$ vim /ect/apt/sources.list
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#北邮
#deb [url]ftp://openware.byr.edu.cn/pub/mirror/debian/debian[/url] lenny main non-free contrib
#deb-src [url]ftp://openware.byr.edu.cn/pub/mirror/debian/debian[/url] lenny main non-free contrib

#中科大
deb [url]ftp://debian.ustc.edu.cn/debian[/url] lenny main non-free contrib
deb-src [url]ftp://debian.ustc.edu.cn/debian[/url] lenny main non-free contrib

#清华
deb [url]ftp://ftp3.tsinghua.edu.cn/mirror/debian/debian[/url] lenny main non-free contrib
deb-src [url]ftp://ftp3.tsinghua.edu.cn/mirror/debian/debian[/url] lenny main non-free contrib

#access by proxy
deb [url]http://security.debian.org/[/url] lenny/updates main
deb-src [url]http://security.debian.org/[/url] lenny/updates main

deb [url]http://volatile.debian.org/debian-volatile[/url] lenny/volatile main
deb-src [url]http://volatile.debian.org/debian-volatile[/url] lenny/volatile main

deb [url]http://ftp.debian.org/debian/[/url] lenny main contrib non-free
deb-src [url]http://ftp.debian.org/debian/[/url] lenny main contrib non-free

deb [url]http://www.debian-multimedia.org/[/url] lenny main
deb-src [url]http://www.debian-multimedia.org/[/url] lenny main

deb [url]http://ftp.us.debian.org/debian/[/url] lenny main contrib non-free

deb [url]http://debian.cn99.com/debian/[/url] lenny main contrib non-free

deb [url]http://ftp.de.debian.org/debian/[/url] lenny main contrib non-free

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$ vim /etc/apt/apt.conf
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Acquire::http::proxy "http://sakya:[email protected]:8888/";
------
proxy和“间有空格，末尾的；不要丢。遵循这种格式 [url]http://user:password@ip:port/[/url]
编辑保存然后运行命令:
$ apt-get update
$ apt-get dist-upgrade（注意：普通升级用apt-get upgrade，发行版升级用apt-get dist-upgrade）