Reading Files

| Command | Description | |-------------------|---------------------------| | cat | read entire file | | head | read top of a file | | head -n 20 | read top of file 20 lines | | tail | read bottom of a file | | tail -f | stream file as it's updated, | eg: an error log | | tail -n 20 | read bottom of file 20 lines |

Users

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| Command | Description | |--------------------------------------------|---------------------------------| | passwd | change logged in users password | | su - username | switch users | | sudo su | switch to root | | useradd -m -s /bin/bash username | Create User | | usermod -a -G existinggroup existinguser | Add User to Group | | who | show all logged in users | | whoami | show which user you are |

Groups

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Do not delete groups you don't know what they are used for, that's dangerous!

| Command | Description | |---------------|-----------------------------------------| | groups | see what groups current user belongs to | | groupadd name | create a group | | groupadd -g 900 name |create a group with | custom GroupID aka gid| ||| |groupdel name |delete a group| |useradd |add current user to a |group| |usermod -aG |append any user to an |additional group| ||| |cat /etc/group | list all groups| |cut -d: -f1 /etc/group | list all groups, cleaner|

Permissions

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There are two ways to manage permissions, one is by text the other is by an octal value.

Easy Permissions

; Change Mode
; Options: (O)wner (U)sers (G)roup or (A)ll
; File:    Owner: rwx, Group: rwx, User: rwx
; Misc:    Besides rwx there is:
;          s = setuid of owner for old/new files

; Single File read/write permissions
chmod g+rw file
chmod og+rw file.txt
; Change Ownership
chown user:group files_or_folder
chgrp group files_or_folder
; Recursively:
chown -R user:group files_or_folder
chgrp -R group files_or_folder
chmod -R og+rw files_or_folder
chmod -R g+s files_or_folder

Preserve Group Permissions

A fantastic way to structure your users is within groups. A common example would be your

www-data

jesse

sudo usermod -aG www-data jesse

After adding any users I would like, I want to have a folder where all the members of the

www-data

To accomplish this, here is an example:

sudo chown -R deploy:www-data /var/www
sudo chmod -R g+rws /var/www

The

g+s

setgid

Octal Permissions

You may have seen this a lot, you can use octal or decimal (begins with a 0) to do the same thing.

Permissions:
0 = None
1 = Execute (e)
2 = Write (w)
4 = Read (r)

• There are 3 Permission types (Read, Write, Execute), or 4 if you count "None".
• There are 3 Sets: Owner/User/Group (In that order)
• So if you did

  chmod 700 file.txt

  it would allow the user to Read, Write and Execute
  • Because

    7

    is the total of

    4 + 2 + 1

Octal Examples

chmod 600 file.txt – Owner Read, Write
chmod 660 file.txt – Owner Read, Write; User Read, Write
chmod 770 file.txt – Owner Read, Write, Execute
chmod 770 file.txt – Owner Read, Write, Execute; User Read, Write, Execute
chmod 666 file.txt – All Read, Write
chmod 777 file.txt – All Read, Write, Execute

OS Details

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Get fundamental information about your OS with the following commands, you may have to run them as

sudo

sudo lsb_release -a

Operating System

lsb_release
lsb_release -a
lsb_release -as     # Short Information
lsb_release --help

CPU Info

nproc               # How many Processing Units
cpuid               # Must install cpuid from terminal
cat /proc/cpuinfo   # Lots of info

Usage Info

free -h             # Human readable, or do --help for options
vmstat -s
cat /proc/meminfo   # Lots of info

Disk Space

df
df -B MB    (In Megabtyes, KB for Kilobytes, GB for Gigabytes)

System Processes

top
htop  # If you installed it

IP Address

Your IP is after

inet addr

eth0 (Ethernet)

wlan0 (Wireless LAN)

ifconfig
ip
ip addr show
ip addr show wlan
ip addr show eth0

GUI Processes

gnome-system-monitor

CLI Processes

top
htop     (My favorite, sudo apt-get install htop)
nmon

List all Keybindings

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gsettings list-recursively  org.gnome.desktop.wm.keybindings | sort | more

See Keypressed

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xev

; Or for a lot of details:
xev | grep KeyPress

Kernal

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The Kernal is the lowest level item that ties everything together from hardware to software. Without a kernal you cannot do anything on linux.

