Using launchd to send an email on startup and shutdown

Question

Hello All !
I'd like to get an email whenever my Mac starts up and shuts down, since I have to leave it unattended for quite some long periods of time (and even with the help of a UPS, power goes out anyway...). My Mac runs under Mac OS X Lion.
I found some help on the Internet, mainly from this page : http://www.syntaxtechnology.com/2009/06/email-on-shutdown-and-restart/ , which applies to Linux, and hoped it could work on Mac OS X (I thought at first I could just drop a script in something like /etc/init.d/ or /etc/rc.d/rc5.d but well... we have launchd instead...).
The first method listed in the page above worked well, but sends an email only on startup (for a reminder: you add a line that starts with @reboot in your crontab, and a command that sends directly an email).
I then tried to adapt the second method to Mac OS X, and succeeded partially: I wrote a small script based on what was shown on that page (a start and stop function, start gets called when the script is started, and stop gets called based on a trap on various kill signals, with an infinite wait loop: see below). I also wrote the plist file, loaded it in launchd and rebooted my Mac several times to test everything.
I get an email on each startup (yeah!), but the shutdown mail gets sent only at the next startup. So I guess that postfix gets killed by the shutdown process *before* being able to send my shutdown email :-(
So here are my main questions, if someone can help me:
1. is there a way to precisely call a script during the shutdown process, meaning giving it a priority so it gets called before postfix dies ? (like the rc directories and the naming conventions (KnnScriptName and SnnScriptName) found on some Linux/Unix).
2. is it possible to do that with launchd ? if not, what would be the Mac OS X sanctionned way of doing this ?
Other things:
3. my shell script writing ability is kind of rusty, so maybe I made some "very bad shell writingTM": l'm not sure putting an infinite while loop with a 15 second pause in it is the best way of telling a script to do nothing. There might other things in there that would make an Unix guru jump out of his chair: please tell me :-)
This is my plist:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC “-//Apple Computer//DTD PLIST 1.0//EN” “http://www.apple.com/DTDs/PropertyList-1.0.dtd”>
<plist version=“1.0”>
<dict>
<key>Disabled</key>
<false/>
<key>Label</key><string>org.amarante.startshutemail</string>
<key>ProgramArguments</key>
<array>
<string>/Library/Scripts/startshutemail-launchd.sh</string>
<string>start</string>
</array>
<key>RunAtLoad</key><true/>
</dict>
</plist>
And this is the script that does the job:
#!/bin/bash
# PHL 20120604 startshutemail-launchd.sh
# Send an email on startup and shutdown (version for launchd)
# Based on script and explanations found here:
# http://www.syntaxtechnology.com/2009/06/email-on-shutdown-and-restart/
# Modification history
# PHL 20120604 v01 First version
# Environment variables #################################################
DEST_EMAIL="[email protected]"
SRV_NAME=Amarante
EVENT_TIME=$(date +%Y/%m/%d-%H:%M:%S)
RESTART_SUBJECT="[$SRV_NAME] $EVENT_TIME : System Startup"
RESTART_BODY="This is an automated message to notify you that $SRV_NAME started successfully at $EVENT_TIME."
SHUTDOWN_SUBJECT="[$SRV_NAME] $EVENT_TIME : System Shutdown"
SHUTDOWN_BODY="This is an automated message to notify you that $SRV_NAME is shutting down now ($EVENT_TIME)."
# Functions ##########
stop()
echo "$SHUTDOWN_BODY" | mail -s "$SHUTDOWN_SUBJECT" $DEST_EMAIL
return 0
start()
echo "$RESTART_BODY" | mail -s "$RESTART_SUBJECT" $DEST_EMAIL
return 0
# Main part #########
case $1 in
stop)
stop
start)
start
esac
# trap kill signals to send an email
trap stop HUP INT QUIT ABRT KILL ALRM TERM TSTP
# sleep until killed
while :
  do
    sleep 15
  done
Thanks for your help, and any comment :-)
Paul-Henri

Answer 1

Thanks a lot for your answer, Camelot, even if it sorts of confirm what I suspected. Pinging a machine from an external observer is a solution, but it will also report broken links problems and not only a computer shutting down, and it raises the next tier of problems, general network reliability after individual system reliability. It's something I'll have to look at for sure.
It's weird there isn't any way to access the way the shutdown process works.
One of the commenters (#14) on the page from Syntaxtechnology had a similar problem: he added a "sendmail -q" in his script to force sendmail to go to work and service the queue before shutting down, which I can try, but he also added a delay to the stop process of sendmail, which is something I'm not sure I can do on Mac OS X (and that might disappear one day with one of the OS updates).
Unless there is a way to change the launchd.plist file for postfix and add an ExitTimeOut option in it (I found this idea here : https://discussions.apple.com/message/17229690#17229690 )
Cheers,
Paul-Henri