Change MacOS X guest screen resolution for VirtualBox

VBoxManage setextradata "mac" "VBoxInternal2/EfiGraphicsResolution" "1920x1080"

did the trick for me on high sierra

I am using VirtualBox under Ubuntu Linux, and a Mac OSX (Mountain Lion) as guest OS.

For me, the full resolution started working when I did all of the following:

0) Install MultiBeast 4, making sure that the system boots from the virtual hard disk rather than from any booting CD. I followed the instructions here:

http://www.macbreaker.com/2012/07/mountain-lion-virtualbox.html

However, at the end of the procedure I did not have the full resolution, which for me must be 1920x1080x32.

1) In the virtual machine, edit these PLIST files,

sudo pico /Extra/com.apple.boot.plist/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

In this file, inside <dict>...</dict>, insert:

<key>Graphics Mode</key>
<string>1920x1080x32</string>
<key>Kernel Flags</key>
<string>"Graphics Mode"="1920x1080x32"</string>

sudo pico /Extra/com.chameleon.Boot.plist

In this file, inside <dict>...</dict>, insert:

<key>GraphicsEnabler</key>
<string>y</string>
<key>Graphics Mode</key>
<string>1920x1080x32</string>
<key>Kernel Flags</key>
<string>npci=0x3000 darkwake=0 "Graphics Mode"="1920x1080x32"</string>

I noticed that I already had some "kernel flags", so I just added another one for "Graphics Mode". Also note that "Graphics Mode" has a space inside it.

2) Shutdown the virtual machine and do the commands

vboxmanage setextradata "MAC OS X" "CustomVideoMode1" "1360x768x32"
vboxmanage setextradata "MAC OS X" "GUI/CustomVideoMode1" "1360x768x32
VBoxManage setextradata MountLion VBoxInternal2/EfiGopMode 3

After this, the virtual machine boots with full resolution.

Now, this might be overkill, and the result could be achieved perhaps with fewer options, but I tried various things until it started working.

For the record, I found this advice that allowed me to change the resolution:

VBoxManage setextradata "vmname" VBoxInternal2/EfiGopMode 3

where the last param is one of:

0 – 640×480
1 – 800×600
2 – 1024×768
3 – 1280×1024
4 – 1440×900
5 – 1920×1200 

I'm running VBox 5.0.14 on OSX 10.9 (host), and the guest is OSX 10.11.