Archives April 2009

HowTo: Fix MythTV’s Frontend not going full-screen in Ubuntu Jaunty.

The next version of Ubuntu is here – 9.04 aka “Jaunty Jackalope”. Along with a wealth of new features comes a wealth of new minor bugs to fix. Not enough to be show-stoppers, but enough to annoy the heck out of you, and here’s a doozy.

If, like most people, you have Compiz enabled and you start the MythTV Frontend, you will notice that rather than go full-screen, Myth will start as a window, essentially, even if your settings within Myth say to go full-screen.

In a single-screen scenario, the MythTV window will start just underneath the upper Gnome panel and the lower Gnome panel will sit over the top of the Myth window, obscuring part of the display. Proof that it’s a window can be found by holding down the ALT key and then dragging the MythTV display around with your mouse.

If you’re like me and use two displays with Myth being run on the second screen, you will see a gap at the top of the screen that is the same height as the upper Gnome panel and you will see your wallpaper showing through there, as shown in the illustration below.

Ugly titlebar gaps

Here’s how to fix this problem.

EDIT June 2010: This problem still plagues Ubuntu 9.10 and 10.04, and this fix will work for those releases as well.

The simplest fix is to disable Compiz altogether and MythTV will suddenly go full-screen, but that’s not really a solution – you want to keep your eye-candy! So follow the next few steps instead:

  1. Go to System->Preferences->CompizConfig Settings Manager. If you do not have this option in your Preferences, then you need to add it. Quickly jump into a terminal and type in at the $ prompt:$ sudo apt-get install compizconfig-settings-manager…and hit Enter. Once installed, go back into the Preferences menu and bring it up.
  2. Scroll down until you get to the “Utility” section and then click on “Workarounds”. It should alredy be selected as enabled, but if not, also make sure the checkbox next to it is enabled too.
Compiz Workarounds Plugin
  1. The window changes to show you the Workaround options. The very first option is “Legacy Fullscreen Support”. This is unchecked by default. Click on the checkbox so that it IS checked, and then click on the Back button, then close the window.
Compiz Legacy Fullscreen support
  1. Quit the MythTV Frontend if you had it open already and then restart it. You will now find that the gap has disappeared, and that the MythTV display is now appearing full-screen properly instead of just being a window.
  2. Pat yourself on the back.

Happy viewing! Smilie: :)

Please note: This workaround is just that – a workaround. One minor problem that arises with it is that you may get occasional screen “flashing” or a flash of the background wallpaper appearing when a DBus message is displayed, or if you scroll a window or terminal on the same or other screen in a multi-screen setup. This does not occur often, however, and so may not bother you at all! The bug has been reported, and no doubt will be fixed in due course. When it is fixed, this workaround should be reversed.

HowTo: Reclaim reserved disk space on non-system drives taken by the Ext3 filesystem.

I made a rather alarming discovery today, quite by accident.

Like most people, I use an external hard-drive to backup data to, or to shift things around if I’m low on space on my PC’s internal drive. Well, today that external drive reported that it was full. Damn.

So I fire up Ubuntu’s Disk Usage Analyser, aka Boabab, to find out what’s consuming the most space. I use a 1TB external drive and it’s formatted total is about 916GB, which is about right, however Boabab reported that the total consumption of data on the drive only added up to about 860GB – wtf? Even Nautilus’s Volume Properties window was reporting that the drive still had 50GB-odd free, so why is the system telling me it’s full?

I use Ext3 on my drives and, being a journalled filesystem, some space on the drive is reserved to record these journals among other functions which is expected, but 50GB worth? I did some research and found out that the Ext3 filesystem reserves 5% of disk space by default for itself! In this day and age of large drives, that’s a huge chunk of lost space!!

Thankfully there is a way to tell Linux not to reserve so much space. Read on…

  1. First up, unmount your drive. You can do that by either right-clicking on the drive icon on the desktop and choosing “Unmount volume” or by clicking on the Eject icon next to it in the Places pane of any Nautilus window.
  2. Next, open up a terminal and type the following:

    $ sudo fdisk -l

    This will list all your available drives. Identify which one is your external drive and take note of the device name, eg: in my case my external drive appears as /dev/sdb with one partition on it, sdb1.
  3. Now type in the following:

    $ sudo tune2fs -m 1 /dev/sdb1

    This will modify the filesystem on that drive, on that one partition, to only reserve 1% instead of the default 5%.
  4. Now re-mount your drive by clicking on its name in the Places pane in a Naultilus window.
  5. The Nautilus Device Properties window will still show the same free space as before, because it reports the true total free space, but any Nautilus File Manager window only reports usable free space, which in the case of my external drive had now freed up a very sizable 37GB!
  6. Lather, rinse, repeat on any other non-system drive partitions on the same or different drive you want to reclaim space back for.

