kugelfish

<- Raspberry Pi as Classroom Server and Digital Pet Encouraged by the performance of running a basic wiki engine on the new Raspberry Pi 3, we can try a more resource intensive service. OwnCloud is a popular web based file-sharing solution, similar to Google drive or Dropbox. Reports of running OwnCloud on the original Raspberry Pi have generally been discouraging for performance reasons. We continue using the same lightweight web server setup from the last tutorial. Although not really recommended, we are using sqlite instead of a server based database, primarily out of simplicity and to minimize the amount of services we need to run within the tight memory constraints of the Raspberry Pi. The basic installation of the ownCloud server is as simple as downloading the desired version and moving it to a path in the web server root directory: $ sudo wget https://download.owncloud.org/community/owncloud-8.2.3.tar.bz2 $ sudo tar xvf owncloud-8.2.3.tar.bz2 $ sudo mv owncloud /v...

With the new Raspberry Pi 3 just out and presumably much faster than the original, I wanted to try again how well it would hold up as a really small scale server for hosting web applications. Over the last few years, Raspberry Pi had mostly made its mark in the maker community as a small low-power embedded computer. Even the official Raspbian image is now available in a "lite" version, optimized for headless servers. It now has out of the box IPv6 as well as the avahi daemon enabled, making the changes described in this earlier tutorial no longer necessary. Installing a Raspberry Pi server is now easier than ever: copy image to a flash card , plug into any network (including direct tethering) and connect to it under its default name : ssh pi@raspberrypi.local . The hostname can easily be changed when running s udo raspi-config along with other settings (extend filesystem, change GPU memory allocation etc.). Back to the original education use-case, a Raspberry Pi is ...

When looking for a platform to learn Linux and Python programming, Raspberry Pi would be on top of most peoples mind today. The success of the Raspberry Pi brand has created an active and novice friendly community, where help and advice is easy to find. However, just using a Raspberry Pi as a low-end desktop computer is surprisingly complex and setting up a room for a programming workshop requires a few crates of additional equipment (keyboards, mice, monitors etc.). It seems that the strength of Raspberry Pi platform is in low-cost, low-power embedded and physical computing applications, like robotics, control and measurements systems. Despite the enthusiasm for Raspberry Pi, it may not be the best choice for organizing a programming class/workshop, specially if the school already has plenty of PC hardware available. The Lernstick is a Debian live-image based distribution which can be booted off a DVD or USB stick. It is being developed by the School for Teacher Education...

One of the most conspicuously absent standard interfaces on the Raspberry Pi is built-in support for 802.11 WiFi wireless LAN networking. A low-cost, low-power way to remedy this is for example the Edimax EW-781Un USB WiFi adapter which plugs easily into one of the USB ports on the Raspberry Pi and is supported out of the box by the current Raspbian distribution. It seems to be very popular for use with Raspberry Pi and is available for about $10 in many places where Raspberry Pi are sold. WiFi Client Connecting to an existing WiFi network is trivial, once we know the SSID and access password for the network we are trying to connect to. After plugging in the adapter, it should be automatically recognized by the linux kernel - the output of lsusb should contain an entry like this: Bus 001 Device 004: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS] In order to connect to a typical home wifi network, we only need to add the f...

If your Internet access is down and you are not watching, is it really down? For most people the answer is most likely - who cares! Since our Internet connection had recently been down a few times, when I did notice it and I was getting curious about how frequently this was happening. Besides, it might be interesting to get a long term record on the stability and "quality" of our ISP and maybe even compare it with the results from users of competing ISPs. What does it mean for Internet access to be working? Is it enough to check that the link between our home router and the ISPs access router is up and working (a DOCSIS cable plant in my case). Or should we include end-end application layer scenarios like the ability to get my email or my files from some place "in the cloud"? But what exactly represents the "the cloud" or "the Internet"? In reality they are massively large distributed systems at a global scale, consisting of millions o...

Bluetooth is a relatively low-powered short-range wireless technology, which can among others provide a networking connection between devices and is widely supported in portable devices like laptops and mobile phones.  Low power and ubiquitous support should in principle make Bluetooth an ideal solution for tethering. Nothing beats the simplicity, robustness and performance of a simple Ethernet cable for a tethered network connection - as long as both devices support it. For the upcoming Raspberry Pi model A or certain ultra-portable devices without Ethernet port, Bluetooth might be serious option. Wi-fi would probably be the most obvious choice of wireless networking technology. However using the ad-hoc wi-fi hotspot option for tethering on my Android phone turns it into a pocket heater and drains the battery in no time  - while not so much when using Bluetooth tethering instead. Besides wi-fi networking is very well documented, while there is very little documentation...

