What are the correct repository for Jetson TK1?

Hi, all:

I just want to update the repository, but obtained all the following error messages.

ubuntu@tegra-ubuntu:/etc/apt$ sudo apt-get update
Ign file:  InRelease
Err http://ports.ubuntu.com trusty InRelease
  
Err http://ports.ubuntu.com trusty-updates InRelease
  
Err http://ports.ubuntu.com trusty-security InRelease
  
Err http://ports.ubuntu.com trusty Release.gpg
  Could not resolve 'ports.ubuntu.com'
Err http://ports.ubuntu.com trusty-updates Release.gpg
  Could not resolve 'ports.ubuntu.com'
Err http://ports.ubuntu.com trusty-security Release.gpg
  Could not resolve 'ports.ubuntu.com'
Get:1 file:  Release.gpg [198 B]
Get:2 file:  Release [196 B]    
Ign file:  Translation-en   
Reading package lists... Done
W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty/InRelease  

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty-updates/InRelease  

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty-security/InRelease  

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty/Release.gpg  Could not resolve 'ports.ubuntu.com'

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty-updates/Release.gpg  Could not resolve 'ports.ubuntu.com'

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/trusty-security/Release.gpg  Could not resolve 'ports.ubuntu.com'

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

My /etc/apt/sources.list is as follows:

ubuntu@tegra-ubuntu:/etc/apt$ cat sources.list
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://ports.ubuntu.com/ubuntu-ports/ trusty main restricted universe
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty main restricted universe

## Major bug fix updates produced after the final release of the
## distribution.
deb http://ports.ubuntu.com/ubuntu-ports/ trusty-updates main restricted universe
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-updates main restricted universe

## Uncomment the following two lines to add software from the 'universe'
## repository.
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
# deb http://ports.ubuntu.com/ubuntu-ports/ trusty universe
# deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty universe
# deb http://ports.ubuntu.com/ubuntu-ports/ trusty-updates universe
# deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-updates universe

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://ports.ubuntu.com/ubuntu-ports/ trusty-backports main restricted
# deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-backports main restricted

deb http://ports.ubuntu.com/ubuntu-ports/ trusty-security main restricted universe
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-security main restricted universe
# deb http://ports.ubuntu.com/ubuntu-ports/ trusty-security universe
# deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-security universe
# deb http://ports.ubuntu.com/ubuntu-ports/ trusty-security multiverse
# deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-security multiverse
ubuntu@tegra-ubuntu:/etc/apt$

cheers
Pei