By default you’re unable to set a custom resolution in Ubuntu 13.10 while running on HyperV. This is how I set it up.
Modify the following file and make sure that you include the listed modules:
Update the initramfs:
Install the linux-image-extra-virtual package:
GRUB_CMDLINE_LINUX_DEFAULT line in the GRUB file to reflect your desired screen resolution:
You can see that I changed from
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=hyperv_fb:1920x1080"
And now reboot and the changes should take effect