Using percona toolkit and Xtrabackup on RHEL 6.4 results in a hidden defect caused by the percona toolkit rpm installing mysqlclient16, this causes the perl library location to be changed resulting in a failure of the Xtrabackup scripts where unix socket logins are used. The remedy is simply to remove the mysqlclient16 RPM and everything works again as long as a mysql client RPM is installed, this seemed to me to be a defect as it appears that the mysqlclient16 RPM requirement is a legacy rather than current requirement.