"apt-get update" always failed to fetch

I don't understand why this issue could be survive. It display this error message all the time

Fetched 32.8 MB in 1min 16s (430 kB/s)                                         
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/main/binary-amd64/Packages  Hash Sum mismatch

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/universe/binary-i386/Packages  Hash Sum mismatch

E: Some index files failed to download. They have been ignored, or old ones used instead.

I was tried to using these commands (which found in this question)

sudo apt-get clean
sudo rm -vf /var/lib/apt/lists/*
sudo rm -vf /var/lib/apt/lists/partial/*
sudo apt-get update

No luck for me. That dump message show up again. Always failed with security.ubuntu.com. My internet connection is OK, I'm able to ping to security.ubuntu.com without any trouble.

So, the question here is why? And anyone out there can help me out of this? I'm going to crazy!

Solution 1:

Configure your proxy in network settings of your PC for each of items like HTTP, HTTPS, FTP and Socks and apply settings to system wide if you are using proxy.

Remove the existing packages and then try as follows:

apt-get clean
rm -rf /var/lib/apt/lists/*
apt-get clean
apt-get update 
apt-get upgrade

(copied from above message)

Solution 2:

This worked for me:

 apt-get clean
 rm -rf /var/lib/apt/lists/*
 apt-get clean
 apt-get update 
 apt-get upgrade

Solution 3:

I have Ubuntu 14.04 LTS, and sometimes when I use this command, I encounter with this problem. For solving this you can use the following way:

1. please go to system settings.

   

2. click on software & updates

   

3. go to other software section. You can find the links that are relative to this error. Uncheck the relative links and click close. If you can't find relative link you can go to ubuntu software section and uncheck options that may can relative to this error. Sometimes with changing Download Server to Main Server your problem can be solved. For changing download server you can go to ubuntu software section and change Download From and choose Main Server.