CentOS 7: GRUB2 and Linux with serial console

Change /etc/default/grub as below.

• Change GRUB terminal to console and ttyS0. This will provide one GRUB to a monitor display and serial console.
• Change linux kernel console to tty1 and ttyS0. ttyS0 will be managed by login prompt and tty1 will be managed by display manager like gdm.

$ diff -uprN /etc/default/grub{.org,}
--- /etc/default/grub.org       2016-06-06 18:15:52.523805194 +0900
+++ /etc/default/grub   2016-06-07 02:14:47.402552066 +0900
@@ -2,6 +2,8 @@ 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="rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet"
+GRUB_TERMINAL="console serial"
+GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
+GRUB_CMDLINE_LINUX="rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb"
+GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=ttyS0,115200"
 GRUB_DISABLE_RECOVERY="true"

Update /boot/grub/grub.cfg with grub2-mkconfig.

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-327.18.2.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.18.2.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-327.10.1.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.10.1.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-d3468c0a2b594d38be0918b5ae2a5ced
Found initrd image: /boot/initramfs-0-rescue-d3468c0a2b594d38be0918b5ae2a5ced.img
done

Reboot CentOS 7.

$ sudo reboot

GRUB to monitor display is as below.

GRUB to serial console is as below.

This article used "sudo virsh console <vmname>" for connecting serial console.

tty1 is managed by display manager.

If pressing Ctrl + Alt + F2, tty2 will be managed by login prompt.

Login prompt to serial console is as below.