When I install a VirtualBox Linux guest virtual machine on a Windows host, I often have two annoying issues:

1. The guest display is locked in at a lower resolution, refusing to match the host's higher resolution.  The menu option “Auto-resize Guest Display” is disabled.
2. The clipboard won't communicate between the host and the guest, even though I have enabled the bidirectional clipboard.

I set out initially to solve the display issue, and after solving that I discovered that it also solved the clipboard issue!  I came up with this solution originally for Debian systems, but have also used it with Ubuntu, so it will probably work for most varieties of Linux.

Boot up your Linux guest and open a terminal.

Before proceeding, make sure your system is up-to-date:

> sudo apt-get update

If any updates were made, it would be a good idea to reboot the guest before continuing on to the next step, in order to make sure the entire system has refreshed, otherwise you might get some temporary errors that will send you on a wild goose chase.

From the VirtualBox Menu of your virtual machine's window, select “Devices” | “Insert Guest Additions CD image...”  This should mount the CD image.  If an autorun prompt appears, close it, because we're doing this from the command line.  (If you get a error message stating, “Unable to insert the virtual optical disk,” most likely you already mounted the Guest Additions CD image and can ignore the error.)

Change to the directory of the mount.  If you're not sure where that is, enter the following to view a list of all mounted devices, filtered for optical drives:

> cat /etc/mtab|grep 'media'

which might yield something like

/dev/sr0 /media/cdrom0 iso9660 ro,nosuid,nodev,noexec,relatime 0 0

or

/dev/sr0 /media/username/VBox_GAs_6.1.22 iso9660 ro,nosuid,nodev,noexec,relatime...

The path beginning with /media/ is the CD image.  If you don't see a line like that, or if you do but the location appears to be empty, it may be because the system for some bizarre reason won't actually mount the CD image until you actively access it by other means.

Access the CD image via the file explorer (double-click its icon on the desktop if there is one) and then again try cat /etc/mtab|grep 'media'.  You should now be able to find a line containing “cdrom.”

If you're trying to install Guest Additions on a system that doesn't have a graphical interface, use the following to manually mount the disc image:

> sudo mkdir --p /media/cdrom
> sudo mount -t auto /dev/cdrom /media/cdrom/

Output may look something like

mount: block device /dev/sr0 is write-protected, mounting read-only

You should now be able to find the mounted CD-ROM via cat /etc/mtab|grep 'media'.

In one example, the line is:

/dev/sr0 /media/cdrom0 iso9660 ro,nosuid,nodev,noexec,relatime 0 0

...and our target directory is the second path listed on that line, which in this case is /media/cdrom0.  Switch to the CD-ROM's directory:

> cd /media/cdrom0

Alternatively, you may be able to open the disc in a graphical file browser, then right-click its contents and click on “Open in Termanl”.

List the directory contents:

> ls -la

and you should see something like this:

total 51403
dr-xr-xr-x 6 root root     2048 Apr 18 03:02 .
drwxr-xr-x 3 root root     4096 Sep 30  2014 ..
dr-xr-xr-x 2 root root     2048 Apr 18 03:02 32Bit
dr-xr-xr-x 2 root root     2048 Apr 18 03:02 64Bit
-r-xr-xr-x 1 root root      647 Aug 16  2016 AUTORUN.INF
-r-xr-xr-x 1 root root     6381 Apr 18 03:52 autorun.sh
dr-xr-xr-x 2 root root     2048 Apr 18 03:02 cert
dr-xr-xr-x 2 root root     4096 Apr 18 03:02 OS2
-r-xr-xr-x 1 root root     4824 Apr 18 03:52 runasroot.sh
-r-xr-xr-x 1 root root  8129998 Apr 18 03:53 VBoxLinuxAdditions.run
-r-xr-xr-x 1 root root 17771008 Apr 18 03:54 VBoxSolarisAdditions.pkg
-r-xr-xr-x 1 root root 16399216 Apr 18 04:01 VBoxWindowsAdditions-amd64.exe
-r-xr-xr-x 1 root root   268496 Apr 18 03:53 VBoxWindowsAdditions.exe
-r-xr-xr-x 1 root root 10037640 Apr 18 03:54 VBoxWindowsAdditions-x86.exe

