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  • Computer Basics
    • Operating System Basics
    • Processes explained
    • Difference Between Process and Thread
    • The Basics of Hypervisors
      • A simple explanation of virtualization by VMinformer
      • What is a Hypervisor?
    • What’s a Kernel?
    • Processes and VM Videos
      • Create, Execute & Exit from a Process | frok() System Call
      • Process, Process Stack, PCB & Attributes
  • Linux
    • Linux Basics
      • What is Linux?
        • What is a Linux Package?
        • Stages of Linux booting process – explanation, step by step
        • Whats an Inode
        • Explanation-System calls and System call types in operating system
        • Linux Package Management
        • How the ls -l command works
        • Linux Isolation Basics
        • Understanding Linux File Permissions
        • Understanding UMASK value in Linux
        • What is Umask and How To Setup Default umask Under Linux?
        • File descriptor
        • Understanding Special Permission SGID in Linux
        • Searching with grep
        • Introduction to Linux and Basic commands
        • fstab explained
        • Introduction to mounting filesystems in Linux
      • SSH
        • What is Secure Shell (SSH)
        • SSH Layers
        • SSH using Putty
        • 4 Reasons Why SSH Connection Fails
        • Enabling MFA on Ubuntu and Amazon Linux
        • Enabling MFA on your Instance
        • Howto remove Google authenticator from SSH logins
        • How to use multiplexing to speed up the SSH
        • How to access RDP over SSH tunnel
      • Ram & Disks
        • What is the difference between memory and disk storage?
        • How to check disk space utilization
        • Monitoring RAM
        • RAID
      • Video tutorial on extending swap partition and creating a swapfile
      • Commands
        • 15-basic-curl-command-in-linux-with-practical-examples
      • SystemD
        • Systemd Boot Process, a closer look
        • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Useful SystemD commands and info
        • The Story Behind ‘init’ and ‘systemd’
        • Basic journal use
        • Unit files: what are they?
        • Unit dependencies
      • What is a Unix Socket?
      • How to check disk space on Unix servers
      • 3 commands to reboot Linux (plus 4 more ways to do it safely)
      • See Detailed History Of yum history Commands
      • How to Transfer Files with Rsync over SSH
      • How to Use the mkfs Command on Linux
    • Linux +
      • GRUB bootloader – Full tutorial
      • How to Change Kernel Runtime Parameters in a Persistent and Non-Persistent Way
      • Linux Basics – LVM (Logical Volume Manager)
      • A video overview of OOM(Out Of Memory)
      • Linux Storage Stack Diagram
      • Basics-of-bash-for-beginners
      • CPU & LOAD AVERAGE
        • Linux Load Averages: Solving the Mystery
      • How to Run Sudo Command Without Password
      • Virtualization
        • Difference between PV and HVM virtualization
        • Virtualization Performance: Zones, KVM, Xen
      • Commands
        • strace explained
      • Ram & Disk Space
        • Why is space not being freed from disk after deleting a file in Red Hat Enterprise Linux?
        • Understanding I/O: Random vs Sequential
      • Memory Management
        • Introduction to Memory Management in Linux
      • Processes
        • Process, Process Stack, PCB & Attributes
        • Create, Execute & Exit from a Process | frok() System Call
        • CPU Context Switching & Its Overheads
        • What is an Interrupt? Types of Interrupts
        • CPU Scheduling: FCFS, SJF, SRTF, Round Robin
        • Background and Foreground Processes
      • Virtual filesystems in Linux: Why we need them and how they work
      • Overview of Forks, Threads, and Asynchronous I/O
    • RHEL(RedHat)
      • File-management-red-hat-enterprise-linux-8
      • Enable ENA driver on EC2 for RHEL 6 & 7
    • Amazon Linux 2
      • How to install XRDP in Amazon Linux 2
    • Centos 8
      • Centos8 dig command not found. How to install dig on centos8
      • How to install whois on RHEL 8 / CentOS 8
    • Ubuntu
      • Ubuntu 18.04 remove all unused old kernels
    • SUSE
    • Tools
      • Filezilla
      • SSH using Putty
      • WinSCP
        • WinSCP Portable 5.15.2 (ftp, sftp, scp client) Released
    • My Study Guide
      • CPU
        • A Guide to the Linux “Top” Command
        • Understanding CPU Steal Time – when should you be worried?
        • CPU Steal Time. Now on Amazon EC2
        • USER SPACE VS KERNEL SPACE
        • What is the Difference Between Hardware and Software Interrupt
        • What exactly is “iowait”?
        • Difference Between Process And Thread in Linux
        • Operating Systems | States of a process
      • Linux OS related
