“Error: Boot loader didn’t return any data” when booting up Xen guest

Error: Boot loader didn't return any data

I have come across this error two or three times before, and each time I spend hours trying to figure out how to get my virtual machine to boot.  This blog post is just to document a fix so that I can refer back to it, and hopefully it will help people out if they’re experiencing the issue as well.

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A week with the Google Glass

I had the opportunity to borrow the Google Glass from my workplace last week.

Google Glass is a wearable miniature computer mounted on a frame you wear like glasses. It has a small display that you can see through on the right eye.  Glass is still in the development process and these units aren’t the final product, so some of the issues may be solved by the time the final product ships.

First impressions

The Google Glass I had borrowed was one without prescription lenses.  Since I need to wear my own glasses, it was hard for me to get the Google Glass to fit on top of my glasses in a way where I could see the full screen. The left edge was cut off so my experience with it was affected.

The screen is also quite small, so there’s not a lot of things to see on the screen.  The main menus are just a scrollable list of words.  The two ways to interact with the Glass are by voice control, and a touch pad mounted on the right side of the frame.


Vancouver City Hall, taken from Google Glass
Vancouver City Hall, taken from Google Glass

I walked around with the Google Glass for a bit.  Took some photos and videos just to give it a try.  I didn’t have that many apps on the Glass so there wasn’t really much I could do (also one should probably be concentrated on walking in any case…).

More photos and videos taken from my walk with the Glass can be found on my Google Plus album.

In the car

I wrote an email to ICBC to get the official word on the rules about wearing Google Glass while driving, and as you may have guessed, it’s prohibited. Here’s a copy of the email I got back.

Based on information from Road Safety BC, we can inform you that the use of Google Glass while driving in BC is prohibited.

There are several sections of the Motor Vehicle Act that apply:

  • The most directly applicable section is Section 214.2 that lays out “Prohibition against use of electronic device while driving”. The “Use of Electronic Devices While Driving Regulation” prescribes “television” as an electronic device subject to the prohibition. Mobile operating systems and devices with wireless telephony, e.g. Google glass, smart watch, etc., are considered to be a variant of a “television” for purposes of the Act. They are considered as such because they fit within definitions of a television, for example, according to the Oxford English dictionary, Television is a system for converting visual images (with sound) into electrical signals, transmitting them by radio or other means, and displaying them electronically on a screen.
  • Section 144 of the Motor Vehicle Act lays out the prohibition against “careless driving” which could apply if using Google Glass while driving.
  • Sections 181 and 183 of the Motor Vehicle Act also require that drivers and cyclists exercise due care and attention when driving, so failing to do so due to distraction from using Google Glass is another way a person could violate of the rules.

So due to this I wasn’t able to try out the GPS navigation.


It’s pretty cool wearing the Google Glass. It feels like something from a sci-fi movie. But on the practical side of things there doesn’t seem to be that much useful stuff that can be done with the Glass right now as there are only a limited number of apps.  But I’m sure as time passes there will be more and more interesting apps that will make Glass a lot more useful.

More Detailed Wi-Fi Info on Mac OS X

Wi-Fi Detail Menu
Option-clicking on the Wi-Fi icon in the menu bar brings up additional information about the Wi-Fi network to which you are connected.

The option button can be used to reveal hidden options and information in various places around Mac OS.  One example of this is if you option-click the Wi-Fi icon in the menu bar, you will be presented with additional information about the network you are currently connected to, including the type of the Wi-Fi you’re using, the base station’s MAC address, the frequency channel you’re on, and the strength of the connection, among other details.  In addition, there is an additional option to open Wireless Diagnostics which might be able to help you with Wi-Fi issues (however, in my experience it doesn’t really give useful information).

Network Utility

Network Utility on the Info tab
Info tab in Network Utility

An additional tool to help debug network connections is a neat little utility called “Network Utility” that comes bundled with Mac OS X.  You can find it in the Utilities subfolder in the Applications folder, or just use Spotlight to find it.

This utility provides a friendly interface for many tools that are commonly used on the command line for network debugging, such as ping, nslookup, traceroute, whois, and finger. An interesting tool though is the last tab: Port Scan.  Yes, Mac OS comes with a port scanner bundled with it.  Obviously one would hope that the port scanner be used for diagnostic purposes and not malicious purposes.

FreeNAS and ZFS

Since I built my home server back in 2012, I’ve had a FreeNAS virtual machine running on it as the file server of my home network.  For the past two years, I’ve been using it for the simplest of tasks (serving files).  But over the past week, I’ve started looking deeper at some of the cool things FreeNAS and ZFS can do.  The descriptions of each of these are going to be brief; they can probably be expanded to a full blog post, which I may do if I have time.  However, until then, if your interest has been piqued, you will have to do some additional research on your own.

FreeNAS web interface
One of the configuration screens on the FreeNAS web interface

First, let me briefly introduce what FreeNAS is.  FreeNAS is a system based on FreeBSD that primarily provides a network-attached storage (NAS) service for your network.  It uses the ZFS file system, which as you’ll see in a bit has quite a number of interesting features.  FreeNAS comes with a web interface where you can easily configure everything.

So with that introduction out of the way, let’s get into FreeNAS and ZFS!


