I have a Fedora 23 system which I have updated with the latest updates.  I rebooted the system and ran

sudo dnf upgrade --refresh

RPM Fusion for Fedora 23 - Free                 584 kB/s | 457 kB     00:00   
RPM Fusion for Fedora 23 - Nonfree - Updates    1.0 kB/s | 257  B     00:00   
RPM Fusion for Fedora 23 - Free - Updates       552  B/s | 257  B     00:00   
Adobe Systems Incorporated                      7.1 kB/s | 1.8 kB     00:00   
Fedora 23 - x86_64 - VirtualBox                 253 kB/s |  74 kB     00:00   
RPM Fusion for Fedora 23 - Nonfree              119 kB/s | 156 kB     00:01   
google-chrome                                    46 kB/s | 3.5 kB     00:00   
Dependencies resolved.
Nothing to do.
Complete!

I rebooted the system at this point and went int emergency maintenance mode.

I ran journalctl -xb, but I don't know what to look for.  One of the last entries says:

Received SIGRTMIN+21 from process 322(plymouthd)

I found bug 1254874 which refers to SIGRTMIN+21, but the bug was closed as not a bug.

Can someone tell me what I need to do to fix the system so it boots correctly?

All the partitions are mounted so I don't think it's due to filesystem corruption.

Any help is appreciated.

Paolo