To enable the serial port in order to use the KVM vmconsole to connect to a VM:
#1 Edit /etc/sysconfig/grub to add “console=ttyS0” to the GRUB_CMDLINE_LINUX variable:
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=ol_okvp/root rd.lvm.lv=ol_okvp/swap rhgb quiet console=ttyS0"
GRUB_DISABLE_RECOVERY="true"#2 Run the following command
stty -F /dev/ttyS0 speed 9600
grub2-mkconfig -o /boot/grub2/grub.cfg
systemctl start getty@ttyS0