"The root file system (named rootfs in our sample error
message) is the most basic component of Linux. A root file system
contains everything needed to support a full Linux system. It
contains all the applications, configurations, devices, data, and
more. Without the root file system, your Linux system cannot run.
"You may have experienced the cannot mount rootfs error
(followed by your Linux host getting a kernel panic) after you
reboot your system. This will most likely happen after you have
attached some storage volumes from external storage. Or, it can
also happen when you have finished copying files and need a reboot
to finish installation.
"If this happens, your system will not restart. It could take
time to troubleshoot this problem and fix it. This set of tips
should help you solve the problem and save time.
"Another culprit could be the fact that your Linux kernel needs
to mount the root file system, but it can't find the target device.
In other words, your root file system doesn't show up where it is
supposed to be. For example, you install your Linux root file
system on disk /dev/sda, but your system can't mount it during
reboot. There are two possible reasons for this:"