dnf system-upgrade fails with key verification

[Joe Zeff]

On 12/18/2015 04:01 PM, Sam Varshavchik wrote:
>
>> On Fri, Nov 6, 2015 at 6:30 AM, Sam Varshavchik
>> <<URL:mailto:mrsam at courier-mta.com>mrsam at courier-mta.com> wrote:
>>
>>    One upgrade to F23 succeeded. The second server fails, repeatedly with
>>    "dnf system-upgrade --releasever 23 download" resulting in:

I'm having trouble getting my desktop to go from F20 to F21; among other 
things, I tried the above command (with 21 instead of 23) and got this:

No such command: system-upgrade. Please use /bin/dnf --help