Remove Old Kernals

See What version you are currently using

sudo uname -a

See all the Kernals on the OS

sudo dpkg --get-selections | grep linux

The BYOBU is quite nice

sudo apt install byobu
sudo purge-old-kernels

OS Shutdown

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shutdown
reboot
shutdown -h now
shutdown -h +10     (shutdown 10 mins)
shutdown -r now     (reboot now)

Crontab

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crontab -e              (edit crontab for current user)
crontab -l              (list crontab for other user)
crontab -u jesse -l     (see crontabs for specific user)

Services

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Service Commands

Use the service command (Requires sudo)

service ssh status      (service status)
service --status-all    (all services status)

Almost every service has the following commands, some may have more like apache

graceful-restart

service servicename start
service servicename stop
service servicename restart
service servicename status
service servicename force-reload

Autostart

Add Service links:

sudo update-rc.d servicename defaults

Whether you get a warning if they already exist or not, enable it now:

sudo update-rc.d servicename enable

Remove Autostart

Pass the Force flag

sudo update-rc.d -f servicename remove

Autostart Daemons

There is are several startup popular daemons: - CentOS uses SystemV - Ubuntu 14 uses Upstart - Ubuntu 14.10+ uses SystemD (15, 16, 17..)

Focus on SystemD.

SystemD Commands

This would only apply to Ubuntu 14.10+, otherwise you would use Upstart.

systemctl     
System State



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```
uname -a (get linux info)

top (See running processes/system status, I suggest installing 
htop
)
top -u www-data
htop -u www-data

df          (display disk space in bytes, default)
df -h       (display disk space human readable)
df -Th      (display disk space with partitions)

free (see memory used)
free -g (in gigabytes)
```

Processes



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```
ps -ef | more       (current running processes)
ps -efH | more      (current running processes in a tree)

ps -ef | grep vim   (find vim process id)
kill -9         (no brackets)
```

Bash



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Bash is my shell of choice, which is why I have a 
.bashrc
 file.

Bash Paths

Executables and commands are automatically in the path, see your path with:
echo $PATH


Add to Path
# I suggest editing your ~/.profile

vim ~/.profile
if [ -d "/path/to/your/bin" ] ; then
  PATH="$PATH:/path/to/your/bin"
fi

Note: Order of Linux Reading files: ~/.bashprofile, ~/.bashlogin, and ~/.profile, so don't try to use a ~/.profile variable within ~/.bash_profile

Bash Completions

The locations for bash completio0ns can be found at:
cd /usr/share/bash-completion/completions.d/
cd /etc/bash_completions.d/


Fix Broken Bash Completions
sudo apt-get install --reinstall bash-completion

Log Script from Bash

At the top of your file, find the executable you are using one of these, eg:
which bash     # /usr/bin/bash
which python   # /usr/bin/python
which php      # /usr/bin/php


At the top of your shebang for the executable file add:
#!/bin/bash
#!/usr/bin/php
#!/usr/bin/python

make sure to 
+x
 it:
chmod +x app.sh
chmod +x app.php
chmod +x app.py


You can then run the script via Bash:
/scripts/app.sh >> /scripts/output.log 2>&1
/scripts/app.php >> /scripts/output.log 2>&1
/scripts/app.py >> /scripts/output.log 2>&1


You could even crontab it the same way:
*/10 * * * * app.php >> /output.log 2>&1
*/10 * * * * app.py >> /output.log 2>&1


Finding Files



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Generally the following arguments are as follows:
- 
-type f
 file
- 
-type d
 directory
- 
-iname
 case insensistive (book.txt would the same as BOOK.TXT)
- 
*
 is a wildcard to find anything, usually you put it at the start or end of a filename.
find . -name tecmint.txt
find /home -name tecmint.txt
find /home -iname tecmint.txt                        (case ignore)
find / -type d -name Tecmint                         (directory)
find . -type f -perm 0777 -print (with perms)
find / -type f ! -perm 777 (find without)
find . -type f -name "tecmint.txt" -exec rm -f {} \; (find and remove a file)
find . -type f -name "*.txt" -exec rm -f {} \;       (find and remove multiple)
find /tmp -type f -empty                             (Find empty files)
find /tmp -type d -empty                             (find empty directories)
find / -size +50M -size -100M (findby swize)