You learn something new everyday. Smilie: :)

HowTo: Prevent other sites hot-linking to images on your own Apache website on your Ubuntu Server.

Personal websites, blog pages, etc. You can spend a lot of time, effort, and sometimes money setting them up and maintaining them. The pay-off is when you see lots of people visit your site, take an interest and even provide feedback. The annoyance comes when you notice in your logs that a select handful of images are being downloaded a helluva lot more than every other image on your server, and further scruitiny shows that it wasn’t even your own website requesting them – it was someone elses.

So you go and have a look at the referring site. Worse-case scenario was that they had blatantly plagerised your site – copied everything as their own. Not so bad is that someone has found an interesting pic on your site and linked directly to it on another site to tell people about it, but not necessarily atrributed your site to it.

Hot-linking files between sites is considered bad nettiqette if you have not got permission from the site owner. Image copyright issues aside, it is preferred that if you have an interest in an image that you download a copy and host it yourself, or that you link to the hosting website itself so that people can see proper attribution.

This has already happened to me a few times with the most notable being some Korean blogger’s site blatantly copying word for word one of my articles, but he decided to leave all the images in it hot-linking to my server. I couldn’t believe it, but I knew it wouldn’t be long before someone did that. I dropped a politely worded, but firm, message on his blog where everyone could see it, and he has since deleted the plagerised entry from his blog.

So, how do we go about preventing your Apache web server from serving up images to invalid referrers? Read on…

This HowTo was written with Ubuntu Server 8.04.2 Hardy Heron in mind since most server users would be likely still be using the LTS release for public-facing servers, however these instructions should apply to any version Ubuntu Server until Apache make any radical changes to how their http daemon configuration works. I will also assume that you already have a web site up and running. We are just going to add to its configuration here.

To prevent hot-linking is a simple matter of checking what file is being requested from your server. We can do this by checking for certain file extensions such as .jpg, .png etc. We then have a rule to ensure that such requests are coming from your website, eg: instead of someone else’s site. If the rule matches your site, the requested image is served, otherwise an alternate image is served instead.

What’s the alternate image? Simply it’s a small-sized image that provides a small message to the hot-linker to tell them that you shouldn’t be hot-linking images to your site. The small size ensures that  it is transferred quickly and doesn’t chew up much bandwidth on your connection.

Here is the one I use for

Anti hot-linking message

Can be anything you want, really. Just make it polite or funny. This one was created in The GIMP and saved out with extremely high compression to make it as small as possible without compromising image quality so much that the image is unreadable with compression artifacts. From memory, I think it was 40% quality instead of the usual 80-85% you’d save most photos with.

Create your own message in a picture and save it out to somewhere on your website with some arbitrary name. I use “noop.jpe” in reference to “no operation” and the file extension is deliberately mangled for reasons you’ll see later. I also save it in the root of my website so I don’t have a long convoluted URL to refer to it with. Eg: if your website resides in /var/www on your server, then save this image to /var/www/noop.jpe accordingly.

Now we need to tell Apache to use this image in place of serving other hot-linked images.

If you use SSH to manage your server:

  1. SSH into your web server as normal.

    $ ssh
  2. Change directory to the /etc/apache2/sites-available directory.

    $ cd /etc/apache2/sites-available
  3. Bring up your website’s configuration file into your favourite text editor. In this case, the config file is called “” and i’ll use the Nano editor to edit it.

    $ sudo nano
  4. Add the following lines to the end of the configuration file, but before the </Virtualhost> line:

    # Prevent hotlinking of images from foreign sites and redirect to a new image.
    RewriteEngine on
    RewriteCond %{HTTP_REFERER} !^http://www\.acmecorp\.com/.*$ [NC]
    RewriteCond %{HTTP_REFERER} !^$
    RewriteCond %{HTTP_REFERER} ^http://.*$
    RewriteRule .*\.(jpe?g|gif|bmp|png)$ [NC,R,L]

    (Change to what is relevant to your site, of course)

    What the above does in order is turn on URL re-writing, then check to see if the referrer does NOT start with the string “” (the NC means “not case-sensitive”, so it matches on things like WWW.ACMECORP.COM and as well), the referrer is also checked to ensure that is is not blank, and that the referrer had a “http://” string at the start.