Run VBoxLinuxAdditions.run:

> sudo sh VBoxLinuxAdditions.run

If you see something like “Verifying archive integrity...Error in MD5 checksums” it might just be that the system hasn't been refreshed after the update.  Make sure that you've updated everything and let the updates complete, remove any mounted discs from the virtual optical disk, reboot the guest, then try again.  (Start over at “Insert Guest Additions CD image...”)  If running VBoxLinuxAdditions.run literally does nothing (quits without any messages^[1]) it could be that there's an issue with the disc mount.  Try shutting down you guest completely and exiting the VirtualBox launcher and any other VirtualBox guests.  (Maybe even reboot your host.)  Restart your guest and try again.

If all goes well, you should see something like the following:

Verifying archive integrity... All good.
Uncompressing VirtualBox 5.1.20 Guest Additions for Linux...........
VirtualBox Guest Additions installer
You appear to have a version of the VirtualBox Guest Additions
on your system which was installed from a different source or using a
different type of installer.  If you installed it from a package from your
Linux distribution or if it is a default part of the system then we strongly
recommend that you cancel this installation and remove it properly before
installing this version.  If this is simply an older or a damaged
installation you may safely proceed.

Do you wish to continue anyway? [yes or no]

Enter

> yes

At this point there's a good chance you'll encounter some errors preventing you from proceeding.  I'll address the ones I've experienced^[2].

On an old Sony Vaio running Windows Vista 32-bit, I got the following error.  (If you don't have this problem, skip ahead.)

Copying additional installer modules ...
Installing additional modules ...
vboxadd.sh: Starting the VirtualBox Guest Additions.
Failed to set up service vboxadd, please check the log file
/var/log/VBoxGuestAdditions.log for details.
This system appears to be running a version of Mesa with a known problem
which will prevent VirtualBox 3D pass-through from working.  See
  https://bugs.freedesktop.org/show_bug.cgi?id=26663
The following, run as root should fix this, though you will have to run it
again if the system version of Mesa is updated:
  strip -R .note.ABI-tag /usr/lib/i386-linux-gnu/libGL.so.1
  ldconfig

View the log file:

> tail /var/log/VBoxGuestAdditions.log

You might see something like this:

vboxadd-x11: unrecognized service
vboxvfs: unrecognized service
vboxadd-timesync: unrecognized service
vboxadd-service: unrecognized service
vboxadd: unrecognized service
vboxadd.sh: failed: Configuration file /var/lib/VBoxGuestAdditions/config not found.
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: modprobe vboxguest failed.

...telling you to look at yet another log file:

> tail /var/log/vboxadd-install.log

which might look like this:

/tmp/vbox.0/Makefile.include.header:112: *** Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR= and run Make again.  Stop.
Creating user for the Guest Additions.
Creating udev rule for the Guest Additions kernel module.

It looks like we're supposed to manually define KERN_DIR, but we're not, so don't worry about that.  The problem here is that the script is unable to find information about your build, somewhere like /lib/modules/[kernel_version_number]/build, which the script should automatically use to define KERN_DIR, which in my case was /lib/modules/3.2.0-4-486/build.  My problem was that /lib/modules/3.2.0-4-486/build did not exist.  You can confirm that this is your problem too by viewing /lib/modules/[kernel_version_number] and seeing whether or not it contains “build”:

> ls -la /lib/modules/`uname -r`/build

If the directory doesn't exist, you'll see something like this:

ls: cannot access /lib/modules/3.2.0-4-486/build: No such file or directory

To resolve this issue, enter

> sudo apt-get install linux-headers-`uname -r`

To confirm this was successful, view /lib/modules/[kernel_version_number]/build:

> ls -la /lib/modules/`uname -r`/build

You will successfully see a directory listing.

