Just re-install Virtual Box and it will repair the problem. You'll not
lose your virtual OS's. Just a thought - are you using the VBox as
supplied through Ubuntu or the full version from VBox themselves ? The
full version is preferable and can be installed over the top of the
Ubuntu version without any problem.

Did you re-install Virtualbox? It does not come with Ubuntu and if you used
the one outside of the repositories then you would have to re-install VB,
then try again. I don't know if you need to re-boot since installation
compiles specific parts from the kernel you are using.

Nope, no reboot needed when installing software on linux.

Generally this is true, but when it is something that must load on boot up
then you cannot use it till you re-boot or if the kernel is a new version
then it does not come into effect until you re-boot. In the case of
VirtualBox and certainly VMWare parts are compiled against the kernel as
part of the installation process and if you watch the boot process (instead
of using the graphical screens) you will see that components for VirtualBox
are loaded upon boot. I know that for sure VMWare will not work until you
re-boot and think that it is the same for the first time installation of
VirtualBox.

According to the VB manual you can work on configuring VMs in VirtualBox but
cannot RUN them until the kernel module is loaded. It also suggests that if
the kernel is updated this will have to be repeated unless you are running
DKMS. This can be easily done on Ubuntu by installing the package, but it is
not universally available across all distros.

So generally there is no need to re-boot, but there are a few exceptions.
Ubuntu will continue to work and you can even use upgraded applications, but
sometimes you are running the old package and not the upgrade until you
logout or in some cases even re-boot. In some applications such as Firefox
you need to re-start the application to take advantage of newly installed
parts. There is no universal rule such as you never need to re-boot.
However, you don't get nagged to death as you do in some OSes.

Other than booting up into a new kernel, I can't think of any linux
software install process that involves a reboot - and if you're using
ksplice, even booting into a new kernel isn't necessary, as it actually
replaces the running kernel with a new one in-place.

At my day job at a large firm, I manage a number of busy linux
infrastructure servers which have been up for over 1500 days since the
last boot (which was for a kernel upgrade) But I've upgraded
applications and libraries numerous times during the past 3 years - and
nary a reboot required.

As far as building and loading a kernel module, I've never rebooted a
system for that, since the kernel itself isn't changing, you're just
building and loading a dynamic kernel module against the current running
kernel.

In most cases, people reboot linux because either they come from a
microsoft background and think that is how things should be done, or
they don't want to figure out how to load a module or run an init
script, so they just reboot to make it happen.

Other than booting into a new kernel, do you have any specific examples
where a reboot is required?

You obviously missed my comment re: the VirtualBox manual. The kernel module
must be loaded once it is compiled and installed or you are limited. You can
create VMs, but not run them. VMWare is the same.

Many times I have installed a new graphics driver and it tells me the
changes will take effect when I re-boot. Technically I do not HAVE to
re-boot, but then again I can't use what I want until I do. Since I need the
proprietary Nvidia driver for compositing then I cannot use Compiz until I
re-boot. The same can be said for installing a new kernel. It will advise
you to reboot, but you can still work if you want to.

As I see it my original comment re: Virtualbox stands and your correction
should be qualified to say that you don't have to re-boot but you can't boot
your VM until you re-boot your host machine on Linux. I can admit it if I am
wrong, but this is not one of those cases.

Who ever made up this rule that you have to reboot to load a kernel
module? I've loaded and unloaded kernel modules all the time without
rebooting. For instance, I've built netfilter kernel modules to add new
firewall capabilities, and and after making the module and making
install, a simple "modprobe <module_name>" is all that's required to
load it and start using the new fw rules. I've unloaded network card
drivers and loaded newer ones, etc and didn't have to reboot.

I've had nvidia cards for years. After installing the nvidia drivers,
all I had to do was log out of X and restart GDM and voila! accelerated
3D on my next login.

BTW I've used VB and VMware, and never had to reboot after building the
modules. Is this obligatory reboot some sort of new feature to make
linux more like windows?

I don't get it. I am reporting what VirtualBox says in their own manual and
what Ubuntu tells you after you install a new proprietary driver and you are
all over me for passing it on. Perhaps you should take that up with those
developers. I was only interested in helping a third party who has since
fallen silent due to all of our bickering.

didn't know you took it that way. I was just reflecting my own
experience on the thread in order to illuminate things. There's no lack
of bad advice on the matter, even the redhat.com site awhile back
advised installing an rpm and then rebooting, when all that had to be
done was to restart the service in question. As you might have gathered,
unnecessary reboots are a pet peeve of mine.

But in the end, your system is your system, you can reboot it every hour
if that's what you like.

It's okay. Sometimes I am in the mood for these kinds of discussions, but in
this case I was trying to help someone and was concerned that we were taking
over and maybe even turning off the person since he kind of disappeared from
the radar.

We've had several discussions that weren't at the point of being
abusive but were still IMHO not helpful. I'm not currently a Rotarian
but I've always been impressed with their "4-way Test" and suggest it
might be useful for all of us to consider before we press "Send"...

"Of the things we think, say or do:

"1. Is it the TRUTH?

2. Is it FAIR to all concerned?

3. Will it build GOODWILL and BETTER FRIENDSHIPS?

4. Will it be BENEFICIAL to all concerned?"

www.rotary.org/.../070917_news_Four-WayTest.aspx

As one of my tech friends once told me: "everything I know is yours",
with that attitude, and a bit of tolerance, we can't go far wrong.

Understand what you are saying but you are approaching this from
the point of view of a Linux specialist. Ubuntu appeals to a much
wider audience and many will be converts from Windows so the re-boot
is firmly entrenched. It's not a case of 'not being bothered to learn'
it's using this new OS to do their daily computing. If a re-boot is
what they need to do then they aren't fazed by it - and as mentioned,
it's a lot quicker than re-booting Windows

Horses for courses ??

If you re-booted the servers just to load / unload a module you'd not
be a Linux Server Admin for long.

No reboot needed when installing software on Linux *most of the time*
but some things do need a re-boot. So if faced with a strange problem
after an install it's always worth trying - doesn't take long