Find in Files (GREP)



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GREP means: Global Regular Expression Pattern (or Parser)

Some common GREP flags:
- 
-r
 is Recursive
- 
-n
 is Line Number
- 
-w
 Match the whole word
- 
-l
 is lowercase only
- 
-c
 supresses normal output and counts number of matching lines
grep -rn /path - "pattern_or_string"

; Output results to File
grep -rnw /path - "pattern_or_string" > output.txt

Look only in certain filetypes
; notice I used a regex ^ starts with, you can use a string or regex
grep --include=*.sh '^mysql' ./


More Examples:
grep "hello" file.txt (if in file)
grep "hello" files*  (if in many files)
grep -i "hello"  file.txt  (case insesitive)
grep -iw "is" file.txt (get full words, case insensitive)
grep "regex" file.txt


Pipe Grep
php -i | grep ini

Reading Files



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Without having to open a file you can simply read a part of it without 
nano
, 
pico,
vi
, or
vim
:
cat file.txt            (view file contents)
tail file.txt           (view end of file contents)
tail -n20 file.txt      (view top 20 lines)
tail -f filetxt         (follow a filename keep updating)
head file.txt           (view top of file contents)
head -n20 file.txt      (view top 20 lines)
`

Downloading Files



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Using Wget
wget http://file.com/something.txt                (Download a file locally)
wget -O newname.txt http://file.com/something.txt (Download file locally w/new name)

You can also use 
SCP
, yet the above are easier for non-SSH connections.

Using cURL
curl -O http://file.com/something.txt               (Download a file locally)
curl -o newname.txt http://file.com/something.txt   (Download file locally w/new name)
curl -O http://url_1 -O http://url_2                (Download multiple files)

Compressing and Uncompressing Files



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To Compress a file you can use a variety of tools. You can type 
man gzip
 to see the full manual and line of commands, and use 
esc
 + 
:x
 and 
ENTER
 to exit from the Manual (It usually uses the Vi editor).

Most often in the Linux word you use and create 
*.tar.gz
 files, it has the most options. Whatever you prefer is up to you.

What the flags often stand for:
- 
-c
 is create
- 
-f
 is file
- 
-k
 is for Keep
    - 
gzip
 & 
bzip2
 will remove the original file once compressed
    -  Or they will remove the 
.gz
 when decompressing is done
- 
-r
 is recursive (for gzip and zip)
- 
-v
 is verbose (show details of what's happening)
- 
-z
 is for tar to gzip as well
- 
--exclude='file'
 is for tar (+gz if needed) to exclude certain files)

Compressing Files

Note: You can compress more than one file at a time eg: 
bzip2 file1.txt file2.txt file3.txt
gzip -vk file.txt                   (Creates file.txt.gz)
bzip2 file.txt                      (Creates  file.txt.bz2)
tar -cvf file.tar file.txt          (Creates tar)
tar -czvf file.tar.gz file.txt      (Creates tar.gz)
zip filename.zip file.txt           (Creates filename.zip)
zip -r folder.zip path/to/folder    (Creates  folder.txt.bz2)

Include/Exclude a few files:
```
; Exclude certain files
tar -czvf file.tar.gz / --exclude='*.jpg' --exclude='bigfile.sql'

; Include one file type
tar -czvf file.tar.gz /*.sh

; Include multiple files types
tar -czvf file.tar.gz 
find  | grep '.sh\|.py'
```

Decompressing Files

To Uncompress we use similar commands for most of them
gunzip -dvk file.txt.gz
gzip -dvk file.txt.gz       (Same as above)
bzip2 -d file.txt.bz2
tar -xvf file.tar
tar -zxvf file.tar.gz
unzip test.zip


SCP



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Download from server to local
scp [email protected]:/path/to/file.txt file.txt

Upload from local to server
scp file.txt [email protected]:/path/to/file.txt

SSH



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Connecting to a server
ssh [email protected]  (default port is 22)
ssh [email protected] -p 8000 (connect to specific port)
ssh [email protected] -i ~/.ssh/rsa_key.pub (connect with ssh key)

