Ubuntu – Ubuntu 18.4 is extremely slow and laggy in VirtualBox

Freezes are generally hard to debug because your system becomes unresponsive then. This is even more the case when the cause of this could be anywhere

• a problem of the host OS (Windows 7),
• the guest OS (Ubuntu 10.10),
• or from Virtual Box.

From your descriptions we can only guess what might be the cause. In your case the system slows down before freezing, indicating problems in memory management, or from applications that eat up the CPU power you gave your virtual environment.

In the Ubuntu guest you can find out if an application causes this by running top in a terminal (or if you prefer a GUI in System -> Administration -> System Monitor -> Processes) to list CPU and memory usage of individual processes.

Other valuable informations on problems, or error messages from applications can also be found in the .log files that can be viewed with System -> Administration -> Log File Viewer.

If you had suspicious findings there don't hesitate and edit your question to include these informations.

Sometimes it can help to increase the performance and stability of the guest OS with different settings (most can be done in the Virtual Box Manager GUI after a shut down of the guest OS):

• disable screensaver in the guest OS
• enable VT-x/AMD-V (if your host system can do this)
• regularly update Virtual Box to current stable version
• install Guest Additions
• disable 3D acceleration
• increase video memory
• allow more RAM
• but avoid to allow more than 50% of total system RAM
• use one CPU core only
• enable or disable Nested Paging
• try using another audio driver (or disable audio)

Settings in bold are recommended in any case. The other points are suggestions on what you can try out to improve the performance of your virtual Ubuntu.

Other than on bare metal a virtual machine does not always benefit from maxed out resources. This is because the supervisor (here Virtual Box) running on the host will also need some resources to run smoothly.

1. Memory

   Leave as much memory for the host OS to operate without having to swap on the hard drive. If we had used 8 GB of 16 GB for an intergrated GPU then from the remaining 8 GB leave 2 GB or more for the host.

2. CPU

   It is true that any guest OS will run the better the more cores we assign to the guest. If we assign all cores we may slow down the host and the performance of the virtual machine slows down with it. So it is often better to leave at least one core to the host, or define an execution cap of say 90% in the VirtualBox settings.

3. Hard drive

   By using a dynamically growing drive we can assign a huge virtual drive that is physically much smaller as long as it was not filled with data. It will only use as much space as needed.

4. Graphics card

   For 3D acceleration the host GPU is passed through to the guest with the guest additions graphics driver. This also means that all graphic card memory can also by accessed from the guest. Increasing the guest VGA memory to more than 128 MB is rarely needed.