Erase/wipe free space using Mac OS X

When deleting a file, most operating systems just delete the reference to this file, not its actual content. For illustration, that’s like removing a chapter from a book’s table of contents without actually removing (and shredding) the according pages in the book.

So, in order to really (securely) delete a file on a hard disk, there are basically two methods (simplified; from a technical point of view it’s both the same):

  • Overwrite the file content (i.e. its clusters) with random data
  • Delete the file as usual, empty the trash and overwrite the whole free space on the according hard disk with random data

For the second method, here’s how to do it using Mac OS X:

  1. Delete the file(s) and empty the trash
  2. Find out the device name of the according hard disk by opening a new ‘Terminal’ window and executing the “df” command. For example, for a RAID 1 disk, the path of the disk might be something like “/dev/disk2”
  3. In the opened ‘Terminal’ window, execute:
    diskutil secureErase freespace 1 /dev/disk2
    where “1” stands for “single-pass random-fill erase” and “/dev/disk2” is the disk device  (adjust this to match your disk). When prompted, enter the admin’s credentials.

Note that overwriting free space like this takes quite some time depending on the amount of free space there is and how many passes you need (e.g. use “2” for a US DoD 7-pass secure erase or “3” for a Gutmann 35-pass secure erase). For more information about diskutil and its options, see “man diskutils”.

Kimai – Open Source Time Tracking Tool

So far, I’ve always used “good old” spreadsheets for time tracking on projects. Custom ones I pimped up with some nifty formulae, but still just spreadsheets. Advantage: I can easily adjust them to any special needs anytime – be it the inclusion or exclusion of specific work or just a customization of the sheet’s design or layout. The price for this flexibility is the generally higher effort to track the time “manually” rather than using a specialized time tracking tool – which makes time tracking a tedious task.

Of course I’ve evaluated many proprietary and open source time tracking tools over the years, but so far, none of them managed to fully convince me.

Today, I’ve just stumbled over Kimai – an open source, web-based time tracking tool written in PHP. And so far, Kimai looks promising. Installation is dead easy – just make sure you’ve compiled PDO support into PHP (Gentooers: enable the PDO flag for dev-lang/php and remerge php), else the nice web-based installation wizard will abort without printing any error message.

Once you’ve logged in, you’ll be presented a very clean, intuitive GUI where you can setup customers, projects and tasks. On the top-right there’s a big push-button to start/stop/pause the time tracking.

During my quick evaluation, I haven’t found the functionality yet to export the timesheets, but as far as I know, such functionality will be provided by extensions that can be installed. Let’s see. [Addition 20091009: There’s a stats extension quick-hack for Kimai 0.8.x that can be used to list and print selected reports. To use it, simply download it, extract it in the extensions folder and navigate to {Kimai install folder}/extensions/stats/]

Here’s a screenshot of Kimai

Kimai Screenshot
Kimai Screenshot

With the currently still very limited feature-set, Kimai doesn’t compete with full-grown project management solutions (I’ve recently seen a quick demo of a very sophisticated and cool, Django-based project management solution I’m not allowed to tell any details about yet). But it looks like a promising start. I hope the Kimai project will gain momentum, grow and mature as there’s definitely a need for open source time tracking tools – particularly web-based ones.

P.S. I haven’t had the time yet to audit Kimai’s source code, but if the orderly, clean GUI is any indication, it can’t be too bad.

Django custom model field for an unsigned BIGINT data type

Web 2.0 social media platforms tend to think “big”. They hence often use big integers (8 bytes / 64 bits long instead of just 4 bytes / 32 bits like a normal integer) for user IDs (or sometimes message IDs) to be prepared for even the most extreme potential future growth of their user base. Usually, these big integers are unsigned, allowing for up to 18’446’744’073’709’551’615 UIDs to be stored (which is probably enough to register the inhabitants of quite a few other blue planets too ;).

Facebook, with currently more than 300 million active users, also uses  a 64 bit unsigned integer for storing user IDs and expects Facebook applications to be able to handle this. Of course, 300 M user IDs would still easily fit into a 32 bit unsigned integer, but Facebook already goes beyond the 32 bit limit by issuing 15 digit UIDs like 100’000’xxx’xxx’xxx to registered test users (which allows Facebook to better distinguish between test accounts and real accounts).

Now if you happen to use Django to build your Facebook application, this fact needs special attention as Django doesn’t support 64 bit integer field types for its ORM models by default. As a Django developer, you could thus resort to using a CharField for storing Facebook UIDs (which would be odd) or, better, define a custom model field you can use in your models instead of IntegerField. Fortunately, Django offers an elegant way to define custom model fields. You can write your custom PositiveBigIntegerField by simply subclassing (extending, inheriting from) models.PositiveIntegerField:

So, in your add the following code:

from django.db import models
from django.db.models.fields import PositiveIntegerField

class PositiveBigIntegerField(PositiveIntegerField):
    """Represents MySQL's unsigned BIGINT data type (works with MySQL only!)"""
    empty_strings_allowed = False

    def get_internal_type(self):
        return "PositiveBigIntegerField"

    def db_type(self):
        # This is how MySQL defines 64 bit unsigned integer data types
        return "bigint UNSIGNED"

class Mytest(models.Model):
    """Just a test model"""

    huge_id = PositiveBigIntegerField()

    def __unicode__(self):
        return u'id: %s, huge_id: %s' % (, self.huge_id)

(NB: The “Mytest” class is just for testing the PositiveIntegerField definition, it’s not part of the PositiveIntegerField definition.)