.SSH Permissions

These are safe permissions to use for SSH
```
chmod 700 ~/.ssh
chmod 644 ~/.ssh/idrsa.pub
chmod 600 ~/.ssh/idrsa

Put your pubkeys (one per line) for SSH login

chmod 600 ~/.ssh/authorized_keys
```

Using the Config

You can also create a 
~/.ssh/config
 file and store entries such as:
```
Host aws
Hostname ec2-50-50-130-50.compute-1.amazonaws.com
Port 22
Identityfile ~/.ssh/id_rsa
User myusername

Host my-vps
Hostname 50.50.130.50
Port 22
User root
```

You can then simply type:
ssh aws
ssh my-vps


SSH to PEM

Sometimes you may need a 
PEM
 format SSH Key. You can easily add this alongside your other SSH keys.
openssl rsa -in ~/.ssh/keyname_rsa -outform pem > keyname_rsa.pem
chmod 700 keyname_rsa.pem


Firewall



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A firewall prevents unauthorized access to your machine, you should use 
UFW
 (Uncomplicated Firewall). You must always run this with 
sudo
. If you don't have UFW installed, run:
sudo apt-get install ufw

UFW Status

To see the Firewall Status run one of these:
sudo ufw status
sudo ufw status verbose


UFW Enable/Disable
sudo ufw enable
sudo ufw disable

UFW Example Customization

Please do not do this unless you know what you are doing.

You could start out with blocking all incoming connections.
sudo ufw default deny incoming
sudo ufw default allow outgoing


Then we allow only what we want
sudo ufw allow ssh
sudo ufw allow http
sudo ufw allow https
sudo ufw allow ftp


These are the same as:
sudo ufw allow 22   # same as ssh
sudo ufw allow 80   # same as http
sudo ufw allow 443  # same as https


UFW More Options

If SSH was on port 
3333
 rather than the default 
22
 you would do:
sudo ufw allow 3333/tcp


Some more options:
sudo ufw allow 25 # SMTP
sudo ufw allow 110 # POP3
sudo ufw allow 995 # POP3S
sudo ufw allow 143 # IMAP
sudo ufw allow 993 # IMAPS
sudo ufw allow 3306 # MySQL
sudo ufw allow 5432 # Postgres
sudo ufw allow from 192.168.255.255 # Custom IP Address

UFW Deleting Rules

Easily delete named rules
sudo ufw delete allow ssh


Delete rules that are numbered
sudo ufw status numbered
sudo ufw delete [number]


UFW Reset Rules
sudo ufw reset

Regex



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Regex stands for Regular Expression. It's used for locating or replacing files or
strings of text. It is used all the time. These can be used in Linux itself and programming
languages.
; Symbolism
; ------------------
()          (captures groups)
[]          (set)
{}          (quantifier)
?           (optional, matches 0 or 1 character)
*           (matches 0 or more characters)
.           (match any character)
+           (match one or more character)
\           (escape character)
!           (false, is not)
^           (starts with)
$           (ends with)
|           (or statement, eg: (jesse|dan|jenkins) )

; Basic Primer
; ------------------
\w          (word)
\W          (non-word)
\s          (whitespace)
\S          (non-whitespace)
\d          (digit)
\D          (non-digit)
[ab]        (character set)
[^ab]       (negated set)
[a-m]       (range)
(hello)     (group)
(hello)+    (group, more than once)
; Groups
; ------------------
(hi)        (gets all "hi" occurances)
(^hi)       (gets all text starting with "hi")
(es$)       (gets all text ending with "es")
(hi)\1      (gets the first occurance of "hi")
; Flags
; ------------------
/i          (case insensitive)
/g          (global)
/m          (multiline)
; Escaped Characters
; ------------------
; Since characters such as ".", "+", etc are actual Regex pattern makers, if you
; need to check your content for the literal item you must escape them.
.          (matches . character)
+          (matches + character)
?          (matches ? character)
*          (matches * character)
^          (matches ^ character)
$          (matches $ character)
[          (matches [ character)
(          (matches ( character)
\t          (matches tab character)
\n          (matches newline)
\r          (matches return carriage)
\0          (matches NULL character)
\          (matches \ character)
/          (matches / character)

Regex Examples
Put Examples here, like phones, names, etc..


