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Activating the Serial Port on Linux

Introduction

It's often convenient to access a machine via the serial port. Unfortunately, we usually realize this too late. Here's how to activate it.

For usage information, please refer to the documentation on Minicom.

Configuration

Debian

Modify the following lines to ensure that the console part loads correctly during the Grub boot:

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# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.

GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,9600n8"

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

# Uncomment to disable graphical terminal (grub-pc only)
GRUB_TERMINAL=console
GRUB_SERIAL_COMMAND="serial --speed=9600 --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

# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_LINUX_RECOVERY="true"

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"

Then update Grub:

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update-grub

Uncomment the following line (/etc/inittab):

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[...]
# Example how to put a getty on a serial line (for a terminal)
#
T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100
#T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100
[...]

Verify that ttyS0 is also present (/etc/securetty):

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[...]
# UART serial ports
ttyS0
[...]

Reboot your machine! Your system will then be accessible via the serial port.

References