makes /dev/ttyAMA0 usable on a new raspbian image by freeing it from logging kernel output

free-ttyAMA0.sh

#!/bin/bash

# free-ttyAMA0 script written by mdk
# http://www.amescon.com

# this script configures the raspbian image to not use the ttyAMA0 port for debugging purposes and makes it useable in userland

function configure_ttyAMA0_fix_cmdlinetxt() {

  local file="/boot/cmdline.txt"
  local file_backup="${file}.bak"

  # we need to remove all references of ttyAMA0 from /boot/cmdline.txt
  echo -n "checking ${file}..."

  # count the number of lines that contain a reference to /dev/ttyAMA0
  local count=`grep ${file} -e ttyAMA0 -c`

  if [[ "${count}" == "0" ]]; then
    echo "OK"
    return 0
  else
    echo "update required"

    # create a backup
    echo "backing up orig. file to ${file_backup}"
    cp ${file} ${file_backup}

    # stip all sequences that contain ttyAMA0 
    echo "updating file ${file}"
    sed -i 's/[^\ ]*ttyAMA0[^\ ]*//g' /boot/cmdline.txt
    return 1
  fi
}

function configure_ttyAMA0_fix_etc_inittab() {

  local file="/etc/inittab"
  local file_backup="${file}.bak"

  # we need to comment all lines that contain a reference to ttyAMA0
  echo -n "checking ${file}..."
  local count=`grep ${file} -e ttyAMA0 -c`

  if [[ "${count}" == "0" ]]; then
    echo "OK"
    return 0
  else
    echo "update required"

    # create a backup
    echo "backing up orig. file to ${file_backup}"
    cp ${file} ${file_backup}

    # strip all lines that contain ttyAMA0
    echo "updating file ${file}"
    sed -i '/ttyAMA0/d'  /etc/inittab

    return 1
  fi
}

# configures the raspberry pi to not use the /dev/ttyAMA0 for startup logging
function configure_ttyAMA0() {

  local reboot_required=0

  # we need to remove all references of ttyAMA0 from /boot/cmdline.txt and /etc/inittab so that the ttyAMA0 device becomes usable

  configure_ttyAMA0_fix_cmdlinetxt;
  if [[ ${?} -eq 1 ]]; then
    reboot_required=1
  fi

  configure_ttyAMA0_fix_etc_inittab;
  if [[ $? -eq 1 ]]; then
    reboot_required=1
  fi

  # inform the use that a reboot is required
  if [ $reboot_required == 1 ]; then
    echo "startup files patched -> reboot required to use /dev/ttyAMA0 port"
  fi
}

function main() {
    # check if we're running as root
  if [[ $EUID -ne 0 ]]; then
    echo "This script must be run as root. Try 'sudo ./free-ttyAMA0.sh'."
  else
    configure_ttyAMA0;
  fi
}

main $*; # entrypoint