 After some initial experiments  with using a Raspberry Pi as a home server, I wanted to try out some configurations  useful to the intended purpose of the Raspberry Pi: promote computer technology literacy among students. At least some of the initial feedback from trying to deploy Raspberry Pis in a classroom settings seems to indicate that getting the necessary hardware to operate the Pis is non-obvious. Setting up a room full of Pi based workstations requires HDMI or composite connected TVs or monitors, USB mice and keyboards, micro-USB power supplies and ethernet connectivity routed to each workstation. The cost and logistical complexity of doing that seems to defeat the initial low-cost advantage of the Raspberry Pi. Furthermore, many schools might already have fully equipped computer facilities with incompatible equipment (e.g. SVGA monitors, standard on any not-so-new PC), which could be used, but just not "messed with" for low-level programming and syst...

With the Raspberry Pi board now up and running on the network, I needed something "reasonable" for it to do. Maybe an homage to the famous Trojan room coffe pot camera - 20 years later, at a fraction of the cost? Hosting a download mirror for Raspberry Pi boot images on a Raspberry Pi? A probe for network performance monitoring? A twitter robot which recites The Iliad 140 characters at a time? Finally, I settled for a robot which reposted a summary and link to all my public Google+ postings to my otherwise unused Twitter account . In addition to Python 2.7 already included in the boot image, the following ingredients were used: tweepy (Twitter api library, recommended by Twitter ) google-api-python-client (Google+ api library, provided by Google) daemon (small library to run python script as a daemon, easy_install daemon) In order to read public posts via the Google+ API , no authentication is required, but a developer key is needed for quota tracking, which...

Looking for low-cost linux hardware , I had come across the Raspberry Pi project a few months ago and been hopefully intrigued by its goals to promote " computer literacy " (whatever that means). Now that you can actually get them more easily, I ordered myself one from Farnell and surprisingly it arrived in a few days. I am glad to see that the popularity of the Raspberry Pi device is creating an active community, where detailed help and instructions are easily available - not an obvious thing for other niche and esoteric hardware. I was going to set it up as a network server and access it from my PowerBook via ssh, X11 and/or VNC. Getting a bootable SD card was very easy, also in part thanks to such detailed instructions , but requires access to another computer with SD-card reader and Internet access. Using a spare micro-USB cellphone-charger and an ethernet cable to connect directly to the home router was all that is needed to complete the setup. After that, it got a...

For heavy users of Google services, the gmail account has over the years evolved into a "Google account" and holds the key to an increasing amount of our online activities and presence. Judging from a random sampling of the gmail support forum or some reports in the press (E.g. this recent article from the Atlantic Magazine ) - gmail account hijacking is an increasingly widespread and serious problem. Stolen account IDs from major web-mail providers (gmail, hotmail, yahoo mail etc.) seem to be collected and used at industrial scale for spam generation and fishing for  419 style advance fee fraud  schemes like the infamous " mugged in London " scam described in the article above. The mechanics of some common threats used to steel account passwords is described in this blog post in some detail, but in short it boils down to weak passwords, password re-use and password sniffing malware. Given how prevalent malware infestations are on major OS platforms, even use...

At least since the "Y2K problem" entered the public consciousness around the turn of the last century, nobody doubts that correctly representing time in computer systems is somehow hard. While today nobody is hopefully trying to save a few bytes by representing years in 2 digits, the state of time computations in many programming environment is still over-simplistic to say the least. Having (almost) gotten caught by surprise by last years changes to civil time in Russia, this article is an attempt to understand, what it takes to handle time somewhat correctly for business related computer applications. There are 2 common uses of time in computer systems: a monotonically increasing measure representing a global reference clock of some sorts and which can be used to determine an absolute ordering of all events in the system as well as their relative duration. Representation of civil time as it is used by communities of people living in some particular place to go about t...

I am notoriously bad at memorizing. If not, I might have gone to medical school and chosen a more lucrative career than Engineering... But as the number of online services I uses increases, so does the number of account username and password combinations. I try to standardize as much as I can on the same usernames(s) but some sites make this really hard by requiring strange and unusual conventions (name must be at least 8 characters long and include at least special character and number??? Whose name looks like that?) or by dictating that the username be whatever 10 digit number their database uses as the unique key for the account record. Same drama for the passwords, except that using a standard password everywhere has the added disadvantage that once the password is compromised, the attacker would have access to all my various online service accounts - if sHe could guess those bloody convoluted usernames... ;-) Things got particularly bad for accounts, which I use very rarely and w...