Linac4 Commissioning Status and Challenges to Nominal Operation

Linac4 will be connected to the Proton Synchrotron Booster (PSB) during the next long LHC shutdown in 2019 and it will operationally replace Linac2 as provider of protons to the CERN complex as of 2021. Commissioning to the final beam energy of 160 MeV was achieved by the end of 2016. Linac4 is presently undergoing a reliability and beam quality test run to meet the beam specifications and relative tolerances requested by the PSB. In this paper we will detail the main challenges left before achieving nominal operation and we will re-port on the commissioning steps still needed for final validation of machine readiness before start of operation.