Linux Quickstart — Complete Summary
1. Linux Introduction
What is Linux
Linux is an open-source operating system widely used for servers, development, DevOps, and cloud infrastructure.
Why Linux
Reasons Linux is popular:
- Open Source
- Strong community support
- Highly customizable
- Most servers run on Linux
- DevOps tools mainly support Linux
- Automation friendly
- Highly secure
Linux Architecture (Basic Idea)
Linux OS architecture generally consists of:
Applications
Shell
Kernel
Hardware
- Applications – Programs like browsers, editors.
- Shell – Interface between user and kernel.
- Kernel – Core of the OS managing memory, CPU, devices.
- Hardware – Physical components.
Linux Distributions (Distros)
Popular Desktop Linux
- Ubuntu
- Linux Mint
- Arch Linux
- Fedora
- Debian
- OpenSuse
Popular Server Linux
- Red Hat Enterprise Linux (RHEL)
- Ubuntu Server
- CentOS
- SUSE Enterprise Linux
Most Used in Industry
Two major families:
RPM-based
- RHEL
- CentOS
- Fedora
Debian-based
- Ubuntu
- Debian
Difference: RPM vs DEB
Both are package formats used to install software.
| Feature | RPM | DEB |
|---|---|---|
| Used in | RedHat family | Debian family |
| Package extension | .rpm | .deb |
| Package manager | RPM/YUM/DNF | APT/DPKG |
DEB Packages
Example:
google-chrome-stable_current_amd64.deb
Installation:
dpkg -i google-chrome-stable_current_amd64.deb
RPM Packages
Example:
google-chrome-stable-57.0.x86_64.rpm
Installation:
rpm -ivh package.rpm
2. Basic Linux Commands
Open Terminal
The terminal is used to interact with the Linux system.
Show Current Directory
pwd
Displays Present Working Directory.
Create Directory
mkdir directory_name
Example
mkdir linux-practices
Change Directory
cd directory_name
Example
cd linux-practices
List Files and Directories
ls
Create Empty Files
touch filename
Example
touch file1 file2 file3
Absolute Path vs Relative Path
Path
A path is the location of a file or directory.
Example
/home/imran/file.txt
Absolute Path
Complete path starting from root.
Example
/home/imran/linux-practices
/etc/samba.conf
/boot/grub/grub.conf
Always begins with /.
Relative Path
Path relative to current directory.
Example
cd linux-practices
File Operations
Copy File
cp file1 destination
Example
cp file1 /home/imran/
Copy Directory
cp -r directory1 destination
Move Files
mv file1 destination
Delete Files
rm filename
Delete Directory
rm -r directory_name
3. VIM Editor
What is VIM
VIM = Vi Improved
Popular Linux text editor.
Other editors:
- emacs
- gedit
VIM Modes
VIM has 3 modes
1️⃣ Command Mode
2️⃣ Insert Mode
3️⃣ Extended Command Mode
Enter Insert Mode
Press:
i
Save and Exit
:wq
Exit Without Saving
:q
VIM Command Mode Shortcuts
| Command | Function |
|---|---|
| gg | Start of file |
| G | End of file |
| w | Move forward word |
| b | Move backward word |
| u | Undo |
| Ctrl + r | Redo |
| yy | Copy line |
| nyy | Copy n lines |
| p | Paste |
| dd | Delete line |
| ndd | Delete n lines |
| dw | Delete word |
| x | Delete character |
| /word | Search word |
Extended Commands
| Command | Function |
|---|---|
| :w | Save |
| :q | Quit |
| :wq | Save + quit |
| :w! | Force save |
| 😡 | Save + quit |
| :set nu | Show line numbers |
| :set nonu | Hide line numbers |
| :20 | Go to line 20 |
Types of Files in Linux
Linux has multiple file types.
Common ones:
- Regular file
- Directory
- Symbolic link
Symbolic Links
Similar to shortcuts in Windows.
Create symbolic link:
ln -s source destination
Example
ln -s /var/log loglink
4. Grep Command
grep searches text inside files.
Example:
grep root /etc/passwd
Case Insensitive Search
grep -i root /etc/passwd
Show Lines Not Matching
grep -v root file
Filter Commands
less
Shows file page by page.
less file.txt
more
Similar to less.
head
Shows first lines.
head file.txt
tail
Shows last lines.
tail file.txt
cut
Extracts columns from text.
sed
Used for editing text streams.
Example: replace text
I/O Redirection
Used to redirect output.