        • Boot process
          • Systemd Boot Process, a closer look
          • Stages of Linux booting process – explanation, step by step
          • 6 Stages of Linux Boot Process (Startup Sequence) sysVinit:
          • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Init and Initramfs
          • Initrd vs Initramfs
          • Do you need initramfs to boot?
        • The difference between booting MBR and GPT with GRUB
        • The Master Boot Record (MBR) and Why it is Necessary?
        • GRUB bootloader – Full tutorial
      • Memory
        • free command
        • Buffer vs Cache
        • How to Clear RAM Memory Cache, Buffer and Swap Space on Linux
        • OOM explained
        • How to Configure the Linux Out-of-Memory Killer
        • Surviving the Linux OOM Killer
      • Disk
        • Amazon EBS
        • Linux iostat command
        • How to Read Linux Iostat’s Output and Interpret System Performance
        • Video tutorial on extending swap partition and creating a swapfile
        • Linux Basics – LVM (Logical Volume Manager)
        • RAID
        • Video tutorial on extending swap partition and creating a swapfile
  • Networking
    • Networking basics
      • Introduction to Networking
        • What is a Computer Network?
        • Types of Networks
        • MAN
        • WAN
        • Parts of a Network
        • How the internet works
        • Servers
        • Clients and Hosts
        • Network Interface Card NIC
        • What is a Protocol
        • Bus Topology
        • Ring Topology
        • Star Topology
        • Mesh Topology
        • OSI Model
        • More on the OSI Model
      • TCP/IP explained
      • TCP connection states
      • TCP three way handshake
      • TCP/IP Ports and Sockets Explained
      • DNS Name Resolution Process
      • What happens when we hit a URL in our browser
      • What is SSL
      • SSL or TLS handshake
      • What is an SSL Certificate and How Does it Work?
      • DHCP Explained
      • The Certificate Authority vs. The Handshake
    • Networking +
      • A tcpdump Tutorial and Primer with Examples
      • How To Use Traceroute and MTR to Diagnose Network Issues
      • tcpdump command to capture full-sized packets
      • Commands
        • Commands to monitor network bandwidth on Linux server
        • Linux Route Command Examples (How to Add Route in Linux)
  • Application Services and Packages
    • Apache
      • What is Apache?
      • Apache Basics Video
      • Apache Cheat Sheet
      • Apache Performance Tuning: MPM Modules
      • How To Use Apache as a Reverse Proxy with mod_proxy on CentOS 7
      • Tune memory allocation for an Apache web server
      • Failed to restart httpsd.service: The name org.freedesktop.PolicyKit1 was not provided by any .service files
      • Redirecting from one URL to another using .htaccess
      • USING .HTACCESS REWRITE RULES
      • URL Rewriting for Beginners
      • How to Enable Apache Userdir Module on RHEL/CentOS
      • How to set up password authentication in apache (httpd) with htpasswd and .htaccess on RHEL / CentOS 7
      • How to redirect HTTP to HTTPS Using .htaccess
      • How to Enable TLS 1.3 in Apache and Nginx
      • Apache Benchmark
    • Nginx
      • How To Install Linux, Nginx, MySQL, PHP (LEMP stack) on Ubuntu 18.04
      • Nginx Bible
      • Basic Nginx commands
      • Basic configuration parameters
      • SSL certificate Installation
      • Full configuration Example
      • Nginx Rewrite examples
      • Nginx redirect from www to none www domain name
      • How to Set Up an Nginx Certbot
      • Urgent security issue in NGINX/php-fpm
      • Moving from Apache2 to Nginx Webserver
    • PHP
      • What is PHP?
      • The PHP Process Explained
      • What does PHP-FPM do?
      • PHP troubleshooting tip
      • max_execution_time in php explained
      • Why You Should Upgrade WordPress to PHP 7 Now Rather Than Later
    • MYSQL
      • What Is MySQL?
      • MySQL Command cheat sheet
      • Creating and editing MySQL DB Dumps
      • MySQL – MySQL Introduction
      • MySQL – Structure Introduction
      • MySQL – Data Types Introduction
    • Fail2ban
    • Magento2
      • Magento explained plus commands for an easy install on Ubuntu 16.04
    • VNC Installation on Ubuntu
    • How to install XRDP in Amazon Linux 2
  • My issues
    • WordPress
      • WordPress FTP error
      • Unable to upload file to WordPress
      • WordPress Posts Returning 404 Error
      • How to Fix the 500 Internal Server Error on Your WordPress Website
      • How to Fix Corrupted Files and Databases in WordPress
      • Max_upload exceeded..!!! WordPress
      • 6 Ways To Increase the Maximum Upload File Size in WordPress
    • Being prompted for password after not setting one (RHEL/Amazon Linux)
    • Unable to transfer files from one instance to another using SCP
