virbr0: starting userspace STP failed, starting kernel STP
ADDRCONF(NETDEV_UP): eth0: link is not ready
e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: None
0000:00:19.0: eth0: 10/100 speed: disabling TSO
ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

In the beginning, I thought it is related to network or libvirtd. But I did not solve the problem by turning off libvirtd. I did not change anything in my last boot. But I updated Fedora packages using Software Update. However, I did not pay attention what I updated. By searching on web, I found some people talked about this issue after upgrading video drivers. I felt it may be the same reason.

My video card is Nvidia. I used nvidia linux driver (NVIDIA-Linux-x86-190.42-pkg1.run) downloaded from nvidia web site. To give it a try, I decided to reinstall it. So I boot at runlevel 3, and run the driver installer NVIDIA-Linux-x86-190.42-pkg1.run again in text mode. It rebuilt the driver and reset xorg.conf. Then, the problem was fixed.

After that, I found that there are actually a lot of errors in /var/log/Xorg.?.log such as

NVIDIA: Failed to load the NVIDIA kernel module. Please check
your system's kernel log for additional error messages.

Also, /var/log/messages log has error message as follows.

WARNING: GdmLocalDisplayFactory: maximum number of X display failures
reached: check X server log for errors
init:prefdm main process terminated with status 1

So this weird boot error is really caused by video driver. The errors related to virbr0 were just coincident errors that showed up after X failed to start. I checked my logs. Such errors have been there for every boot. I just did not see them. Now I turn off libvirtd service.

FYI, to boot into runlevel 3 in this hanging case. Select the linux image entry to boot in GRUB, press ‘e’. In next screen, move to the kernel line, press ‘e’. In my case, it ends up with ‘rhgb quiet’, which is redhat graphic boot. Delete ‘rhgb, quite’, replace it with ‘3′. Then press ‘b’. It will boot to runlevel 3 without starting those daemons or X window. Just log in as root and reinstall the video driver. If runlevel 3 does not work, try single user mode, i.e. replace ‘rhgb quite’ with ’single’.