How to Install Google Authenticator on Ubuntu Server

Install Google Authenticator:

Install qrencode:

Install JDK 11.0.1 (LTS) on Ubuntu 18.04

Update: End of Public Updates for Oracle JDK 8

Java SE 8 is going through the End of Public Updates process for legacy releases. Oracle will continue to provide free public updates and auto updates of Java SE 8, until at least the end of December 2020 for Personal Users, and January 2019 for Commercial Users. Source:

Here is a step by step procedure how to install JDK 11.0.1 (LTS) on Ubuntu 18.04 x64

Download: jdk-11.0.1_linux-x64_bin.tar.gz

update-alternatives: –install needs <link> <name> <path> <priority>

The priority is an important option when you have more than one Java version installed.

Use your favorite text editor.

You might need to reboot your system.
Use the following command to configure Java on your system:
There are 2 choices for the alternative java (providing /usr/bin/java).

[Linux] Enable universe, multiverse and restricted repositories on Ubuntu

Use the following terminal commands to enable universe, multiverse and restricted repositories on your Ubuntu system. It works well on the latest Ubuntu Server 18.04 LTS

How to temporarily disable IPv6 on Ubuntu? You need to diagnose a communication issue or track down a network problem?

IPv6 provides solution of the IPv4 address exhaustion as it’s offering a much larger addressing space.
However, there are few instances in which IPv6 is casing network problems.
Some hardware doesn’t utilize it or take any advantages of IPv6 communications protocol. There are instances in which the temporary and easy solution is to (permanently) disable it. It can be easily re-enabled when it needed again.

In case you need to disable it, either only for troubleshooting or permanently, you can use the following terminal commands.

First of all, let’s verify the current status of your IPv6 communications protocol.

If this command returns 0 that means IPv6 is enabled in your system.

Scroll down to the end of the file and insert these three lines below.

Save and quit your editor, then reboot your system.

Verifying the status of IPv6.

This command should return 1 meaning you successfully disabled IPv6 communications protocol.

To re-enable IPv6 just simple delete or comment out those 3 lines above.

You can use

to read values from file, it should return:

There are some additional commands if this method does not work.

Disable the network manager

Get the IP address from the server using:

List of IP address

Removing all IP information from an interface (enp2s1 in my case)

Assign the first ip addresses like this:

You can repeat for other IP addresses.
You can add the default route using:

List of network devices:

Restart the networking.service


Ipv6 test is a free online service to diagnose connection problems:

Install Java SE Development Kit 10.0.1 on Ubuntu 18.04 LTS x64

Download: jdk-10.0.1_linux-x64_bin.tar.gz

You might need to reboot your system.

[C++] How to install gcc-7 on Ubuntu LTS 16.04