I use serial over lan console on intel S1200V3RPL server board. It worked nicely, but filesystem got corrupted and I had to reinstall. I've setup serial console the same way,but there is no input in grub2. Input works in BIOS and centos console after boot, but not in group. I can't select other option or interrupt the boot process. After boot I can login and everything works fine.
# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_TERMINAL_OUTPUT="serial console"
# I tried with and without following line
#GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8 quiet"
GRUB_DISABLE_RECOVERY="true"
The only difference is that I installed previous CentOS via EFI and now is legacy boot.