Comment 6 for bug 1488411

That's the pw-cache process (backintime pw-cache start). They communicate through a FIFO in ~/.local/share/backintime/password_cache/FIFO

root doesn't have a password-keyring (like seahorse or kwallet). So you can't store passwords for root like it is done for normal users. That's why you've to enter it manually. The password-cache in this case caches the password only for subsequent runs so you don't have to type the password again.