sudo add-apt-repository ppa:nginx/stable
sudo apt-get update
sudo apt-get install nginx

sudo apt-get install nginx
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
nginx : Depends: nginx-full (>= 1.8.0-1+vivid1) but it is not going to be installed or
                 nginx-light (>= 1.8.0-1+vivid1) but it is not going to be installed or
                 nginx-extras (>= 1.8.0-1+vivid1) but it is not going to be installed
        Depends: nginx-full (< 1.8.0-1+vivid1.1~) but it is not going to be installed or
                 nginx-light (< 1.8.0-1+vivid1.1~) but it is not going to be installed or
                 nginx-extras (< 1.8.0-1+vivid1.1~) but it is not going to be installed

W: Duplicate sources.list entry http://ports.ubuntu.com/ubuntu-ports/ vivid/main arm64 Packages (/var/lib/apt/lists/ports.ubuntu.com_ubuntu-ports_dists_vivid_main_binary-arm64_Packages)
W: Duplicate sources.list entry http://ports.ubuntu.com/ubuntu-ports/ vivid/universe arm64 Packages (/var/lib/apt/lists/ports.ubuntu.com_ubuntu-ports_dists_vivid_universe_binary-arm64_Packages)
W: You may want to run apt-get update to correct these problems
E: Unable to correct problems, you have held broken packages.