How to resize desktop on VirtualBox Ubuntu

Have you installed the virtualbox guest additions?

Have you ran full updates on the guest?
This with the guest additions should sort this

Yes I've ran the guest additions script thru the terminal, but i can only do it when i am logged in under my user ID, i cannot run the guest script thru the guest log in. I get an error. That being said I've attempted to run the guest script multiple times along with multiple restarts when i am logged in. It seems to complete but i get no changes afterwards

So when I try running the guest additions script thru the terminal logged in as guest, i get the following error ..."sudo: unable to change to root gid: Operation no permitted" ... When I try Devces>Insert Guest Additions CD ... I get a dialogue box from the VM with an error of
"Unable to insert the virtual optical disk C: ... " With a destination, asking me if I would like to force an Unmount. If I choose to force an unmount, still nothing occurs.

What is the output of:

cat /etc/issue

The first user you made at install time is by default able to use sudo.

Don't confuse guest additions and logging in as guest!

Why do you want to log in as guest? You should use a named user. The guest user does not have any rights to make system modifications (and cannot install the guest additions), and all data that you store as guest will be deleted after logout (somewhat like using a public internet kiosk).

The "guest additions" is an additional package that adds functionality into the operating system that is running inside virtualbox ("the guest system") to better cooperate with the operating system where virtualbox is installed ("the host system"). This has nothing to do with the possibility of logging in as unnamed guest in Ubuntu.

Log in as the named user that you created when installing Ubuntu, and try Devices>Insert Guest Additions CD. This should ask for your password as confirmation for an administrative task, and should ask whether you want to run the guest addition installer.

Sorry guys i only thought i had to be logged in as a guest .... regardless i do run the guest additions script when i am logged on. The script seems to run fine and completes, nothing changes afterwards. That is when running the script thru the terminal. If i try Devices>insert guest additions ... i get the same error mentioned above "unable to insert the virtual disk C ... "

If you run the install script ok then it is done.

What is the output of:

cat /etc/issue

Thanks

Gentleman, I removed/ re-installed Ubuntu. At first log in I was able to run the guest partitions thru Devices>Insert guest additions CD. The script ran smoothly, I restarted and BAM ! Finally, everything looks normal ... Thank you guys so much for your attentive assistance. It is greatly appreciated by a novice like me. Again, thanks for all the help - Ben