Hello,
i am the very beginner of openHab2, i’ve manage to install it and use it. But why does this thing keep asking me for password although i didn’t set any?
where can i get this password or somehow reset it?
It looks like you logged in to the openhab/karaf console.
But you should log in to the ssh console of your linux in order to do anything os-related.
thank you for your quick response 
unfortunately i can’t set putty on windows 10. it always says “Network error: Connection refused.” i still havent figured why.
but, i was following this tutorial to get remote access to openhab: https://www.youtube.com/watch?v=joz5f4ejJVc
and (at 1:56) he also write that command in karaf console… he is also asked for a password?
He logs into ssh and not karaf.
Since he uses openHABian (distribution) the login screen looks similar to the karaf login screen.
Did you install openhab on windows?
In that case, there is no ssh console!