    • Website running and reachable via a browser however giving a 403 when running a CURL
    • Issue installing Cerbot on Amazon Linux 2
    • How to restore “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
    • Renewing your SSL certificate using Certbot/Letsencrypt manually:
  • AWS(Amazon Web Services)
    • Instance Health Checks failing
      • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
      • Reasons why an instance with root on LVM might fail to boot
      • Instance failing health checks with a Kernel Offset: disabled error
    • EC2 SSH ISSUES
      • Injecting userdata to allow ssh
    • Amazon EBS
    • AWS Workarounds
      • Steps to install python3.7 on Amazon Linux 1
      • Using userdata to resolve ssh issues to your EC2 instance
      • How to use the same SSH key pair in all AWS regions
      • Accidentally enabled UFW on your Ubuntu instance and cant SSH as a result?
    • Lightsail Loadbalancer failing health checks
    • AWS Docs
      • How can I avoid DNS resolution failures with EC2 Linux?
      • Extending a Linux File System after Resizing the Volume
    • Service Introduction Videos
      • What is AWS?
      • Introduction to Amazon EC2
      • Amazon Elastic Block Store (EBS) Overview
    • Troubleshooting videos
      • How do I recover access to my EC2 instances if I lost my SSH key pair?
      • How do I move my EC2 instance to another subnet, Availability Zone, VPC, or region?
  • Troubleshooting
    • Server A Can’t Talk to Server B
    • Troubleshoot Slow Networks
    • How To Troubleshoot Common Site Issues on a Linux Server
    • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
    • How to fix high memory usage in Linux ?
    • Troubleshooting a Linux kernel panic after patching
    • Reproducing a “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
  • Articles
    • How to get notified whenever someone logs in via SSH?
    • procSpy : Python tool that monitors and logs user-run commands on a Linux system
    • How to identify duplicate files on Linux
    • Power of SSH Tunneling
    • Linux commands you should never run on your system
  • Redis
    • ElastiCache
      • Redis restore from S3 snapshot fails
    • An introduction to Redis data types and abstractions
    • Redis – Commands
    • Redis – Keys
    • Redis – Strings
    • Redis – Hashes
    • Redis – Lists
    • Redis – Sets
    • Redis – Sorted Sets
  • My Curriculum Vitae (CV)
LinuxByImraan
Primary Menu
  • Computer Basics
    • Operating System Basics
    • Processes explained
    • Difference Between Process and Thread
    • The Basics of Hypervisors
      • A simple explanation of virtualization by VMinformer
      • What is a Hypervisor?
    • What’s a Kernel?
    • Processes and VM Videos
      • Create, Execute & Exit from a Process | frok() System Call
      • Process, Process Stack, PCB & Attributes
  • Linux
    • Linux Basics
      • What is Linux?
        • What is a Linux Package?
        • Stages of Linux booting process – explanation, step by step
        • Whats an Inode
        • Explanation-System calls and System call types in operating system
        • Linux Package Management
        • How the ls -l command works
        • Linux Isolation Basics
        • Understanding Linux File Permissions
        • Understanding UMASK value in Linux
        • What is Umask and How To Setup Default umask Under Linux?
        • File descriptor
        • Understanding Special Permission SGID in Linux
        • Searching with grep
        • Introduction to Linux and Basic commands
        • fstab explained
        • Introduction to mounting filesystems in Linux
      • SSH
        • What is Secure Shell (SSH)
        • SSH Layers
        • SSH using Putty
        • 4 Reasons Why SSH Connection Fails
        • Enabling MFA on Ubuntu and Amazon Linux
        • Enabling MFA on your Instance
        • Howto remove Google authenticator from SSH logins
        • How to use multiplexing to speed up the SSH
        • How to access RDP over SSH tunnel
      • Ram & Disks
        • What is the difference between memory and disk storage?
        • How to check disk space utilization
        • Monitoring RAM
        • RAID
      • Video tutorial on extending swap partition and creating a swapfile
      • Commands
        • 15-basic-curl-command-in-linux-with-practical-examples
      • SystemD
        • Systemd Boot Process, a closer look
        • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Useful SystemD commands and info
        • The Story Behind ‘init’ and ‘systemd’
        • Basic journal use
        • Unit files: what are they?
        • Unit dependencies
      • What is a Unix Socket?
      • How to check disk space on Unix servers
      • 3 commands to reboot Linux (plus 4 more ways to do it safely)
      • See Detailed History Of yum history Commands
