Warning: Unable to open /dev/fd0 read-write (Read-only file system).  /dev/fd0 has been opened read-only.

That's a very annoying error, it's simply because Centos for some reason thinks it's wise to load the "floppy" kernel module, who has a floppy drive?  I haven't seen or used a floppy for over 12 years!

It's more than just annoying, if you probe the drives attached to your system, eg. with grub or partprobe, it keeps trying to locate a floppy dirve that doesn't exist and literally takes a few minutes to let you complete the task of grub or partprobe or related commands.

The solution, remove the "floppy" kernel module

rmmod floppy

That takes effect right away,now grub will load right away and partprobe will take a few seconds at most.

You'll also want to prevent it from loading again in the future at boot time:

For Centos/RHEL

echo "alias floppy off" >> /etc/modprobe.conf

For Debian based Distros

echo "blacklist floppy" >> /etc/modprobe.d/blacklist

The command above tells the kernel not to load the "floppy" module ever again by adding "blacklist floppy" to the blacklist list.