When starting sfptpd in one of the supported NTP modes on Ubuntu, it is important to setup NTP authentication correctly (see NTP Authentication) and important to identify the NTP configuration file being used by the NTP service.
The usual files will probably exist i.e /etc/ntp.conf and /etc/ntp/keys.
But the NTP service might be using another ntp.conf file and this prevents sfptpd from controlling the local NTP
client when the authentication settings have not been enabled in the correct NTP
configuration file.
This results is output from sfptpd (stats_log or message_log) similar to the following:
notice: ptp ptpm: ptp ptpm: now in state: PTP_LISTENING
warning: ntpclient: mode6: failed to set NTP daemon system flags, Permission denied
error: ntp: failed to disable NTP clock control
critical: failed to create sync module ntp, Permission denied
critical: couldn't create sync engine thread, Permission denied