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• Friday Spotlight - October 25, 2013

  - by Chris Kawalek

  Happy Friday, everyone! Our spotlight this week is on a really cool technical tip on the Oracle Technology Network from Yuli Vasiliev called "How to Launch Linux Utilities from Oracle Database". From Yuli's introduction: "By wrapping a Linux utility in a script and using an external database table's preprocessor directive, you can launch the utility from within Oracle Database and have the utility's output be inserted into the external table. This allows you to do things such as query operating system data and then join it with data in Oracle Database." Head on over to OTN to read the full article. -Chris

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• Please explain some of the features of URL Rewrite module for a newbie

  - by kunjaan

  I am learning to use the IIS Rewrite module and some of the "features" listed in the page is confusing me. It would be great if somebody could explain them to me and give a first hand account of when you would use the feature. Thanks a lot! Rewriting within the content of specific HTML tags Access to server variables and HTTP headers Rewriting of server variables and HTTP request headers What are the "server variables" and when would you redefine or define them? Rewriting of HTTP response headers HtmlEncode function Why would you use an HTMLEncode in the server? Reverse proxy rule template Support for IIS kernel-mode and user-mode output caching Failed Request Tracing support

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• Install unetbootin on Ubuntu 12.04

  - by Matteo

  I'm trying to install UNetbootin on Ubuntu 12.04 LTS. I downloaded the executable file from this link and followed the instructions below: If using Linux, make the file executable (using either the command chmod +x ./unetbootin-linux, or going to Properties-Permissions and checking "Execute"), then start the application, you will be prompted for your password to grant the application administrative rights, then the main dialog will appear, where you select a distribution and install target (USB Drive or Hard Disk), then reboot when prompted.\ So I typed on my terminal sudo chmod +x unetbootin-linux-584 and tried to execute the binary file with ./unetbootin-linux-584 but got this output: ./unetbootin-linux-584: error while loading shared libraries: libXrandr.so.2: cannot open shared object file: No such file or directory However when I checked for libraries libXrandr on my system I actually found them $> locate libXrandr /usr/lib/x86_64-linux-gnu/libXrandr.so.2 /usr/lib/x86_64-linux-gnu/libXrandr.so.2.2.0 /usr/lib/x86_64-linux-gnu/libXrandr_ltsq.so.2 /usr/lib/x86_64-linux-gnu/libXrandr_ltsq.so.2.2.0 so I really don't have a clue of what's the problem and how can I fix it, any ideas?

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• grub-probe: error: cannot find a GRUB drive for /dev/sda1

  - by Thilina

  I'm trying to add windows 7 for my new 12.10 grub bootloader. None of the things worked out; such as .. copying bootx64.efi methods, I'm getting this output: grub-probe --target=fs_uuid /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi grub-probe: error: cannot find a GRUB drive for /dev/sda1. Check your device.map. ....... my device map ....... (hd0) /dev/disk/by-id/ata-WDC_WD6400BPVT-55HXZT3_WD-WXD1EA1MSVR4 ....... 40_custom ..... menuentry "Microsoft Windows x86_64 UEFI-GPT" { insmod part_gpt insmod fat insmod search_fs_uuid insmod chain search --fs-uuid --no-floppy --set=root 80BD-E086 chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi } When booting to windows 7 give me blank black screen with a cursor blinks for 2 seconds then reboot, I've tried boot-repair too. I think I'm missing Windows UEFI Bootloader files.

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• How to handle mutiple API calls using javascript/jquery

  - by James Privett

  I need to build a service that will call multiple API's at the same time and then output the results on the page (Think of how a price comparison site works for example). The idea being that as each API call completes the results are sent to the browser immediately and the page would get progressively bigger until all process are complete. Because these API calls may take several seconds each to return I would like to do this via javascript/jquery in order to create a better user experience. I have never done anything like this before using javascript/jquery so I was wondering if there was any frameworks/advice that anyone would be willing to share.

