OS unbootable and show the following message:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
- At waiting to boot loader
- click any key to access the boot kernel menu
- Select previous kernel version other than the default latest installed one
- CentOS 6.4
- Kernel 2.6.32-422.214.171.124.1.el6.x86_64
Upon upgrading the kernel or installed the kernel-devel packages, the system was still running the current kernel until next system reboot. In case, the reboot schedule was long after this kernel-devel, it is not easy to remember kernel-devel was installed and as a side effect also upgraded the kernel.