为了更新，我在终端输入了以下内容sudo update-manager -d并得到了以下代码（我必须编辑链接）：
W:GPG error: h.ttp://linux.dropbox.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FC918B335044912E,
W:GPG error: h.ttp://extras.ubuntu.com quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192,
W:GPG error: h.ttp://ppa.launchpad.net jaunty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F104610CF0876AC9,
W:GPG error: h.ttp://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B187F352479B857B,
W:GPG error: h.ttp://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 86D36DFDE6A250EA,
W:GPG error: h.ttp://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A9A06AEF9CB8DB0,
W:GPG error: h.ttp://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886,
W:GPG error: h.ttp://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886,
W:Failed to fetch h.ttp://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/quantal/main/source/Sources 404 Not Found,
W:Failed to fetch h.ttp://ppa.launchpad.net/pmcenery/ppa/ubuntu/dists/quantal/main/binary-i386/Packages 404 Not Found,
E:Some index files failed to download. They have been ignored, or old ones used instead.
答案1
使用以下命令删除您的内容/etc/apt/sources/list：
#############################################################
################### OFFICIAL UBUNTU REPOS ###################
#############################################################
###### Ubuntu Main Repos
deb http://....archive.ubuntu.com/ubuntu/ quantal main restricted universe multiverse
deb-src http://....archive.ubuntu.com/ubuntu/ quantal main restricted universe multiverse
###### Ubuntu Update Repos
deb http://....archive.ubuntu.com/ubuntu/ quantal-security main restricted universe multiverse
deb http://....archive.ubuntu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb http://....archive.ubuntu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb http://....archive.ubuntu.com/ubuntu/ quantal-backports main restricted universe multiverse
deb-src http://....archive.ubuntu.com/ubuntu/ quantal-security main restricted universe multiverse
deb-src http://....archive.ubuntu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb-src http://....archive.ubuntu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb-src http://....archive.ubuntu.com/ubuntu/ quantal-backports main restricted universe multiverse
###### Ubuntu Partner Repo
deb http://archive.canonical.com/ubuntu quantal partner
deb-src http://archive.canonical.com/ubuntu quantal partner
###### Ubuntu Extras Repo
deb http://extras.ubuntu.com/ubuntu quantal main
deb-src http://extras.ubuntu.com/ubuntu quantal main
看看是否有效。