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• How to remap Fn key combinations (Lenovo G500)

  - by Anatoli

  I am running Kubuntu 13.10 on a Lenovo G500 laptop. My question is similar to this one: How can I remap my F keys on my HP laptop? That is to say, my F1-F12 keys are mapped to certain special functions, and only holding down the Fn key restores access to the standard F1-F12 keys. How do I remap certain keys? I would like to know if there is a way to remap Fx to Fn+Fx and vice-versa. As per the instructions of #87043 I checked my BIOS and there is no option to switch the Fx/Fn key functionality. Googling through Leonovo's support forums indicates a BIOS update enabling this is in the works, but there's no indication of when it will be complete. Using xev I was able to see what X sees when F1-F12 are pressed. Some send separate keycodes, but some are somehow mapped to key combinations or other unknown things: F1 - XF86AudioMute F2 - XF86AudioVolumeLower F3 - XF86AudioVolumeRaise F4 - Alt_L + F4 F5 - F5 F6 - Disables touchapd, cannot quite understand what xev tells me is happening, reenables if disabled (Kernel log reveals these have well-defined scancodes not assigned to any keycodes) F7 - XF86WLAN F8 - Alt_L + Ctrl_L + Tab F9 - Turns off LCD backlight, xev sees nothing F10 - Super_L + p F11 - XF86MonBrightnessLower F12 - XF86MonBrightnessRaise Following the instrusctions on this page: How do I remap certain keys? I remapped all the keys that have definite keycodes (F1, F2, F3, F5, F7, F11, F12) This still leaves the F4, F6, F8, F9, F10 keys not functioning properly. This is especially frustarting since F4, F6, F9 now kill the current window, the touchpad and screen, respectively. Any help on remapping these keys to their proper functions would be much appreciated! -Anatoli xev output for these 5 keys: F4 KeyPress event, serial 40, synthetic NO, window 0x4800001, root 0x9d, subw 0x0, time 3674037, (228,298), root:(911,321), state 0x0, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False FocusOut event, serial 40, synthetic NO, window 0x4800001, mode NotifyGrab, detail NotifyAncestor FocusIn event, serial 40, synthetic NO, window 0x4800001, mode NotifyUngrab, detail NotifyAncestor KeymapNotify event, serial 40, synthetic NO, window 0x0, keys: 4294967197 0 0 0 0 0 0 0 65 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeyRelease event, serial 40, synthetic NO, window 0x4800001, root 0x9d, subw 0x0, time 3674040, (228,298), root:(911,321), state 0x8, keycode 70 (keysym 0xffc1, F4), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4800001, root 0x9d, subw 0x0, time 3674042, (228,298), root:(911,321), state 0x8, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False ClientMessage event, serial 40, synthetic YES, window 0x4800001, message_type 0x12a (WM_PROTOCOLS), format 32, message 0x12b (WM_DELETE_WINDOW) F6 disabling touchpad MappingNotify event, serial 40, synthetic NO, window 0x0, request MappingKeyboard, first_keycode 8, count 248 FocusOut event, serial 40, synthetic NO, window 0x4600001, mode NotifyGrab, detail NotifyAncestor FocusIn event, serial 40, synthetic NO, window 0x4600001, mode NotifyUngrab, detail NotifyAncestor KeymapNotify event, serial 40, synthetic NO, window 0x0, keys: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 MappingNotify event, serial 41, synthetic NO, window 0x0, request MappingKeyboard, first_keycode 8, count 248 F6 enabling touchpad MappingNotify event, serial 42, synthetic NO, window 0x0, request MappingKeyboard, first_keycode 8, count 248 FocusOut event, serial 42, synthetic NO, window 0x4600001, mode NotifyGrab, detail NotifyAncestor FocusIn event, serial 42, synthetic NO, window 0x4600001, mode NotifyUngrab, detail NotifyAncestor KeymapNotify event, serial 42, synthetic NO, window 0x0, keys: 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 MappingNotify event, serial 43, synthetic NO, window 0x0, request MappingPointer, first_keycode 0, count 0 F8 doing whatever it is F8 does KeyPress event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508985, (13,-12), root:(696,11), state 0x0, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False KeyPress event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508986, (13,-12), root:(696,11), state 0x8, keycode 37 (keysym 0xffe3, Control_L), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False KeyPress event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508988, (13,-12), root:(696,11), state 0xc, keycode 23 (keysym 0xff09, Tab), same_screen YES, XLookupString gives 1 bytes: (09) " " XmbLookupString gives 1 bytes: (09) " " XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508989, (13,-12), root:(696,11), state 0xc, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508991, (13,-12), root:(696,11), state 0x4, keycode 37 (keysym 0xffe3, Control_L), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3508994, (13,-12), root:(696,11), state 0x0, keycode 23 (keysym 0xff09, Tab), same_screen YES, XLookupString gives 1 bytes: (09) " " XFilterEvent returns: False F9 gives no output to xev F10 doing whatever it is F10 does KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3586076, (9,-14), root:(692,9), state 0x0, keycode 10 (keysym 0x31, 1), same_screen YES, XLookupString gives 1 bytes: (31) "1" XFilterEvent returns: False KeyPress event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3586552, (9,-14), root:(692,9), state 0x0, keycode 133 (keysym 0xffeb, Super_L), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False KeyPress event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3586554, (9,-14), root:(692,9), state 0x40, keycode 33 (keysym 0x70, p), same_screen YES, XLookupString gives 1 bytes: (70) "p" XmbLookupString gives 1 bytes: (70) "p" XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3586557, (9,-14), root:(692,9), state 0x40, keycode 33 (keysym 0x70, p), same_screen YES, XLookupString gives 1 bytes: (70) "p" XFilterEvent returns: False KeyRelease event, serial 40, synthetic NO, window 0x4600001, root 0x9d, subw 0x0, time 3586560, (9,-14), root:(692,9), state 0x40, keycode 133 (keysym 0xffeb, Super_L), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False