      • How to Transfer Files with Rsync over SSH
      • How to Use the mkfs Command on Linux
    • Linux +
      • GRUB bootloader – Full tutorial
      • How to Change Kernel Runtime Parameters in a Persistent and Non-Persistent Way
      • Linux Basics – LVM (Logical Volume Manager)
      • A video overview of OOM(Out Of Memory)
      • Linux Storage Stack Diagram
      • Basics-of-bash-for-beginners
      • CPU & LOAD AVERAGE
        • Linux Load Averages: Solving the Mystery
      • How to Run Sudo Command Without Password
      • Virtualization
        • Difference between PV and HVM virtualization
        • Virtualization Performance: Zones, KVM, Xen
      • Commands
        • strace explained
      • Ram & Disk Space
        • Why is space not being freed from disk after deleting a file in Red Hat Enterprise Linux?
        • Understanding I/O: Random vs Sequential
      • Memory Management
        • Introduction to Memory Management in Linux
      • Processes
        • Process, Process Stack, PCB & Attributes
        • Create, Execute & Exit from a Process | frok() System Call
        • CPU Context Switching & Its Overheads
        • What is an Interrupt? Types of Interrupts
        • CPU Scheduling: FCFS, SJF, SRTF, Round Robin
        • Background and Foreground Processes
      • Virtual filesystems in Linux: Why we need them and how they work
      • Overview of Forks, Threads, and Asynchronous I/O
    • RHEL(RedHat)
      • File-management-red-hat-enterprise-linux-8
      • Enable ENA driver on EC2 for RHEL 6 & 7
    • Amazon Linux 2
      • How to install XRDP in Amazon Linux 2
    • Centos 8
      • Centos8 dig command not found. How to install dig on centos8
      • How to install whois on RHEL 8 / CentOS 8
    • Ubuntu
      • Ubuntu 18.04 remove all unused old kernels
    • SUSE
    • Tools
      • Filezilla
      • SSH using Putty
      • WinSCP
        • WinSCP Portable 5.15.2 (ftp, sftp, scp client) Released
    • My Study Guide
      • CPU
        • A Guide to the Linux “Top” Command
        • Understanding CPU Steal Time – when should you be worried?
        • CPU Steal Time. Now on Amazon EC2
        • USER SPACE VS KERNEL SPACE
        • What is the Difference Between Hardware and Software Interrupt
        • What exactly is “iowait”?
        • Difference Between Process And Thread in Linux
        • Operating Systems | States of a process
      • Linux OS related
        • Boot process
          • Systemd Boot Process, a closer look
          • Stages of Linux booting process – explanation, step by step
          • 6 Stages of Linux Boot Process (Startup Sequence) sysVinit:
          • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Init and Initramfs
          • Initrd vs Initramfs
          • Do you need initramfs to boot?
        • The difference between booting MBR and GPT with GRUB
        • The Master Boot Record (MBR) and Why it is Necessary?
        • GRUB bootloader – Full tutorial
      • Memory
        • free command
        • Buffer vs Cache
        • How to Clear RAM Memory Cache, Buffer and Swap Space on Linux
        • OOM explained
        • How to Configure the Linux Out-of-Memory Killer
        • Surviving the Linux OOM Killer
      • Disk
        • Amazon EBS
        • Linux iostat command
        • How to Read Linux Iostat’s Output and Interpret System Performance
        • Video tutorial on extending swap partition and creating a swapfile
        • Linux Basics – LVM (Logical Volume Manager)
        • RAID
        • Video tutorial on extending swap partition and creating a swapfile
  • Networking
    • Networking basics
      • Introduction to Networking
        • What is a Computer Network?
        • Types of Networks
        • MAN
        • WAN
        • Parts of a Network
        • How the internet works
        • Servers
        • Clients and Hosts
        • Network Interface Card NIC
        • What is a Protocol
        • Bus Topology
        • Ring Topology
        • Star Topology
        • Mesh Topology
        • OSI Model
        • More on the OSI Model
      • TCP/IP explained
      • TCP connection states
      • TCP three way handshake
      • TCP/IP Ports and Sockets Explained
      • DNS Name Resolution Process
      • What happens when we hit a URL in our browser
      • What is SSL
      • SSL or TLS handshake
      • What is an SSL Certificate and How Does it Work?
      • DHCP Explained
      • The Certificate Authority vs. The Handshake
    • Networking +
      • A tcpdump Tutorial and Primer with Examples
      • How To Use Traceroute and MTR to Diagnose Network Issues
      • tcpdump command to capture full-sized packets
      • Commands
        • Commands to monitor network bandwidth on Linux server
        • Linux Route Command Examples (How to Add Route in Linux)
  • Application Services and Packages
    • Apache
      • What is Apache?