MySQL



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• -u

  is for User (default: root)

• -p

  is for Password

• -p password

  is for password which skips the prompt (not recommended)

• -h

  is for host (default: localhost)

• -port or -P

  is for a port, default is 3306

• -f

  will force SQL import and skips errors

• -v

  will display verbose output
• In the

  mysql>

  terminal you can get clean data by doing

  \g

  :

  • mysql> SELECT * FROM users LIMIT 10\g";

Connecting

mysql -u root -p (username, password prompt)
mysql -u root -p -h localhost (username, password prompt, host)
mysql -u root -p password -h localhost -P 3306

; AWS Example (AWS Defaults to 3306 as most MySQL connections do)
mysql -u username -p password -h myinstance.123456789012.us-east-1.rds.amazonaws.com

Exporting Database to SQL

You can dump a single database easily:

mysqldump -u root -p DATABASE_NAME > file.sql

Or Dump all databases on your MySQL server with the

--all-databases

mysqldump -u root -p --all-databases > file.sql

Importing SQL Files

You can do this through the shell only, or MySQL, first is the shell:

mysql -u root DATABASE_NAME < path/to/file.sql

To continue when there are MySQL Errors use -f or --force below:

mysql -u root DATABASE_NAME < path/to/file.sql --force

To use a password, just pass in the -p flag and type it in after running:

mysql -u root -p DATABASE_NAME < path/to/file.sql --force

Second, you can do it through MySQL once you connect:

mysql> use DATABASE_NAME;
mysql> source path/to/file.sql;

Exporting Compressed Database

This will save a lot of space in this one liner:

mysqldump -u root -p DATABASE_NAME | tar -cvzf > output.sql.tar.gz
mysqldump -u root -p DATABASE_NAME | gzip -v > output.sql.gz

Importing Compressed Database

Here is how you can import with the one liner:

mysql -u root -p DATABASE_NAME | tar -xzOf output.sql.tar.gz
mysql -u root -p DATABASE_NAME | gunzip < output.sql.gz

Get Database Encoding

USE DATABASE_NAME;
SELECT @@collation_database;

Get Table Encoding

SELECT default_character_set_name FROM information_schema.SCHEMATA
WHERE schema_name = "TABLE_NAME";

Get Column Encoding

Look at the collation table. Numeric fields won't have a collation.

SHOW FULL COLUMNS FROM TABLE_NAME

Fix Broken Characters

First, try this query without affecting anything to see:

SELECT CONVERT(BINARY CONVERT('We’re Here!' using latin1) using utf8);

To update a column:

UPDATE TABLE_NAME SET COLUMN_NAME = CONVERT(BINARY CONVERT(COLUMN_NAME using latin1) USING utf8);

Git

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Populate a Repository

You have to first create a repostory, through BitBucket, GitHub, GitLab, etc.

git init
touch README.md
git remote add origin [email protected]/username/yourrepo.git
git add .
git commit -m "Starting with one file"
git push origin master

Add or Remove Files

git add file.txt
git rm file.txt

Ignoring files

Create a

.gitignore

.tmp
.py[co]
.cache
.DS_Store

Create a Branch

Branches are used like when you don't want to ruin a main branch with working code.

git checkout -b develop
git push origin develop

Switch Branches

git checkout master
git checkout develop

Pull One File From Another Branch

If you were on your

master

develop

; Pull a single file into master from develop git checkout develop -- relative/path.txt

; Continue by comitting and pushing to master ```

Create a Tag

Tags create a snapshots of current code, you may name it as a version such as

1.0.1

tar.gz

zip

git tag -a 1.0
git tag -a 1.0 -m "Optional Message"
git push --tags

Remove a Tag

This will remove a tag from the Git host.

git tag -d 1.0
git push origin :refs/tags/1.0

Clone a Respository

git clone [email protected]/username:your_repo.git

Clone into current directory

git clone [email protected]/username:your_repo.git .

