You need to install the VBox guest utilities to add support for the virtualised graphics hardware.

sudo apt-get install virtualbox-guest-utils virtualbox-guest-x11 virtualbox-guest-dkms

Previously you might have needed the "ose" versions:

sudo apt-get install virtualbox-ose-guest-utils virtualbox-ose-guest-x11 virtualbox-ose-guest-dkms

Edit: http://www.linuxformat.com/forums/viewtopic.php?p=103289

1. Start Virtual Box and log into Ubuntu.

2. Hit your host key(right Ctrl by default)so you can get your mouse pointer outside the virtual machine.

3. Go to top of virtual window, click on devices then select Install Guest Additions You will see a window pop up inside Ubuntu showing you that there are some new files mounted in a virtual CDROM drive. One of those files should be VBoxLinuxAdditions.run

You must run the file with some admin permissions so do that this way...

4. Click inside the Ubuntu screen again then go to Applications > Accessories then Terminal. The terminal window is where you will run the file from, but first we must navigate to the correct directory.

5. Type cd /media/cdrom0 (then hit enter, there is a space after cd!)

6. Next type dir (You should seeVBoxLinuxAdditions.run among the files displayed)

7. Finally type sudo sh ./VBoxLinuxAdditions.run (yes, that is a full stop before the slash!)

After you hit enter and it has done its stuff, the files are now accessible from Ubuntu.

8. You now need to reboot the virtual machine or press Ctrl+Alt+Backspace.

9. Log onto the Ubuntu desktop and go to System > Preferences then Screen Resolution. You should now have more options than the three low resolution options you had at the beginning of the day!

If the resolution you want is not one of the newly listed ones displayed then follow these steps:

1. Open the terminal window (Applications > Accessories then Terminal)

2. Type sudo gedit /etc/X11/xorg.conf (case sensitive)

3. It will ask you for a password which is the same as the one you log in with(see sudo ^[1]).

4. The text editor loads and you should see a lot of text in the window. First make a backup of this file by going to File then Save as and change the filename to xorgbak.conf

5. You now need to hunt through the text until you see the display resolutions listed. The ones you will be concerned about will be listed under bit depth 24 or bit depth 16 (as these depths are the ones that give you a large array of colors.)

6. The idea here is to have your favorite screen resolution included in this list. Do this by either inserting it before the other listed resolutions in the exact same manner or typing it over one of the others. (you will only need to do this for the ones under bit depth 24 and 16)

7. You must now do a "save as" but be careful here as this time we need to call the file xorg.conf again. If you just hit save here you would have overwritten the backup file you created which is not what we want.

8. Once you have completed the previous step, you are done. Hit Ctrl+Alt+Backspace to restart your Virtual Box instance, log in and enjoy your new screen resolution options!

Devices > Install Guest Additions, let it run then log out.

When you've been returned to the login screen you'll see it's the full size of your monitor. Log in and you're good to go.

I had the same problem and then found out that if you launch the virtual machine > click "view" on the toolbar > click "auto-resize guest display, then your virtual machine will have the same screen resolution as your own screen.

Once the Vbox Additions has been instaled (and reboot the guest os), press Host + H, then maximise the window, thats sould do the trick..
If not, maybe you are using an old version of vbox (therefore, the Vbox Additions might has an incompatibility..)

Try increasing the amount of RAM allocated to the Virtual Box. Worked for me.

To do this, stop the VM, then in VirtualBox go to the Settings for the VM. Go to the Display section. You can increase the Video Memory there. Mine was 1MB; I increased it to 32MB and that allowed me to use my 24" monitor fully.

• Settings > Video > Video Memory = 128 MB, Enable 3D acceleration = true.
• Install GuestAdditions

• On Host machine, in cmd/bash, run

  VBoxManage setextradata global GUI/MaxGuestResolution any
  

• create /etc/X11/xorg.conf file with content:

  Section "Device"
    Identifier      "Configured Video Device" 
  EndSection
  Section "Monitor" 
    Identifier      "Configured Monitor"
  EndSection 
  Section "Screen"  
    Identifier      "Default Screen" 
    Monitor         "Configured Monitor"
    Device          "Configured Video Device" 
    SubSection "Display"
      Modes "1920x1080" 
    EndSubSection
  EndSection
  

• For running VM:

  Host Key Right Ctrl at default + Home = view full screen.

I have tried to exclude every step except GuestAdditions installation. You need every one of them.

Apart from installing the Guest Additions plugin, note that the maximun display size may be capped in VirtualBox general preferences panel:

Also, check autoResize option and VirtualBox will automatically set the display size as you resize or maximize the window.

I can tell you how I do this with Mac OS X as the host system. Maybe it will work on Windows too.

• I start ubuntu in VirtualBox
• I open up the terminal on Mac OS X
• and execute "VBoxManage controlvm [name] setvideomodehint 1280 1024 24" (replace [name] with the name of your ubuntu vm)

I had the same problem and was able to fix it by using the xrandr utility. I followed this article to fix the issue.

http://www.ubuntugeek.com/how-change-display-resolution-settings-using-xrandr.html

Sometimes this may help you. Give it a try.

