Você parece estar usando um proxy HTTP. Você pode desativá-lo - veja como aqui .
Talvez valha a pena descobrir por que você está usando um proxy.
Eu não consigo executar o comando sudo apt-get update, assim como instalar qualquer pacote. Aqui está o retorno do sudo apt-get update:
sabo@Ace:/etc/apt$ sudo apt-get update
Err h ttp://security.ubuntu.com precise-security Release.gpg
Could not connect to Ace:80 (127.0.1.1). - connect (111: Connection refused)
Err h ttp://us.archive.ubuntu.com precise Release.gpg
Could not connect to Ace:80 (127.0.1.1). - connect (111: Connection refused)
Err h ttp://us.archive.ubuntu.com precise-updates Release.gpg
Unable to connect to Ace:80:
Err h ttp://us.archive.ubuntu.com precise-backports Release.gpg
Unable to connect to Ace:80:
Reading package lists... Done
W: Failed to fetch h ttp://us.archive.ubuntu.com/ubu ntu/dists/precise/Release.gpg Could not connect to Ace:80 (127.0.1.1). - connect (111: Connection refused)
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise-updates/Rel ease.gpg Unable to connect to Ace:80:
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise-backports/R elease.gpg Unable to connect to Ace:80:
W: Failed to fetch h ttp://security.ubuntu.com/ubuntu/dists/precise-security/Rele ase.gpg Could not connect to Ace:80 (127.0.1.1). - connect (111: Connection ref used)
W: Some index files failed to download. They have been ignored, or old ones used instead.
Qualquer ajuda é muito apreciada, não consegui descobrir o problema por algum tempo.