In English, FreeNAS supports file sharing with Windows, Mac, and *nix computers. That was a pro for me because I have all flavours of operating systems on my computers at home.

The support for AFP (Apple Filing Protocol) includes Time Machine endpoints, which is something worth discussing in its own section below.

Networked Time Machine backups

It’s easy to setup Time Machine on your Mac using an external hard drive. However, unless you actually plug the drive in, there’s no backup opportunity.  For me, sometimes I use my computer in my living room, other times in my bedroom.  Sometimes my backup drive isn’t where I am working and I’m too lazy to go get it.  There must be a better solution.

If you’re willing to spend a couple hundred dollars for an AirPort Time Capsule, it will allow you to make backups over the network, even over Wi-Fi.  I actually bought one to try, but I returned it within a week because what it did really didn’t justify the cost.

Fortunately, FreeNAS has the option of enabling Time Machine endpoint functionality on AFP shares.  Now, whenever I’m at home within Wi-Fi range, my Mac will automatically make Time Machine backups.  Hands-free backups!  Awesome!  And with multiple Time Machine targets in OS X Mountain Lion, I’m able to have a backup to the NAS as well as a backup to an external drive whenever I get that plugged in.

Time Machine
My Time Machine configuration

One note is that networked backups are somewhat more finicky. The backup target gets corrupted more often than the one on the external drive.  However, I’ve noticed using OS X Mavericks and the latest FreeNAS builds that generally it is a lot more stable than when I first configured it.  Mostly, remembering to stop any current backups before turning off the computer will reduce the chance of corruption.

For more information about this, check out the following links:

Snapshots and replication

Now let’s talk about some of the features of ZFS, which FreeNAS nicely gives us access to through the web configuration.

At some point in time you may want to ensure that your data on the NAS is backed up at a remote location (because even the most complex RAID setups won’t save you in the case of a fire or flood).  This is where snapshots and replication comes into play.

ZFS snapshots are light weight and only store changed blocks.  This means that they are fast (don’t require downtime) and don’t take up much extra space on the disk.  Then, snapshots can be sent to another host with a ZFS volume over SSH.

FreeNAS’s web interface makes setting up automatic snapshots and replication very easy.  In addition, the replication target is quite flexible because all that is required is a host that has ZFS and SSH.  That means, it’s not necessary to be locked in to using a FreeNAS system as a replication target.  In fact, using packages from ZFS on Linux, most 64-bit Linux distributions can be used as replication targets.  I went with Debian as that was the easiest to setup for my particular case.

For more information about this, check out the following links:

FreeNAS plugins

I came across the plugins last week when I was diving a bit deeper into FreeNAS.  I haven’t explored this fully yet.

FreeNAS is primarily a file server.  However, as it’s a computer that’s almost always running, it makes sense to have other services run off of it so that a separate application server isn’t necessary.  This is where plugins come in.

The list of plugins is available on the FreeNAS wiki.  There is also an article on installing the plugins.

The plugins that I’m interested in are btsync (BitTorrent Sync), owncloud, and the media plugins.  Right now, I have a separate virtual machine that serves these applications while storing the data on the NAS.  Using plugins, this extra virtual machine may not be necessary!

Final comments

If you take a look at Wikipedia article on ZFS, there are a lot of interesting features in ZFS.  It supports its own type of software RAID to protect against drive failures.  It’s possible to encrypt and compress data sets as well.  This is just scratching the surface on what ZFS can do.

ZFS is a robust, reliable, and practical file system to be used as network-attached storage.  Combined with the web interface provided by FreeNAS, this functionality is able to be unleashed for usage in diverse environments.

Are you using FreeNAS or ZFS in an interesting configuration?  Have other tips for other users?  Post your ideas in the comments!

Secure your Mac’s infrared port against random Apple Remotes

If you have a MacBook with an infrared receiver, did you know your Mac could be open to other people controlling your computer?  By default, Mac OS will recognize the signal of any Apple Remote.  Although the effect is relatively harmless (they will probably be able to randomly play some tracks on iTunes), it can range from being annoying if you were studying in the library and your friend happened to prank you, to embarrassing if you happened to be doing a presentation.

Most people do not need to allow any Apple Remote to control their computer.  Why would you want other people’s Apple Remotes to control your computer?  Here is a tutorial for securing your infrared port so that only your own Apple Remote can control your computer.

If you have an Apple Remote…

The icon showing a paired Apple Remote.
The icon showing a paired Apple Remote.

You can pair your remote with your computer by pressing and holding the Menu and Next (right) buttons for several seconds, while pointing the remote to the infrared receiver (on the MacBook Pro unibody models, the port is beside the power/sleep light on the front edge of the computer).  The pairing logo will show up in the middle of your screen when the pairing is complete.

If you don’t have an Apple Remote…

You can disable the infrared port so that nobody with a random Remote can control your computer.

  1. Open System Preferences → Security & Privacy.
  2. If the preferences are locked, you will need to click on the lock at the bottom left and enter your password.
  3. Click the Advanced… button at the bottom right.
  4. Check “Disable remote control infrared receiver.”
Security & Privacy - Advanced Options
The advanced options of the Security & Privacy system preferences panel.

Hopefully this tutorial will help you avoid annoying or embarrassing situations when people try to prank you with their own Apple Remote.

Featured image by Julien Gong Min on Flickr.