CentOS 7: GRUB2 and Linux with serial console

Another method:

1.add the following line to the boot grub command line

console,console=tty0,115200n8

2.using the grubby command.

CentOS 7: GRUB2 and Linux with serial console

1/etc/default/grub

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"

2grub2-mkconfig

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

https://www.hiroom2.com/2016/06/07/centos-7-grub2-and-linux-with-serial-console/