Convert dmesg timestamps to UTC format

dmesg_to_utc.sh

#!/bin/bash
# Translate dmesg timestamps to human readable format

# desired date format
date_format="%Y-%m-%dT%H:%M:%SZ"

# [    3.469072] EXT4-fs (xvda1): mounted filesystem with ordered data mode. Opts: (null)
# [    3.483769] dracut: Remounting /dev/disk/by-label/\x2f with -o noatime,ro
# [    3.495019] EXT4-fs (xvda1): mounted filesystem with ordered data mode. Opts: (null)
# [    3.506417] dracut: Mounted root filesystem /dev/xvda1

# run only if timestamps are enabled
if [ "Y" = "$(cat /sys/module/printk/parameters/time)" ]; then
  dmesg | sed "s/^\[[ ]*\?\([0-9.]*\)\] \(.*\)/\\1 \\2/" | while read timestamp message; do
    printf "[%s] %s\n" "$(date --date "now - $(awk '{print $1}' /proc/uptime) seconds + $timestamp seconds" +"${date_format}")" "$message"
  done
else
  echo "Timestamps are disabled (/sys/module/printk/parameters/time)"
fi