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Ubuntu frozen BLACK SCREEN ERROR If you have a black screen after your upgrade from  Ubuntu 18.04  to  Ubuntu 20.04  or from  Ubuntu 19.10  to  Ubuntu 20.04  or any version to the latest version. Or If you have a frozen black screen on startup. Here is my tip to overcome this problem! 1. Power OFF your system. 2. Power ON again and press ESC. Go to the GNU GRUB screen, where you can choose the OS you want in your system. 3. Choose  Advanced Options for Ubuntu You will be prompted to the screen below. 4. Choose a  RECOVERY MODE If you have a startup black screen error,              Choose the current version's recovery mode  (the one on the top) If you have an after update black screen error,             Choose any of the previous version's recovery mode (excluding the one on the top) Press ENTER The pro...

Upgrade to the latest version of Ubuntu -Using terminal 1. Make sure you have the update-manager-core package sudo apt install update-manager-core 2. To choose which version of Ubuntu you want      whether an LTS version or a normal version. In the file /etc/update-manager/release-upgrades , we need to make sure Prompt=normal for normal releases. (you can also choose Prompt = lts for only LTS releases) **Use any text editor** sudo gedit /etc/update-manager/release-upgrades Edit the Prompt option as per your wish. It is always better to keep it normal. 3. Pre-upgrade steps sudo apt update sudo apt upgrade sudo apt dist-upgrade Make sure all the packages are up to date in your system. Optionally, use sudo apt autoremove  to clear unwanted packages 4. Check whether a new version is available for your system do-release-upgrade -c 5. UPGRADE~! sudo do-release-upgrade The process starts!!! Press ENTER and typ...

CREATE CUSTOM TOPOLOGY IN MININET To create a custom topology in the mininet environment, we are going to use a python code. It is very simple, no need to acquire deep knowledge of python programming language especially for this task. 1. Import necessary packages *Topo from mininet.topo import Topo subpackage topo is being imported from the package mininet. 2. Create a class object class MYTOPO ( Topo ) : (Don't forget to have a similar class name and filename) 3. Create init method init method in python has similar functions as constructors in java. def __init__( self ):    Topo.__init__( self ) 4. Add Hosts Hostname=self.addHost ( "hostname" ) 5. Add switches switch_name=self.addSwitch ( "switch name" ) 6. Add links self.addLink ( "node name 1", "node name 2" ) 7. Name your topology Finally, we name the topo to call it in the command line. topos = { 'cust': ( lambda: MYT...