Ubuntu – Ubuntu Server 18.04 LTS cannot change resolution in Hyper-V

I had the same issue and when I was looking for help I remember seeing your post. Now when I finally got it to work I might as well document it here:

1. Upgraded linux-image and headers sudo apt-get install linux-image-3.11.0-15-generic linux-headers-3.11.0-15-generic (Perhaps virtual would work just as well as the generic one.):

2. Installed linux-image-extras with the hyperv-drivers: sudo apt-get install linux-image-extra-virtual

3. Set video mode (Pretty much what you already did):
   Set GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=hyperv_fb:1680x1050" in /etc/default/grub.

4. Update grub: sudo update-grub
5. Reboot

I guess the critical part was installing the updated hyperv-drivers with linux-image-extra-virtual. Also make sure they are loaded.

The desktop lags because Hyper-V is using software rendering instead of using the GPU:

$ /usr/lib/nux/unity_support_test -p

Not software rendered: no
Unity 3D supported: no

This appears to be because Hyper-V has no 3D GPU acceleration capability. Hyper-V is a server-virtualization techonology that is not meant to be used for virtual desktops:

It is fact that physical servers usually don't come with powerful video adapter cards. Consequently, virtualization technologies limit virtual desktops to run only simple 2-D user-interface's applications. (source)

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Lack of 3D Accelerated Graphics in guest operating systems. Hyper-v client does not give the option to add virtual accelerated graphics card for guest OSes.

That is not what Hyper-V was designed to do. If you want improved video performance, run over RDP from the host. Hyper-V is not a replacement for VMware Player! (source)

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Hyper-V was being developed solely for server virtualization and therefore is mainly for developers or IT admins looking to test out multiple environments. (source)