Category Archives: Linux

Bitcoin Mining with Amazon EC2

My curiosity got the better of me and I decided to start playing with Bitcoins, which inevitably led to mining and then using Amazon’s High Performance Computing EC2 instances to do the brunt of the work.

It’s actually very easy to get up and running. Once you’ve found a mining pool — e.g. Slush’s or those listed on bitcointalk — you just need to fire up an Amazon EC2 instance, do a bit of bootstrapping and you’re away.

Assuming you’ve an Amazon Web Services account, browse to to the EC2 instances dashboard and click “Launch instance”. From here you’ll need to follow the “Quick launch wizard”, reuse or create a private/public key pair, select “More Amazon Machine Images” and use the Amazon Machine Instance “starcluster-base-centos-5.4-x86_64-ebs-hvm-gpu-rc2 (ami-12b6477b)”. Make sure before completing the wizard you select the type “cg1.4xlarge”.

According to htop and free -m this is an EC2 VM with 8 cores, 21GB RAM and 2 Tesla GPUs. Easy and super fun.

Install dependencies
Once connected, there will be a few dependencies that you need to install. This EC2 instance uses CentOS and thus yum for its package (software) management.

  1. Install git: yum install git
  2. Install pyserial: pip-2.6 install pyserial

Clone the bitcoin mining tools
Now you’ll need to get hold of a couple of tools.

First up, clone poclbm, the python-2.6 mining toolset that utilises your GPU for the number crunching:

git clone

You can start running your mining against the GPUs by just running python26 -d0 http://$USERNAME:$PASS@hostname:port for the first Tesla GPU and -d1 for the second. It’s best to run those in a screen session in case you disconnect.

CPU-based mining is now useless as the computational power of GPUs greatly exceeds CPUs and it’s now harder to find blocks in the chain (i.e. successfully complete the bitcoin “proof”). Most if not all mining software now has CPU features disabled. It’s a shame as 8 cores are just sitting there doing nothing!

Automatically lock your Linux machine via bluetooth

I had a requirement to lock my laptop at work automatically without having to touch it. The way devised by a friend was to enable the screensaver and its locking mechanism every time my phone’s bluetooth was out of range i.e. could not be seen via hcitool scan. It works *really well*! Now my laptop locks whenever I leave the room.

Update: It seems this was popular with, so I’ve uploaded the script to github and added unlocking support!

Here’s the code:

DEVICE=the bluetooth MAC id
DEV_NAME="The actual device's alias/name"
INTERVAL=5 # in seconds
# Start xscreensaver if it's not already running
pgrep xscreensaver
if [ $? -eq 1 ]; then
echo "Starting xscreensaver..."
xscreensaver &
# Assumes you've already paired and trusted the device
while [ 1 ]; do
opt=`hcitool name $DEVICE`
echo $opt
if [ "$opt" = "$DEV_NAME" ]; then
echo "Device found. Not locking"
echo "Can't find device $DEVICE ($DEV_NAME); locking!"
xscreensaver-command -lock

Holiday Hack: reading Java class files

I spent a week by the pool in Egypt with my girlfriend, relaxing and…hacking. The lack of WiFi meant I had to rely on instinct and intellect to get me through my pet project and it proved a worthy exercise in problem solving and perseverance…

I had the crazy idea of practicing my C programing skills by reading the binary .class file format and…doing something with it. A friend even suggesting writing my own Java Virtual Machine, which I’m probably going to do at some point.

Anyhow, a week by the pool meant no WiFi, lots of food and drink, sunburn and…boredom. I set it upon myself to rely purely on the documentation I had to hand — at first just a cached Wikipedia page, later on the JVM specification — to read .class files and practice C.

It turns out this basic task proved to be a useful exercise not only in practicing C but in perseverance and relying on one’s intuition and experience to solve a problem, not just on “googling it” and Stackoverflow.

Lesson #1: having the source makes things easier

Though I’ve learned this many times before in other languages, having the source to hand means you can truly debug an issue.