Note that this solution only works for MySQL as a database backend (as MySQL supports the “bigint UNSIGNED” data type for columns which isn’t defined in the SQL standard).

For testing, define a “Mytest” model as shown above and execute “python syncdb” to create a new myapp_mytest table with an unsigned bigint(20) column named huge_id. Register this new model “Mytest” in, restart runserver and you’ll be able to enter 64 bit integer values through Django’s admin application.

The only minor “issue” is that Django admin’s CSS class (.vIntegerField) used for HTML form input fields representing integer values defines the width as “5em” which is a bit too narrow to display the entire 64 bit integer. This can be adjusted however (e.g. by writing your own ModelForm and telling ModelAdmin to use that, see the Django admin documentation and the Widget.attrs documentation).

P.S. Note that for Django to be able to access and use a “bigint UNSIGNED” data type, you don’t necessarily need to define a PositiveBigIntegerField and adjust your models. Instead, you could simply adjust the column type in MySQL accordingly as a quick-fix. If you use syncdb (like most Django devs) and want it to create your tables and columns correctly however, defining a custom model type as described is the way to go and strongly recommended for consistency and QA.

Thunderbird Add-on: S/MIME Security for Multiple Identities

I’ve just found and installed the following add-on for Mozilla Thunderbird:

S/MIME Security for Multiple Identities

It allows you to use a different S/MIME certificate for each of the different identities (i.e. “e-mail address aliases” or “profile aliases”) you defined in your Thunderbird profile.

It’s currently still marked as an experimental add-on and I’ve noticed a minor glitch in v0.3.0 when using it (see my add-on review), but this might also be related to the fact that I also use the Virtual Identity add-on (another nice add-on which allows you to use an arbitrary sender address for sending messages).

The “S/MIME Security for Multiple Identities” add-on is very convenient if you have multiple e-mail accounts and want to use S/MIME message signing and/or encryption with all of them.

Bonus hint: You can get your own, personal S/MIME certificates for free at Thawte (for e-Mail only) or StartCom/StartSSL (also offers free class 1 SSL/TLS certificates for FTP servers, web servers etc. -> the latter don’t “work” with Internet Explorer, however).

Google Chrome from a business and “techie” view

If Google will really deliver what it promises with its new Chrome browser plans (Google blog) (personally, I have no doubts about this), the line between web applications and standalone applications will further blur and hereby enable a better, seamless user experience and probably a whole new class of powerful applications.

Some thoughts:

  • From a technical point of view, Google’s Chrome will be the WebOS others have been dreaming about for a long time already. It basically offers memory management, process management, markup renderers, a GUI and a VM with a JIT compiler (V8).
  • It will finally unify the ideas behind the WebOS, “The network is the computer”, cloud computing, SaaSRIA and virtualization.
  • Actually, it’s astonishing it took so long for someone to come up with something like this. The concepts as such are not new at all, but the combination of all these different concepts is what makes the thing cool. It’s typical for a good idea that, once you’ve heard of it, you almost can’t imagine living without it anymore, as it seems all so natural.
  • Detachable tabs on top: Not a new idea either. For example, I remember that the Fluxbox window manager actually offered the same feature back in 2001/2002 (or even earlier) already. I remember it as I used it myself too (and I liked it a lot, despite of its “suboptimal” scalability), as illustrated in these animations:
    Fluxbox Window Grouping Feature (2002) 1/2 (small animated GIF screenshot)
    Fluxbox Window Grouping Feature (2002) 2/2 (large animated GIF screenshot)  

    I guess there were other window managers and GUIs that had the same features even before fluxbox had them.