I was able to fix this problem by shutting down my VirtualBox virtual machines, quitting VirtualBox, and running this command in a Terminal:

VBoxManage setextradata global GUI/MaxGuestResolution any

Then start VirtualBox back up and the problem should be fixed!

Following command worked for me
Open Terminal and type:
sudo apt-get install dkms

Source: http://www.virtualbox.org/manual/ch04.html ^[1]
Restart VirtualBox

What driver is specified in ur xorg.conf? AFAIK, after installing guest additions the 'vboxvideo' should be used:

Section "Device"
    Identifier   "Configured Video Device"
    Driver     "vboxvideo"
EndSection

After installing guest additions: Go to settings > Display Increase video memory and enable 2D and 3D video acceleration.

It is probable that your brand new install of a linux distro on your Virtualbox is still fresh and that much more needs to be done to set up your environment, not the least of which is to enable the X Window system if all that you are seeing are display settings for 4:3 aspect ratio and entering 'startx' at the command prompt does nothing.

..at your terminal prompt, enter the following:

sudo apt-get install dkms
sudo apt-get update
sudo apt-get install linux-headers-`uname -r`
sudo apt-get install --reinstall xorg
startx

If you had set your virtual machine to fullscreen mode prior to entering 'startx', then the screen will automatically adjust to 16:9 aspect ratio, with tool and task bars in their proper places.

I did this setting and all was OK:

This may have already been resolved but I had this issue and fixed it very simply, I just updated VirtualBox to the latest version then re-installed the guest additions.

VirtualBox 4.3.12 was preventing the above solutions from working on my Windows system. 4.3.18 was released somewhen around 2014/10/10 (2014 Oct 10), all of the above works since installing that.

The "VBoxManage setextradata global GUI/MaxGuestResolution any" command appeared to work previously, that is to say it didn't throw any errors.

Installing guest additions had previously complained that the header files were not installed, however they absolutely WERE (& have been left untouched) as evidenced by the fact that installing guest additions under 4.3.18 upgrade does not throw the error when building the shared folders module.

Here is a 2016 updated answer that worked for me.

To start, I'm on Mac 10.11 (El Capitan), and my VirtualBox is 5.0.26. I'm running Ubuntu 14.04 LTS in this example (I need to upgrade my Ubuntu eventually).

1. Start your VM
2. Select "Devices -> Insert Guest Additions CD image..." (no, you don't actually need a CD, this is virtual)
3. This will open a window asking for your root password
4. A terminal window will open. If it asks about re-installing over a previous version of guest additions, type "yes" and hit return
5. Restart your VM
6. Once the VM is up and running again, go to "View -> Virtual Screen 1 -> [whichever resolution you want]".

My options were all the way from 640x480 to 1920x1200. Once I selected a new resolution, I did not have to restart the VM again, it automatically scaled.

If none of the answers helps you fixing the issue (like it was situation with me), then verify on your Host OS that in "Screen resolution" window (Control Panel > Appearance and Personalization > Display) whether the displays are aligned and not like in picture from the following link:

Preview of settings on Host OS that caused me issue with maximum resolution on Guest OS ^[1]

If someone is confused because of the value of shown Display field, the reason is that I don't use Windows 7 as my Host OS, so I've used it on VirtualBox in order to simulate problem.

If you would like to use different resolution on each monitor and/or you are not sure how to align displays in previous window, clicking on "Detect" button should do things properly for you. You probably wouldn't suspect that that causes problem because, if you use Windows 7 (or any newer versions of Windows) as Host OS, it will successfully render image on your monitors, even when the set positioning is distorted as shown.

I've been struggling with this problem on many tested Guest OSs like Ubuntu, Windows XP and Windows 7 (so the issue in my case wasn't related to Ubuntu nor Linux at all) and after properly configuring that setting, I was able to choose larger desired resolution in my Guest OS (of course, you should previously install VBox Guest Additions as it is stated in several answers).

My problem/solution was actually strange, I had a another laptop/monitor with a lower resolution set up in Windows as a main display. Therefore no matter what, even if I had a max option in View/Virtual Screen 1920x1200, this time it was not checked. I am using i3 GUI , gnome behaved even more strangely. Once I configured my 4k 3840x2160 in Windows as a main monitor, VirtualBox adapted correctly. (Maybe I combine it with a lot of solution here at stackexchange and other websites.) ,but setting up the 4k display as a main display in Windows was basically a solution for me.

Note: Also previously I configured linux ubuntu resolution via command line by a process of these commands - How to set a custom resolution? ^[1]

otherwise a one-liner resolution appliance command line and few easy steps

eval $(cvt 2220 1250 60 |sed 's/Modeline/xrandr --newmode /g'|sed -n '1!p') what this one liner does: (1st/3 part generates dimensions, 2nd/3part uses output and replaces with xrand to create logical display, 3/3part it has on the first line comment so it starts at 2nd line)

as a proper result resolution might be afterwards reevaluated and adjusted, therefore find out the created resolution by xrand command appended in the end of output,

1) assign the resolution to a specific display -

xrandr --addmode VGA-1 "2224x1250_60.00"

2) output the desired resolution on the display

xrandr --output VGA-1 --mode "2224x1250_60.00"

Because my reputation is not enough to add a comment for @maco's answer ^[1], I'm writing this as an answer.

