blog.jphoude.qc.ca

I may have missed something obvious, but it seems that the default ntp.conf shipped with RHEL 5 is not working…

I just want to configure my servers to sync time with a public NTP server. Using the default configuration (/etc/ntp.conf), ntpd starts correctly but never writes anything to /var/log/messages besides the first lines at startup.

What I have found is that the “restrict” lines in the default ntp.conf file do not seem to allow ntpd to connect to the servers that are listed there (*.centos.pool.ntp.org by default). Adding the following lines fix the problem :

restrict 0.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 1.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 2.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
# the following is in the default ntp.conf file
server 0.centos.pool.ntp.org
server 1.centos.pool.ntp.org
server 2.centos.pool.ntp.org

Also (as an alternate fix) I had success with the following servers :

server ntp.isc.org
server clock.redhat.com

I’m not sure why, I suspect that’s because in the DNS they resolve to a single IP address, but I don’t really understand what would cause this.

Anyway, with these changes my NTP now sync properly, and I can see the “synchronized to 206.248.171.198, stratum 1″ lines in the /var/log/messages file.