Installing the following additional packages has also been recommended for this situation.  You might get away with skipping this step, but this has actually been proven to also solve other unrelated issues that may crop up later when installing other services:

> sudo apt-get install dkms build-essential

Run VBoxLinuxAdditions.run again:

> sudo sh VBoxLinuxAdditions.run

Sample program output:

Verifying archive integrity... All good.
Uncompressing VirtualBox 5.1.20 Guest Additions for Linux...........
VirtualBox Guest Additions installer
Removing installed version 5.1.20 of VirtualBox Guest Additions...
vboxadd.sh: Stopping VirtualBox Additions.
Copying additional installer modules ...
Installing additional modules ...
vboxadd.sh: Starting the VirtualBox Guest Additions.
This system appears to be running a version of Mesa with a known problem
which will prevent VirtualBox 3D pass-through from working.  See
  https://bugs.freedesktop.org/show_bug.cgi?id=26663
The following, run as root should fix this, though you will have to run it
again if the system version of Mesa is updated:
  strip -R .note.ABI-tag /usr/lib/i386-linux-gnu/libGL.so.1
  ldconfig

Note that in my case, I am advised regarding a known issue with Mesa.  If you see something like that, run the commands advised by program output, which in my case were:

> sudo strip -R .note.ABI-tag /usr/lib/i386-linux-gnu/libGL.so.1
> sudo ldconfig

On an HP Pavilian running Windows 10 64-bit, VBoxLinuxAdditions.run gave me this message telling me to install additional packages.  (If you don't have this issue, you can skip ahead.)

This system is currently not set up to build kernel modules.
Please install the gcc make perl packages from your distribution.
Please install the Linux kernel "header" files matching the current kernel
for adding new hardware support to the system.
The distribution packages containing the headers are probably:
    linux-headers-amd64 linux-headers-4.9.0-4-amd64

Install these missing packages:

> sudo apt-get install build-essential linux-headers-`uname -r`

On a desktop running Windows 10 64-bit, I got the following error.  (If you don't have this issue, you can skip ahead.)

VirtualBox Guest Additions: Kernal headers not found for target kernel 4.19.0-5-amd64. Please install them and execute
  /sbin/rcvboxadd setup
VirtualBox Guest Additions: Running kernal modules will not be replaced until the system is restarted

Install these missing packages:

> sudo apt-get install build-essential linux-headers-`uname -r` dkms

Another error you might see could be:

This system is curently not set up to build kernal modules.
Please install the gcc make perl packages from your distribution.

and need to run the following installation:

> sudo apt-get install build-essential gcc make perl dkms

After VBoxLinuxAdditions.run successfully finishes running, shut down and restart your guest.  After you log into your profile on the guest, its display should now match the host's.  (You may have to restart twice for this to work.)  If the bidirectional clipboard still doesn't work, run VBoxLinuxAdditions.run again and restart.

Note that one time I created a new virtual machine and I couldn't get the guest to increase its resolution until I told the emulator to go fullscreen (go emulator menu View -> Full-screen Mode or press Host+F).

Note that each time you update VirtualBox, it would be wise to also update, and maybe even upgrade, your guest's packages.  In any case, you should run VBoxLinuxAdditions.run again.  (In one case I experienced, upgrading VirtualBox caused the titular issues of this article to manifest, and I couldn't get VBoxLinuxAdditions.run to work until after I upgraded the guest.)

Once when installing a guest running Ubuntu 20, after the first time I maximized the window, every time I logged in the screen would go blank and stay that way.  (I could still reach the terminal by pressing Ctrl+Alt+F5, but the desktop never loaded.)  This seems to be a known issue no issue with no official fix at the time of this writing (2021.05.14), but upon rebuilding the system I found that resizing the emulator window by slowly dragging its corner before maximizing seemed to avoid this issue.