Hacking Your Portable Linux Server

If you followed my advice to set the device name and workgroup earlier, your hostname is taken care of already. The device boots in DHCP mode by default, which can be altered easily for those who want a tiny, power-conscious but rather homebound server at their disposal. I find the greatest promise of the WDMBII in its easy mobility, however, and that poses the question of how to recognize its location quickly in a new setting—nothing that a good bit of scripting cannot fix.

The first approach to this is to have the device notify you of its IP address as it boots. I personally leverage instant messaging for these sorts of system notifications and have an “automation” group in my contact list featuring several borg-looking avatars that are authorized to send me all manner of alerts when the situation warrants. The key to this script is the SendXMPP tool (see Resources), which provides the ability to send instant messages with ease from the console. SendXMPP carries a few Perl module dependencies that you need to download from the CPAN archive and build. Retrieve the tarfiles via wget, extract and follow the customary perl Makefile.PL; make; make install procedure as root—the CPAN shell does not seem to work in the strict RAM confines of the WDMBII. After building two or three modules, you will be able to include the following one-line wizardry in /etc/init.d/post_network_start.sh (line 20):

#    $SCRIPTS_PATH/mionet.sh start
     touch $POST_NETWORK_STARTED_FILE

     # Announce IP address of operation to admin
     OUT=`ifconfig | grep -A2 "eth0"`; \
         echo -e "(lander) now operational: \n$OUT" \
             | /usr/local/bin/sendxmpp -r lander-notifier \
                 -f /root/.sendxmpprc lucifred@jabber.org
fi

The script parses the current network configuration and sends it with appropriate text wrapping and an XMPP resource (-r) describing the device to one of my notification accounts. The user ID and password are retrieved from /root/.sendxmpprc (-f). Once the script is installed, the device will notify me of its IP address at every bootup in any network where DHCP is enabled and access to the Jabber server in question has not been restricted. The result message is very effective in allowing me to locate the device and possibly even troubleshoot occasional connectivity glitches:

(lander) now operational:
eth0     Link encap:Ethernet
              HWaddr 00:90:A9:15:DD:73
         inet addr:164.99.120.96
              Bcast:164.99.121.255
              Mask:255.255.254.0
         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

This approach will serve most road warriors willing to put up with connecting to IP addresses. But, power users controlling their own domains can do even better. By setting up a dynamic DNS subdomain, one can enable the device to update at boot a fully qualified domain name, valid to the Internet at large. The intricacies of DNS zone configuration are beyond the scope of this article, but the Perl script to leverage a properly configured domain remains relatively simple:

# Variables to configure the script's operation
my $hostname   = 'ooga';                     # Device hostname
my $domain     = 'dynamic.booga.org.';       # Domain name
my $nameserver = 'ns1.booga.org';            # Primary nameserver
                                             # for your zone
my $keyname    = 'md5key';                   # Name of the key
my $key        = 'se64bAsE64BASE64BasE64=='; # HMAC-MD5 TSIG key
my $interface  = 'eth0';                     # Interface whose IP
                                             # is to be published

Refer to the Resources section of this article for a reference to the Web page where the author maintains the script. This more extensive solution makes our briefcase-friendly, quick-booting mini-server a full-fledged participant in the Internet.

The most obvious workload for our portable server is file-centric: well equipped with SMB support from Samba and NFS support built in to the kernel, as well as the lighttpd Web server and the rsync client, the system is ready to shine in this space. Enterprising users have built HOWTOs describing how to expand further the array of services to FTP and even BitTorrent, but I should not forget to mention that the system has a healthy complement of essential dæmons: ntp, cron and even Apple's mDNS are at your disposal out of the box.

The built-in toolchain enables the compilation of packages natively, but cross-compilation also is a possibility for jobs requiring more RAM than the device has available. It is, however, possible to find prebuilt packages for a number of services, as the device shares the ARM core of many others, its closest cousin being the Gumstix micro-board (check the many Gumstix sites for suitable binaries before starting a large cross-compiled build).