I ran into this issue after updating with Yum, on the next reboot, the system wouldn’t boot properly. In my case, the error I received was
Kernel panic – not synching:
VFS: Unable to mount root fs on unknown-block(0,0)
Picture of the full error below:
In my case, I’m running CentOS 6.7 in a virtual machine running on Oracle VirtualBox.
You should be able to get around the error pretty easily, just reboot the computer, and when you see the “Press any key to enter the menu” pictured below, press a key.
You should be presented with a list of the kernels you have installed, pictured below, select the previous one, and press enter.
After doing that I was able to boot into CentOS.
I did a little digging, and found this bug report, which matched my error, the only difference I can see is that the kernel version was different.
The first solution I ran across was to run “yum reinstall kernel”, which is what I did, and the issue was resolved. Evidently in some cases the kernel doesn’t fully install, and in some cases fails transaction checks.
If the reinstall doesn’t work for you, keep reading the comments, there’s several other solutions, hopefully one of them will help you out. Feel free to let me know what worked for you.