Dec 282012

RAM disks are available since 1979. They offer a filesystem in RAM and therefore outperform most of all other storage systems. This can be used to do disk intensive operations in a fraction of the normally required time. This article covers Mac OS X 10.5 and later. If you STILL use earlier versions take a look at the article posted by OSXDaily.

Mac OS X includes a way to create RAM disks using the following Terminal command:

diskutil erasevolume HFS+ 'My 4GB RAM Disk' `hdiutil attach -nomount ram://8388608`

The size of the disk is based on the page size number of 512 bytes sectors. That means the size in bytes has to be divided by 512. For example to calculate the size parameter for a volume with 4GiB the following formular is used:

Be aware that the content of a RAM disk is permanently deleted as soon as it is ejected! Only use it as temporary storage!


To simplify the process I created RAMDiskCreator. It’s a freely available tool and offers a graphical user interface for the RAM disk creation. Only the size and the volume name have to be provided. In the background the same command is used as described above.

You can download RAMDiskCreator 1.4 for Mountain Lion or better here. If you are still on Lion or Snow Leopard please download RAMDiskCreator 1.2. Furthermore I will happily provide the source code on request.


  • 2014-04-26 – Version 1.4: Fixed a bug that could lead to a wrong RAM disk size (Thanks to John VanDyk for reporting)
  • 2014-04-10 – Version 1.3: The configuration is stored after a successful RAM disk creation for easier usage (Thanks to rxflyer for suggesting this feature)
  • 2013-05-24 – Version 1.2: Fixed broken free memory calculation (Thanks Dave for reporting)
  • 2012-12-28 – Version 1.0: Initial version released
Dec 212012

Mac OS X extensively uses file metadata. As this post explains there are two fallback mechanisms if a volume is not able to handle this data.

On the one hand .DS_Store files are created to store mostly Finder specific settings. On the other hand metadata like resource forks or creator types are stored in “Dot Underscore” Files. For example the metadata for the file “Demo.avb” is stored in “._Demo.avb”. Both mechanisms are great in an all Mac environment but can cause troubles in mixed setups. Luckily there are ways to at least minimize the pain.


Even Apple thought that this files are not always necessary and build in a setting to disable the creation on network drives.

defaults write DSDontWriteNetworkStores true

Furthermore the guys from BinaryAge (the creators of the epic TotalFinder) build a tool called Asepsis. It is used to redirect all .DS_Store files into a folder buried in the depth of the system. Thereby the Finder is still able to store folder specific settings but external drives aren’t effected anymore.

Dot Underscore Files…

… cause more trouble. As they eventually store application specific data there is no official way to disable them. A possible workaround is to schedule a script to delete them (every night). This is exactly what I did for Windows (Powershell script) and Unix (Bash script) operating systems. On Windows the script can be scheduled using the “Scheduled Tasks” system setting. On Mac OS X a launchd configuration should be used – it can easily be created using Lingon. Other Unix operating systems can use a cronjob!

The script recursively searches a given folder for Dot Underscore Files and deletes them. Be aware they will most likely be recreated! You can download the Windows and Unix version using this link.

Dec 062012

qt_tools is a free command line for the Quicktime infrastructure in Mac OS. As it is only a wrapper all audio and video formats supported by Quicktime can be used. This also allows the usage of products like Flip4Mac in automated workflows.

The problem is, that it is not that easy to find the needed parameters in the man page. Furthermore encoder specific settings can not always be configured using parameters. To work around this problem configuration files can be used. The following example illustrates how a specific Flip4Mac configuration can be created.

As already explained we first have to create a configuration file for the desired operation. To do that the –dodialog parameter is used to show the exporter specific configuration interface. As soon as the dialog is closed the configuration is saved to /tmp/wmv.conf.

qt_export --exporter=ASF_,TELE --savesettings=/tmp/wmv.conf --dodialog

After that it can be used to encode a file. It it important to note that Quicktime requires an existing display (as noted in the man page) and therefore can not be used in remote contexts like a webserver.

qt_export --loadsettings=/tmp/wmv.conf /path/to/your/input/video.m4v /path/to/your/export/video.wmv
Dec 052012

SAMBA the open source SMB implementation got replace in Lion with SMBX. SMBX supports SMB2 which is was first used in Windows Vista and reduces the chattiness of the protocol. Additionally Samba 3 was release under the GPLv3 licence which prevent Apple from packaging it in a commercial package.

While there are several advantages the overall stability decreased. Two examples are given below:

  1. Several multifunction printers are not able to connect to the new SMBX service to deliver scanned images as they only support SMB1. A possible workaround is to use a FTP server like PureFTPd.
  2. A race condition can occur after booting the system that prevents any user  to log in. The message “NTLM domain not configured” is logged. A possible solution is discussed here.

