Linux Notes & Commands

What is Linux?

Linux is an operating system that appears very similar to UNIX which is an operating system built by AT&T.

It was created by a man named Linus Torvalds. The idea was to create an operating system that is open source unlike other operating systems that have software licenses.

Linux comes in many flavors such as Ubuntu, which are customized versions of the operating system with additional features.

NOTE Linux is not Unix. Linux is modelled very closely to UNIX but it is not the same operating system or an operating system built on top of UNIX.

General Terms

BASH - Born Again Shell

This is the terminal that is used to interact with the computers features, such as copying and creating files, running applications, find information about your computer, and etc.

Note that it is used in addition to the Operating System's GUI which is the buttons and colorful interactive environment people commonly use.

#	Command	Explanation
1	pwd	Print working directory - shows you your current directory (where am I currently)
2	ls	Show me what is accessible from my current directory. (Where can I go, what is available to me)
3	cd	Change Directory - change the folder that I'm in or currently viewing. NOTE: "cd" is generally followed by the name of the directory you want to move to or a path to another directory relative to where you are currently located.
4	touch newfile.txt	Touch - this command allows you to create a file that can be specified as a specific type by addding the extension.
5	cp filename.txt	Copy - the command is used to copy a file specified after "cp" as well as a directory for the copy to be stored.
6	rm filename.txt	Remove/Delete - This command deletes the file from your computer
7	rm -rffolderIc folderIChose	Similar to the above command, this variation allows you to remove/delete the directory specified after "-rf".
8	mkdir newFolderName	Make Directory - creates a folder in your current directory.
9	man commandIwantInfoOn	Manual - Command that provides an explanation and information on a command you specify
10	top	Top - Shows the processes/software/applications that are consuming the most CPU.
11	ps	Basic Command viewing the processes running on the system. It provides a snapshot of the current processes along with detailed information like user id, cpu usage, memory usage, command name etc.
12	shutdown [-r , -h] [+60, now, etc.]	The command allows you to power off the computer. The command takes two arguments which indicate restart or turn off. The next argument is a time which can be "now" or "+" with a number of minutes to wait until the command is executed.

Cron Jobs / Crontab

-Crontab is a program that allows the user to schedule jobs/processes you would like to have executed automatically at a specified time.

For example, you can set up a job that will run every month and backup your files to a folder somewhere

sudo crontab -e Opens a text file in your editor. Generally "vim".

This is where you will set up a schedule of processes you would like to run at the specified times. -Example Job:

# minute hour dayOfMonth month dayOfWeek command * * * * 0 /usr/bin/local/python3 updateCsv.py

Each line in the file represents a job that will run.

In the example above, your machine will run at any minute, hour, day of month, or month ON A SUNDAY updateCsv.py using the python3 interpreter located at the file path specified. "0" here represents Sunday. Each one of these parameters expect either an * or a number within a range.

TAR

Tar is program in Linux machines that allow you to back up files on your machine to folder of your choosing.

Creating a .tar or .tar.gz backup

sudo tar -cvpzf backup.tar.gz --exclude=/Desktop/longVideosFolder /Desktop

The above creates a "tar ball" or compressed tar file that contains the contents of the repository Desktop, excluding the contents of the folder longVideosFolder.

c = create a file or overwrite, v = verbose or display files being copied in terminal, p = keep permisions associated with backup, z = zip the file or produce .gz file, f = provide file name for backup of files.

--exclude allows you to exclude certain files from the back up. (Not Required)

The final parameter is what to back up.

Unpacking a .tar or .tar.gz backup

sudo tar -xvpzf backup.tar.gz -C /folderDestination

Similar to the creation command, this allows you to unpack the contents of the file into the folder of your choice.

NOTE x = extract, "z" is only used if the file you are unpacking is a .gz file.