Enabling Network Time Protocol (NTP)

Data damage and performance issues might occur if you change host NTP settings while the database is running. Before you change the NPT settings, stop the database. If you cannot stop the database, stop the Vertica process of each host and change the NTP settings one host at a time.

For details, see Stopping Vertica on Host.

The network time protocol (NTP) daemon must be running on all of the hosts in the cluster so that their clocks are synchronized. The spread daemon relies on all of the nodes to have their clocks synchronized for timing purposes. If your nodes do not have NTP running, the installation can fail with a spread configuration error or other errors.

Different Linux distributions refer to the NTP daemon in different ways. For example, SUSE and Debian/Ubuntu refer to it as ntp, while CentOS and Red Hat refer to it as ntpd. If the following commands produce errors, try using the other NTP daemon reference name.

Verify That NTP Is Running

To verify that your hosts are configured to run the NTP daemon on startup, enter the following command: 

$ chkconfig --list ntpd

Debian and Ubuntu do not support chkconfig, but they do offer an optional package. You can install this package with the command sudo apt-get install sysv-rc-conf. To verify that your hosts are configured to run the NTP daemon on startup with the sysv-rc-conf utility, enter the following command: 

$ sysv-rc-conf --list ntpd

The chkconfig command can produce an error similar to ntpd: unknown service. If you get this error, verify that your Linux distribution refers to the NTP daemon as ntpd rather than ntp. If it does not, you need to install the NTP daemon package before you can configure it. Consult your Linux documentation for instructions on how to locate and install packages.

If the NTP daemon is installed, your output should resemble the following:

ntp 0:off 1:off 2:on 3:on 4:off 5:on 6:off

The output indicates the runlevels where the daemon runs. Verify that the current runlevel of the system (usually 3 or 5) has the NTP daemon set to on. If you do not know the current runlevel, you can find it using the runlevel command:

$ runlevel
N 3

Configure NTP for Red Hat 6/CentOS 6 and SLES

If your system is based on Red Hat 6/CentOS 6 or SUSE Linux Enterprise Server, use the service and chkconfig utilities to start NTP and have it start at startup.

$ /sbin/service ntpd restart
$ /sbin/chkconfig ntpd on
  • Red Hat 6/CentOS 6—NTP uses the default time servers at ntp.org. You can change the default NTP servers by editing /etc/ntpd.conf.
  • SLES—By default, no time servers are configured. You must edit /etc/ntpd.conf after the install completes and add time servers.

Configure NTP for Ubuntu and Debian

By default, the NTP daemon is not installed on some Ubuntu and Debian systems. First, install NTP, and then start the NTP process. You can change the default NTP servers by editing /etc/ntpd.confas shown:

$ sudo apt-get install ntp
$ sudo /etc/init.d/ntp reload

Verify That NTP Is Operating Correctly

To verify that the Network Time Protocol Daemon (NTPD) is operating correctly, issue the following command on all nodes in the cluster.

For Red Hat 6/CentOS 6 and SLES: 

$ /usr/sbin/ntpq -c rv | grep stratum

For Ubuntu and Debian: 

$ ntpq -c rv | grep stratum

A stratum level of 16 indicates that NTP is not synchronizing correctly.

If a stratum level of 16 is detected, wait 15 minutes and issue the command again. It may take this long for the NTP server to stabilize.

If NTP continues to detect a stratum level of 16, verify that the NTP port (UDP Port 123) is open on all firewalls between the cluster and the remote machine to which you are attempting to synchronize.

Red Hat Documentation Related to NTP

The preceding links were current as of the last publication of the Vertica documentation and could change between releases.