Centos7 serial console enabled by grub /etc/default/grub, "grub-mkconfig -o /boot/grub/grub.cfg"

centos7-grub-console.sh

#!/bin/bash
if [ "$(id -u)" != "0" ]; then
   echo "This script must be run as root" 1>&2
   exit 1
fi
cat << EOF > /etc/default/grub
# grub-mkconfig -o /boot/grub/grub.cfg
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=false
GRUB_TERMINAL="serial console"
GRUB_SERIAL_COMMAND="serial --speed=115200"
GRUB_CMDLINE_LINUX="rd.lvm.lv=centos/root rd.lvm.lv=centos/swap console=ttyS0,115200n8"
GRUB_DISABLE_RECOVERY="false"
EOF
grub2-mkconfig -o /boot/grub2/grub.cfg
reboot