    If all these rules match true, then one last rule is applied before re-writing the URL – if the URL string requested ends with .jpg, .jpeg (the e? part tests for whether the “e” exists or not so it matches on jpg or jpeg), .gif, .bmp or .png, then re-write the requested URL as “” with no case-sensitivity on the match (“NC”Smilie: ;), the “R” parameter will tell your visitor’s browser that they were redirected (you don’t have to do this – you may want the visitor to think this is actually what they requested), and the “L” parameter will stop processing of anymore re-write rules here, ie: this is the “Last” re-write rule.
  5. Save your work and exit the editor by pressing CTRL + X and then “Y” to save.
  6. We’re almost there! Now that we have the rules written, we now need to enable the URL re-writing module of Apache called “mod_rewrite”. Without it, the changes we did to the configuration will cause Apache to error out on startup. Ubuntu has the re-write module pre-compiled in, so all we have to do is enable it. To do this, simply enter the command:

    $ sudo a2enmod rewrite
  7. Now we are ready to rock and/or roll. Restart your Apache server with:

    $ sudo /etc/init.d/apache2 restart
  8. Ensure that no errors were reported during startup and then test hot-linking to your site. NOTE: If you already tested hot-linking from another site and can still see your images, more than likely they have been served up from your web browser’s cache – clear your cache and try again.
  9. Pat yourself on the back. You’re done.

If you use WEBMIN to manage your server:

This HowTo section assumes you’re using Webmin version 1.430 or later.

  1. Open your web browser and get into your Webmin interface as normal.
  2. Click on “Servers” in the left pane. A list of server daemons will be listed underneath.
  3. Click on the “Apache Webserver” daemon. The right pane will then show you your available web sites.
  4. Click on the “Global Configuration” tab at the top-left of the Virtual Server list. The pane will change to show global Apache options.
  5. Click on the “Configure Apache Modules” icon. The pane will change to show the currently available and enabled Apache modules.
  6. Locate “rewrite” in the list and ensure a checkbox is enabled against it. Do not change anything else.
  7. Scroll to the bottom of the list and click on the “Enable selected modules” button. You will be returned to the Virtual Server list page.
  8. Now click on the icon relevant to your virtual server, eg: “”. The window changes to show the options available for that virtual server.
  9. Click on the “Edit Directives” icon. You will be presented with a text editor showing the configuration file.
  10. At the end of the file, paste the following in:

    # Prevent hotlinking of images from foreign sites and redirect to a new image.
    RewriteEngine on
    RewriteCond %{HTTP_REFERER} !^http://www\.acmecorp\.com/.*$ [NC]
    RewriteCond %{HTTP_REFERER} !^$
    RewriteCond %{HTTP_REFERER} ^http://.*$
    RewriteRule .*\.(jpe?g|gif|bmp|png)$ [NC,R,L]

    (Change to what is relevant to your site, of course.)

    See the description of what all this does in the SSH instructions.
  11. Click on the Save button.
  12. Click on “Apply changes” at the top-right of the Webmin window.
  13. Test hot-linking images on a foreign site to your own.  NOTE: If you already tested hot-linking from another site and can still see your images, more than likely they have been served up from your web browser’s cache – clear your cache and try again.
  14. Pat yourself on the back. You’re done.


Now, you’ll rember that I called the anti hot-linking image “noop.jpe” instead of “noop.jpg”. Want to know why? Well, it’s the only image on your entire server that you DON’T want to be matched on for anti hot-linking. Despite the URL being re-written to deliver that image to the visitor’s web browser, that very image is still subject to the re-write rules as well. If you were to tell your Apache server to re-write the URL for every .jpg image on your server, then the “noop.jpe” file served as “noop.jpg” instead would be re-written to “noop.jpg” again and again and again in an infinite loop, hanging your server and not actually serving it to the visitor! Thankfully Apache today is a little smarter and will detect and abort an infinite loop, but it still serves nothing to the visitor. This is why we called the file “noop.jpe” so that it does NOT match the “.jpg” or “.jpeg” rules. We could fix this by simply adding another rule that says “don’t re-write if noop.jpg is being requested” but I’m just lazy. Smilie: ;) You want the rule? OK, fine – add this before the “ReWriteRule” line:

RewriteCond %{HTTP_REFERER} !^http://www\.acmecorp\.com/noop\.jpg.*$ [NC]

Now what if you participate on other forums and want to allow hot-linking of images on your site from that site? What about Google and other search engines – can you omit them from being blocked? You sure can. Just add these rules in before the “ReWriteRule” line, and modify them to your requirements:

RewriteCond %{HTTP_REFERER} !^http://(www\.|forums\.)?overclockers\.com\.au/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://(images\.)?google.*$ [NC]

The first condition says “don’t re-write if the referrer string starts with either “” or “” and the second condition says “don’t re-write if the referrer string starts with either “<whatever>” or “google.<whatever>” (so that means it’ll allow things like,,, etc, but will NOT allow things like or”Smilie: ;). You can adapt this easily enough to other search engines like Yahoo etc.

Finally, what if you simply want to be a bastard and present a broken link to the hot-linker instead of a friendly message? Hot-linkers be damned! An easy way to do that is to re-write the “ReWriteRule” line as follows:

RewriteRule .*\.(jpe?g|gif|bmp|png)$ - [F]

The dash and the “F” parameter essentially drops the request and serves nothing back. Not even an acknowledgement. As far as your hot-linker is concerned, the image file doesn’t exist.

Happy blocking!