Linux Flashcards
What is Linux
Open Source OS
UNIX alternative
Highly customizable
Many home IoT devices use it
Linux Kernel
Core of Linux OS
Establishes communication between software and hardware
Kernel’s Responsibilities
Device, Memory, and Process Management
Handling system calls
File Manager
Allows users to access files in the system
Desktop Environment
Provides a user-friendly GUI
Package Manager
Used to download, install, and update applications
/bin and /sbin
Store binaries
/media and /mnt
Used to mount drives
/home
Stores personal user files
/tmp
Stores temporary files (do not save personal files in this directory)
/etc
Important: system configurations files
Directory
/var
Stores system logs
/boot
Kernel image
/sys
Interface to the kernel
/proc
A directory for each running process, including kernel processes
Root User
Highest Privileges
Can perform any task
Shown by # in CLI
Sudo Users
Can perform only what they are permitted to do in the system
Regular Users
Can perform only basic tasks in the system
Shown by $ in CLI
whoami
Returns current user name
pwd
Print Working Directory
Finds current system location
uname
Gets info about the operating system
touch
Command that creates a file
mkdir
Command creates directories and folders
Cat
Concatenate
Reads data from the file and gives its content as output
Relative Path
Navigation to directories w/o specifying the root and relative to the working directory
Absolute Path
/ Indicated root folder
>
Outputs and overwrites a file
> >
Appends the output to a file
<
Input
STDIN
Standard Input
taking text as an input
0
STDOUT
Standard Output
used to test output of any command you type in the terminal, and then that output is stored in the stdout stream
1
STDERR
Standard Error
is invoked whenever a command faces an error, then that error message gets stored in this data stream
2
grep
Filters data
/etc/shadow
Contains encrypted passwords
Need to be Root or Root privilaged
R
Read
4
W
Write
2
X
Execute
1
Path
Environment variable
Instructs the shell to find an executable path
Paths are separated with : colons
apt update
Updates package lists for upgrades
apt upgrade
Installs all available package updates
dmesg
Displays messages from the kernel ring buffer.
Diagnostic tool for failures
dhclient
IP addresses can be changed, released, renewed, or removed
/etc/network/interfaces
Configure network interfaces
What 2 commands can start a service
Service
systemctl
netstat
NOT installed by default
Samba
Allows computers to communicate within the local network via SMB protocol. Port 137-139 and 445
SCP
Secure Copy Protocol
Securely transfer files between remote & local stations
Can use flags to set parameters
Bash
Bourne Again SHell
Scripting includes system commands.
File extension .sh
Automates tasks
First line #!/bin/bash
$
#
“ “
Variable
Comment
Text
sed
Command used to replace words
chmod
Command to change permissions of a file or directory
iptables
Protects from possible attacks
Firewall
smb.conf
File to be edited to set up Samba services
Fail2ban
Daemon that protects against brute force attacks
What is used for math
let
expr
(( ))
/etc/skel
Where templates for new users are stored
cd/
Command to get to the root directory
Apache
Web server
