sudo apt-get update fails with error below

sudo apt-get update
Get:1 file:/var/cuda-repo-8-0-rc InRelease
Ign:1 file:/var/cuda-repo-8-0-rc InRelease
Get:2 file:/var/cuda-repo-8-0-rc Release [574 B]
Get:2 file:/var/cuda-repo-8-0-rc Release [574 B]
Hit:3 xenial InRelease
Hit:4 xenial-updates InRelease
Hit:5 xenial-backports InRelease
Get:7 xenial-security InRelease [102 kB]
Hit:8 stable InRelease
Hit:9 ubuntu-xenial InRelease
Hit:10 xenial InRelease
Hit:11 xenial InRelease
Fetched 102 kB in 0s (141 kB/s)
Reading package lists… Done
W: file:///var/cuda-repo-8-0-rc/Release.gpg: Signature by key 889BEE522DA690103C4B085ED88C3D385C37D3BE uses weak digest algorithm (SHA1)
W: Invalid ‘Date’ entry in Release file /var/lib/apt/lists/_var_cuda-repo-8-0-rc_Release

Those are warnings, not failures.

If you want to use cuda 8, follow the instructions in the linux install guide. You should not be using cuda 8 rc anymore.