Monthly Archives: July 2010

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]

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_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_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'

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

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.

| 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.


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How to find AS Number from an IP

Yesterday there was a slight problem on the office network. IP blocks for upstream B was passed from upstream A. Once the problem is finished, it’s fun to see record ASN from the internet provider company here: (7713 is the U.S. from Telkom)

I’m curios who’s Google peering with? Finally a little Googling found this link, from IP to ASN Finding ASN from IP Address, turned out quite easily.

First we search first one ip from Google. We use the command ‘host’ It would appear many ip, I Choose, then we use whois command:

whois -h -v

The result is as below

Warning: RIPE flags Used with a traditional server.
AS   |IP            | BGP Prefix     | CC   | Registry | Allocated  | U.S. Name
15169| | | U.S. | ARIN     | 2004-11-10 | GOOGLE - Google Inc..

Left column is Google’s ASN. We enter into his looking glass so it looks like:

Please see BGP peering and statistics from Google.

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