dkms will not build for correct kernel, only running one

[Thadeu Lima de Souza Cascardo]

Whenever we try to build the dkms package for a kernel that is not running, it will fail.

# uname -r
4.20.0-0-generic
# dkms build rtl8812au/4.3.8.12175.20140902+dfsg -k 4.18.0-11-generic
Kernel preparation unnecessary for this kernel. Skipping...

Building module:
cleaning build area...
'make' all...(bad exit status: 2)
Error! Bad return status for module build on kernel: 4.18.0-11-generic (x86_64)
Consult /var/lib/dkms/rtl8812au/4.3.8.12175.20140902+dfsg/build/make.log for more information.
# head /var/lib/dkms/rtl8812au/4.3.8.12175.20140902+dfsg/build/make.log
DKMS make.log for rtl8812au-4.3.8.12175.20140902+dfsg for kernel 4.18.0-11-generic (x86_64)
Fri Nov 23 13:41:47 UTC 2018
make ARCH=x86_64 CROSS_COMPILE= -C /lib/modules/4.20.0-0-generic/build M=/var/lib/dkms/rtl8812au/4.3.8.12175.20140902+dfsg/build modules
make[1]: *** /lib/modules/4.20.0-0-generic/build: No such file or directory. Stop.
Makefile:1457: recipe for target 'modules' failed
make: *** [modules] Error 2

[Thadeu Lima de Souza Cascardo (cascardo)]

This needs two fixes. One in the Makefile, to make it accept a parameter when calling make that gives the correct version and path to be used. Could be just using KVER ?= instead of KVER :=.

The second fix is in dkms.conf to pass that parameter.

[Daniel van Vugt (vanvugt)]

Can you please attach the full file /var/lib/dkms/rtl8812au/4.3.8.12175.20140902+dfsg/build/make.log ?

[Reinhard Koehn (rekoehn)]

This sounds like a duplicate of bug 1705820, which already contains a patch with a fix.