      • Apache Basics Video
      • Apache Cheat Sheet
      • Apache Performance Tuning: MPM Modules
      • How To Use Apache as a Reverse Proxy with mod_proxy on CentOS 7
      • Tune memory allocation for an Apache web server
      • Failed to restart httpsd.service: The name org.freedesktop.PolicyKit1 was not provided by any .service files
      • Redirecting from one URL to another using .htaccess
      • USING .HTACCESS REWRITE RULES
      • URL Rewriting for Beginners
      • How to Enable Apache Userdir Module on RHEL/CentOS
      • How to set up password authentication in apache (httpd) with htpasswd and .htaccess on RHEL / CentOS 7
      • How to redirect HTTP to HTTPS Using .htaccess
      • How to Enable TLS 1.3 in Apache and Nginx
      • Apache Benchmark
    • Nginx
      • How To Install Linux, Nginx, MySQL, PHP (LEMP stack) on Ubuntu 18.04
      • Nginx Bible
      • Basic Nginx commands
      • Basic configuration parameters
      • SSL certificate Installation
      • Full configuration Example
      • Nginx Rewrite examples
      • Nginx redirect from www to none www domain name
      • How to Set Up an Nginx Certbot
      • Urgent security issue in NGINX/php-fpm
      • Moving from Apache2 to Nginx Webserver
    • PHP
      • What is PHP?
      • The PHP Process Explained
      • What does PHP-FPM do?
      • PHP troubleshooting tip
      • max_execution_time in php explained
      • Why You Should Upgrade WordPress to PHP 7 Now Rather Than Later
    • MYSQL
      • What Is MySQL?
      • MySQL Command cheat sheet
      • Creating and editing MySQL DB Dumps
      • MySQL – MySQL Introduction
      • MySQL – Structure Introduction
      • MySQL – Data Types Introduction
    • Fail2ban
    • Magento2
      • Magento explained plus commands for an easy install on Ubuntu 16.04
    • VNC Installation on Ubuntu
    • How to install XRDP in Amazon Linux 2
  • My issues
    • WordPress
      • WordPress FTP error
      • Unable to upload file to WordPress
      • WordPress Posts Returning 404 Error
      • How to Fix the 500 Internal Server Error on Your WordPress Website
      • How to Fix Corrupted Files and Databases in WordPress
      • Max_upload exceeded..!!! WordPress
      • 6 Ways To Increase the Maximum Upload File Size in WordPress
    • Being prompted for password after not setting one (RHEL/Amazon Linux)
    • Unable to transfer files from one instance to another using SCP
    • Website running and reachable via a browser however giving a 403 when running a CURL
    • Issue installing Cerbot on Amazon Linux 2
    • How to restore “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
    • Renewing your SSL certificate using Certbot/Letsencrypt manually:
  • AWS(Amazon Web Services)
    • Instance Health Checks failing
      • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
      • Reasons why an instance with root on LVM might fail to boot
      • Instance failing health checks with a Kernel Offset: disabled error
    • EC2 SSH ISSUES
      • Injecting userdata to allow ssh
    • Amazon EBS
    • AWS Workarounds
      • Steps to install python3.7 on Amazon Linux 1
      • Using userdata to resolve ssh issues to your EC2 instance
      • How to use the same SSH key pair in all AWS regions
      • Accidentally enabled UFW on your Ubuntu instance and cant SSH as a result?
    • Lightsail Loadbalancer failing health checks
    • AWS Docs
      • How can I avoid DNS resolution failures with EC2 Linux?
      • Extending a Linux File System after Resizing the Volume
    • Service Introduction Videos
      • What is AWS?
      • Introduction to Amazon EC2
      • Amazon Elastic Block Store (EBS) Overview
    • Troubleshooting videos
      • How do I recover access to my EC2 instances if I lost my SSH key pair?
      • How do I move my EC2 instance to another subnet, Availability Zone, VPC, or region?
  • Troubleshooting
    • Server A Can’t Talk to Server B
    • Troubleshoot Slow Networks
    • How To Troubleshoot Common Site Issues on a Linux Server
    • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
    • How to fix high memory usage in Linux ?
    • Troubleshooting a Linux kernel panic after patching
    • Reproducing a “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
  • Articles
    • How to get notified whenever someone logs in via SSH?
    • procSpy : Python tool that monitors and logs user-run commands on a Linux system
    • How to identify duplicate files on Linux
    • Power of SSH Tunneling
    • Linux commands you should never run on your system
  • Redis
    • ElastiCache
      • Redis restore from S3 snapshot fails
    • An introduction to Redis data types and abstractions
    • Redis – Commands
    • Redis – Keys
    • Redis – Strings
    • Redis – Hashes
    • Redis – Lists
    • Redis – Sets
    • Redis – Sorted Sets
  • My Curriculum Vitae (CV)

