From ArchWiki

[edit] Q: How can I turn OFF clearing the screen after system has booted so I can see the messages that are printed out during system startup?

A: Delete the first character of /etc/issue It looks like: ^[c

In some cases you'll need to delete the whole first line of this file, as there is more than one instructions, i.e. one clears the screen and the other one places the cursor at the top.

[edit] Q: How do I put it back again?

A: You can't just type the characters back as you have to put a literal escape character. This is editor dependent. In vim:

i (insert)
ctrl-v (insert literal character)
ESC (insert escape character)
c
ESC (exit insert mode)
ZZ (Save and Exit)

In emacs:

C-q ESC (to insert literal escape)

But if you want to keep the screen clear after logging out on a virtual terminal, without clearing after system has booted, just do:

echo clear >> ~/.bash_logout