Current Status

git status

Commit Log and Show

To see log data and more details use the short or long commit ID.

git log
git show eb7c86a5fbdc6c64df608f4c143c2718a100983b

Reset Hard

This will reset your repository to the last revision and undo everything, use with caution.

git reset --hard HEAD

Prune

Removes cached items no longer read by git

git prune

Docker

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To install visit https://docs.docker.com/engine/installation/linux/ubuntulinux/ - Images: (Blueprints of an application) - Image BASE: No parent Image (An OS) - Image CHILD: Builds on a Base Image (Eg: Webserver, MySQL) - Containers: Created from an IMAGE and run an application. - Docker Daemon: Background service that builds, runs, and does everything. - Docker Client: Allows us to interact with the Docker Daemon. - Docker Hub: A registry of images (Like: npmjs, pip, packagist, bower)

Docker Compose

This is a great utility that makes managing docker easier from a

docker-compose.yml

docker-compose up
open http://localhost:3000

Test Box Run

This is a sample box to test once you installed docker

dock pull busybox
docker images
docker run busybox "Hi from the box"

See Running Containers

docker ps (running containers)
docker ps -a (see all containers that ran)

Run Container Interactively

This allows you to get inside the container

docker run -it busybox sh (interactive)

Remove Container

Removes a CONTAINER, not an IMAGE

docker ps -a
docker rm 

Bulk Remove Containers

You can remove containers based on their status in bulk, eg:

docker rm $(docker ps -a -q -f status=exited)
docker rm $(docker ps -a -q -f status=created)

Webserver Test Image

This will download the IMAGE and run it if it doesn't exist

docker run prakhar1989/static-site

This doesn't expose ports for us to use, so we do the following:

docker run -d -P --name static-site prakhar1989/static-site

• -d

  detaches terminal so we can run commands in our terminal

• -P

  publishes all exposed ports to random ports

By doing the above command we are given random ports, eg:

  443/tcp -> 0.0.0.0:32768
  80/tcp -> 0.0.0.0:32769

Your ports may be different, you can use specific ports with a lowercase

-p

docker run -p 8888:80 prakhar1989/static-site

Stop Container

docker stop static-site

Get New Docker Image

This would be a docker BASE IMAGE

docker pull ubuntu:14.04

Create Docker Image

This is a flask Example using a Python-3 Base IMAGE

• Create

  requirements.txt

  and just put

  flask

• Create an

  app.py

• Use the following sample code in

  app.py

  :

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

• Create a docker file, title it

  Dockerfile

• Enter the following

FROM python:3-onbuild
EXPOSE 5000
CMD ["python", "./app.py"]

Now build the image

docker build -t boyus .
docker images

Remove Docker Image

Get a list of images, then just delete by image id with

rmi

remove image

docker images
docker rmi 

Pushing Images

You need a repository at docker.io to push this, or probably some private hosting.

docker push boyus

Installing GUI's

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Linux has a lot of GUI's and you are not limited to what you get. I'll list a few popular ones with the installation instructions in Ubuntu. You can have as many GUI options as you like, just change the default at the login screen.

Tip: After you install, logout and in the login menu or the top right you can select what GUI you want to login with. Whenever you install a new GUI you can select a Display Manager, I recommend using

lightdm

.

--

Unity

Unity Website

Installed in Ubuntu 12+ by Default (`ubuntu-desktop`)

XUbuntu

XUbuntu Website

; Install:
sudo apt-get install xubuntu-desktop

; Remove:
sudo apt-get remove xubuntu-desktop

Cinnamon (Linux Mint)

Linux Mint Website

; Install:
sudo add-apt-repository ppa:moorkai/cinnamon
sudo apt-get update && sudo apt-get install cinnamon

; Remove
sudo ppa-purge ppa:moorkai/cinnamon

GNOME

GNOME Website

This has been one of the all time most popular GUI's for Linux ever made, in particular the

gnome-classic

; Install:
sudo apt-get install ubuntu-gnome-desktop    (For legacy gnome use you can use gnome-shell, this install both)

; Remove:
sudo apt-get remove ubuntu-gnome-desktop     (Removes gnome-shell as well)

Gnome3 has been my favorite GUI due to how I can customize it. However, for unknown reasons I have issues running only Gnome3 in VMWare Workstation 11. It works fine as a complete install.

