I’ve done a bunch of VirtualBox installs, upgrades and VM migrations recently. I’ve found that the automated Guest Additions installation hasn’t always kicked off. Typically the installation can be started by selecting Device -> Install Guest Additions from the menu when the VM is running. But this wasn’t working for me, so I needed to manually install the additions. This was done with both Windows and OS X hosts with Windows guest OS’s.
This procedure gets down to the basics. In most cases I did not have to locate the Guest Additions ISO as it was already available in the library and just needed to be mounted. You can skip to “Installing Guest Additions” and see if the ISO is already available.
Locate the Guest Additions ISO
Mac OS X is a little more involved. First locate VirtualBox in the Application folder, right-click it and select show package contents.
Then browse to Contents/MacOS/VBoxGuestAdditions.iso. Copy it to a location that accessible when browsing for files.
On Windows PC hosts the VBoxGuestAdditions.iso file is located in c:\program files\oraclevirtualbox. It can be accessed directly and does not need to be moved.
Installing Guest Additions
Start the VM that needs the guest additions.
Click the CD icon in the bottom task bar.
If it’s listed, select VBoxGuestAdditions.iso. If it’s not listed select “Choose…” and browse to the ISO file identified in “Locate Guest Additions ISO” above.
If autorun kicks in then run VBoxWindowsAdditions.exe. If autorun is disabled then browse to it in file explorer and run it. You’ll need to reboot when the installation is done.
For the record, this was with VirtualBox 4.2.4.