Estou usando uma versão 14.09 do Ubuntu. Quando eu atualizo o sistema para 16.04, recebo o erro
A problem occurred during the update. This is usually some sort of network problem, please check your network connection and retry.
Mas minha conexão é estável e estou usando o servidor principal, então qual poderia ser o problema?
W:Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/restricted/binary-arm64/Packages 404 Not Found [IP: 91.189.88.162 80]
W:Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/universe/binary-arm64/Packages 404 Not Found [IP: 91.189.88.162 80]
W:Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.162 80]
W:Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/multiverse/binary-arm64/Packages 404 Not Found [IP: 91.189.88.162 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/restricted/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/universe/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/multiverse/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/restricted/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/universe/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/multiverse/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/restricted/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/universe/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/multiverse/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-proposed/universe/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-proposed/restricted/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-proposed/main/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
W:Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-proposed/multiverse/binary-arm64/Packages 404 Not Found [IP: 91.189.88.149 80]
E:Some index files failed to download. They have been ignored, or old ones used instead.
A sua versão do Ubuntu 14.04 ou 14.10? Sua pergunta afirma que você está tentando atualizar o Ubuntu 14.09. O Ubuntu só permite que você salte versões intermediárias ao atualizar LTS para LTS (14.04 a 16.04). Se você estiver atualizando a partir de 14.10 (que não é mais suportado), você precisará atualizar para 15.04, depois para 15.10 e depois para 16.04. Se esse for o caso, seria mais fácil simplesmente fazer uma nova instalação do 16.04.