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• Encrypt folders out of Home

  - by igi

  Is there a way to encrypt a folder, which is not in /home but even in a different partition, so only my user can access/read contained files? Alternatively, I would like to understand if it is possible to turn a complete ext4 partition into an encrypted volume, which would be mounted at user login. If possible, I would like to make the change without reinstalling Ubuntu. My PC has (mount output): /dev/sda1 on / type ext4 (rw,errors=remount-ro) /dev/sda3 on /home type ext4 (rw) /dev/sda4 on /home/igor/Personale type ext4 (rw) sda4 is the partition containing folders I would like to protect. Thanks!

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• Battery Indicator Missing

  - by Edwin

  Duplicate of: No Battery Status Icon I have just recently upgraded from 11.04 "Natty Narwhal" to 11.10 "Oneiric Ocelot" on my laptop, but do not have any battery indicator (which should be located between the volume and date indicator in Unity). I have already run sudo apt-get install indicator-power and got the following output: Reading package lists... Done Building dependency tree Reading state information... Done indicator-power is already the newest version. indicator-power set to manually installed. The following packages were automatically installed and are no longer required: //list of packages Use 'apt-get autoremove' to remove them. 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. In addition, I have already tried reinstalling, but still don't have a battery indicator. What else can I do?

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• Process arbitrarily large lists without explicit recursion or abstract list functions?

  - by Erica Xu

  This is one of the bonus questions in my assignment. The specific questions is to see the input list as a set and output all subsets of it in a list. We can only use cons, first, rest, empty?, empty, lambda, and cond. And we can only define exactly once. But after a night's thinking I don't see it possible to go through the arbitrarily long list without map or foldr. Is there a way to perform recursion or alternative of recursion with only these functions?

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• Destroy guest OS using php

  - by Alee

  I am using libvirt-php to manage my virtual machines, and I need to shutdown/destroy domU. For this I used the following php script: < ? php $conn=libvirt_connect("xen:///"); $name=libvirt_domain_lookup_by_id($conn,4); $dest=libvirt_domain_destroy($name); echo $dest; ? When I run this on xampp server i get the following output: Warning: libvirt_domain_destroy() [function.libvirt-domain-destroy]: operation virDomainDestroy forbidden for read only access in /opt/lampp/htdocs/xampp/byname.php on line 5. Here is the documentation: http://libvirt.org/php/api-reference.html#libvirt_domain_destroy

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• Stream audio to mobile device

  - by blackn1ght

  I'd like to stream the audio from Ubuntu 10.10 to my HTC Desire HD (Android 2.2). I've seen solutions so far for streaming from audio players, but I'd like to stream any audio output from the PC to my phone. My use case is for watching TV/Films in VLC or online (BBC iPlayer) in bed, without having to use my surround sound system which is likely to wake up my house mates. I'm not just talking about music from Banshee, but any audio that the system makes. I was thinking that PulseAudio is pretty powerful, is it possible to route audio through that to a mobile device? Can it be done through bluetooth? Cheers in advance!

