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While running 64-bit Ubuntu 16.04 on the 4.7.4 kernel, my laptop no longer recognizes my projector when I plug in the VGA video adapter to my laptop. My system correctly recognizes the projector when I use kernel 4.6.7. (On 4.7.4, I've tried using System Settings > Displays to force the laptop to use the projector, but the system doesn't recognize the presence of the projector. On 4.6.7, the computer automatically displays through the projector when I plug it in, and changes the laptop display to the projector's lower resolution.) I had the same problem with earlier revs of the 4.7 kernel.

Is there any change I can make to get the Ubuntu to recognize my projector on kernel 4.7.4?

The projector is a ViewSonic DLP 5223 with a standard VGA multi-pin monitor plug. I'm using a System76 Lemur laptop with an Intel Core i7-6500U CPU @ 2.50GHz × 4. The graphics "card" is the onboard Intel HD Graphics 520 (Skylake GT2).

(Secondary question: should I just be happy with a nicely running machine on kernel 4.6.7? I've read that kernel 4.7.4 patches some security issues, which is why I tried updating to 4.7.4. I use my laptop for professional and personal productivity. As a teacher, I use the projector display several times a day, so it's a deal-breaker if the system can't display to the projector.)

trinkner
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  • I believe you can put the KASLR security fix on earlier versions too but I'm on my phone. Its just that 4.7 series is more nagging about it. If I remember correctly. I would go with 4.6.7 if it works for you even though entire 4.6 line is obsolete and possibly no longer supported going forward. – WinEunuuchs2Unix Sep 19 '16 at 22:11
  • Thanks. I'll look into the KASLR fix. I had upgraded to 4.7.4 when I read that 3.6.7 was EOL. (Love your username, by the way.) – trinkner Sep 20 '16 at 00:04
  • Yeah name was chosen at time of angst. It abbreviates nicely to "WE2U" I discovered 6 months later. I thought "KASLR" was the security hole you were referring to. It made international news. – WinEunuuchs2Unix Sep 20 '16 at 00:07

1 Answers1

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KASLR - Kernel Address Space Layout Randomizer - has been around for a long time but is not implemented in most Linux distributions by default. Starting with Kernel 4.7 large text messages started appearing telling you it wasn't installed during the boot. When you install it however hibernation is not allowed.

Most of the world's media servers are running Linux (facebook too, etc) and the security hole was discovered in Kernel version > 2.6 but kept under wraps until just this year when it was announced on international media web sites such as Russia Today. I believe this is the security hole the OP was alluding to. I believe KASLR is the answer to that security hole.

The technique of KASLR security is each time the kernel is loaded modules are in a different memory location making it harder to hack because a snooper program can expect code to always be at a given location in RAM.

To enable KASLR as parameter to the Kernel type:

gksu gedit /etc/default/grub

Search for the line:

GRUB_CMDLINE_LINUX_DEFAULT="nosplash vt.handoff=7 kaslr"

As you can see kaslr option has already been added to the end of mine. Simply add those five characters to yours, save the file and exit. Please note most people have "quiet splash" as options and you should leave existing options as is the point here is to add kaslr.

kaslr may break hibernation if you use that feature, or kaslr may be ignored if Hibernation is used. Simply put, they do not work together (in kernel 4.7 at least). Personally I don't like hibernation because it takes 15 seconds which is small savings from 45 second boot and pales in comparison to 2 second suspend to RAM. Suspend does work with KASLR enabled.

After saving the grub kernel changes, you need to recompile your boot strap loader by typing:

sudo update-grub

Now you will have the best, easiest security fix available for Linux, other than unplugging the internet.

As far as the OP is concerned feel free to use the Kernel version that makes your hardware work. Even though 4.6 is no longer going to be updated the fact it works now for your projector is what is important. Keep checking on future kernel versions once a month see if 4.7.x projector problems are fixed. If not file a bug report when you feel you've waited long enough.

Please post a comment if I've missed something or if clarification is needed. Otherwise mark qusetion as solved & up vote so others can see the answer works.

WinEunuuchs2Unix
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  • Thanks very much for the thorough explanation. I've made the edits to my grub configuration as you suggested, and my system seems to boot well on kernel 4.6.7. Now, is there a way to check that the system is actively using KASLR? I Googled around a bit for CLI command, but couldn't find one. – trinkner Sep 20 '16 at 17:48
  • @trinkner In AskUbuntu someone asked that question and the CLI command is cat /proc/cmdline. It wasn't anywhere else on the net in 10 minutes of google searching I did. Thanks for the compliments! – WinEunuuchs2Unix Sep 20 '16 at 23:23