- "Read-only filesystem..."
- "The system is running on low graphics mode..."
- "Cannot find/install package X..."
- Or, you are able to start the OS somehow but you're not allowed to do any package update/install.
Then you might have a disk space or memory issue. Although your VM might seem to have enough space, there are couple of things you can check:
- Check your_vm->Settings->System->Motherboard, that you have enough RAM allocated.
- Check your_vm->Settings->Storage->Controller->harddisk_name, that the destination it is mapped to (under Attributes, the little harddisk symbol) have enough actual disk space.
- Again, at the same tab, check that the virtual size of the controller is more than ~4GB (a full ubuntu update would take ~3.5GB).
- Finally, if none of the above works, re-partition your virtual disk at the ubuntu installation step. ~350MB swap area, ~5GB system folder, and ~4GB home folder would be minimums.
After that, Finally, if you're complaining about the visual performance and want more functionality (like, obviously, full-screen VM), then don't forget to install Guest Additions. For the above configuration I explained, Chapter 4.2.2 of this tutorial is helpful if not a little bit confusing. Note that if you don't solve the space issue in the first 3 items, then you won't be able to mount the VBoxLinuxAdditions.iso, so do not waste time poking the filesystem :)
I hope this helps someone to not waste time, just like I did!