Author: sudoimraan

MySQL – Data Types Introduction

MySQL – Data Types Introduction

15th Nov 201915th Nov 2019 By : sudoimraan
MySQL – Structure Introduction

MySQL – Structure Introduction

15th Nov 201915th Nov 2019 By : sudoimraan
MySQL – MySQL Introduction

MySQL – MySQL Introduction

15th Nov 201915th Nov 2019 By : sudoimraan
Urgent security issue in NGINX/php-fpm

Urgent security issue in NGINX/php-fpm

8th Nov 20198th Nov 2019 By : sudoimraan
Moving from Apache2 to Nginx Webserver

Moving from Apache2 to Nginx Webserver

8th Nov 20198th Nov 2019 By : sudoimraan
40 Useful Linux Network Commands for Modern SysAdmins

40 Useful Linux Network Commands for Modern SysAdmins

8th Nov 20198th Nov 2019 By : sudoimraan
Queueing in the Linux Network Stack

Queueing in the Linux Network Stack

23rd Oct 201923rd Oct 2019 By : sudoimraan
SUSE clear credentials

SUSE clear credentials

16th Oct 201916th Oct 2019 By : sudoimraan
Reasons why an instance with root on LVM might fail to boot

Reasons why an instance with root on LVM might fail to boot

16th Oct 2019 By : sudoimraan
Redis restore from S3 snapshot fails

Redis restore from S3 snapshot fails

15th Oct 201915th Oct 2019 By : sudoimraan

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Imraan Abrahams

Welcome to my website. So this page was initially created as a repo for myself saving information I might find useful down the line which eventually evolved into a site which I used to teach newbies to the world of Linux and Networtking. This page focuses mainly on Linux and touches the basics of networking. We've all been there, running into issues, googling searching for answers. My hope is that the answer you are looking for is here. Remember, start with the basics first and build your way up.... for example, do you know what a kernel is and why its so important?

LinkedIn profile

Abrahams Imraan

 

What is AWS?

https://www.youtube.com/watch?v=mZ5H8sn_2ZI

What is Amazon EC2?

https://www.youtube.com/watch?v=TsRBftzZsQo

What is Amazon EBS?

https://www.youtube.com/watch?v=77qLAl-lRpo

How do I benchmark network throughput between Amazon EC2 Linux instances in the same VPC?

https://www.youtube.com/watch?v=0ATwiU346Ug&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=4

How do I convert ssh .pem key files into .ppk key files and vice versa?

https://www.youtube.com/watch?v=vCMDHPHBen4&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=179

Tune memory allocation for an Apache web

https://www.youtube.com/watch?v=Qyr3geZwXQY

Update GRUB to load a previous kernel

https://www.youtube.com/watch?v=QiMpJi2YWxA&index=6&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw

How does DNS work, and how do I troubleshoot partial DNS failures?

https://www.youtube.com/watch?v=qIetJGi7TW0&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=23

How do I expand an EBS root volume of a Linux instance?

https://www.youtube.com/watch?v=9znrrZNW_9o&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=268

How do I create a subdomain with AWS Route 53?

https://www.youtube.com/watch?v=kpHeE3HZHZA&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=8

How do I extend my Linux filesystem using Elastic Volumes?

https://www.youtube.com/watch?v=yYbX5U6CsKM&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=8&t=0s

How do I migrate my DNS service for an existing domain to Amazon Route 53?

https://www.youtube.com/watch?v=W4FPZ29Trpw&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=293

How to enable secondary interface Ubuntu

https://www.youtube.com/watch?v=RmwGYXchb4E&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=22

Add an additional SSH User account with my cloud-init and user data

https://www.youtube.com/watch?v=OGj0Lj5DOBg&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=13&t=0s

“How do I set up a NAT gateway?”

