Make sure that your /boot partition and your / partition actually are not mounted in ro mode and if you are operating from a live system then you can't change that but if it is a barebone system then you could change it.
mount and post output of the command
or better run
mount | grep -i boot and check do you have
ro flag which mean that your /boot partition is mounted in ReadOnly mode.
If its not a live system then you could run
mount -o remount,rw /boot
if you get answer like
cannot remount /boot read-write, is write-protected that mean that you are trying to mount ro volume as rw like the partition on CD/DVD or the iso image that was dd into the usb drive.