What Guest Additions does and how to install it

Guest Additions is a software package that runs inside your virtual machine and improves how it talks to your host computer. It gives you better video performance, lets you resize the window smoothly, enables shared folders between your host and guest, and allows your mouse to move freely between screens without getting trapped. Installing it is a one-time task that takes about five minutes.

The process has two parts: mounting the Guest Additions CD image inside your virtual machine, then running the installer that comes on it. VirtualBox provides the CD image automatically — you do not download it separately. The steps differ slightly depending on whether your guest operating system is Windows, Linux, or macOS, but the mounting step is the same for all three.

Key Takeaways

  • Guest Additions mounts as a virtual CD inside your running virtual machine, not on your host computer.
  • You start the installation from the Devices menu in VirtualBox while the virtual machine is running.
  • Windows guests run an .exe installer; Linux guests run a shell script from the terminal; macOS guests run a .dmg installer.
  • After installation completes, you must restart the virtual machine for the changes to take effect.
  • If the CD does not appear on your desktop or in your file manager, check that your virtual machine has a CD/DVD drive configured in its settings.

Mounting the Guest Additions CD from the Devices menu

Start with your virtual machine running and focused in the VirtualBox window. Click the Devices menu at the top of the VirtualBox window — not your guest operating system's menu, but VirtualBox's own menu bar. You will see an option that says Insert Guest Additions CD Image. Click it.

VirtualBox will mount a virtual CD drive inside your guest operating system. On Windows, the CD usually appears as a new drive in File Explorer within a few seconds. On Linux, it typically appears on your desktop or in your file manager's sidebar. On macOS, it appears as a mounted volume on the desktop. If nothing appears after 10 seconds, your virtual machine may not have a CD/DVD drive configured — see the troubleshooting section below.

Installing on Windows guests

Open the CD in File Explorer and double-click the file named VBoxWindowsAdditions.exe. A setup wizard will open. Click through the prompts, accepting the default installation path. When asked whether to install USB support and network drivers, leave both checked unless you have a specific reason not to.

The installer will copy files and may ask you to restart. Let it restart the virtual machine when prompted. After the restart completes, Guest Additions will be active. You can verify this by opening the Devices menu again — if Insert Guest Additions CD Image is grayed out, the installation succeeded.

Installing on Linux guests

Open a terminal inside your virtual machine. The CD is usually mounted at /media/cdrom or /mnt/cdrom, but you can check by typing mount and looking for a line that mentions VBoxGuestAdditions. Navigate to that directory by typing cd /media/cdrom (or whichever path your system shows).

Type sudo sh ./VBoxLinuxAdditions.run and press Enter. You will be asked for your password. The script will compile and install the Guest Additions kernel modules — this takes a minute or two and produces a lot of text output. When it finishes, type sudo reboot to restart the virtual machine. After the restart, Guest Additions will be active.

Installing on macOS guests

The mounted CD will appear as a volume on your desktop. Double-click it to open the folder. Inside, you will see a file named VBoxDarwinAdditions.pkg. Double-click this file to start the installer.

The installer will ask for your password and then proceed with installation. When it finishes, restart your virtual machine by going to the Apple menu and selecting Restart. After the restart, Guest Additions will be active.

Troubleshooting when the CD does not appear

If the CD does not appear in your guest operating system after you click Insert Guest Additions CD Image, the most common cause is that your virtual machine does not have a CD/DVD drive configured. Power off the virtual machine, right-click it in the VirtualBox main window, and select Settings. Go to the Storage tab on the left.

Look for a line that says IDE or SATA with a CD icon next to it. If you see one, click it and check that the dropdown next to Optical Drive is not set to Empty. If there is no CD/DVD controller at all, click the icon that looks like a CD with a plus sign, select IDE or SATA depending on your guest OS, and confirm. Then power the virtual machine back on and try mounting the CD again.

If the CD appears but the installer will not run, make sure you are running it with administrator or root privileges. On Windows, right-click the .exe and select Run as Administrator. On Linux, use sudo as shown above. On macOS, the installer will prompt you for your password automatically.

What to do after installation is complete

After you restart and Guest Additions is active, you can eject the virtual CD. Right-click the CD in your file manager or on your desktop and select Eject, or open the Devices menu in VirtualBox and click Optical Drives, then select the CD and click Remove Disk from Virtual Drive.

You can now use the features Guest Additions provides: resize your virtual machine window and watch the guest desktop resize with it, drag files between your host and guest if you have set up shared folders, and move your mouse between screens without it getting stuck. If you ever need to reinstall Guest Additions — for example, after a major guest OS update — repeat these steps.

Frequently Asked Questions

Do I need Guest Additions to run a virtual machine?

No. A virtual machine runs without it, but the experience is slower and less convenient. Your mouse will be trapped inside the window, you cannot resize the window smoothly, and video performance will be noticeably worse. Guest Additions is optional but strongly recommended.

Can I install Guest Additions on a paused virtual machine?

No. The virtual machine must be running. If it is paused, resume it first by clicking the play button in the VirtualBox toolbar, then go to the Devices menu.

What if the installer says it cannot find the kernel headers?

On Linux, Guest Additions needs to compile against your kernel. Install the kernel headers package for your distribution — on Ubuntu or Debian, type sudo apt install linux-headers-$(uname -r). Then run the installer again.

Will Guest Additions slow down my virtual machine?

No. Guest Additions actually improves performance by enabling hardware acceleration for video. It uses a small amount of disk space and memory, but the benefit far outweighs the cost.

Can I update Guest Additions after installing it?

Yes. When you update VirtualBox on your host computer, mount the new Guest Additions CD image and run the installer again inside your guest. It will replace the old version with the new one.