Most likely the OP issue was not being in the vboxusers group and also trying to install the vbox-extpack failed because was not able to install it as there was no password prompt when doing it. All that was fixed once he did what i recommended.
My “issue” here, and confusion is that the wiki has, as i said
Done! @bogdancovaciu @j77h
(My information came from another user in the original update announcement)
That was caused by having both ‘virtualbox-host-dkms’ and ‘virtualbox-host-modules’ installed at the same time.
The manjaro wiki does not mention dkms.
The arch wiki mentions both, and says you must choose one or the other.
(How it happened that you were not in the vboxusers group I have no idea – it’s a different issue.)
I figured that not having dkms will save me the unload/reload time that happens on every kernel update, so I switched.
I used the following commands.
They might help if you decide to uninstall virtualbox-host-dkms.
sudo pacman -Rcu virtualbox-host-dkms
This uninstalled 3 packages (we re-install 2 of them later) :
virtualbox-6.1.14-1
virtualbox-ext-oracle-6.1.14-1
virtualbox-host-dkms-6.1.14-1
sudo pacman -S linux54-virtualbox-host-modules
sudo pacman -S virtualbox
sudo modprobe vboxdrv
sudo vboxreload
pikaur -S virtualbox-ext-oracle-manjaro
EDIT:
Have changed “virtualbox-ext-oracle” above, to “virtualbox-ext-oracle-manjaro”,
because Arch’s ‘virtualbox-ext-oracle’ can have a later version than Manjaro’s virtualbox.
EDIT2: later I realized that “virtualbox-ext-oracle-manjaro” can be out-of-date sometimes, so we still need to check versions before installing.
pikaur is the AUR helper that I normally use.
You can use whichever AUR helper you normally use (pamac can do it).
None of the above affects your VMs (as long as they’re not running at the time).
I’ve used my Win10 VM since I made those changes, and installed the new Guest Additions.
I would discourage using aur/virtualbox-ext-oracle on stable.
The version of the extension pack should always match the version of VirtualBox, the AUR package assumes you have the same version that Arch has.
I’ll try in a moment…
Maybe the reboot (recommended by @bogdancovaciu) did the trick.
Using octopi will remove dkms too
Can I proceed?
True. I mentioned this yesterday at [HowTo] VirtualBox - Installation - USB - Shared Folder, and it’s now covered in the main post there.
EDIT (3h later) :
Have just noticed “virtualbox-ext-oracle-manjaro” on that page.
Have edited it into my earlier post.
Also learned how to search with pikaur :
$ pikaur -Ssa virtualbox-ext-oracle
Searching... [--]##
aur/virtualbox-ext-oracle 6.1.14-1 [installed] (1305, 5.21)
Oracle VM VirtualBox Extension Pack
aur/virtualbox-ext-oracle-manjaro 6.1.14-1 (4, 2.99)
Oracle VM VirtualBox Extension Pack for Manjaro
aur/virtualbox-ext-oracle-5 5.2.x-1 (8, 0.07)
Oracle VM VirtualBox Extension Pack 5.2.x (stable)
aur/virtualbox-ext-oracle-beta 6.1.0_RC1-1 (1, 0.00)
Oracle VM VirtualBox Extension Pack (Beta)
aur/virtualbox-ext-oracle-5-test-build 5.2.35_135314-1 (0, 0.00)
Oracle VM VirtualBox Extension Pack Test Build 5.2.35_135314
aur/virtualbox-ext-oracle-5.0 5.0.40-1 [outofdate: 2018/12/29] (6, 0.00)
Oracle VM VirtualBox Extension Pack
Pamac is a GUI for pacman, and is an AUR helper.
At the moment I think: use the pacman commands from my message,
as there’s less that could go wrong, and you’ll get clear feedback.
(post text here off your terminal if it didn’t go right.)
Pamac might do it OK, but I never use it myself, so I can’t be sure.
Where I wrote “use whatever AUR helper you normally use”, you can use pamac for that part (installing virtualbox-ext-oracle-manjaro from the AUR).
Good find. I hope it gets reflected in the wiki.
At home I have a system installed before 2015, at work one installed in January 2018.
In both I had problems to start virtualbox, although at home I did everything I could find to correct it (no very wise), in the end the solution was what @bogdancovaciu suggested above:
This worked for me today at work, here I didn’t need to reboot for it to work.
I barely remember that I found this dkms suggestion a long time ago when I installed virtualbox at home. In this new installation at work I don’t even have it.
As I’m not running virtualbox, I need some guidance as what needs to be changed in the wiki.
@j77h unless J77 can edit the wiki? (Unsure if you need to be TL2 or TL3)
At section Install the Extension Pack(Optional):
Currently installation of extension pack is advised as:
pamac build virtualbox-ext-oracle
This is fine as long as you have the same version of VirtualBox as Arch has, but stable can lag behind in that, which may lead to similar errors as the one described in this thread until stable catches up.
As @j77h pointed out, there is the aur/virtualbox-ext-oracle-manjaro package, which from the dates seems to align with stable.
In short pamac build virtualbox-ext-oracle-manjaro should also be mentioned with the notification that the version of the extension pack should always match the version of VirtualBox.
I added that in that after 1 (one) TL2 user said he couldn’t. I just wanted confirmation…
It should be fine.
A bit of nitpick, but aur/virtualbox-bin-guest-iso is linked above it, which is a different package, an installer ISO for guest utils. Even then is there a reason it is advised above community/virtualbox-guest-iso?
Feel free to copy-paste and DM me what you want it to be exactly…
P.S. But I’m going to
We need to clarify a few points.
The wiki is at wiki.manjaro.org : VirtualBox - Manjaro Linux
It’s separate from the forum, so nothing like a “wiki post”.
To edit it we need a separate login, and we need to ask for it by email.
(See here: Basic Submission Rules - Manjaro Linux)
There is a HowTo in the Tutorials section of this forum
[HowTo] VirtualBox - Installation - USB - Shared Folder
made by @linux-aarhus. It’s more up-to-date than the wiki page.
That’s not a wiki post either. (Well, it could be, but he didn’t mention it,
and I’m on TL2 so I can’t see an edit button even if it is.)
We I should have checked virtualbox-ext-oracle-manjaro more carefully.
AUR (en) - virtualbox-ext-oracle-manjaro
There is nothing on that page that says it’s an ‘official’ Manjaro production,
so it’s not guaranteed to be always there.
It was 2 days late for the 2020-09-11 stable update.
(Edit: it would be great if Manjaro maintainers would make it part of their update process, but until then — )
We still need to check versions before installing.
yay and pikaur both can use -Ssa to search in the AUR, e.g.
pikaur -Ssa virtualbox-ext-oracle
With that command, they list each package that has “virtualbox-ext-oracle” in any part of the name or description (so they get the manjaro one as well), and show its version number.
up the wrong 
(I’m just an editor here on the site, not a package maintainer nor am I a wiki editor yet…)
My last reply was to everyone here in general – don’t take it as personal 
You are not alone with the current VirtualBox issues. I use virtualbox daily - as I use Visual Studio on Windows 10 for contract work.
I have had several issues lately with the combo Nvidia, VirtualBox, extension pack and kernel modules - even on pure Arch.
I was on the brink of insanity - until I got it working - running Arch with zen kernel and no Nvidia card.
Because this is a manual action - the installer cannot know which users to add to vboxusers group.
It has never really been an issue with the extension pack so a 
to @j77h for the improvements to the VirtualBox topic with relation to the extension pack.