Mdthbs

I'm using Virtual Box on my windows 8.1 host machine. I have installed CentOS & Ubuntu in 'Graphical Mode' and had sufficient practice. But now I wanted to switch to 'Command Line Mode" completely. Therefore created a machine for that purpose and installed 'CentOS6.6 Basic Server'/'CentOS7 Minimal.

On Graphical Mahines, I could easily install VBox Guest Additions with these few commands.

yum update

yum install gcc

yum install kernel-devel

sh VBoxLinuxAdditions.run (From mounted Location For CDrom)

But since I installed CLI machine and when tried same commands on it, it does not install properly, gives this error: Could not find X.Org or Xfree86 Window System, skipping.

I just installed this on my Ubuntu CLI VM using these commands:

sudo mount /dev/cdrom /mnt

sudo /mnt/VBoxLinuxAdditions.run

I found a page suggesting installing dkms first but I seem to have had that already installed. If you don't, run this command before those above (this should work on the Ubuntu, but you can probably find the equivalent yum command):

sudo apt-get install dkms

Now, this ran correctly. I also got the error you mention ("Cannot find the X.Org or XFree86 Window System, skipping) but that's just a warning. That's why it says "skipping". It simply skipped installing the parts of the guest additions that deal with X. The rest was installed correctly.

As per the question, OP wants to install the Guest Addition so that he can change the resolution of his Guest. This is not possible. Guest Additions can only change the resolution when there is an X-server installed.

To quote from Wikipedia:

The Guest Additions for Windows, Linux, Solaris, OpenSolaris, or OS/2 guests include a special video-driver that increases video performance and includes additional features, such as automatically adjusting the guest resolution when resizing the VM window or desktop composition via virtualized WDDM drivers .

However, if you do want to install the Guest Addition, you can try this command:

./VBoxLinuxAdditions.run --nox11

But then again, even if it works, it is not going to solve your problem. Because you wouldn't be able to change the resolution of your non-graphical guest OS.

UPDATE

However, if you want to work on the command line in a bigger resolution, you can just ssh into your virtual machine using putty. This is the standard procedure.

The solution posted here addresses the problem. The solution is to change the terminal window size within the VM machine.

If setting in grub2 using this solution the entries as:

GRUB_TERMINAL_OUTPUT="gfxterm"

GRUB_GFXMODE=1024x768x32

GRUB_GFXPAYLOAD=keep

GRUB_GFXPAYLOAD_LINUX=keep

did only change the Grub menu resolution (even if putting the 1024x768x32 on the PAYLOAD entries) and did not solve the problem.
I had to add the vga=0x344 to the GRUB_CMDLINE_LINUX

I know that this is not an answer to the question above but it is an answer to the problem that Sollosa actually wanted to address.

If you are on a computer with a very high resolution screen, the VirtualBox window and the font on the terminal can be tiny!

I have a very easy solution to this problem. You could simply use the shortcut:
CTRL + C

Then, you will be able to stretch the VirtualBox window and, as a result, increase the font size.

If your "Host Key" is something else, you will have to replace the "CTRL" key with your "Host Key".

I want Vbox Guest Additions so on a non-gui interface so I can automount a folder from my Host system.