CentOS 7: GRUB2 and Linux with serial console

Table of Contents

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”

2 grub2-mkconfig

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

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfgGenerating grub configuration file …Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.imgFound linux image: /boot/vmlinuz-3.10.0-327.18.2.el7.x86_64Found initrd image: /boot/initramfs-3.10.0-327.18.2.el7.x86_64.imgFound linux image: /boot/vmlinuz-3.10.0-327.10.1.el7.x86_64Found initrd image: /boot/initramfs-3.10.0-327.10.1.el7.x86_64.imgFound linux image: /boot/vmlinuz-0-rescue-d3468c0a2b594d38be0918b5ae2a5cedFound initrd image: /boot/initramfs-0-rescue-d3468c0a2b594d38be0918b5ae2a5ced.imgdone

Reboot CentOS 7.

$ sudo reboot

3 Execution result

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.


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