If you use Sun’s great (and free!) virtualization software VirtualBox, then you’ve ran into their “Guest Additions.” They’re for making one’s VirtualBox guest OS experience as good as possible. This is a short guide to getting Guest Additions installed on a CentOS 2.6 guest via command line (without a desktop GUI like Gnome). It finishes after the jump…

Prerequisites:

• working and internet-ready CentOS 2.6 guest OS (only needed if you don’t have the prerequisite software)
• root or sudo access to your server (prefix commands shown here with sudo)
• GNU compiler (Run yum install gcc)
• Kernel development kit (Run yum install kernel-devel-`uname -r`)

Steps:

1. Startup your guest OS and login (either the console or SSH will do).
2. Go to the Devices -> CD/DVD Devices menu and select “VBoxGuestAdditions.iso”. If the option is not available, click on More CD/DVD Images… then add and attach the image.
3. Mount the CD image using mount -o ro -t iso9660 /dev/cdrom /mnt/cdrom. If you get an error that /mnt/cdrom doesn’t exist, use mkdir /mnt/cdrom to create it. if you get an error that /dev/cdrom doesn’t exist or isn’t mountable, try restarting your guest.
4. Run the installation script using sh /mnt/cdrom/VBoxLinuxAdditions-(your architecture: either x86 or amd64).run. Example: sh /mnt/cdrom/VBoxLinuxAdditions-x86.run.
5. If the GNU compiler and kernel development kit have been successfully installed, it will finish.
6. Reboot your system using reboot.

And now you’re done. :) I hope that helps someone.

You can thank Tux Training for some of the information in this tutorial.