During the boot of Ubuntu, you may see the message ("No symbol table found").
The message appears because the symbol table was not found. Usually, it's not a critical error, and your operating system will boot nevertheless. However, if you would like to fix it, you can try to follow one of the methods available in this article.
Execute the following commands, depending on either or not you are using virtio on your system.
If you are using Virtio
The following will work if you have a cloud server (KVM-Linux) using virtio with the operating system installed on the first storage device:
sudo grub-install /dev/vda
Not using virtio
The following will work with the operating system installed on the first storage device (you cannot be using virtio):
sudo grub-install /dev/sda
You shouldn't see that message anymore in the following reboots.