Enable Serial Console on CentOS/RHEL 7

Edit “/etc/sysconfig/grub”
Add to end of GRUB_CMD_LINELINUX,“console=ttyS0” Replace ttyS0 with your serial port.
Mine looks like this:

GRUB_TIMEOUT=5
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=centos/root rd.lvm.lv=centos/swap crashkernel=auto rhgb quiet console=ttyS0"
GRUB_DISABLE_RECOVERY="true"

Run the following commands as root: Again replace ttyS0 with your serial port

stty -F /dev/ttyS0 speed 9600
grub2-mkconfig -o /boot/grub2/grub.cfg
systemctl start getty@ttyS0