Can ntpd/chronyd be used with two NTP servers, specifying one as primary and another as backup? - Red Hat Customer PortalEnvironment Red Hat Enterprise Linux (RHEL) 6 7 8 9 ntp chrony Issue Can ntpd/chronyd be used with two NTP servers, specifying one as primary and another as backup? How many upstream time servers should be configured in the NTP configuration file? Resolution Recommended Configuration It is NOT recommended to use only two NTP servers. If more than one NTP server is required, four NTP servers is the
CentOS7.3 chronyでの時刻同期の設定（詳細）
http://www.fujitsu.com/jp/documents/products/computing/servers/primequest/J2UL-1337-11Z0.pdf
