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Date: Thu, 7 Jun 2012 21:14:11 -0400 (EDT)
From: Chris Hill <chris@monochrome.org>
To: Fbsd8 <fbsd8@a1poweruser.com>
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Cc: FreeBSD Questions <freebsd-questions@freebsd.org>
Subject: Re: find date of last boot
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On Thu, 7 Jun 2012, Fbsd8 wrote:

> dmesg command does not show date of last boot.
>
> Are there some other commands to find date of last boot?

That was fun. Google helped me with this; the crappy skillz are all 
mine.

  --- cut here ---
#!/bin/sh
#
# Find date of last boot
#
DAYS_UP=`uptime | awk '{print $3}'`
SEC_UP=`echo "${DAYS_UP} * 86400" | bc`
DATE=`date`
EPOCH_DATE=`date -j -f "%a %b %d %T %Z %Y" "${DATE}" "+%s"`
BOOT_SEC=`echo "${EPOCH_DATE} - ${SEC_UP}" | bc`
BOOT_DATE=`gawk -v duh=${BOOT_SEC} 'BEGIN{print strftime("%Y-%m-%d",duh)}'`
echo "Last boot on ${BOOT_DATE}"
  --- cut here ---

Example from this machine:
$ ./boot_date.sh
Last boot on 2010-12-26
$

Enjoy.

-- 
Chris Hill               chris@monochrome.org
**                     [ Busy Expunging </> ]