Fedora 28: 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. This setting will be taken over to userland, and there will be two login prompt for tty1 and ttyS0.

$ sudo cp /etc/default/grub /etc/default/grub.orig$ C=”resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap”$ S=”serial –speed=115200 –unit=0 –word=8 –parity=no –stop=1″$ cat <<EOF | sudo tee /etc/default/grubGRUB_TIMEOUT=1GRUB_DISTRIBUTOR=”$(sed ‘s, release .*$,,g’ /etc/system-release)”GRUB_DEFAULT=savedGRUB_DISABLE_SUBMENU=trueGRUB_TERMINAL=”console serial”GRUB_CMDLINE_LINUX=”${C}”GRUB_CMDLINE_LINUX_DEFAULT=”console=tty1 console=ttyS0,115200″GRUB_SERIAL_COMMAND=”${S}”GRUB_DISABLE_RECOVERY=”true”EOF

2 grub2-mkconfig

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

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfgGenerating grub configuration file …Found linux image: /boot/vmlinuz-4.16.7-300.fc28.x86_64Found initrd image: /boot/initramfs-4.16.7-300.fc28.x86_64.imgFound linux image: /boot/vmlinuz-4.16.3-301.fc28.x86_64Found initrd image: /boot/initramfs-4.16.3-301.fc28.x86_64.imgFound linux image: /boot/vmlinuz-0-rescue-3ba892070dae45849f0ccc5e362387a9Found initrd image:/boot/initramfs-0-rescue-3ba892070dae45849f0ccc5e362387a9.imgdone

Reboot system.

$ 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.


Login prompt to monitor display is as below. tty1 is displayed with press Ctrl + Alt + F1.


Login prompt to serial console is as below.


4 Change serial console window size

The default value of serial console window size is 80×24. This will effect emacs, tmux and screen.

$ echo $COLUMNS $LINES80 24


There are several ways for changing serial console window size. I think resize command in xterm package is the easiest way.

$ sudo dnf install -y xterm$ resizeCOLUMNS=90;LINES=36;export COLUMNS LINES;


Make resize command to be run after login.

$ cat <<EOF >> ~/.bashrccase “$(tty)” in /dev/ttyS*) resize > /dev/null 2>&1;;esacEOF

“trap ‘resize > /dev/null’ DEBUG” will call resize command many times. If you need to change serial console window size after ~/.bashrc, you had better call resize command manually.

$ trap ‘resize > /dev/null’ DEBUG$ for i in $(seq 0 9); do echo $i; done # resize will be called 10 times.

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