Linux Fundamentals

💡 List of Common Commands

Command	Description
echo	Output any text that we provide
whoami	Find out what user we're currently logged in as!
ls	listing
cd	change directory
cat	concatenate
pwd	print working directory
find	search for files in a directory hierarchy
grep	search for patterns in a file
touch	Create file
mkdir	Create a folder
cp	Copy a file or folder
mv	Move a file or folder
rm	Remove a file or folder
file	Determine the type of a file
su	Switch user
wget	Used to download files from the web via HTTP
scp	Secure copy a file from host to remote or vice versa
ps	Provide list of current running process'
kill	Kill a process
systemctl	Systemd Control and Service Manager
dig	Manually perform the DHCP lookup

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💡 List of Common Operators

Symbol / Operator	Description
&	This operator allows you to run commands in the background of your terminal.
&&	This operator allows you to combine multiple commands together in one line of your terminal.
>	This operator is a redirector - meaning that we can take the output from a command (such as using cat to output a file) and direct it elsewhere.
>>	This operator does the same function of the > operator but appends the output rather than replacing (meaning nothing is overwritten).

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💡 Common Directories

Directory	Description
/etc	The etc folder (short for etcetera) is a commonplace location to store system files that are used by your operating system.
/var	The "/var" directory, with "var" being short for variable data, is one of the main root folders found on a Linux install. This folder stores data that is frequently accessed or written by services or applications running on the system.
/root	The /root folder is actually the home for the "root" system user. There isn't anything more to this folder other than just understanding that this is the home directory for the "root" user.
/tmp	This is a unique root directory found on a Linux install. Short for "temporary", the /tmp directory is volatile and is used to store data that is only needed to be accessed once or twice. Similar to the memory on your computer, once the computer is restarted, the contents of this folder are cleared out.

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Terminal Text Editors

• VIM
• NANO

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Maintaining Your System

Automation

• CRON Generator or Cron Guru
  • cron -e

Value	Description
MIN	What minute to execute at
HOUR	What hour to execute at
DOM	What day of the month to execute at
MON	What month of the year to execute at
DOW	What day of the week to execute at
CMD	The actual command that will be executed.

Package Management

Normally we use the apt command to install software onto our Ubuntu system. The apt command is a part of the package management software also named apt. Apt contains a whole suite of tools that allows us to manage the packages and sources of our software, and to install or remove software at the same time.

One method of adding repositories is to use the add-apt-repository command we illustrated above, but we're going to walk through adding and removing a repository manually. Whilst you can install software through the use of package installers such as dpkg, the benefits of apt means that whenever we update our system -- the repository that contains the pieces of software that we add also gets checked for updates.