I'm using Ubuntu 16.04 and I installed the VBox utilities as @maco's answer ^[2] however when I locked the screen I could not used my keyboard and mouse anymore. There is a bug report ^[3] about that. I found the solution here ^[4] and totally it took me 2-3 hrs.

I hope it helps for whom having the same issue :)

The scale factor in the virtual machine settings did the trick for me. I set it from 100% to 200%.

Note: I have a Huawei Matebook X Pro.

It took me quite a while to finally make it work (I think it was installation of VirtualBox Guest Additions ^[1] and VirtualBox Extension Pack ^[2] which did the trick for me eventually) but before I managed to make it work I was just using Remote Desktop to connect from my Linux host to Windows guest. I used Remmina ^[3] (RDP protocol) and by just selecting Use client resolution option I got my host system native resolution straight away.
I still like this approach actually: you can start VM in a headless mode and it just feels... lighter, but the drawback of this method is that the video throughput via RDP connection, at least in my case, is substantially lower than when using native VirtualBox window, though it is noticeable only when you try to do GPU-intensive things like playing HD videos, I don't see much of a difference otherwise. I did try to improve Host <-> Guest network connection performance using dedicated Host Only network ^[4] with virtio ^[5] network adapter but I guess the bottleneck is probably somewhere in FreeRDP ^[6] implementation.

Still Remote Desktop could be a quick solution for someone who is struggling to make it work and needs native host resolution in Guest VM.

Running Mint 20.1. Got a VM to resize with bigger resolution. Here’s how:

1. Ran VirtualBox. Got the Oracle VM VirtualBox Manger. 
2. Made a new VM “Virtual Mate”. Type: Linux. Version: Ubuntu 64 bit. 
3. Gave it 8192 GB memory. 
4. Virtual hard disk. VDI. Dynamically allocated. 20 GB. 
5. Settings – Display – gave it 128 MB. 3D acceleration for the VMSVGA. 
6. Settings - Storage – attached the Mate iso.
7. Ran it. Immediate installation, erase and install. Done. 
8. Restarted. To “Remove the installation media”, just hit Enter. Logged in.
9. Closed the VM window, and saved this machine state. 
10. Ran it. Devices – inserted guest additions CD – did the autorun. 
11. It wanted the restart; did that. Logged in. 
12. Resized with resolution change worked. 

It won’t resize until you’ve logged in.

The issue for me was virtual box additions were not installed. I thought I install them however it actually failed because GCC and Perl and Make were not installed. Before you install the virtual box additions run the following (in ubuntu)

sudo apt-get install gcc make perl

Then install guest additions like described in previous posts

All I had to do was go into the guest OS's display settings and change it to maximum resolution. (Make sure in the VirtualBox settings that you don't have it set to a maximum width of about 600px).

Setup: I am using an Ubuntu VM in VirtualBox on a Windows host

VirtualBox has a feature called "Scaled Mode" (View > Scaled Mode) - When enabled, it allows you to simply drag and resize the window. However, this does not change the resolution of the window (you will find the icons and text to be a little blurry). To actually change the resolution you must install the GuestAdditions software.

You can read about GuestAdditions in the official VirtualBox docs: https://www.virtualbox.org/manual/ch04.html

From the above documentation: The Oracle VM VirtualBox Guest Additions for Linux are provided on the same virtual CD-ROM file as the Guest Additions for Windows. See Section 4.2.1.1, “Installing the Windows Guest Additions”.

TIP: I followed all of the steps above, but found that the window was not resizing when I dragged it. I then clicked on the CDROM icon (GuestAdditions was still mounted) and just right clicked the autorun.sh file and selected "Run as program" - This seemed to do the trick in terms of actually installing it. Rebooted again and this time I was able to drag the window and found that it would actually change the resolution.

Version 7.0.0 of VirtualBox, along with the Guest Additions Extension Pack should do the trick, just run this command:

sudo apt-get install virtualbox-guest-utils virtualbox-guest-x11

and then click Devices > Install Guest Additions CD Image and reboot.

https://www.virtualbox.org/wiki/Download_Old_Builds_7_0

I'm on Pop!Os with Wayland and VirtualBox 7.0.10.

In order to enable screen resolution, I've installed the following packages:

sudo apt-get install virtualbox-guest-utils virtualbox-guest-x11

Now download the right guest additions iso for your vbox version:

(mine) https://download.virtualbox.org/virtualbox/7.0.10/

Start the VirtualBox image, and from the "Devices" menu select insert image of guest additions cd iso.

It will reboot after the setup is completed.

You should be able to select a new resolution in the "Visualize" > "Virtual screen 1" menu (translation may be different, anyway it can be accessed from the monitor icon in the bottom right corner, where all vbox interfaces are displayed).