1. First Step:
sudo gedit /etc/apt/sources.list
2. Add Soures List Content:
1 # deb cdrom:[Ubuntu 12.04.1 LTS _Precise Pangolin_ - Release i386 (20120817.3)]/ precise main restricted
2
3 # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
4 # newer versions of the distribution.
5
6
7 #Tanwan
8 deb http://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
9 deb-src http://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
10 deb http://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
11 deb-src http://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
12 deb http://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
13 deb-src http://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
14
15
16 #Wangyi
17 deb http://mirrors.163.com/ubuntu/ precise main universe restricted multiverse
18 deb-src http://mirrors.163.com/ubuntu/ precise main universe restricted multiverse
19 deb http://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted
20 deb-src http://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted
21 deb http://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted
22 deb http://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted
23 deb-src http://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted
24 deb http://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted
25 deb-src http://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted
26 deb-src http://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted
27
28 #Bone Source
29 deb http://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
30 deb-src http://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
31 deb http://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
32 deb-src http://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
33 deb http://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
34 deb http://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
35 deb-src http://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
36 deb http://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
37 deb-src http://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
38 deb-src http://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
39
40 #mirror.lupaworld.com
41 deb http://mirror.lupaworld.com/ubuntu/archive/ precise main restricted universe multiverse
42 deb http://mirror.lupaworld.com/ubuntu/archive/ precise-security main restricted universe multiverse
43 deb http://mirror.lupaworld.com/ubuntu/archive/ precise-updates main restricted universe multiverse
44 deb http://mirror.lupaworld.com/ubuntu/archive/ precise-backports main restricted universe multiverse
45 deb http://mirror.lupaworld.com/ubuntu/ubuntu-cn/ precise main restricted universe multiverse
46
47 #ubuntu.cn99.com
48 deb http://ubuntu.cn99.com/ubuntu/ precise main restricted universe multiverse
49 deb http://ubuntu.cn99.com/ubuntu/ precise-updates main restricted universe multiverse
50 deb http://ubuntu.cn99.com/ubuntu/ precise-security main restricted universe multiverse
51 deb http://ubuntu.cn99.com/ubuntu/ precise-backports main restricted universe multiverse
52 deb http://ubuntu.cn99.com/ubuntu-cn/ precise main restricted universe multiverse
53
54
55 #Electric University
56 deb http://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse
57 deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
58 deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
59 deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
60 deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
61 deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse
62 deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
63 deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
64 deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
65 deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
66
67
68 #China Eletric University
69 deb http://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse
70 deb http://debian.ustc.edu.cn/ubuntu/ precise-backports restricted universe multiverse
71 deb http://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
72 deb http://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
73 deb http://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
74 deb-src http://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse
75 deb-src http://debian.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
76 deb-src http://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
77 deb-src http://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
78 deb-src http://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
79
80 #Shanghai jiaotong
81 deb http://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
82 deb http://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
83 deb http://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
84 deb http://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
85 deb http://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
86 deb http://ftp.sjtu.edu.cn/ubuntu-cn/ precise main multiverse restricted universe
87 deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
88 deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
89 deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
90 deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
91 deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
3. Close soures.list file ,then input command to update:
apt-get update
4. Waiting....Done!!