Tag Archives: grub

How to setup login prompt and grub via serial console

In my Office, I use a relatively small computer devices. I setup those boxes as router, located in network panel room together with switch and cable closet. There’s no monitor or keyboard there. So when there’s any error, I need an quick solutions to see what happened while boot.

I tried this with Ubuntu 10.04. This tutorial is not compatible with Ubuntu below 10.04.

First we set the getty, so we can log-in through serial console.

$ sudo vi /etc/init/ttyS0.conf
# ttyS0 - getty
#
# This service maintains a getty on ttyS0 from the point the system is
# started until it is shut down again.

start on stopped rc RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn
exec /sbin/getty -L 38400 ttyS0 vt102

Then we setup the grub loader so it can show on serial ports too. Just adjust your grub configuration with this configuration.

$sudo vi /etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.

GRUB_DEFAULT=0
GRUB_TIMEOUT=1
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,38400n8"

# Uncomment to disable graphical terminal (grub-pc only)
GRUB_TERMINAL=serial
GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true

After editing grub configuration, we update our grub with this command:

$sudo update-grub

Before we test the grub loader with serial, we should test the getty program. Now, on client computer, we install minicom program. I’m using USB2Serial that detected on port /dev/ttyUSB0. I use 38400 baud speed. Just adjust the 38400 with other speed if you like.

Let’s install the minicom program with this command:

$sudo apt-get install minicom

After that, launch the minicom program. Set the configuration like this. Press ^ao on the minicom screen.

+-----[configuration]------+
| Filenames and paths      |
| File transfer protocols  |
| Serial port setup        |
| Modem and dialing        |
| Screen and keyboard      |
| Save setup as dfl        |
| Save setup as..          |
| Exit                     |
+--------------------------+

Choose “Serial port setup”

+-----------------------------------------------------------------------+
| A -    Serial Device      : /dev/ttyUSB0                              |
| B - Lockfile Location     : /var/lock                                 |
| C -   Callin Program      :                                           |
| D -  Callout Program      :                                           |
| E -    Bps/Par/Bits       : 38400 8N1                                 |
| F - Hardware Flow Control : No                                        |
| G - Software Flow Control : No                                        |
|                                                                       |
|    Change which setting?                                              |
+-----------------------------------------------------------------------+

After done configurating, Save it as default by choosing “Save setup as dfl”. Then Let’s try to initialized the serial by pressing ^am . If success then we have a login prompt.

Ubuntu 10.04 LTS ro-bb-fa-fb-fe ttyS0                                           

ro-bb-fa-fb-fe login:

On the login screen we know that we use serial console by “ttyS0” It’s mean we use serial 0.

Reference:
[1]https://help.ubuntu.com/community/SerialConsoleHowto
[2]http://www.vanemery.com/Linux/Serial/serial-console.html

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