Let me share the answer to a question that I got in a private mail: > On Tue, Feb 10, 2015 at 10:55:53AM +0100, Reyk Floeter wrote: >> ---snip--- >> servers pool.ntp.org >> constraints from "https://www.google.com/search?q=openntpd"; >> constraints from www.twitter.com >> constraint from www.apple.com >> ---snap--- >> > > Is the last "constraint" in singular pointing to www.apple.com valid or is > it a typo? >
Yes, it is valid. As mentioned in the man page, it works like the existing server vs. servers for NTP peers. When a hostname or URL is specified, ntpd(8) will resolve the host. The singular version will use only one of the returned IP addresses and the plural version will use it as a pool and use all of the returned IP addresses. Following the example, a "dig A" on www.google.com or www.apple.com will typically show you a number of addresses, while the Akamai-hosted www.apple.com only returns one address near you. You're free to use any host, and some people might prefer to use their own trusted servers, I just picked some examples with good availability and seemingly good time. Reyk