https://www.youtube.com/watch?v=zRMMbzw7SsA&list=PLhr1KZpdzukfdjsOHZ-BazZt1iK1J8UUw&index=362
  • Computer Basics
    • Operating System Basics
    • Processes explained
    • Difference Between Process and Thread
    • The Basics of Hypervisors
      • A simple explanation of virtualization by VMinformer
      • What is a Hypervisor?
    • What’s a Kernel?
    • Processes and VM Videos
      • Create, Execute & Exit from a Process | frok() System Call
      • Process, Process Stack, PCB & Attributes
  • Linux
    • Linux Basics
      • What is Linux?
        • What is a Linux Package?
        • Stages of Linux booting process – explanation, step by step
        • Whats an Inode
        • Explanation-System calls and System call types in operating system
        • Linux Package Management
        • How the ls -l command works
        • Linux Isolation Basics
        • Understanding Linux File Permissions
        • Understanding UMASK value in Linux
        • What is Umask and How To Setup Default umask Under Linux?
        • File descriptor
        • Understanding Special Permission SGID in Linux
        • Searching with grep
        • Introduction to Linux and Basic commands
        • fstab explained
        • Introduction to mounting filesystems in Linux
      • SSH
        • What is Secure Shell (SSH)
        • SSH Layers
        • SSH using Putty
        • 4 Reasons Why SSH Connection Fails
        • Enabling MFA on Ubuntu and Amazon Linux
        • Enabling MFA on your Instance
        • Howto remove Google authenticator from SSH logins
        • How to use multiplexing to speed up the SSH
        • How to access RDP over SSH tunnel
      • Ram & Disks
        • What is the difference between memory and disk storage?
        • How to check disk space utilization
        • Monitoring RAM
        • RAID
      • Video tutorial on extending swap partition and creating a swapfile
      • Commands
        • 15-basic-curl-command-in-linux-with-practical-examples
      • SystemD
        • Systemd Boot Process, a closer look
        • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Useful SystemD commands and info
        • The Story Behind ‘init’ and ‘systemd’
        • Basic journal use
        • Unit files: what are they?
        • Unit dependencies
      • What is a Unix Socket?
      • How to check disk space on Unix servers
      • 3 commands to reboot Linux (plus 4 more ways to do it safely)
      • See Detailed History Of yum history Commands
      • How to Transfer Files with Rsync over SSH
      • How to Use the mkfs Command on Linux
    • Linux +
      • GRUB bootloader – Full tutorial
      • How to Change Kernel Runtime Parameters in a Persistent and Non-Persistent Way
      • Linux Basics – LVM (Logical Volume Manager)
      • A video overview of OOM(Out Of Memory)
      • Linux Storage Stack Diagram
      • Basics-of-bash-for-beginners
      • CPU & LOAD AVERAGE
        • Linux Load Averages: Solving the Mystery
      • How to Run Sudo Command Without Password
      • Virtualization
        • Difference between PV and HVM virtualization
        • Virtualization Performance: Zones, KVM, Xen
      • Commands
        • strace explained
      • Ram & Disk Space
        • Why is space not being freed from disk after deleting a file in Red Hat Enterprise Linux?
        • Understanding I/O: Random vs Sequential
      • Memory Management
        • Introduction to Memory Management in Linux
      • Processes
        • Process, Process Stack, PCB & Attributes
        • Create, Execute & Exit from a Process | frok() System Call
        • CPU Context Switching & Its Overheads
        • What is an Interrupt? Types of Interrupts
        • CPU Scheduling: FCFS, SJF, SRTF, Round Robin
        • Background and Foreground Processes
      • Virtual filesystems in Linux: Why we need them and how they work
      • Overview of Forks, Threads, and Asynchronous I/O
    • RHEL(RedHat)
      • File-management-red-hat-enterprise-linux-8
      • Enable ENA driver on EC2 for RHEL 6 & 7
    • Amazon Linux 2
      • How to install XRDP in Amazon Linux 2
    • Centos 8
      • Centos8 dig command not found. How to install dig on centos8
      • How to install whois on RHEL 8 / CentOS 8
    • Ubuntu
      • Ubuntu 18.04 remove all unused old kernels
    • SUSE
    • Tools
      • Filezilla
      • SSH using Putty
      • WinSCP
        • WinSCP Portable 5.15.2 (ftp, sftp, scp client) Released
    • My Study Guide
      • CPU
        • A Guide to the Linux “Top” Command
        • Understanding CPU Steal Time – when should you be worried?
        • CPU Steal Time. Now on Amazon EC2
        • USER SPACE VS KERNEL SPACE
        • What is the Difference Between Hardware and Software Interrupt
        • What exactly is “iowait”?
        • Difference Between Process And Thread in Linux
        • Operating Systems | States of a process
      • Linux OS related
        • Boot process
          • Systemd Boot Process, a closer look
          • Stages of Linux booting process – explanation, step by step
          • 6 Stages of Linux Boot Process (Startup Sequence) sysVinit:
          • Step by Step Linux boot process with GRUB2 and systemd in RHEL 7 / CentOS 7
        • Init and Initramfs
          • Initrd vs Initramfs
          • Do you need initramfs to boot?
        • The difference between booting MBR and GPT with GRUB
        • The Master Boot Record (MBR) and Why it is Necessary?
        • GRUB bootloader – Full tutorial
      • Memory
        • free command
        • Buffer vs Cache
        • How to Clear RAM Memory Cache, Buffer and Swap Space on Linux
        • OOM explained
        • How to Configure the Linux Out-of-Memory Killer
        • Surviving the Linux OOM Killer
      • Disk
        • Amazon EBS
        • Linux iostat command
        • How to Read Linux Iostat’s Output and Interpret System Performance
        • Video tutorial on extending swap partition and creating a swapfile
        • Linux Basics – LVM (Logical Volume Manager)
        • RAID
        • Video tutorial on extending swap partition and creating a swapfile
  • Networking
    • Networking basics
      • Introduction to Networking
