ubuntu14.04无法安装Curl,需要先升级sudo apt-get update

ubuntu14.04无法安装Curl,需要先升级sudo apt-get update
sudo apt-get update
sudo apt-get install curl
-------------------------------
以下是没升级前报错内容

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Err http://mirrors.sohu.com/ubuntu/ precise-security/main libcurl3 amd64 7.22.0-3ubuntu4.14
404 Not Found
Err http://mirrors.sohu.com/ubuntu/ precise-security/main curl amd64 7.22.0-3ubuntu4.14
404 Not Found
Failed to fetch http://mirrors.sohu.com/ubuntu/pool/main/c/curl/libcurl3_7.22.0-3ubuntu4.14_amd64.deb 404 Not Found
Failed to fetch http://mirrors.sohu.com/ubuntu/pool/main/c/curl/curl_7.22.0-3ubuntu4.14_amd64.deb 404 Not Found
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
user@ip82:~$ sudo add-apt-repository ppa:costamagnagianfranco/ettercap-stable-backports
sudo: add-apt-repository: command not found
user@ip82:~$