My deepest apologies .

To understand what happened, here’s a quick lowdown on how my setup works:

I’m self hosting this blog as well as my mail on a converted EasyGate that I got as a beta tester. The machine is connected onto my internet router (a Trio 3D antique) and then onto the internet. My ISP provides a temporary IP address, and as such, I need to use a dynamic DNS record to be able to keep things updated.

Now, the Trio 3D (as with most of it’s features) has a half assed (excuse my French)  DynDNS system built in. I say half assed because it doesn’t accept any provider except the historic DynDNS and because it quite often forgets to update. Last week it completely stopped updating, and as an added bonus, I couldn’t get back into DynDNS to do things manually.

As a work around, I set up OVH (who are my registrar) to route my DNSes manually until I got a permanent fix. That worked until the IP changed Tuesday or Wednesday.

Now things are sorted out. I’m using OVH’s own DynDNS servers (much simpler) and am using a home built client to avoid all the dependancies other clients bought in.

The client is written in bash and depends on bash, sed and wget to work. It’s best used in a cron job, but can also be run on interface specific events if need be.

It uses a web based IP fetcher to work out your IP adresse, and if it’s changed since you last run the script, it updates your DynDNS records for you.

Without further ado, here’s the code:

#/bin/bash

USERNAME='myusername'
PASSWORD='mypassword'
HOSTS=('first_url.test.com' 'second_url.test.com')
SERVER="www.ovh.com"

#
#
#

CURRENT_IP=`wget -O - 'http://checkip.dyndns.org/' 2>/dev/null | sed -e 's/.*Address: \([^<]*\).*/\1/'` if [ -f /tmp/my_ip ]; then 	OLD_IP=`cat /tmp/my_ip`; fi # # Don't update unless ip has changed # if [ "x"$CURRENT_IP == "x"$OLD_IP ]; then 	exit; fi; echo "IP changed from " $OLD_IP " to " $CURRENT_IP echo "Saving new IP" echo $CURRENT_IP > /tmp/my_ip

for HOST in ${HOSTS[@]};
do
	echo "Updating " $HOST " to " $CURRENT_IP
	wget -O - "http://${USERNAME}:${PASSWORD}@${SERVER}/nic/update?system=dyndns&hostname=${HOST}&myip=${CURRENT_IP}&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG" 2>/dev/null
	echo ""
done

Et voila, I hope this helps someone out there

Note: For the rest of this post:

• A square is the un-devidable unit containing 1 number
• A section is a 3×3 grid of squares
• A column is a 10 square vertical strip
• A row is a 10 square horizontal strip
• A board is the 9×9 sudoku board

There a few simple rules that go into solving these puzzles. Namely :

• What are the possible values for this square (based on row, column and section)
• What are the possible places for this number (in this section)

The two questions aren’t identical, since a numbers position can be influenced by the positions of numbers in other columns or rows that share the section.

The first question comes down to :

1. Take the ensemble of possible numbers
2. Remove all that are already in the current row
3. Remove all that are already in the current column
4. Remove all that are already in the current section
5. if there is only one left, put it in the square
6. lather
7. rinse
8. repeat

The second question comes down to:

For each number not entered in each section

1. Check for number in the rows that pass through this section, eliminate the squares that belong to them if found
2. Check for number in the columns that pass through this section, eliminate the squares that belong to them if found
3. if only one square is left, put the number in it
4. …
5. profit

OK, mabey that one’s a bit vague, I’ll try to make it clearer with a drawing

Example of a row and column problem

In the above image, concentrate on the bottom middle section. If you look, you’ll notice that there are 4s in the top 2 rows of this section, we can conclude that our 4 must be on the bottom row. We also notice that there is a 4 in the left most column of this section, which only leaves the bottom middle square as a possibility for this 4.

By combining the 2 rules stated above, we should be able to solve any sudoku puzzle.

Any how, that’s all for now. Proof by code will be comeing in an update.