        • What is a Computer Network?
        • Types of Networks
        • MAN
        • WAN
        • Parts of a Network
        • How the internet works
        • Servers
        • Clients and Hosts
        • Network Interface Card NIC
        • What is a Protocol
        • Bus Topology
        • Ring Topology
        • Star Topology
        • Mesh Topology
        • OSI Model
        • More on the OSI Model
      • TCP/IP explained
      • TCP connection states
      • TCP three way handshake
      • TCP/IP Ports and Sockets Explained
      • DNS Name Resolution Process
      • What happens when we hit a URL in our browser
      • What is SSL
      • SSL or TLS handshake
      • What is an SSL Certificate and How Does it Work?
      • DHCP Explained
      • The Certificate Authority vs. The Handshake
    • Networking +
      • A tcpdump Tutorial and Primer with Examples
      • How To Use Traceroute and MTR to Diagnose Network Issues
      • tcpdump command to capture full-sized packets
      • Commands
        • Commands to monitor network bandwidth on Linux server
        • Linux Route Command Examples (How to Add Route in Linux)
  • Application Services and Packages
    • Apache
      • What is Apache?
      • Apache Basics Video
      • Apache Cheat Sheet
      • Apache Performance Tuning: MPM Modules
      • How To Use Apache as a Reverse Proxy with mod_proxy on CentOS 7
      • Tune memory allocation for an Apache web server
      • Failed to restart httpsd.service: The name org.freedesktop.PolicyKit1 was not provided by any .service files
      • Redirecting from one URL to another using .htaccess
      • USING .HTACCESS REWRITE RULES
      • URL Rewriting for Beginners
      • How to Enable Apache Userdir Module on RHEL/CentOS
      • How to set up password authentication in apache (httpd) with htpasswd and .htaccess on RHEL / CentOS 7
      • How to redirect HTTP to HTTPS Using .htaccess
      • How to Enable TLS 1.3 in Apache and Nginx
      • Apache Benchmark
    • Nginx
      • How To Install Linux, Nginx, MySQL, PHP (LEMP stack) on Ubuntu 18.04
      • Nginx Bible
      • Basic Nginx commands
      • Basic configuration parameters
      • SSL certificate Installation
      • Full configuration Example
      • Nginx Rewrite examples
      • Nginx redirect from www to none www domain name
      • How to Set Up an Nginx Certbot
      • Urgent security issue in NGINX/php-fpm
      • Moving from Apache2 to Nginx Webserver
    • PHP
      • What is PHP?
      • The PHP Process Explained
      • What does PHP-FPM do?
      • PHP troubleshooting tip
      • max_execution_time in php explained
      • Why You Should Upgrade WordPress to PHP 7 Now Rather Than Later
    • MYSQL
      • What Is MySQL?
      • MySQL Command cheat sheet
      • Creating and editing MySQL DB Dumps
      • MySQL – MySQL Introduction
      • MySQL – Structure Introduction
      • MySQL – Data Types Introduction
    • Fail2ban
    • Magento2
      • Magento explained plus commands for an easy install on Ubuntu 16.04
    • VNC Installation on Ubuntu
    • How to install XRDP in Amazon Linux 2
  • My issues
    • WordPress
      • WordPress FTP error
      • Unable to upload file to WordPress
      • WordPress Posts Returning 404 Error
      • How to Fix the 500 Internal Server Error on Your WordPress Website
      • How to Fix Corrupted Files and Databases in WordPress
      • Max_upload exceeded..!!! WordPress
      • 6 Ways To Increase the Maximum Upload File Size in WordPress
    • Being prompted for password after not setting one (RHEL/Amazon Linux)
    • Unable to transfer files from one instance to another using SCP
    • Website running and reachable via a browser however giving a 403 when running a CURL
    • Issue installing Cerbot on Amazon Linux 2
    • How to restore “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
    • Renewing your SSL certificate using Certbot/Letsencrypt manually:
  • AWS(Amazon Web Services)
    • Instance Health Checks failing
      • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
      • Reasons why an instance with root on LVM might fail to boot
      • Instance failing health checks with a Kernel Offset: disabled error
    • EC2 SSH ISSUES
      • Injecting userdata to allow ssh
    • Amazon EBS
    • AWS Workarounds
      • Steps to install python3.7 on Amazon Linux 1
      • Using userdata to resolve ssh issues to your EC2 instance
      • How to use the same SSH key pair in all AWS regions
      • Accidentally enabled UFW on your Ubuntu instance and cant SSH as a result?
    • Lightsail Loadbalancer failing health checks
    • AWS Docs
      • How can I avoid DNS resolution failures with EC2 Linux?
      • Extending a Linux File System after Resizing the Volume
    • Service Introduction Videos
      • What is AWS?
      • Introduction to Amazon EC2
      • Amazon Elastic Block Store (EBS) Overview
    • Troubleshooting videos
      • How do I recover access to my EC2 instances if I lost my SSH key pair?
      • How do I move my EC2 instance to another subnet, Availability Zone, VPC, or region?
  • Troubleshooting
    • Server A Can’t Talk to Server B
    • Troubleshoot Slow Networks
    • How To Troubleshoot Common Site Issues on a Linux Server
    • How to fix a Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
    • How to fix high memory usage in Linux ?
    • Troubleshooting a Linux kernel panic after patching
    • Reproducing a “Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)”
  • Articles
    • How to get notified whenever someone logs in via SSH?
    • procSpy : Python tool that monitors and logs user-run commands on a Linux system
    • How to identify duplicate files on Linux
    • Power of SSH Tunneling
    • Linux commands you should never run on your system
  • Redis
    • ElastiCache
      • Redis restore from S3 snapshot fails
    • An introduction to Redis data types and abstractions
    • Redis – Commands
    • Redis – Keys
    • Redis – Strings
    • Redis – Hashes
    • Redis – Lists
    • Redis – Sets
    • Redis – Sorted Sets
  • My Curriculum Vitae (CV)
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