Ubuntu 20.04 LTS (Server)- tasksel: apt-get failed (100) while installing ubuntu-desktop

Question

PROBLEM: On Ubuntu 20.04 LTS (Server), installing ubuntu-desktop through tasksel fails with error "tasksel: apt-get failed (100)".

SOLUTION 1: Restore last good checkpoint. The simplest solution is to roll back your system to your last good checkpoint and install tasksel then ubuntu-desktop cleanly. If that is not an option for you, see the next solution.

SOLUTION 2: Check that you have tasksel dependencies installed using the commands:

• sudo apt list --installed debhelper*
• sudo apt list --installed dpkg-dev*
• sudo apt list --installed gettext*
• sudo apt list --installed po-debconf*

If you are missing these packages or they are not the correct version, install/upgrade them. In my case, debhelper was not present. The debhelper package cleans up your machine if partial or conflicting files are present. tasksel actually lists it as a dependency, probably for this reason. Details on tasksel dependencies are here.

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System Details: My server is Ubuntu 20.04 LTS (focal) on amd64 architecture on a VM in Hyper-V. The Ubuntu OS is up to date.

Steps to Produce Error:

• I installed tasksel using sudo apt install tasksel.
• I called tasksel using sudo tasksel.
• I highlighted the package "ubuntu desktop" and pressed Enter.
• Install failed with the error:
• tasksel: apt-get failed (100)

Remedies Attempted:

• I checked that /etc/apt/sources.list enabled my focal repos (they are enabled).
• I tried several combinations of sudo apt update, sudo dpkg --configure -a, and restarting the server. Sources here.
• After all this, using sudo tasksel and attempting Ubuntu-desktop installation failed with the same error.
• tasksel: apt-get failed (100)

I checked the Ubuntu tasksel Launchpad page and saw that tasksel has 4 dependencies as follows:

1. debhelper (>= 9)
2. dpkg-dev (>= 1.9.0)
3. gettext
4. po-debconf

Remedy That Worked:

• I checked my Ubuntu installation using sudo apt list --installed debhelper and saw that I do not have debhelper installed. The other 3 dependencies were installed and the correct minimum versions.
• I installed debhelper using sudo apt install debhelper.
• I reran sudo tasksel and selected ubuntu-desktop.
• This time, tasksel ran without error.

Answer 1

I was also stuck apt-get error following the steps you used to reproduce error. But then I was looking at the guide for install KDE GUI and directly used this command: sudo tasksel install ubuntu-desktop

and it was able to install what's needed. I'm using ubuntu Ubuntu 20.04.1 LTS as well.