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• 3d environments and managing them on iOS

  - by alJaree

  I would like to start learning 3d game development and currently only develop 2d games. A few basic questions I am interested in are: What is used to create the 3d environments? Are they all done in e.g. Maya, Lightwave, 3d modeling software? What is the output format for these models and how are they manipulated in iOS? Is it all done using openGL(GL ES on iOS)? e.g a monster needs to be spawned in the game world. What coordinates are used? Are the concepts the same as 2d in terms of collision on the coordinates and movement on the coordinates of the game world? How are 3d games managed in iOS on the low available memory. (e.g. FPS games) Lastly, Can someone please recommend a good book that is up to date and can be applied to todays techniques. Thanks

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• kubuntu - what's the best smplayer configuration for best quality in hd movies (mkv)

  - by Frank

  I have ubuntu x64 13.04 with kde 4.11 and smplayer v0.8.6 and the last mplayer version from ppa. I have ATI video card HD6870 MSI with fglrx driver v13.4. My kde settings are: Composition mode: Opengl 3.1 graphic system qt: Raster scaling mode: precise Vsync: auto So what's the best configuration for quality over performace in smplayer according to my system specs? For example what do I have to set for the following options? enable postprocessing by default and postprocessing quality output driver Deinterlacing method software equalizer direct rendering double buffering draw video using slices threads for decoding (MPEG-1/2 and H.264 only loop filter use CoreAVC Thanks

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• LWJGL - OpenGL - Texture shading

  - by Trixmix

  I want to use LWJGL to create a shader that all it does is change the color of the given texture. For example I tell it to draw the letter A using a sprite sheet then I can tell the shader to draw the letter in a certain color. How would you do something like this without needed to create different colored letter sprite sheets? Task for the shader: Simply change all pixels to a certain color in the texture. Input: Color , texture. Output: it draws onto the screen the new colored texture. How do i accomplish such a thing?

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• Installing old Loki games on 12.04 64-bit results in no audio

  - by FlabbergastedPickle

  All, Here's an interesting problem. I followed instructions provided online for installing Loki Games' Heroes of Might and Magic 3 (see http://www.swanson.ukfsn.org/loki/ and http://wtanaka.com/node/7641) and got it installed and patched to the latest version. However, every time I start it regardless whether the pulseaudio is running, I get the following error: LD_LIBRARY_PATH=/usr/local/lib/Loki_Compat/ /usr/local/lib/Loki_Compat/ld-linux.so.2 /usr/local/games/Heroes3/heroes3.dynamic ALSA lib conf.c:3314:(snd_config_hooks_call) Cannot open shared library libasound_module_conf_pulse.so ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM default Couldn't open audio: My first soundcard is HDMI output and my second one is the actual soundcard (HP DM1 running 12.04 64-bit with latest updates). I did set up /etc/asound.conf as follows: asound.conf pcm.!default { type hw card 1 } ctl.!default { type hw card 1 } So, the default soundcard should work ok. Between Shadowgrounds that also stopped working and this it appears a there may be some unfinished business/regressions in 32-bit support on 64-bit systems in 12.04. Any thoughts?

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• C# creating a simple snake game

  - by Guy David

  I was thinking about creating a snake game with C#, so I ran ideas in my head, and some problems came up. How can I track and output in the correct location the blocks that run after the snake's head? If the snake is built of five blocks, and the user starts going in a circle, how can I print the snake body in the right location? Also, how can I create an action that will run on the background, which will move the snake forward, no matter what the user does? What structure should my code have? (code design structure) This should be a console application, since it's the only framework I am familiar with. I am not looking for finished code, since I want to really understand how it should work.

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• TOR Error permission issue

  - by LeChiffte

  I've tried reinstalling, updating, and removing and then reinstalling. Nothing seems to work. See screenshot below: the output of gedit /home/skynet/.tor-browser-en/LOG (The installation log) is: /usr/bin/tor-browser-en.sh: Your version in /home/skynet/.tor-browser-en is outdated or you do not have installed tor-browser-en yet. /usr/bin/tor-browser-en.sh: Extracting files to /home/skynet/.tor-browser-en/INSTALL. tar (child): /opt/tor-browser-en/tor-browser-linux64-3.6.2_en-US.tar.xz: Cannot open: No such file or directory tar (child): Error is not recoverable: exiting now tar: Child returned status 2 tar: Error is not recoverable: exiting now

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• I need acpi=off to boot, but this seems to disable wifi

  - by TheExp3rt

  To boot my computer, I have to use acpi=off in kernel options. Doing this apparently causes my wifi adapter to be switched off and prevents my mouse and USB keyboard to not work. If I change acpi=off to nomodeset, it fixes these problems. But then it sets my computer at a lower resolution. I am currently running Kubuntu 13.10, although none of the updates, starting from 12.04, changed the need for acpi=off. I assume I need acpi=off in because I have an oldish computer with an intel motherboard How can I boot without acpi=off? Output of uname -a: 3.11.0-13-generic #20-Ubuntu SMP Wed Oct 23 07:38:26 UTC x86_64 x86_64 x86_64 GNU/Linux

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• How is this number calculated?

