Отсутствуют зависимости .netCore: невозможно найти пакет libkrb5

Я - новичок в мире Linux, и я пытаюсь установить зависимости .netCore на «Ubuntu Server 16.04.3 LTS», и я получаю сообщение об ошибке, например, я бегу команда:

sudo apt install libkrb5

я уже запустил обновление / обновление apt, и все обновлено (я думаю: D)

у меня есть это сообщение в ответ:

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package libkrb5

Что я могу сделать?

Благодарю заранее за вашу помощь:)

Удачное хранилище зеркал

/etc/apt/sources.list:#
/etc/apt/sources.list:
/etc/apt/sources.list:# deb cdrom:[Ubuntu-Server 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)]/ xenial main restricted
/etc/apt/sources.list:
/etc/apt/sources.list:#deb cdrom:[Ubuntu-Server 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)]/ xenial main restricted
/etc/apt/sources.list:
/etc/apt/sources.list:# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
/etc/apt/sources.list:# newer versions of the distribution.
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial main restricted
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial main restricted
/etc/apt/sources.list:
/etc/apt/sources.list:## Major bug fix updates produced after the final release of the
/etc/apt/sources.list:## distribution.
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial-updates main restricted
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
/etc/apt/sources.list:
/etc/apt/sources.list:## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
/etc/apt/sources.list:## team. Also, please note that software in universe WILL NOT receive any
/etc/apt/sources.list:## review or updates from the Ubuntu security team.
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial universe
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial universe
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial-updates universe
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial-updates universe
/etc/apt/sources.list:
/etc/apt/sources.list:## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
/etc/apt/sources.list:## team, and may not be under a free licence. Please satisfy yourself as to
/etc/apt/sources.list:## your rights to use the software. Also, please note that software in
/etc/apt/sources.list:## multiverse WILL NOT receive any review or updates from the Ubuntu
/etc/apt/sources.list:## security team.
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial multiverse
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial multiverse
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial-updates multiverse
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
/etc/apt/sources.list:
/etc/apt/sources.list:## N.B. software from this repository may not have been tested as
/etc/apt/sources.list:## extensively as that contained in the main release, although it includes
/etc/apt/sources.list:## newer versions of some applications which may provide useful features.
/etc/apt/sources.list:## Also, please note that software in backports WILL NOT receive any review
/etc/apt/sources.list:## or updates from the Ubuntu security team.
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
/etc/apt/sources.list:# deb-src http://pt.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
/etc/apt/sources.list:
/etc/apt/sources.list:## Uncomment the following two lines to add software from Canonical's
/etc/apt/sources.list:## 'partner' repository.
/etc/apt/sources.list:## This software is not part of Ubuntu, but is offered by Canonical and the
/etc/apt/sources.list:## respective vendors as a service to Ubuntu users.
/etc/apt/sources.list:# deb http://archive.canonical.com/ubuntu xenial partner
/etc/apt/sources.list:# deb-src http://archive.canonical.com/ubuntu xenial partner
/etc/apt/sources.list:
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security main restricted
/etc/apt/sources.list:# deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security universe
/etc/apt/sources.list:# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security multiverse
/etc/apt/sources.list:# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
/etc/apt/sources.list.d/dotnetdev.list:deb [arch=amd64] https://packages.microsoft.com/repos/microsoft-ubuntu-xenial-prod xenial main