sudo sysv-rc-conf------to say bootup settings
go to /etc/apt
change sources.list
into
deb http://ftp.sjtu.edu.cn/ubuntu/ intrepid main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ intrepid-backports main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ intrepid-proposed main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ intrepid-security main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ intrepid-updates main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ intrepid main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ intrepid-backports main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ intrepid-proposed main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ intrepid-security main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ intrepid-updates main multiverse restricted universe
then update will be faster