apt-get update doesnt work .Cant fetch update .But i can browse the net in my search engine otherwise.

Do you use a proxy for web access?

no, no provy

What is the output of:

grep -i proxt /etc/apt/*
grep -i proxy ~/.bashrc
grep -i proxy ~/.profile
grep -i proxy /etc/environment
echo $http_proxy
echo $ftp_proxy

Thanks

chhavi@ubuntu:~$ grep -i proxt /etc/apt/*
grep: /etc/apt/trustdb.gpg: Permission denied
chhavi@ubuntu:~$ grep -i proxy ~/.bashrc
chhavi@ubuntu:~$ grep -i proxy ~/.profile
chhavi@ubuntu:~$ grep -i proxy /etc/environment
http_proxy="http://172.19.1.3:8080/"
chhavi@ubuntu:~$ echo $http_proxy
http://172.19.1.3:8080/
chhavi@ubuntu:~$ echo $ftp_proxy

chhavi@ubuntu:~$

well that's embarassing.
i commented that line but still it doesnt work

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
chhavi@ubuntu:~$ gksudo gedit /etc/environment
chhavi@ubuntu:~$ unset http_proxy
chhavi@ubuntu:~$ sudo apt-get update
Err http://security.ubuntu.com precise-security Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://extras.ubuntu.com precise Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://ppa.launchpad.net precise Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://archive.canonical.com precise Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://dl.google.com stable Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://archive.ubuntu.com precise Release.gpg
  Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out
Err http://archive.ubuntu.com precise-updates Release.gpg
  Unable to connect to 172.19.1.3:8080:
Err http://archive.ubuntu.com precise-backports Release.gpg
  Unable to connect to 172.19.1.3:8080:
Reading package lists... Done
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/precise/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/precise-updates/Release.gpg Unable to connect to 172.19.1.3:8080:

W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/precise-backports/Release.gpg Unable to connect to 172.19.1.3:8080:

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/precise-security/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Failed to fetch http://archive.canonical.com/ubuntu/dists/precise/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/precise/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Failed to fetch http://dl.google.com/linux/talkplugin/deb/dists/stable/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Failed to fetch http://ppa.launchpad.net/stevedh/smap/ubuntu/dists/precise/Release.gpg Could not connect to 172.19.1.3:8080 (172.19.1.3), connection timed out

W: Some index files failed to download. They have been ignored, or old ones used instead.
chhavi@ubuntu:~$

Thanks actionparsnip, that solved my question.