  • With this move, Google will be gradually taking control and power away from traditional Desktop OS manufacturers such as Microsoft and Apple. Being open source, Chrome and its components like V8 will be the “Linux of the web” and thus a big threat particularly to Microsoft that still generates most of its revenue with Windows and standalone applications like Office.
  • The ongoing process, that (desktop) operating systems are becoming commodities more and more, will further be accelerated. Will there be an “unsacred” alliance between Apple and Microsoft to fight these tendencies or will they shift their businesses further into the “web” application (SaaS), content (music, videos, TV, e-books, multimedia etc.) and lifestyle (design, hardware, ethics) spaces?
  • Of course that’s in the best interest of Google (as their business is data/content and webapps/SaaS). I wouldn’t call this move an evil move, but it’s definitely not a friendly move in the eyes of the competition.
  • From a “techie” point of view, this move will enable many interesting applications in the future. As the framework will be open source, the dev community will potentially be as vital and dynamic as in other high-profile OSS projects (like Mozilla, Linux)
  • What about the Mozilla, Safari, IE, Opera camps? They will have to adapt themselves to the concept and try to top it. IE (and perhaps also Safari) might try to take the “embrace and extend” route.
  • With the birth of the WebOS, there will probably be a need of an open, standardized webapp GUI toolkit and webapp GUI guidelines soon (and there’s a big potential for conflicts here). Who will provide these? What will be the roles of the current big players? Also, standardized, open specs for user authentication and user data exchange will be required – here, there’s already some progress with OpenID, OAuth etc.
  • I like that Google communicates its plans using an easy-to-follow cartoon and that they give credit to individual internal and external contributors and players (though I assume there were much more people involved in the process than those mentioned)
  • The thing that disappoints me a bit is that when talking about V8, they only talk about targeting JavaScript. I’d prefer a more generic approach providing a VM and JIT for various languages (similarly to a CLI VM – why not re-use/extend Mono, for example?). Maybe that’s what V8 actually provides and they just don’t emphasize it at this point in order to not confuse or upset end-users, devs, big players etc..
  • Taking a look at the big picture, it seems that there’s a very pragmatic driver behind this whole development: It’s the laziness of us end-users (just as a fact, not meant in a negative sense – being “lazy” is usually quite rational). Or in other words: The information takes the line of the least resistance. And so far, that line for the “Network OS” happens to be the web, i.e. basically HTTP, despite of its known shortcomings.

[UPDATE 20080902: Corrected a typo. And here’s a statement regarding the Google Chrome news by John Lilly, CEO of Mozilla Corp.]

Jingproject, and Logitech G9 Laser Mouse SetPoint 5.0

I’ve just installed the free (as in ‘free beer’) Jingproject client by that allows to capture screenshots or screen videos and store or upload and share them (e.g. on It’s amazing, how easy and convenient it is to use – good job! There are clients for both Windows and Mac OS X (which will likely be important for me very soon as I intend to buy a new MacBook Pro with LED backlit display and a Penryn Core 2 Duo processor). The only thing missing is a Linux client (but we’re used to that, aren’t we? ;). Jingproject is provided by TechSmith, the creators of the well-known (and also great) SnagIt screen capture application.

Here’s an example of a screencast I just recorded (no sound, though):

Logitech G9 Laser Mouse SetPoint 5.0 German

It shows the great variety of configuration options you have for customizing your Logitech G9 Laser Mouse using SetPoint 5.0. The Logitech G9 Laser Mouse is Logitech’s latest “gamer” mouse and the best and most accurate mouse I ever used. I bought it though I’m not much of a “gamer” actually, but the form factor, features and its high quality convinced me. It’s quite a small mouse compared to other mice, but that’s intentional as you move it with your fingers rather than with your wrist or arm. This makes it a very user friendly (and particularly gamer friendly) pointing device as you’re much quicker in pointing and clicking while using less energy. The small form factor however might be a problem for you if you have really big hands (check it out in the next hardware store before you buy!).

Further, it’s a mouse with a cord, so you don’t need to worry about batteries, lag or interferences. So in short, I highly recommend the Logitech G9 Laser Mouse. For me, the only minuses are its rather high price and the fact that there is no SetPoint for Mac OS X (let’s hope Logitech will port it soon).

9 out of 10 points from me.

How to “reset” a Mac OS X installation

Here’s how to “reset” an installed Mac OS X and virtually return to a “virgin” state with a welcome screen prompting the user to setup and customize his Mac OS X installation:

0. To reset a Mac OS X v10.7 Lion installation to factory default, check Mark’s comment @ Apple forum (basically, deleting users before booting into single user mode seems to do the trick). For Mac OS X v10.6 Snow Leopard and older, follow the procedure below.

1. Press Command-S during startup to get into single user mode
2. Check the filesystem:
# /sbin/fsck -fy
3. Mount the root partition as writable:
# /sbin/mount -uw /
4. Remove the hidden .AppleSetupDone file:
# rm /var/db/.AppleSetupDone
5. a) For Mac OS X 10.5 ‘Leopard’ and newer, do:
# launchctl load /System/Library/LaunchDaemons/
Repeat for every user previously defined on the machine (replace {username} with the real user name):
# dscl . -delete /Users/{username}
# dscl . -delete /Groups/admin GroupMembership {username}

5. b) For older versions of Mac OS X, do:
# rm -rf /var/db/netinfo/local.nidb
6. Remove the home directories of users. For every user do (replace {username} with the real user name):
# rm -rf /Users/{username}
7. If applicable, remove already created files in root’s home directory, e.g.
# rm /root/.bash_history
8. Shutdown (or reboot to verify the procedure worked):
# shutdown -h now
# reboot

That’s it! :)

[Update 20081106]: Thanks to Macs R We for the update 5 a) regarding Mac OS X Leopard! See the comments below for more information.

[Update 20090429]: Added “dscl . -delete /Groups/admin GroupMembership {username}” to 5b) as suggested by rello (see rello’s comment below)

[Update 20110731]: Some updates about resetting Mac OS X v10.7 Lion (unverified) and a clarification that rebooting at the end isn’t strictly necessary (just to verify the procedure worked). Thanks to David, Adrien and Adam for the hints.