When you are setting up a form of Redhat on VirtualBox you might have a little trouble getting the guest additions set up and running. Here is what I did to get both Fedora and Oracle linux up and running…

Im assuming you have the Guest OS installed…

Once you log in for the first time you want to add yourself to “sudoers”.

1. Open a terminal and become root. (su root).
2. Type: visudo
3. Find this line: root ALL=(ALL) ALL
4. Just underneath that line add this: user ALL=(ALL) ALL REPLACE user with YOUR username
5. Save and exit  (  :wq!  )

Next we need to update the kernel…

1. At your terminal prompt type:  sudo yum install kernel* dkms gcc
2. Say YES at the following prompt. You will see a lot of stuff go by and after a few minutes this will complete.
3. Reboot your system and log in as root to complete the next part.

Now we can finally install the Guest Additions…

1. Mount the GuestAdditions ISO file that im sure you have downloaded. If not you can follow the link found in this post. (It will open in a new window for you)
2. Once you have the ISO mounted the directions veer off from what VirtualBox tells you to do…
3. On your guest desktop mount the ISO so that you see it in your PLACES or the icon is present on your desktop.
4. Open that and find the “.run” file. (Likely VBoxLinuxAdditions.run)
5. Double click it and choose “Run In Terminal”.
6. From here since you are already logged in as root it should open a xterm window and start running.
7. When it is complete reboot and log back in as your own user. You should be able to adjust the resolution size for your guest monitor then.

DISCLAIMER:
Yes I realize that you shouldn’t log directly in as root but since you are just setting this up and likely don’t have anything important on it and none of the normal tools that do-badders would need are present, you are safe. Just remember to log in as your self when you are done. Dont do anything extra while you are logged in as root. Always use sudo as your own user. If you hose your own system im not at fault, I told you not to do anything extra. I also cant help you…check with linuxquestions.org if you need further help with your hosed system.