See [this askubuntu question](https://askubuntu.com/questions/33416/how-do-i-disable-the-boot-splash-screen-and-only-show-kernel-and-boot-text-inst)

Edit `/etc/default/grub` and change
```
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
```
for
```
GRUB_CMDLINE_LINUX_DEFAULT=""
```
and then
```
$ sudo update-grub2
```