How To: Disable SELinux in Fedora

WARNING: by continuing following this guide you are putting your machine at risk by disabling the secuity features within SELinux, I strongly advise if you do not know what you are doing, stop and read up on the implications this action will have before continuing. Some information is avaible in the Fedora Wiki here .

Open up this file:

sudo gedit /etc/selinux/config

Change the line that looks like this:

SELINUX=enforcing

To this:

SELINUX=permissive

Save and reboot and it should be working, although again be warned this has disabled the security mechanism on your system. To re-enable this, simply do the same however change from permissive to enforcing and again reboot your machine.

How To Fix: Error: Cannot retrieve repository metadata (repomd.xml) for repository: Dropbox. Please verify its path and try again

After installing dropbox from the RPM package availble on the site on a new Fedora 15 install, I was unable to use yum without coming across this error:

$ update
Loaded plugins: langpacks, presto, refresh-packagekit
http://linux.dropbox.com/fedora/15/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found : http://linux.dropbox.com/fedora/15/repodata/repomd.xml
Trying other mirror.
http://linux.dropbox.com/fedora/15/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found : http://linux.dropbox.com/fedora/15/repodata/repomd.xml
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: Dropbox. Please verify its path and try again

For some unknown reason dropbox repos dont seem to work past 13 so you’ll need to change the dropbox.repo file from detecting the current release to 13 like so:

Open the dropbox.repo file:

sudo gedit /etc/yum.repos.d/dropbox.repo 

Change the baseurl from $relesever to 13 like so:

Original:

[Dropbox]
name=Dropbox Repository
baseurl=http://linux.dropbox.com/fedora/$releasever/
gpgkey=http://linux.dropbox.com/fedora/rpm-public-key.asc

New:

[Dropbox]
name=Dropbox Repository
baseurl=http://linux.dropbox.com/fedora/13/
gpgkey=http://linux.dropbox.com/fedora/rpm-public-key.asc

Save and close and everything should be working, try using sudo yum update to check and the error should have gone away. If not give a reboot a try.

Kinect Development – Day 1

Head over to this page if you want some tutorials on getting started with the Kinect and libfreenect, I’ll update more as time goes on and I have free time.

I’ve been meaning to grab myself an Xbox 360 Kinect for a while, not because I’m a big motion controlled game fan but for machine vision development. Within the first month of the Kinect open source drivers being released the coolest things were seen, from motion controlled media centres to 3D modelling. I’ll admit, I’m a little late to the game, mostly due to the amount of work in my final year at university and other general business. Over the summer I’ll have plenty of time to do a couple of projects and hopefully come up with something cool and contribute to the scene.

Anyway enough of the small talk, I’ve decided to blog in as much detail the journey through the development, from the installation of the libraries to writing the first and last bit of code as a sort of a set of tutorials for anyone else who wants to get into it.

There are currently two main sets of drivers/libraries out there libfreenect and OpenNI both sporting hip, cool, open source names. So which one do you choose? Well, here’s a brief description of both.

Let’s start with OpenNI, these are the Official PrimeSense (the people that Microsoft paid to actually create the Kinect) these allow access to audio, video and depth with the addition of PrimeSense’s NITE Middleware. NITE is the software library used for skeletal tracking, hand gesture recognition and scene analyzer (used to separate figures in the foreground from the background) .

Alternatively there is the libfreenect libraries, from the community over at openkinect.org. While these are admittedly lacking slightly in features such as skeletal tracking and hand gesture recognition they much make up for it in the dedication to open source and the creation of the best suite available. These have access to video, microphones, motors and LED with speakers currently being worked on. They work under a variety of language wrappers for most OS’s and will of course by my personal library of choice.

Fortunately, you won’t have to decide which one you’d prefer ’cause you can run them both on the same machine but you’ll have to look into licencing information for releasing projects with OpenNI so it’s unlikely you’ll want to combine them (or even allowed?).

libfreenect Installation:

OpenKinect’s getting started page provides a well enough documented installation guide that anyone should be able to get them up and running under Windows/Linux or OSX. With Ubuntu being the distro of choice for installation guide. - http://openkinect.org/wiki/Getting_Started

If you’re running Arch, there are a few AUR packages available however they all seem to have lacked updates for a few months but the manual build is pretty simple on the getting started page, I’ve also added a quick list of commands to get you there:

Grab the git copy of the libraries:

git clone https://github.com/OpenKinect/libfreenect.git
cd libfreenect/

Make, install:

mkdir build
cd build/
cmake ..
make
sudo make install
sudo ldconfig /usr/local/lib64/

Add your user to allow access to the connect by creating a group called video and adding your user to it:
note: this can be skipped if you don’t mind running as root/sudo

sudo nano /etc/udev/rules.d/66-kinect.rules
sudo usermod -G video username

Test the kinect with the example program:

bin/glview

If all went well you should have seen a sight similar to the screenshot above, if not check out the OpenKinect page for more information and see if the problems you’re having haven’t already been resolved.

OpenShot, libmp3lame and Ubuntu

If you’re getting the following error while trying export a video under several different codecs in OpenShot including AVI, MOV and MPEG using (mpeg2, mpeg4 or h.264) chances are this might help you with that error.

The following formats/codecs are missing from your system:

libmp3lame

You will not be able to use the selected export profile. You will need to install the missing formats/codecs or choose a different export profile.

This is a simple fix:

  • Open up Synaptic Package Manager
  • Search “libavformat”,
    • If the current package installed is “libavformat52″ select “libavformat-extra-52″ (alternativly “libavformat-unstripped-52″ should also work).
    • Else the package might be “libavformat53″ so simply change to “libavformat-extra-53″, basically it might end in different numbers, it should work the same.
  • Hit Apply and approve the changes.