I happened to be using uthash.h for a hash table as part of my data structures. The mistake I’d made was define my id type as a uint16_t — i.e. a 2-byte unsigned integer type — and then use the HASH_ADD_INT and HASH_FIND_INT convenience macros for manipulating/searching the hash table. Of course an int is 4-bytes on my Debian x86 laptop, so when the macro expanded to something along the lines of HASH_FIND(hh, table, id, sizeof(int), ptr); I was never finding items because the generated memcmp call was comparing the wrong amount of bytes. A rookie error, but a lesson nonetheless.

Lesson #2: don’t quit

Building on lesson #1, I was reminded that I am only limited by time, my own stamina/patience and ability to think around a problem. My limited experience with C and the advanced nature of uthash.h‘s source code meant it was daunting trying to debug and understand what it was doing and ultimately where I was going wrong. Alas, by the end of the debugging exercise I was much the wiser as to the workings of C and its true power. Reading the source code of others is always a useful task and had I quit when seeing the wall of #defines I’d have not better understood macros, C or the inner-workings of data types in C. The lesson? Keep chugging away – even when it’s frustrating you and you think you’re lost it can pay wonders to take 5 minute swim in the pool and a coffee to re-tackle a bug.

Lesson #3: DVCS is really useful

The only time I had WiFi was when we ventured up to the dedicated area near reception. Our room and the majority of facilities were nowhere near it, which meant we’d have to dedicate half an hour to trekking up to reception, hoping the connection’s working (Egypt’s infrastructure isn’t what we’re used to here in the west!) and frantically downloading what I can whilst the bandwidth isn’t saturated by Facebook pokes.

The point, though, is that I had versioning control on all the time. I didn’t have to commit to a remote server to save my small changes, improvements or fixes, I had it right where I needed it: on my hard-drive. This meant I could push to the Github repository irregularly but still have the power of versioning whenever I needed it: in this case in the form of Git.

Lesson #4: the UNIX mentality a.k.a. “do one thing and do it well”

I often get into the habit of concentrating on one programming task and sticking to it. Though I also stray from the task — by hyper-focusing for a bit and changing several things at once, ultimately confusing myself — one is almost always better off just following the UNIX mantra of doing one thing and doing it well: in my case implementing and committing the parsing code in one step and then the utilisation of that feature in the next.

Lesson #5: stop the features and tidy the code

It doesn’t always have to be a frantic race to the finish line for implementing all the features. In my process of learning and trial and error I wrote some crappy code. Once I’d felt I had a handle on what I was working on and ensured my understanding of the structure of the .class files, I spent time removing bits I hated, simplifying the complex parts of the codebase and satisfying my pedantic nature. The added benefit of this is that you stop the head-wind for how you’re implementing features which when the break for refactoring is over can mean you change your approach for a better solution and thus better code.

Lesson #6: cut the WiFi

Seriously: stop relying on Google so much and solve it yourself. Your skills, knowledge and ego will thank you.

My code’s over on Github if you’re interested.

Private Window in Firefox Nightly

One of things I disliked about using Firefox was the lack of “Private Window”. Whenever you wanted a private session it would reuse the current window. This is contrary to how Chrome has always done it.

Now, in Firefix Nightly (version 20 onwards), you get a private window instead of replacing the tabs. This is a neat little feature that lets you keep your current tabs open and browse privately in the new window. Anonymity online just got a little easier!

Server Backup with Spider Oak

I’m a SpiderOak fan. It’s secure, easy and well documented. Some really good traits. Their support is fantastic too.

After using it on my Laptop, I thought I’d start using it for my Debian server’s backup. It makes sense to use something that bundles encryption and zero-knowledge to satisfy offsite backup.

The same client you would use on your Linux desktop can be used in headless or batch modes. Combined with the --backup command, you can target your essential backup areas quickly and easy.

Assuming you have signed up (you get 3GBs free with this referral link), all you need to do is follow these easy steps.

Step 1 – Get SpiderOak on your sever

Extract it to a place of your choosing and cd there (for argument’s sake, we’ll call this extraction directory $SO_HOME).

