OSX: /tmp Not Writable : Operation not permitted
Recreation the link /tmp -> /private/tmp helped me (with csrutil disabled in recovery mode) : https://superuser.com/questions/1133065/unable-to-write-to-tmp-osx-unable-to-correct-permissions-operation-not-permitt#comment1629612_1133065

Looks like the Sierra installer makes /tmp rootless if you download and cancel it on the very first step of installation.