Eu tenho um Ubuntu 15.04 e toda vez que eu tento baixar algo (usando o sudo apt-get install), ele diz:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package <packagename> is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package '<packagename>' has no installation candidate
Eu tentei "sudo apt-get update" e disse no final:
W: Failed to fetch http://ppa.launchpad.net/irie/blender/ubuntu/dists/vivid/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/irie/blender/ubuntu/dists/vivid/main/binary-i386/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Também verifiquei se todas as caixas de seleção da guia "Ubuntu Software" da janela "Software and Updates" foram selecionadas e tentei "sudo apt-get upgrade", mas nenhuma delas funcionou.
Além disso, aqui está o meu arquivo sources.list, que parece bem:
# deb cdrom:[Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)]/ vivid main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://old-releases.ubuntu.com/ubuntu vivid main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://old-releases.ubuntu.com/ubuntu vivid-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://old-releases.ubuntu.com/ubuntu vivid universe
deb http://old-releases.ubuntu.com/ubuntu vivid-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://old-releases.ubuntu.com/ubuntu vivid multiverse
deb http://old-releases.ubuntu.com/ubuntu vivid-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://old-releases.ubuntu.com/ubuntu vivid-backports main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu vivid-security main restricted
deb http://old-releases.ubuntu.com/ubuntu vivid-security universe
deb http://old-releases.ubuntu.com/ubuntu vivid-security 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 vivid partner
# deb-src http://archive.canonical.com/ubuntu vivid partner
deb http://www.openprinting.org/download/printdriver/debian/ lsb3.2 contrib
Além disso, sei que existem outras questões semelhantes a esta, mas nenhuma das soluções funcionou para mim.
Editar:
Como eu vi, muitas pessoas nos comentários sugeriram que eu mudasse as linhas 'archives.ubuntu.com' no sources.list para 'old-releases.ubuntu.com' porque eu tenho uma versão desatualizada do Ubuntu. Eu tentei isso e a mesma mensagem aparece quando eu digito 'sudo apt-get update' (alguns arquivos de índice falharam em baixar), e quando tento instalar um pacote acontece a mesma coisa.
Algumas outras pessoas nos comentários sugeriram que eu atualizasse para uma versão mais recente do Ubuntu, que eu também tentei (sudo do-release-upgrade), mas no final diz:
Cannot upgrade, an upgrade from 'vivid' to 'xenial' is not supported with this tool.
Eu também tentei atualizar usando o sudo do-release upgrade -d, mas então ele diz:
Checking for a new Ubuntu release
No new release found
Eu consertei sozinho. Eu segui um grupo de pessoas no conselho de comentários substituindo os links 'archives.ubuntu.com' no arquivo sources.list com 'old-releases.ubuntu.com' e também excluí um monte de repositórios desatualizados que estavam impedindo me de executar 'sudo apt-get update'.