How to invoke kernel with serial console?

Question

How do I invoke the kernel with serial console on 12.04?

In 10.04 I could just add console=ttyS0 in kernel line or install quiet console=ttyS0 on boot: line

How do I do that in 12.04?

Solution

There is nothing special in 12.04. Just follow the information from: https://help.ubuntu.com/community/SerialConsoleHowto

1) Paste the following into /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 or RUNLEVEL=[2345]
stop on runlevel [!2345]

respawn
exec /sbin/getty -L 9600 ttyS0 vt102

2) Ask upstart to start the getty

sudo start ttyS0

This will get you access to console. To get access to Linux init console, configure grub.

1) Edit /etc/default/grub to contain the following lines

GRUB_CMDLINE_LINUX="console=tty1 console=ttyS0,9600n8"
GRUB_TERMINAL=serial
GRUB_SERIAL_COMMAND="serial --speed=9600 --unit=0 --word=8 --parity=no --stop=1"

2) update grub

sudo update-grub

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I am using 9600 just because I am using a server where the BIOS is already redirected over seria using 9600. If you don't care about the BIOS settings, feel free to use a faster serial line.

Enjoy!