Doing geolocation lookups in command line
Did you know that it's possible to do your own geoip lookups from the linux command line?
You need to install the geoip-bin package in Ubuntu/Debian's APT system:
sudo apt-get install geoip-bin
Then after which, lookups can be done as simply as:
$ geoiplookup 8.8.8.8 GeoIP Country Edition: US, United States
Note that the lookups are based on the GeoLite Country database. For more detailed geoip lookups you will need to buy the better databases.
Converting IDNs in Ubuntu
With the start of Internationalized domain names (IDNs) it sparked my interest since it requires conversion to punycode in order to continue working with existing DNS systems/applications, which work with ASCII.
Taking a search through Ubuntu's APT system, to see whether any IDN related tools are available...
$ apt-cache search punycode libidn11 - GNU Libidn library, implementation of IETF IDN specifications libidn11-dev - Development files for GNU Libidn, an IDN library idn - Command line and Emacs interface to GNU Libidn libidn11-java - Java port of the GNU Libidn library, an IDN implementation libidna-punycode-perl - encodes Unicode string in Punycode
There's the idn package! Which allows encoding of IDNs in punycode in the command line...
Doing an install...
$ sudo apt-get install idn -y
And trying it out!
$ idn правительство.рф libidn 1.15 Copyright 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Simon Josefsson. GNU Libidn comes with NO WARRANTY, to the extent permitted by law. You may redistribute copies of GNU Libidn under the terms of the GNU Lesser General Public License. For more information about these matters, see the file named COPYING.LIB. xn--80aealotwbjpid2k.xn--p1ai
And resolving the domain...
$ nslookup xn--80aealotwbjpid2k.xn--p1ai Non-authoritative answer: Name: xn--80aealotwbjpid2k.xn--p1ai Address: 95.173.135.62
Note that resolving the domain directly results in rubbish!
$ nslookup правительство.рф Non-authoritative answer: Name: \208\191\209\128\208\176\208\178\208\184\209\130\208\181\208\187\209\140\209\129\209\130\208\178\208\190.\209\128\209\132 Address: 67.215.65.132
So, basically from this we understand that applications will need to use the punycode encoded version of the IDN, NOT the original IDN, when resolving. And there're tools out there already can do that for us.
Since Ubuntu has these packages, Debian would also have the corresponding packages available too.
Getting your server to send an email whenever anyone logs in
Running on a VPS like Linode give me plenty of control over what is run, and also plenty of chances to learn more about network administration (along with the heartaches). 
The code that I used was based from this forum post. This one presumes that your MTA has been setup properly. The original code was for protecting your root account (i.e. when anyone logs into your server's root account, you get the notification).
(Note: it is usually not advisable to login as root. Create a user account and give it sudoer rights instead. I'd say that's advisable even for servers where there is only one person expected to login, which is you.)
[Edit: a more powerful, updated version of this script can be found here]