  - by Hamid

  I have numbers; A == 0x20000000 B == 18 C == (B/10) D == 0x20000004 == (A + C) A and D are in hex, but I'm not sure what the assumed numeric bases of the others are (although I'd assume base 10 since they don't explicitly state a base. It may or may not be relevant but I'm dealing with memory addresses, A and D are pointers. The part I'm failing to understand is how 18/10 gives me 0x4. Edit: Code for clarity: *address1 (pointer is to address: 0x20000000) printf("Test1: %p\n", address1); printf("Test2: %p\n", address1+(18/10)); printf("Test3: %p\n", address1+(21/10)); Output: Test1: 0x20000000 Test2: 0x20000004 Test3: 0x20000008

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• Why is my partition claiming to be out of space?

  - by Dr C

  My file system claims to only have 4.5 GB left. While my OS (a folder with in file system) still has 75.2 GB left. I put something near 130 GB on my Ubuntu partition, it should have enough space. I confirmed that I can put things in OS that exceed the space in available file systems, but that makes no sense, OS is listed as a folder inside of file system, why would it have more space than it's parent folder? What is going on? Here is the output of df: Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda5 113773200 103741440 4252408 97% / udev 2004600 4 2004596 1% /dev tmpfs 804756 848 803908 1% /run none 5120 0 5120 0% /run/lock none 2011884 436 2011448 1% /run/shm /dev/sda2 127526908 54045584 73481324 43% /media/OS /dev/sda3 39144708 89016 39055692 1% /media/DATA`

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• MPD to play music to single channel of my multi-channel card?

  - by hany tawfik

  I installed an Ubuntu 12-04 LTS server for a special background music application of mine, where I am using the server with an Asus Xonar DS sound card. The installation is successful, the MPD is working, the sound card is working with Alsa and its libraries installed accept for Alsa-oss. Alsamixer is working fine with left/right sides of each channel volume control through Q/Z letters shortcut when alsamixer is open in terminal . using the command " speaker-test -Dplug:surround71 -c8 -l1 -twav " I can hear every voice message coming out from the card at the right connector, so "front right/ front left" voice message are coming from first output in the card back, while the other outputs are silent..so on. The problem is that MPD is playing on all outputs simultaneously the same audio. I have been trying various configurations for the last 12 days with out any success, including trying to put mappings in the /etc/asound.conf Can any body help me achieve the above, or direct me to the right configuration of MPD or asound.conf

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• No sound after installing a new Graphics Card

  - by Dan

  I've just upgraded my graphics card to an Asus Geforce 210 and now my system has no sound. I've ran Update Manager and the Additional Drivers utility which installed the latest Nvida driver. The graphics card is connected to my TV via a DVI-to-HDMI (DVI at the PC end) cable for the visual connection, and an audio jack from my onboard soundcard for my audio connection. Any ideas on how to resolve this? I ran this command ubuntu-bug audio And it outputted this: You seem to have configured PulseAudio to use the "pci-0000_05_00.1" card, while you want output from "NFORCE - NVidia CK804". I've tired a bit of messing about with the audio settings but can't get anything to work.

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• How to workaround or diagnose a kernel panic when "safely removing" external hdd?

  - by Shawn

  I'm experiencing an issue when using the "Safely Remove" option to remove my 1TB external HDD from the Unity Launcher. Not every time, but occasionally my screen will go black and display LARGE amounts of text information (which I obviously cannot screen cap). The jist of the info displayed is that unmounting or 'safely removing' the drive causes a kernel panic. Is there a Command Line command to remove mounted drives, or at least one that would show me some sort of error output when the drive is removed? I'm trying to narrow down the cause. I could be imagining this, but it seems to happen most often when I have other programs running when I remove the drive (i.e. Firefox, Transmission). Please note that my external drive is not in use when I attempt to remove it and it is not being used either by Firefox or Transmission at these times. Any help would be appreciated.

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• Ubuntu 12.10, Wireless not working

  - by Karthik

  My Laptop is Acer 5742G with "Npilfy 802.11 wireless". I have both windows 7 and Ubuntu 12.10 Earlier when I had Ubuntu 12.04, the wireless was working fine, but after installing 12.10 wireless is not working at all, although it is still working in windows. I am not able to see "Wireless Networks" in the Network Manager nor in the Network Settings. This was the output I got for rfkill 0: acer-wireless: Wireless LAN Soft blocked: no Hard blocked: no 1: acer-bluetooth: Bluetooth Soft blocked: no Hard blocked: no 2: hci0: Bluetooth Soft blocked: no Hard blocked: no This is a snapshot of my Additional Drivers settings. As you can see, the required driver for wireless is installed.