Noteworthy: Visit Gnome Shell Extensions to customize anything you want. Make sure to use Firefox.

KDE

KDE Website

This is a very popular GUI for people that are used to Windows Desktops.

; Install:
sudo add-apt-repository ppa:kubuntu-ppa/backports
sudo apt-get update && sudo apt-get dist-upgrade
sudo apt-get install kubuntu-desktop

; Remove:
sudo apt-get remove kubuntu-desktop

LXQT

LXQT Website

; Install:
sudo apt-get install lxqt
; Remove:
sudo apt-get remove lxqt

Pantheon (ElementaryOS)

Elementary OS Website

For the best stability I use Elementary OS which is based off of Ubuntu.

; Install:
sudo add-apt-repository ppa:elementary-os/stable
sudo apt-get update
sudo apt-get install elementary-desktop

; Remove:
sudo apt-get remove elementary-desktop

XFCE

XFCE Website

; Install:
sudo apt-get install xfce4

; Remove:
sudo apt-get remove xfce4

Troubleshooting

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Sometimes the system has problems, seldmoly but I'll list things that helped me fix rare occasions.

Ubuntu Infinite Login

When you try to login to Ubuntu and it relogs you back into the login screen, this is an infinite loop. The only way I was able to fix it depsite all the guides was combining a few of these together for Ubuntu 16.04.

If you are using Gnome as I do, I would jump down to the Apt Auto Remove Problem in the list.

The first step is to login to a terminal.

CTRL + ALT + F1  (Or F3)

Next, Login as your user who must be able to run

sudo

• Temp Folder Permissions

  • ls -ld /tmp

    should have these permission exactly as:

    drwxrwxrwt

  • The user:group must be

    root:root

    on

    /tmp

    .
  • To Fix:

    sudo chmod a+wt /tmp

• Xauthority Ownership

  • ls -lta | grep .Xa

    should be owned by your user, for example

    jesse jesse

  • If it is

    root root

    or anything than your user/group it's wrong.
  • To Fix:

    sudo chown jesse:jesse .Xauthority

• Xsession Errors
  • This is just to make sure there are no syntax errors for your reference:
  • To Check:

    cat ~/.xsession-errors

  • You don't need to do anything if there are syntax errors, we will move the file.
• Try Moving XAuthority
  • Sometimes it's as easy to moving Xauthority so a new is generated at login.
  • To Fix:

    sudo ~/.Xauthority ~/.Xauthority.bkup

• Try Reconfiguring LightDM
  • Fix:

    dpkg-reconfigure lightdm

    , then select lightdm in the menu
  • Lastly restart lightdm:

    sudo service lightdm restart

• Apt Auto Remove Problem
  • I read that it's possible

    apt-autoremove

    may accidentally remove

    xubuntu-desktop

    ,

    ubuntu-desktop

    and LightDM reports no errors.
  • The

    ubuntu-desktop

    will load the Unity interface
  • The

    xubuntu-desktop

    will load a different interface I'm not familiar with.
  • To Fix:

    sudo apt-get install xubuntu-desktop ubuntu-desktop

  • If you are using Gnome, try following the post at OMGUbuntu
  • After the Above Try:

    sudo apt-get autoremove gnome-software && sudo apt-get install gnome-software

  • I was able to get Gnome-Classic working but not Gnome.
• How to Ensure it Works
  • You might be able to login after one of the steps above if you don't reboot. However, to be certain, you want to reboot to ensure it is fixed, otherwise you'll be doing this over and over.

Linux Facts

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• Linux Versions refers to The Kernel which ties the OS together.
• Linux Distributions are the named Linux "Flavors" below.
  • Debian
  • Linux Mint (LMDE) forked from Debian
  • Ubuntu forked from Debian
    • Elementary OS forked from Ubuntu
    • Linux Mint forked from Ubuntu
    • Kubuntu forked from Ubuntu
  • Fedora
  • Red Hat Enterprise Linux (RHEL) forked from Fedora
    • CentOS forked from RHEL (Community Edition of RHEL)
  • Gentoo
• ..And many others. Debian -> Ubuntu has been the most popular.