Extension Pack installation failed

[oboh]

Can't install Extension Pack. after acceptance of the license I receive an error:

The installer failed with exit code 127: Error creating textual authentication agent: Error opening current controlling terminal for the process (`/dev/tty'): No such device or address.

Код ошибки: NS_ERROR_FAILURE (0x80004005)
Компонент: ExtPackManagerWrap
Интерфейс: IExtPackManager {edba9d10-45d8-b440-1712-46ac0c9bc4c5}

But:

user@ihvz:~$ ls /dev/tty
/dev/tty

Addition can be installed under root via vboxmanage, but it isn't visible under unprivileged user in additions. gksu package installed.

[Frank Mehnert]

Which Linux distribution is this, Debian 8?