HowTo: Remove Every Other Line in Text Files – Linux

Let’s say you’ve got a text file, of any size, big or small, and you want to remove every other line of that file, well here are a few commands in Linux that allow you to do this.

Example, you want to get from this:

1
2
3
4
5
6
7
8
9
10

To this:

1
3
5
7
9

The sed way:

 sed -n "p;N;" file.txt > newfile.txt

The awk way:

 awk 'NR%2 != 0' file.txt > newfile.txt

Here you can actually specify N lines, replace 2 in the above command and you’ll be able to take out every N’th number. As an example, here’s the above replaced with a 3 on the file:

1
2
4
5
7
8
10

Easy as pie, right?

Error: “end_request: I/O error, dev sr0, sector xxxxx” – Linux

Error:

end_request: I/O error, dev sr0, sector 537392

If you’re getting a similar error filling your screen once you’ve installed Ubuntu, don’t panic. It’s pretty common which is basically because Ubuntu (or any other Linux distro) can’t control your CD/DVD drive properly, it’s probably trying to open/close it but doesn’t know if it has or not. The problem is that you don’t get to see what Ubuntu wrote before because it’s filled your screen up with this error.

If you’ve just installed Ubuntu this probably happened when it wanted you to take the disc out and close the cd tray (if there is one) then hit Enter to finish the installation, so just do that and ignore this error.

Failed to build Planner-0.14.4 in Arch Linux

When trying to install Gnome Planner ( http://live.gnome.org/Planner ) in Arch Linux, I came across this error:

Error:

/usr/bin/pygobject-codegen-2.0: line 11: /usr/bin/python2: No such file or directory
make[2]: *** [planner.c] Error 127
make[2]: Leaving directory `/home/alex/Desktop/planner-0.14.4/python'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/alex/Desktop/planner-0.14.4'
make: *** [all] Error 2

To fix this, I made a symbolic link from /usr/bin/python2.7 to /usr/bin/python2, this should work with other similar errors involving missing python2 file.

sudo ln -s /usr/bin/python2.7 /usr/bin/python2

Once you have made the made the symbolic link continue to make and install the program as usual.

Installing packages from CD in Arch Linux

Okay, so you have Arch Linux installed and let’s say you’re wifi isn’t working and you need the package “iwlwifi-3945-ucode-15.32.2.9-2-any.pkg.tar.gz” to fix this but you don’t have a wired connect. What do you do? Blast in your Arch cd, mount it, mount the packages sqfs file and install using pacman.

Mount cdrom:

mkdir /mnt/cdrom/
mount /dev/cdrom /mnt/cdrom/

Mount *-pkgs.sqfs:

mkdir /mnt/pkgs/
mount -o loop core-pkgs.sqfs /mnt/pkgs/
cd /mnt/pkgs/

Install pkg.tar.gz:

pacman -U package-name.pkg.tar.gz

How To Fix “Fatal server error: no screens found” | Ubuntu

If you’re running off a live USB disk or changing your graphics card the error below might appear when Xorg is looking for the wrong drivers or device. You might also get this error while using the Nvidia drivers, I found however this was caused by some of the extra options added into the xorg.conf file (usually located /etc/X11/xorg.conf). If the case is that it’s a problem with the aditional options I suggest making a backup of the file and attempting to comment out (#) aditional options, this will need a bit more of an expert eye to see what isn’t needed though.. You can also use the following to rollback to a working version when using the Nvidia drivers.

There is a pretty simple fix, if it is caused by broken or changed xorg.conf file:

Fix:
Make a backup of your current Xorg.conf, just in case something goes even more wrong and it can be easily restored:

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.bckup 

Now you’ll want to restore the failsafe (sometimes called xorg.conf.backup) config to be used as the default:

sudo cp /etc/X11/xorg.conf.failsafe /etc/X11/xorg.conf

Yeah, it was that simple (if this error was caused by a broken or changed xorg.conf anyway. So you can continue and start the x server with:

startx

Error:

X.Org X Server 1.9.0
Release Date: 2010-08-20
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.24-27-server i686 Ubuntu
Current Operating System: Linux ubuntu 2.6.35-22-generic #33-Ubuntu SMP Sun Sep 19 20:34:50 UTC 2010 i686
Kernel command line: noprompt cdrom-detect/try-usb=true persistent file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash -- maybe-ubiquity
Build Date: 16 September 2010  05:39:22PM
xorg-server 2:1.9.0-0ubuntu7 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.18.4
 	Before reporting problems, check http://wiki.x.org
	to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
	(++) from command line, (!!) notice, (II) informational,
	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Fri Mar  4 11:35:54 2011
(==) Using config file: "/etc/X11/xorg.conf"
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
(EE) No devices detected.

Fatal server error:
no screens found

Please consult the The X.Org Foundation support
	 at http://wiki.x.org
 for help.
Please also check the log file at "/var/log/Xorg.0.log" for additional information.

 ddxSigGiveUp: Closing log
giving up.
xinit: No such file or directory (errno 2): unable to connect to X server
xinit: No such process (errno 3): Server error. 

ImportError: No module named …

Numeric

Error:

Traceback (most recent call last):
  File "", line 1, in
ImportError: No module named Numeric

Package:

sudo apt-get install python-numeric

ImageTk

Error:

ITraceback (most recent call last):
  File "", line 1, in
ImportError: No module named ImageTk

Package:

sudo apt-get install python-imaging-tk