Plymouth, that image of 'loading' or 'loading' that appears when the system is starting, and then disappears and we are shown the login screen (where we write our username / password and enter our session).
Plymouth, generally has animations, movements that make our wait more pleasant while the system is loading all the services and applications necessary for its operation.
We already put a tutorial on how to install the plymouth in Debian, and I installed it myself and enjoyed it for a while… however, it later became boring, I felt bad not seeing all the service lines starting up, not knowing what was actually happening on the laptop when it started up 
That's why I wanted to disable the Plymouth, and just leave the whole boot log... all the signs that some people consider "strange" and even scare them 
I was looking for how to do this (disable plymouth) when elav simply suggested to remove a line, and this was precisely the solution.
We edit our file / Etc / default / grub with administrative privileges. For this we put in a terminal:
- sudo nano /etc/default/grub
They will be asked for their password, they write it down and press [enter].
We search in the first 15 or 20 lines, one of them will say:
GRUB_CMDLINE_LINUX_DEFAULT = »quiet splash»
We modify it to simply say:
GRUB_CMDLINE_LINUX_DEFAULT = »»
Once this is done (that is, eliminated quiet splash of the line) we push [Ctrl] + [O] (is an or, not a zero) to save the file and press [enter]. Then we press [Ctrl] + [X] to get out of there.
In that same terminal, we put the following:
- sudo update-grub
And voila, you will be shown something like this:
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.2.0-2-686-pae
Found initrd image: /boot/initrd.img-3.2.0-2-686-pae
Found linux image: /boot/vmlinuz-2.6.32-5-686
Found initrd image: /boot/initrd.img-2.6.32-5-686
Found memtest86+ image: /boot/memtest86+.bin
Found memtest86+ multiboot image: /boot/memtest86+_multiboot.bin
done
Then they must reboot and they will no longer have any image that 'hides' the system boot log 
regards