have restricted access to what they can do

○      This is usually a good thing, keeps them from deleting important system files

●      There is always a super user named “root” that can do anything

●      Regular users are sometimes able to perform commands they usually couldn’t by running the command as the super user

○    sudo cat shadow

Note: Even if you are the owner of a server, you usually log in as a non-super user. This help to prevent you from accidentally doing anything bad. 

Every file on Linux is owned by a User and a Group

cd

cd Desktop

ls -la

permissions | owned by user | group

# To add a new user

sudo useradd mom

sudo passwd mom

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Groups

By default, whenever a user is created they belong to a group with the same name

# Create a new group

sudo groupadd girls

sudo usermod -a -G girls mom

-g will edit their primary group

-a -G just adds (appends) them to another group (keeps their primary)

To delete a user

sudo userdel mom

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Linux Directory Overview

# Go to home

cd

# Go up into the root directory

cd ../..

 

ls

 

# Most of your configuration files are in here

cd etc

cat passwd

These are all the users for the system

login name | password | user ID | group ID | real name | home directory | shell path

Password symbols

x  - password stored in separate shadow folder (they are encrypted, never stored in clear text)

*  - can’t log in

::  -  no password required to log in

# won’t work

cat shadow

sudo cat shadow

cat passwd

●      If you ever want to add a new user manually, just add a new line (or delete to remove user) from this file

●      Need to be super user (sudo) to edit

●      There are easier ways to do this, and you can just add users from the command line, but this is what happens behind the scenes

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Groups

Groups are a handy way you can set permissions for a bunch of users at once

cat group

group name | password | group ID | additional members

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SSH

●      If you want to connect to a computer remotely (from another computer) then you can use SSH

●      Buy some server online and they send you default login information

●      By default we use a password, but passwords can be easily hacked

●      Instead we can use a SSH key (almost impossible to crack)

First, we need to login to the server with the default credentials:

ssh root@host

It will make us change the default password, just pick a normal password for now…

Close the terminal, that’s all we needed to do for now

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On our own computer, generate our keys (we will have private key on our computer, and put public key on server)

ssh-keygen -t rsa

Press enter twice (you can protect with pass phrase if you want)

# Add our public key to the server

ssh-copy-id root@host

●      Type your password to verify it’s you and then your public key will be added

●      Close the Terminal and log back in using

ssh root@host

We don’t need a password anymore because the key private saved on our computer get verified by the server’s public key

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For extra security, disable the password login (only our SSH key has access)

sudo nano /etc/ssh/sshd_config

# Modify this line

PermitRootLogin yes

PermitRootLogin without-password

CTRL+X > y > Enter

# Put changes into effect

reload ssh

If anyone else tries to login now (even if they guess the password right)it will say access denied

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SFTP

sftp root@104.236.7.12

# Go to master directory on server

cd ../..

ls -la

# The homepage for your website is in this directory

cd var/www/html

ls -la

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To upload files to the server

# Move back into html

cd html

put Desktop/index.html

Now go open and browser and view:

http://104.236.203.48/

# To upload a whole directory

mkdir Books

put -r Desktop/Books

http://104.236.203.48/Books/harry.html

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To Download Files

# Download a file from the server

get remoteFile localFile

get index.html Desktop/index.html

# To download an entire directory (and all contents)

cd ..

ls

get -r html Desktop

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