Using Wake-on-LAN to power up a XenServer

XenServer Cluster using commodity hardware

I’m a big fan of what can achieved with commodity hardware for free or little cost using virtualization platforms such as XenServer. Sure, ‘real’ server hardware has benefits. It is optimized to excel in certain disciplines. But ordinary gray box PCs are immensely flexible and for a scientist like me who plays with hardware configurations all the time, they are great. (They also save you money if you have the space for non-rack hardware btw.)

One thing where ‘real’ server hardware shines is remote management. Ordinary PCs typically do not have that. But most of the time they have a feature called Wake-on-LAN. This allows powering them up by sending a specially crafted ‘magic’ packet over the Ethernet. Fortunately, XenServer has built-in support to send those packets within a pool of servers and the Windows GUI XenCenter makes using that feature very convenient. Continue reading

Make persistent changes to /system in Android Emulator

The Android Emulator is part of Google´s Android SDK and allows you to run a virtualized Android system within a window on your desktop. With the normal behavior write access to the system partition of that Android is prohibited. That can be changed using the adb tool:

$ ~/android-sdk-linux/platform-tools/adb remount

While this temporarily permits changes to /system until the next reboot, any changes will be gone when you close the emulator. If you want the Android Emulator to remember whatever you did to /system, place a copy of system.img in ~/.android/avd/avdname.avd/ and call it system-qemu.img:

$ cp ~/android-sdk-linux/system-images/android-21/google_apis/x86_64/system.img ~/.android/avd/avdname.avd/system-qemu.img

Note that the paths in this are examplary and depend on which Android version you wish to use and how you name you virtual device.

Fix for Time Machine backup problem “DIHLDiskImageAttach returned: 999”

For the last couple of days I’ve been plagued by a Time Machine problem for which seemingly nobody (that Google could find) had a solution:

23.01.14 09:53:44,125[13516]: Failed to attach to image: /Volumes/Data/Justus MBP13.sparsebundle, DIHLDiskImageAttach returned: 999

After quite a lot of bug searching I finally found a fix.

Continue reading

Droboshare Dashboard for Mac includes free Xtend SAN iSCSI Initiator (kind of)

Rather than not writing about it at all just some quick notes:

  • The Droboshare Dashboard software includes the Xtend SAN iSCSI Initiator.
  • If you want to use the initiator with non-Drobo iSCSI targets you will have to use the command line interface to configure the target and connect to it. The tool is called xtendsancli. This command line interface (cli) is written in Java and using RMI to talk to some backend which could open up some DIY GUI options.
  • The only limitation of the included Xtend initiator (besides the missing GUI) is that it checks if the target name begins with “”. If you can configure the server side there is no difficulty or downside in just using that name and making your iSCSI target look like a Drobo.

Disk Utility with iSCSI target

That way I was able to make the Drobo iSCSI initiator talk to a Ubuntu 13.10 ‘iscsitarget’ (thats the name of the package) on OS X Mavericks.

After Xcode-Update to 4.3 xcodebuild fails

The recent update to Xcode 4.3 marks a change in how Apple sets up developer systems. Until now all development-specific stuff (libraries, headers, Xcode itself, …) resided in /Developer. With 4.3 that directory is obsolete. The new directory is:


So if you use command line build tools like xcodebuild and see errors like this:

Error: No developer directory found at /Developer. Run /usr/bin/xcode-select to update the developer directory path.

… you might need to tell the system about the new path:

sudo /usr/bin/xcode-select -switch /Applications/

Mac OS X Lion 10.7.3 doesn’t sync Mobile Documents (SOLVED)

Before 10.7.3 the somewhat hidden iCloud Documents folder …

~/Library/Mobile Documents

… was a nice DropBox alternative to keep personal data on several Macs in sync. GoodReader on iOS also used that mechanism to synchronize files between GoodReader installations on different iOS devices and the Mac(s) of the user. The latest Mac OS X update 10.7.3 seems to have broken that feature. The folder on the Mac remains empty.

Update 14.02.2011: It looks like Apple has solved the problem. Sync is working again for me.

Update 21.02.2011: If you read the comments you’ll see the problem is not really solved. What can be said so far is that the sync problems are rather related to a bug in Mac OS X 10.7.3 than Apple wanting to keep us from using this nice DropBox-like feature. Workaround after the break… Continue reading

SSH X11-Forwarding auf VServer funktioniert nicht

Mit SSH kann man die X11-Bildschirmausgabe eines entfernt gestarteten Programms problemlos auf sein lokales Display umleiten. Dabei tunnelt und verschlüsselt SSH die übertragenen Bildinhalte und Eingaben. Beim Zugriff auf einen virtuellen Linux-Server kann das jedoch daran scheitern, dass dort das Erstellen bestimmter Socket-Typen nicht gestattet ist. Continue reading