Keeping time synchronized

[George N. White III]

On Mon, 31 Mar 2008, Konstantin Svist wrote:

> Hi all,
>
> Is there a good ["Fedora"] way to keep time synchronized on a laptop?
>
> I've checked around and ntpd seems to be a bad idea because it counts
> CPU cycles - but modern CPUs switch frequencies all the time to save
> power. Some tutorials say this causes NTP to not work properly.

I think those tutorials are outdated, but there are other reasons ntpd may 
not be suitable for laptop use:

1.  the usual "reference" implementation prefers stable, long-lived 
connections.  Recent versions have the ability to deal with interfaces 
going up and down, but were never intended for typical laptop usage 
patterns (long periods off net, intermittent connections, assorted 
networks that may each provide different NTP servers, ...).

2.  the algorithms assume symmetric network delays which not be true
of some links (e.g., VPN) encountered by laptops

3.  ports used by NTP are often blocked, so if you rely on networks
you don't control, you may encounter problems

Chrony <http://chrony.sunsite.dk/> uses the same wire protocols, but has 
algorithms designed for systems with transient network access (dialup, 
laptops that move around).  Another option is a GPS receiver designed for 
time service (cheap, but they need something simpler than USB -- normally 
a real serial or parallel port).

For many people, a simple "sudo rdate -s ..." may be good enough.


-- 
George N. White III  <aa056 at chebucto.ns.ca>