Hi all,

I'm managing more and more of my daemons with daemontools. This is
currently happening on my sysvinit-initted Wheezy, but I think I'll do
it forever. By the way, anything good I say about daemontools goes
even more so for Bruce Gunter's daemontools-encore.

I could have managed my daemons with sysvinit, using the respawn, and a
lot of people ask me "what's the point of the extra software
(daemontools) when it's already doable from your init system?"

Here's why:

* Daemontools has a rich set of tools to start, stop, and restart your
daemons.
* Daemontools has built-in logging that captures everything from the
daemon's stdout (stderr too if you want).
* Daemontools' svstat command gives you the daemon's PID: No guessing,
no .pid files, no parsing ps ax.
* Daemontools is ultra-reliable.
* Daemontools is dead bang simple, constructed purely from Unix
constructs. It's completely understandable.
* Daemontools can be made to run at the end of a boot, thereby removing
complexity from the init itself.
* If you can devise a test to show that a required service is running
correctly, you can implement service dependencies reliably with
Daemontools.
* Daemontools can take any old shellscript or Python/Perl/Ruby/Lua
program you write and turn it into an always starts, reliably managed
daemon, with logging. Daemontools is the easy way to deploy DIY
daemons.
* A deep understanding of daemontools, which is not hard to achieve,
gives you a big head start on understanding actual init programs.
* Daemontools gives you much better ways to declare that daemons run or
don't run than lame, number-in-comments symlinks to five function
init scripts.
* Daemontools init scripts are pretty much all the same, are short and
easy to understand. Contrast this to sysvinit, systemd, OpenRC or
Upstart.

The following is my daemontools run script for ntpd. Note that it
enforces a dependency that the network be up before it starts:

==================================================
#!/bin/sh

######## DON'T START ntpd UNTIL THE NETWORK'S UP #######
pingaddr=8.8.8.8
#pingaddr=8.8.8.86 # for testing unpingable IP address
echo "Starting Litts ntpd daemon"
echo "Litts ntpd daemon checking network"
if ! ping -q -c1 $pingaddr > /dev/null; then
echo failed ping test on $pingaddr
sleep 3
echo "Bailing til next time"
exit 1
fi

####### RUN THE DAEMON #######
echo ping test succeeded, starting ntpd
exec 2>&1
echo About to start ntpd
exec /usr/sbin/ntpd -d -s

==================================================

For the guy who has memorized all of systemd's init keywords, this is a
little bit more complicated than the equivalent systemd unit file. Foor
the guy who hasn't memorized systemd's unit file keywords, this is much
easier and more intuitive. Anyone with a bit of Unix knowledge and the
understanding that a daemontools run script that terminates gets
restarted by supervise in 1 to 5 seconds instantly understands what
this script is doing, and can write it from his/her knowledge.

In my opinion, no matter what init system you're running, daemontools
or daemontools-encore is a great addition to make your system more
understandable and maintainable.

SteveT

Steve Litt                *  http://www.troubleshooters.com/
Troubleshooting Training  *  Human Performance