Linux

To run linux you have to start the virtual machine. Ubuntu is like a flavour of Linux.

What is Git Bash?

Git Bash is like an emulation / translator for windows so it understands linux commands. It is running a version of GNU. Bourne Again SHell (Bash). A shell is software that is an interface which can run commands. There are multiple shells. cat /etc/shells Shows all the shells.

Why learn linux?

• Fast growing - becoming more popular for desktop use
• Stable - Doesnt need to be restarted all the time
• Scales well - scientific, engineering
• More employable

What is linux?

A clone of Unix which was used on large main frames and linux can be run on smaller machines. Made up of a kernal - core operanting system. Many libraries and systems rely on this.

Helpful commands:

--help -> Will give you more information on the command uname -> gives the OS uname -p -> processor uname -n -> hostname uname -a -> all of the information

Command	Description
ls	Lists files and directories in the current directory.
cd	Changes the current directory.
pwd	Prints the current working directory.
mkdir	Creates a new directory.
rm	Removes files and directories.
cp	Copies files and directories.
mv	Moves or renames files and directories.
cat	Concatenates and displays the contents of files.
grep	Searches for patterns in files.
chmod	Changes permissions of files and directories.
chown	Changes the owner of files and directories.
chgrp	Changes the group ownership of files and directories.
ssh	Connects to a remote server using the Secure Shell (SSH) protocol.
ps	Lists currently running processes.
sudo	Executes a command with superuser (administrative) privileges.
history	Lists the command history.
exit	Exits the current shell or terminal.
uname	Prints system information.
nano	A text editor
touch	Creates an empty file
printenv	Prints the enviroment variables
echo	Prints a file or string
export	Creates an enviroment variable
source	Used to reload the .bashrc file

History gives a list of all the commands you have used and they are numbered. They you can use the command ! and it will be the command.

rm -r -> Removes directories and everything within them.

Navigate files and folders

• one dot means current directory (cd .)
• two dots means the parent directory (cd ..)
• home directory (cd OR cd ~)
• present working directory (pwd)
• root folder starts with a slash / (cd /)
• your home directory is the user folder (adminuser)

Not every user gets a folder in the home directory. The super user / root user has a folder in the root directory.

File and folder names are case sensitive.

Managing file ownership

Mangaging file ownership is important as you need to keep track of who has the correct permissions to certain files and directories. To view file ownership the command is ls -la (l for long and a for all).

The file or directory created by a user typically belongs to that user. The owner of a file or directory is determined by the user who creates it. The group ownership of the file or directory is usually set to the primary group of the user. This can vary depending on the system's configuration, such as whether it uses user private groups or assigns a different group ownership.

The permissions of a new file / directory is set by the unmask permissions? The default execute (x) permission is excluded for the owner when creating a file due to security reasons. Users can still grant the execute permission with the chomd command.

File permissions

• Owner / User - U - The Owner permissions apply only the owner of the file or directory, they will not impact the actions of other users.
• Group - G - The Group permissions apply only to the group that has been assigned to the file or directory, they will not effect the actions of other users.
• Others - O - The All Users permissions apply to all other users on the system, this is the permission group that you want to watch the most.

Number	Permission Type	Symbol
0	No Permission	—
1	Execute	–x
2	Write	-w-
3	Execute + Write	-wx
4	Read	r–
5	Read + Execute	r-x
6	Read + Write	rw-
7	Read + Write + Execute	rwx

Example:

-rw-r--r-- 1 user wheel 0 Feb 16 14:22 file2

-(rw-) (r--) (r--) 1 user wheel 0 Feb 16 14:22 file2

(user) (group) (others)

• The owner has read and write permissions
• The group and others only have read permissions
• This code would be 644
• This is a file as it doesnt start with a d

chmod command

You can use chmod to change file permissions.

chmod <what permissions / code> <file_name>

Examples:

• $ chmod u+x file_name
• $ chmod g+rw file_name
• $ chmod o-w file_name
• $ chmod u=rwx,g=rx,o= file_name
• $ chmod 774 file_name

Chown

Notes for 22/06/2023

Pipe symbol | takes the output and gives it to another command grep searches for a thing like a key word. apt also apt-get use to install packages sudo command is like superuser / root user command

Important commands used today

cat chicken-joke.txt | grep chicken Takes the chicken-joke text file and searches for the key word chicken and it gives you all the lines with chicken on it.

sudo apt install tree installed library called tree which shows files in a nicer way

sudo apt update -y update all sources so it can find the packages -y means say yes to everything

Root cd / it is like the base level of the folders

cp chicken-joke.txt bad-joke.txt Copy the chicken joke and give the copy the name bad-joke

mv bad-joke.txt ~ Move the bad-joke file to the home directory

rm -r Remove everything within the folder recursive

Scripting

Provision ngenx

touch provision.sh - create empty file nano provision.sh - edit file

#! is the way to tell linux this is the path to take. We want Bash.

So inside the file type:

#!/bin/bash

Two git bashes open - one to manually test and one to add to the script.

#!/bin/bash

# update
sudo apt update -y

# upgrade
sudo apt upgrade -y

# install nginx
sudo apt install nginx -y

sudo systemctl status nginx

# restart nginx
sudo systemctl restart nginx
# enable nginx - make sure that when the virtual machine restarts nginx will automatically start

sudo systemctl enable nginx

Environment variables

• value stored in memory
• accessible by other tools Linux

printenv shows all the environment variables. They are capitilised. printenv USER

Make a variable

MYNAME=elena echo $MYNAME

Make an environment variable and .bashrc

export MYNAME=elena printenv MYNAME

To have an enviroment variable that will stay when you log out and back in you need a file called .bashrc. It needs to be edited.

nano .bashrc -> edit the file

Go to the bottom of the file and add the variable

export CATSNAME=Iggy

Go out of the file and use the command

source .bashrc -> this will reload the file and the new enviroment variable will be present

Remove an environment variable

unset MYNAME

Processes

2 types:

1. System proceses - ps aux
2. User Processes - ps

ps shows user processes

If your CPU has one core it can handle one process at a time. If it is multicore it can run more than one process at a time. The operating system (OS) has to prioritise what needs to run first.

PID is process ID - Every process has one. The parent process starts the child process.

• TTY is the terminal if there is a ? then it is a system proccess.

ps aux - Shows all processes in detail.