BUT the most frustrating part about SMBX is that there is no official documentation. Furthermore it’s not using plaintext configuration files anymore.

To track down errors it’s essential to have a good error log. To enable logging the launchd configuration file has to be modified. After identifying the problem based on the logs you have to solve it. There are two different places where the configuration is stored. The overall service configuration is stored in the plist file /Library/Preferences/ The share point configuration in turn has been moved into the Directory Service!!!!! This can be accessed using the dscl utility. After that you have to navigator into the “folder” /Local/Default/Sharepoints.

dscl localhost
> cd Local/Default/SharePoints/
> ls #this will list all you share points
> read SharepointName #lists all the configured settings

It’s awful to see a great software like Samba to be thrown out based on licensing issues.

Oct 222012

This time a client requested the ability to change the wireless network key of several dd-wrt Linksys WRT54GL routers at once.

Linksys WRT54G – CC BY-SA 3.0Wiki Commons

To simplify the process I wrote a small bash script that changes the WPA key of a given AP using only the web interface. This means no additional service (like SSH or Telnet) have to be enabled!

In the backend it uses curl to submit a specially crafted HTTP POST request to the router that applies the new key.

You can download under the WTFPL licence.

Sep 152012

Over the last few days I tried to automatically convert Avid OP-Atom MXF files to ProRes 422 HQ MOV files. At first this didn’t sound too hard but it took me several days to come up with an good solution.

So what’s the problem?

The problem is that Avid uses the so called Operational Pattern Atom. This pattern splits each audio channel and the video data into a separat MXF file. Additionally several audio and video MXF files are kept in the same folder without an easy way to match the corresponding files. After hours and hours I discovered mxfdump (based on MXFlib). This tool allows you to gather the UMID (unique material ID) and the data type (either audio or video) from a given file.

With this help I was able to find the associated media files – but the next problem arised immediately!

Another problem?

Sure! Avid uses a codec called DNxHD. My standard en/decoding tool ffmpeg is not able to handle it correctly. I was happy to discover a fork called ffmbc that is able to decode DNxHD and can encode ProRes HQ.

My solution

To create a good workflow I created a small script called MXFMuxer. It monitors a folder for incoming MXF files and builds up groups using their UMID. After that it validates them (for example if is there at least one audio and video file) and kicks in ffmbc to create a single ProRes 422 HQ MOV file.


  • monitor a folder for incoming files
  • validate them to be sure they are OP Atom and we have a video file and one or two audio tracks
  • convert them to a single ProRes mov file
  • use all the available physical cores while converting (not handled by ffmbc)
  • can be daemonized and scheduled using launchd
  • uses ffmbc and MXFlib
  • delete or move the original MXF files
  • can be easily modified to generate previews for Archiware PresSTORE

Where can I get it?

That’s the best part of it! I have release it as a supplementary utility (see the utils folder) to PresSTORE Media Converter – you can freely download it at Google Code.

But be aware: It’s not that easy to install! You have to compile at least libx264, liblame, mxflib yourself. If you need help just leave a comment!

Feb 212012

Mac OS X allows hardlinks on directorys (see stackoverlow) but this has two limitations:

  1. as all hardlinks they work only on one partition
  2. it’s not really supported

With the help of osxfuse and bindfs you can bind a directory to a different folder – like the way you would do it on every other unix based system.

PS: Here’s my patched version (only useful to me): bindfs-1.9

Feb 212012

Mac OS X 10.5 had a great feature that allowed you to use your already created groups as mailing lists. Each group had it’s own mail address ( and postfix delived each mail to all users of that group

In Snow Leopard Server this feature is not available anymore.

With the help of this scripts you can simulate Leopards group mailing abilities. It creates a postfix alias file out of your LDAP groups (Open Directory) and updates you MTA configuration automatically. You can even exclude groups and use nested groups.

Download: sl-groupmailer.tar

Feb 212012

There are great ways to backup your hole Mac OS X Server. But I have not found any script that enabled me to configure service backups the way i wanted.

With sl-backuper you can backup your server on a service based approach. Currently you can export Mail, iCal Server, AddressBook Server and MySQL

sl-backuper runs each night (or the way you configure it) and exports all enabled services to a special folder. This folder is only readable by Administrators and is managed by sl-backuper. sl-backuper keeps as many backups of each services as you want and removes outdates ones. Additionally per job logfiles are created.

Download: sl-backuper.dmg

Feb 212012

superMount uses hfs.util to mount (or at least tries to) your HFS+ partition.

As a mac tech I often have harddisks that are damaged (either physically or software-based). There are a lots of tools out there that help you recover your data – but they cost quite some money and alot of time.

Why not try a tool already included into your operating system?: superMount