hyper-v – Alfred Myers

CentOS 8.0 installation boots into a blank screen

CentOS 8.0 was released earlier today with a bug inherited from RHEL 8.0 upstream.

The bug manifests itself when Server with Gui is selected as the Base Environment when installing on a Hyper-V virtual machine. After copying all the files needed into the hard drive Anaconda will boot into a blank screen.

The problem is made a little worse because Server with Gui is the default selection.

In yesterday’s post, I’ve shown how the solution proposed in RHEL 8.0’s release notes didn’t quite work when the system wasn’t (yet) registered with Red Hat Subscription Management.

Since CentOS has no such thing, the solution described in the release notes can be applied as is. That is, as long as you have internet connectivity.

But what if the system at hand is isolated from the internet? Then again we have to resort to installing from the installation media.

This time though, we can take advantage of the repo configuration files installed with the operating system that point to the installation media.

yum repolist --all

From yesterday, we already know that base-x is contained in AppStream, so from the list above we probably want to take a better look at c8-media-AppStream.

[root@centos-8-1905 ~]# yum repoinfo --all c8-media-AppStream
 Last metadata expiration check: 0:24:40 ago on Tue 24 Sep 2019 09:24:39 PM -03.
 Repo-id      : c8-media-AppStream
 Repo-name    : CentOS-AppStream-8 - Media
 Repo-status  : disabled
 Repo-baseurl : file:///media/CentOS/AppStream, file:///media/cdrom/AppStream, file:///media/cdrecorder/AppStream
 Repo-expire  : 172,800 second(s) (last: unknown)
 Repo-filename: /etc/yum.repos.d/CentOS-Media.repo
 [root@centos-8-1905 ~]#

As can be seen the repo is configured to search for its files at one of the URLs defined by the Repo-baseurl property. Let’s mount the installation media into /media/CentOS.

[root@centos-8-1905 ~]# mkdir /media/CentOS
[root@centos-8-1905 ~]# mount /dev/sr0 /media/CentOS/
 mount: /media/CentOS: WARNING: device write-protected, mounted read-only.

Now we can invoke yum groupinstall specifying c8-media-AppStream as the source repository.

[root@centos-8-1905 ~]# yum --repo=c8-media-AppStream -y groupinstall base-x

yum --repo=c8-media-AppStream -y groupinstall base-x — yum –repo=c8-media-AppStream -y groupinstall base-x

As yesterday, rebooting now should load the graphical user interface for the final steps of the installation process.

Error: There are no enabled repos.

I was installing Red Hat Enterprise Linux 8.0 on a Hyper-V virtual machine. After copying all the packages from the installation media and installing them onto the virtual hard drive, Anaconda booted RHEL into a blank screen.

After some research I found that the problem was a known issue listed in RHEL 8.0’s release notes as well as on Red Hat’s knowledge base:

The xorg-x11-drv-fbdev, xorg-x11-drv-vesa, and xorg-x11-drv-vmware video drivers are not installed by default
…
In addition, virtual machines relying on EFI for graphics support, such as Hyper-V, are also affected. If you selected the Server with GUI base environment on Hyper-V, you might be unable to log in due to a black screen displayed on reboot. To work around this problem on Hyper-v, enable multi- or single-user mode using the following steps:
Reboot the virtual machine.
During the booting process, select the required kernel using the up and down arrow keys on your keyboard.
Press the e key on your keyboard to edit the kernel command line.
Add systemd.unit=multi-user.target to the kernel command line in GRUB.
Press Ctrl-X to start the virtual machine.
After logging in, run the yum -y groupinstall base-x command.
Reboot the virtual machine to access the graphical mode.
(BZ#1687489)

So I started following the instructions, but on step #6 something unexpected happens:

[root@localhost ~]# yum -y groupinstall base-x
 Updating Subscription Management repositories.
 Unable to read consumer identity
 This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
 Error: There are no enabled repos.

Well… Thing is this is a short lived disposable virtual machine and I have no plans on registering it with Red Hat Subscription Management.

Luckily, the installation media contains the two repositories introduced with RHEL 8.0: BaseOS and AppStream.

Base-x is contained in the AppStream repo. We just have to:

Make sure the repositories from the installation media are accessible from the file system;
Import the public keys used to sign the packages into RPM;
Direct yum to install the packages from the AppStream repository.

[root@localhost ~]# mount /dev/sr0 /mnt
 mount: /mnt: WARNING: device write-protected, mounted read-only.
 [root@localhost ~]# rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
 [root@localhost ~]# yum --repofrompath AppStream,file:///mnt/AppStream -y groupinstall base-x

Results of the package installation — base-x installed successfully

Please note the command importing Red Hat’s public keys into RPM before installing the package, otherwise the package wouldn’t have been installed and an error message would have been displayed as seen below.

[root@localhost ~]# mount /dev/sr0 /mnt
 mount: /mnt: WARNING: device write-protected, mounted read-only.
 [root@localhost ~]# yum --repofrompath AppStream,file:///mnt/AppStream -y groupinstall base-x
 Updating Subscription Management repositories.
 Unable to read consumer identity
 This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
 Added AppStream repo from file:///mnt/AppStream
 You have enabled checking of packages via GPG keys. This is a good thing.
 However, you do not have any GPG public keys installed. You need to download
 the keys for packages you wish to install and install them.
 You can do that by running the command:
     rpm --import public.gpg.key
 Alternatively you can specify the url to the key you would like to use
 for a repository in the 'gpgkey' option in a repository section and DNF
 will install it for you.

Once the package is installed, rebooting the system should load the graphical user interface for the final steps of the installation process.

RHEL 8.0 Initial Setup graphical user interface — Initial Setup

Automating my way out of ancillary tasks with PowerShell

After creating a handful of virtual machines for ramping up on the different Linux distros, certain configuration patterns started to emerge. Repeating those same settings over and over again in Hyper-V Manager or even PowerShell’s command line interface is kind of tedious. Good thing is scripts are a great way to automate those repetitive configuration tasks away.

In my case, the settings I kept copying over and over again were:

Two cores;
Network adapter bound to a virtual switch with external connectivity;
Automatic Checkpoints turned off;

And then there were other settings that although varied between distros and installation options within those distros, had to be configured each and every time:

Virtual machine name;
RAM size;
Hard drive size;
Path to installation ISO;
Secure Boot;

So after learning and getting comfortable with the different PowerShell cmdlets, I started prototyping a few scripts. At first, the scripts were kind of lame and buggy, but as I learned more about the features of Hyper-V and how those features are exposed through PowerShell, the scripts were improved little by little much in the spirit of Kaizen – continuous improvement.

The important thing here is realizing this as a learning tool and as such starting small and improving as you go and as new requirements make themselves known.

Important as well is knowing when to stop. The purpose of this exercise isn’t creating a production-ready script, but to create a script that will allow me to get back as soon as possible to what I settled out to do in the first place: Create virtual machines so I could learn something else.

If you are curious enough, you can find the source code for one of the early versions of the scripts as a gist over on GitHub. If you are even more curious, you can see the entire history of how the code evolved also on GitHub.

Since that early prototype, the code has evolved quite a bit from a collection of discrete scripts to the current version which is implemented as a PowerShell module and incorporates all the learnings of the last few weeks – including a best practice for creating virtual hard disks for use with Linux file systems. Good luck trying remember that one every time you create a new VM for Linux!

Certainly there are a lot of opportunities for improvement (documentation, error handling and resilience in general just to name a few), but those are left as an exercise for future self. Meanwhile, let me get back to playing with those VMs.