How to update your linux kernel version on a KimSufi server

(Or why PHP throws random errors in the latest update)

Hello again!

Since I had a bit of a time trying to find some clear information on the subject, I'm writing the blog post so that it might help others. Basically, yesterday night I updated the packages on my server (the one that runs this website!). There was a PHP update, but I didn't think much of it.

This morning, I tried to access my ownCloud instance, only to discover that it was throwing random errors and refusing to load. I'm running PHP version 7.0.16-1+deb.sury.org~xenial+2. It was spewing errors like this one:

PHP message: PHP Fatal error:  Uncaught Exception: Could not gather sufficient random data in /srv/owncloud/lib/private/Security/SecureRandom.php:80
Stack trace:
#0 /srv/owncloud/lib/private/Security/SecureRandom.php(80): random_int(0, 63)
#1 /srv/owncloud/lib/private/AppFramework/Http/Request.php(484): OC\Security\SecureRandom->generate(20)
#2 /srv/owncloud/lib/private/Log/Owncloud.php(90): OC\AppFramework\Http\Request->getId()
#3 [internal function]: OC\Log\Owncloud::write('PHP', 'Uncaught Except...', 3)
#4 /srv/owncloud/lib/private/Log.php(298): call_user_func(Array, 'PHP', 'Uncaught Except...', 3)
#5 /srv/owncloud/lib/private/Log.php(156): OC\Log->log(3, 'Uncaught Except...', Array)
#6 /srv/owncloud/lib/private/Log/ErrorHandler.php(67): OC\Log->critical('Uncaught Except...', Array)
#7 [internal function]: OC\Log\ErrorHandler::onShutdown()
#8 {main}
  thrown in /srv/owncloud/lib/private/Security/SecureRandom.php on line 80" while reading response header from upstream, client: x.y.z.w, server: ownc

That's odd. After googling around a bit, I found this page on the Arch Linux bug tracker. I'm not using arch (Ubuntu 16.04.2 LTS actually), but it turned out that this comment shed some much-needed light on the problem.

Basically, PHP have changed the way they ask the Linux Kernel for random bytes. They now use the getrandom() kernel function instead of /dev/urandom as they did before. The trouble is that getrandom() was introduced in linux 3.17, and I was running OVH's custom 3.14.32-xxxx-grs-ipv6-64 kernel.

Thankfully, after a bit more digging, I found this article. It suggests installing the kernel you want and moving one of the grub config file generators to another directory, but I found that simply changing the permissions did the trick.

Basically, I did the following:

apt update
apt full-upgrade
apt install linux-image-generic
chmod -x /etc/grub.d/06_OVHkernel
update-grub
reboot

Basically, the above first updates everything on the system. Then it installs the linux-image-generic package. linux-image-generic is the pseudo-package that always depends on the latest stable kernel image available.

Next, I remove execute privileges on the file /etc/grub.d/06_OVHkernel. This is the file that gives the default installed OVH kernel priority over any other instalaled kernels, so it's important to exclude it from the grub configuration process.

Lastly, I update my grub configuration with update-grub and then reboot. You need to make sure that you update your grub configuration file, since if you don't it'll still use the old OVH kernel!

With that all done, I'm now running 4.4.0-62-generic according to uname -a. If follow these steps yourself, make sure you have a backup! While I am happy to try and help you out in the comments below, I'm not responsible for any consequences that may arise as a result of following this guide :-)