При вводе:
sudo apt-get update
Hit:2 http://ru.archive.ubuntu.com/ubuntu xenial InRelease
Hit:3 http://archive.canonical.com/ubuntu xenial InRelease
Hit:4 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:5 http://ppa.launchpad.net/atareao/telegram/ubuntu xenial InRelease
Hit:6 http://ru.archive.ubuntu.com/ubuntu xenial-updates InRelease
Ign:7 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial InRelease
Hit:8 http://ru.archive.ubuntu.com/ubuntu xenial-backports InRelease
Ign:9 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial Release
Ign:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
Ign:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
Ign:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Hit:18 https://deb.opera.com/opera-stable stable InRelease
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
Ign:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
Ign:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
Ign:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Err:10 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 Packages
404 Not Found
Err:11 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main i386 Packages
404 Not Found
Ign:12 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main all Packages
Ign:13 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru_RU
Ign:14 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-ru
Ign:15 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main Translation-en
Ign:16 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:17 http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Чтение списков пакетов… Готово
W: The repository 'http://ppa.launchpad.net/tualatrix/ppa/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: http://repo.yandex.ru/yandex-browser/deb/dists/beta/InRelease: Signature by key 67CE018FD19E3CD48189BC69218017D1CC5FDB34 uses weak digest algorithm (SHA1)
E: Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found
E: Некоторые индексные файлы не скачались. Они были проигнорированы или вместо них были использованы старые версии.
Я думаю, может проблемы с sources.list, потому что это все началось после неудачной попытки установки Skype. Cейчас в sources.list следующее:
#deb cdrom:[Ubuntu-Studio 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main multiverse restricted universe
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://ru.archive.ubuntu.com/ubuntu/ xenial main restricted
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://ru.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://ru.archive.ubuntu.com/ubuntu/ xenial universe
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial universe
deb http://ru.archive.ubuntu.com/ubuntu/ xenial-updates universe
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://ru.archive.ubuntu.com/ubuntu/ xenial multiverse
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://ru.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://ru.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
# deb-src http://ru.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner
deb http://security.ubuntu.com/ubuntu xenial-security main restricted
# deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
deb http://security.ubuntu.com/ubuntu xenial-security universe
# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
