It decides how often to ask a server for current time, and how often and how much to change the local clock, based on how the local clock drifts: you can't really control any of the intervals. ntpd runs in the background. To change an NTP server, you edit /etc/ntp.conf, and stop then start ntpd.t decides how often to ask a server for current time, and how often and how much to change the local clock, based on how the local clock drifts: you can't really control any of the intervals. ntpd runs in the background. To change an NTP server, you edit /etc/ntp.conf, and stop then start ntpd.