Why akmod fails on F22 for nvidia (and possible other uses)

[Barry Scott]

I did some investigation as to why akmod will fail to install a
the nvidia dirver when a new kernel turns up.

The problem is that dnf-makecache.service runs at the same time
as akmods.service. DNF locks the RPM data base which prevents
akmods from installing the RPM's it built.
 
Here is a extract from 346.72-2.1-for-4.0.8-300.fc22.x86_64.failed.log
 
Running transaction
RPMDB already locked by 2285
  The application with PID 2285 is: dnf
    Memory : 116 M RSS (677 MB VSZ)
    Started: Sat Jul 18 12:09:56 2015 - 06:20 ago
    State  : Sleeping
2015/07/18 12:16:16 akmods: Could not install newly built RPMs. You can
find them and the logfile 2015/07/18 12:16:16 akmods:
346.72-2.1-for-4.0.8-300.fc22.x86_64.failed.log
in /var/cache/akmods/nvidia/ Looking in the journal shows dnf-makecache
running at the time that akmods.service need RPMDB access.
 
I ended up working around the issue with:
 
	systemctl disable dnf-makecache.service
	systemctl disable dnf-makecache.timer
 
I'm not sure what the right systemd unit change will be to have a
reliable start up. How do you prevent dnf-makecache from running
until after akmods.service has run given that started off a timer?
 
At the next kernel release I'll know if this is successful.
 
Barry