Step 2 – Copy the shared libraries
SpiderOak’s client will expect shared libraries to be available on your system. These are bundled in the .tar.gz you’ve downloaded. Copy these to your /usr/lib/ to make life easy.

cp $SO_HOME/usr/lib/SpiderOak /usr/lib/ -R

Step 3 – Initialise SpiderOak
You need to give SpiderOak a username and password and then let it add the server as a new device. You can do this by executing the following command and completing the prompts:
SpiderOak --setup=-

Step 4 – test the client works
Running a simple $SO_HOME/usr/bin/SpiderOak --help should show no errors and present you with the help message.

Step 5 – run a backup
Now all you’ll have to do is execute SpiderOak with a backup target and let it run!

SpiderOak --batchmode --backup=/home


Raspberry Pi and the Asus USB-N10 WiFi Dongle

If you have an RPi and fancy WiFi then an Asus USB N-10 will do. You’ll need to manually set it up. To save anyone else the pain, the steps to get the dongle up and running on Debian are:
wget -O
cp r8712u*.zip / && cd /&& unzip r8712u*.zip
modprobe r8712u

From here on you can configure it for your network as normal.

Happy RPi!

Update: thanks to Ben for emailing me and pointing out the lack of -O for the wget line which made the remaining commands fail due to the download being saved as 7ZYhZ! So much for ninja-edits to shorten the original URL!

Convert LaTeX to any output format easily

I use LaTeX to take notes, record TODO lists, the shopping and everything in between.

Oftentimes, I’ll need to copy my notes to somewhere: a wiki, this blog, or to put in an email. It’s at this point I need to quickly convert to my target format.

So, to satisfy the above, I wrote a wrapper script that takes a file name and corresponding target format for output (according to Pandoc):

if [ $# -lt 2 ]; then
echo "Please provide a filename and output format compatible with pandoc"
exit 1
pandoc -f latex -t $2 $1

Very simple. Like I said, take a file name and the pandoc output format and then pass it all to pandoc to convert the LaTeX original to a format of my choosing. Very handy!

IPTables Firewall for your Server

Don’t write your own. Why? ’cause you’ll mess it up and end up in a false sense of security.

Some Norwegian dude called Vegar told me of the Debian package arno-iptables-firewall. It’s an iptables-based firewall that can be administered in your favourite text editor or more conveniently by dpkg!

So, remove that crappy iptables script that you wrote to “protect” your public-facing server and go do this:

apt-get install fail2ban arno-iptables-firewall

Linux + svn + ssh+ Samba/NTFS: Operation Not Permitted!

My fancy-dancy and super-awesome SheevaPlug has certainly settled in at home.

It exposes my media from my NAS so I can access it anywhere; runs transmission-daemon headless for all the ISO downloading of open source software I do; runs subversion/svn for my source code versioning needs; cleans the cat when it runs in with…OK, no. Honestly: it’s simply brilliant.

The latter function — subversion — was suffering from a teething problem or two. I run it via ssh login, so I configured openssh-server to match a group and force running svnserve as follows:

Match Group svn
ForceCommand /usr/bin/svnserve -t -r /mnt/code/scm/svn/repo/

which allows me to login using ssh users and be super-secure over-the-wire. Great.

I then mounted my NAS share (still on the SheevaPlug) that holds the (yet to be created) svn repo. using the following line in /etc/fstab:

// /mnt/code smbfs username=alex,password=moo,uid=1002,gid=1002 0 0

all good.

I then create a repository and try to commit some code, but am presented with:

Transmitting file data .svn: Commit failed (details follow):
svn: Can't chmod '/mnt/code/scm/svn/repo/atc/db/tempfile.8.tmp': Operation not permitted


Turns out the uid option in the fstab line was referring to a non-existing user. So I corrected it and added umask=000 to the fstab line and it was all back up-and-running.


Off to code more bugs.

SheevaPlug and Locales

So, I got an awesome SheevaPlug from NewIT; it’s a Linux plug computer the size of a laptop adapter that uses around 5W of power. It’s perfect for an always-on home server.

After getting it installed and setup at home, I had the following locale-related issues when running apt-get and so-on;

locale: Cannot set LC_CTYPE to default locale: No such file or directory

which was spamming my shell far too often.

The simple fix was to apt-get install locales and then run dpkg-reconfigure locales and install those that are relevant to your system; as I’m in the UK and the only user I just installed en_GB.UTF-8.

Now I’ve got no more spam!