I recently updated my ubuntu 16.04 to ubuntu 18.04,
but after updating, my TP Link T9UH wifi adapter doesn't work anymore.
It didn't work perfectly before (see Install rtl8814AU driver on ubuntu 16.04), but after removing and reinstalling the driver now and then, it would work again.
When I enter
sudo dkms install rtl8814au/4.3.21
Kernel preparation unnecessary for this kernel. Skipping... Building module: cleaning build area... 'make'......(bad exit status: 2) ERROR (dkms apport): binary package for rtl8814au: 4.3.21 not found Error! Bad return status for module build on kernel: 4.15.0-22-generic (x86_64) Consult /var/lib/dkms/rtl8814au/4.3.21/build/make.log for more information.
How can I get my wifi adapter working again?
When I try the solution given here: How to install an Edimax EW-7833UAC in 18.04
sudo dkms install rtl8814au/4.3.21 returns: