title: unrecognized syntax identifier "proto3". This parser only recognizes "proto2" on Linkerd
body: <p>I have cloned linkerd (<a href="https://github.com/linkerd" rel="noreferrer">https://github.com/linkerd</a>) repo on my linux ubuntu, and installed protoc, version 2.5. When I try to compile the linkerd using the following command I get the error "unrecognized syntax identifier "proto3". This parser only recognizes "proto2".</p>
  
  <p>command: <code>./sbt linkerd/compile</code></p>