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• Physics System ignores collision in some rare cases

  - by Gajoo

  I've been developing a simple physics engine for my game. since the game physics is very simple I've decided to increase accuracy a little bit. Instead of formal integration methods like fourier or RK4, I'm directly computing the results after delta time "dt". based on the very first laws of physics : dx = 0.5 * a * dt^2 + v0 * dt dv = a * dt where a is acceleration and v0 is object's previous velocity. Also to handle collisions I've used a method which is somehow different from those I've seen so far. I'm detecting all the collision in the given time frame, stepping the world forward to the nearest collision, resolving it and again check for possible collisions. As I said the world consist of very simple objects, so I'm not loosing any performance due to multiple collision checking. First I'm checking if the ball collides with any walls around it (which is working perfectly) and then I'm checking if it collides with the edges of the walls (yellow points in the picture). the algorithm seems to work without any problem except some rare cases, in which the collision with points are ignored. I've tested everything and all the variables seem to be what they should but after leaving the system work for a minute or two the system the ball passes through one of those points. Here is collision portion of my code, hopefully one of you guys can give me a hint where to look for a potential bug! void PhysicalWorld::checkForPointCollision(Vec2 acceleration, PhysicsComponent& ball, Vec2& collisionNormal, float& collisionTime, Vec2 target) { // this function checks if there will be any collision between a circle and a point // ball contains informations about the circle (it's current velocity, position and radius) // collisionNormal is an output variable // collisionTime is also an output varialbe // target is the point I want to check for collisions Vec2 V = ball.mVelocity; Vec2 A = acceleration; Vec2 P = ball.mPosition - target; float wallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; float r = ball.mRadius / (mMap->getWallWidth() + mMap->getHallWidth()); // r is ball radius scaled to match actual rendered object. if (A.any()) // todo : I need to first correctly solve the collisions in case there is no acceleration return; if (V.any()) // if object is not moving there will be no collisions! { float D = P.x * V.y - P.y * V.x; float Delta = r*r*V.length2() - D*D; if(Delta < eps) return; Delta = sqrt(Delta); float sgnvy = V.y > 0 ? 1: (V.y < 0?-1:0); Vec2 c1(( D*V.y+sgnvy*V.x*Delta) / V.length2(), (-D*V.x+fabs(V.y)*Delta) / V.length2()); Vec2 c2(( D*V.y-sgnvy*V.x*Delta) / V.length2(), (-D*V.x-fabs(V.y)*Delta) / V.length2()); float t1 = (c1.x - P.x) / V.x; float t2 = (c2.x - P.x) / V.x; if(t1 > eps && t1 <= collisionTime) { collisionTime = t1; collisionNormal = c1; } if(t2 > eps && t2 <= collisionTime) { collisionTime = t2; collisionNormal = c2; } } } // this function should step the world forward by dt. it doesn't check for collision of any two balls (components) // it just checks if there is a collision between the current component and 4 points forming a rectangle around it. void PhysicalWorld::step(float dt) { for (unsigned i=0;i<mObjects.size();i++) { PhysicsComponent &current = *mObjects[i]; Vec2 acceleration = current.mForces * current.mInvMass; float rt=dt; // stores how much more the world should advance while(rt > eps) { float collisionTime = rt; Vec2 collisionNormal = Vec2(0,0); float halfWallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; // we check if there is any collision with any of those 4 points around the ball // if there is a collision both collisionNormal and collisionTime variables will change // after these functions collisionTime will be exactly the value of nearest collision (if any) // and if there was, collisionNormal will report in which direction the ball should return. checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); // either if there is a collision or if there is not we step the forward since we are sure there will be no collision before collisionTime current.mPosition += collisionTime * (collisionTime * acceleration * 0.5 + current.mVelocity); current.mVelocity += collisionTime * acceleration; // if the ball collided with anything collisionNormal should be at least none zero in one of it's axis if (collisionNormal.any()) { collisionNormal *= Dot(collisionNormal, current.mVelocity) / collisionNormal.length2(); current.mVelocity -= 2 * collisionNormal; // simply reverse velocity along collision normal direction } rt -= collisionTime; } // reset all forces for current object so it'll be ready for later game event current.mForces.zero(); } }

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