[CentOS] ntpd stuck on stratum 16 = not synced

[Sean Carolan]

> This is almost certainly incorrect unless you're running a very, very 
> old RHEL/CentOS release. I believe /var/lib/ntp is the canonical 
> directory for the drift file in 4.x and 5.x. I doubt ntpd is allowed to 
> write to /etc/ntp, especially if SELinux is enabled.

Good observation, Paul.  That configuration is in fact from an ancient version 
of Red Hat which I plan to upgrade this week.

> Have you tried shutting down ntpd and relaunching it manually with the 
> "don't fork and give me lots of debugging output" switches (-n -ddd) 
> enabled?
> 
> Alternatively (or additionally), you might try wrapping ntpd in strace 
> to see if any system calls are being thwarted.

I learned today that our ISP is blocking UDP traffic.  I am going to ask them 
to make an exception for port 123 to fix this.