Redirect Output
command > file
Append Output
command >> file
Redirect Errors
command 2>> errorfile
Redirect All Output
command &>> file
Piping
Send output of one command to another.
command1 | command2
Example
cat file | grep word
Find Command
Used to search files in directories.
Example
find / -name filename
5. Users and Groups
Linux is multi-user system.
Types of Users
| Type | Example | UID | Home |
|---|---|---|---|
| Root | root | 0 | /root |
| Regular | imran | 1000+ | /home/user |
| Service | ftp, ssh | 1-999 | /var |
Important Files
/etc/passwd
Stores user information.
/etc/group
Stores group information.
Format
groupname:password:GID:members
/etc/shadow
Stores encrypted passwords.
Contains:
- Username
- Encrypted password
- Password change info
- Expiry info
User & Group Commands
| Command | Description |
|---|---|
| useradd | Create user |
| adduser | Create user (Ubuntu) |
| passwd | Set password |
| id | Show user info |
| groupadd | Create group |
| usermod -G | Add user to group |
| userdel -r | Delete user |
| groupdel | Delete group |
| who | Who is logged in |
| whoami | Current user |
| last | Last logins |
| lsof -u user | Files opened by user |
6. File Permissions
Linux permissions control file access.
Three permission groups:
User
Group
Others
Permissions:
| Symbol | Meaning |
|---|---|
| r | read |
| w | write |
| x | execute |
Change Permissions (Symbolic)
Example
chmod ugo+r file
Give read permission to all.
Example
chmod o-wx dir
Remove write and execute for others.
Numeric Permission Method
Permissions values:
Read = 4
Write = 2
Execute = 1
Example
chmod 640 file
Meaning
User = 6 (rw)
Group = 4 (r)
Others = 0
7. Sudo
Allows normal users to execute root commands.
Switch to root
sudo -i
Switch user
su -
Add user to sudoers
Edit sudoers file:
visudo
Disable password for sudo
Add:
NOPASSWD
8. Software Management
Installing software packages.
Download Files
Using wget
wget link
Using curl
curl link
curl link -o file
CentOS / RHEL Package Management
Install RPM
rpm -ivh package.rpm
Upgrade RPM
rpm -Uvh package.rpm
Remove Package
rpm -ev package
List Installed Packages
rpm -qa
Package Information
rpm -qi package
YUM Package Manager
Solves dependency issues.
Install Package
yum install package -y
Example
yum install httpd -y
Remove Package
yum remove package -y
Update Packages
yum update
Search Package
yum search package
Repository List
yum repolist
DNF Package Manager (CentOS 8)
Replacement for YUM.
Commands:
dnf install package
dnf remove package
dnf update
dnf search package
dnf repolist
dnf history
dnf clean all
Ubuntu Package Management (APT)
Update Package List
apt update
Search Package
apt search package
Install Package
apt install package -y
Example
apt install apache2 -y
Remove Package
apt remove package -y
Show Package Info
apt show package
9. Search
Used to locate files or data.
Example
find
grep
10. Login (SSH / Telnet)
Remote login into servers.
Example
ssh user@server-ip
11. File Transfer
Files transferred between systems using tools like:
- SCP
- FTP
- SFTP
12. Disk Usage
Used to check disk storage.
Commands:
df
du
13. Directory Traversal
Navigate directories using commands like:
cd
ls
pwd
14. Services
Services are background programs.
Controlled using systemctl.
Service Commands (CentOS)
Start service
systemctl start httpd
Stop service
systemctl stop httpd
Restart service
systemctl restart httpd
Status
systemctl status httpd
Enable service at boot
systemctl enable httpd
Disable service
systemctl disable httpd
Ubuntu Service Commands
Example for Apache
systemctl start apache2
systemctl stop apache2
systemctl restart apache2
systemctl status apache2
systemctl enable apache2
systemctl disable apache2
systemctl is-active apache2
systemctl is-enabled apache2
15. Compression / Archives
Used to compress files.
Common tools:
tar
gzip
zip
16. Process Related
Used to manage running processes.
Common commands:
ps
top
kill
17. System Commands
Commands for system management.
Examples:
uptime
uname
hostname
18. Hardware
Commands to view hardware information.
Examples:
lscpu
lsblk
lspci
19. Statistics
Commands used for system performance monitoring.
Examples:
vmstat
iostat
free
Final Topics Covered in the PDF
The document teaches:
- Linux basics
- Linux commands
- File operations
- Vim editor
- Grep and filters
- IO redirection
- Piping
- Users and groups
- File permissions
- Sudo
- Package management (RPM, YUM, DNF, APT)
- Services
- System utilities
- Disk usage
- Compression
- Process management
- Hardware monitoring