Synchronizing System Clocks

Greenplum recommends using NTP (Network Time Protocol) to synchronize the system clocks on all hosts that comprise your Greenplum Database system. See www.ntp.org for more information about NTP.

NTP on the segment hosts should be configured to use the master host as the primary time source, and the standby master as the secondary time source. On the master and standby master hosts, configure NTP to point to your preferred time server.

To configure NTP

On the master host, log in as root and edit the /etc/ntp.conf file. Set the server parameter to point to your data center's NTP time server. For example (if 10.6.220.20 was the IP address of your data center's NTP server):
```
server 10.6.220.20
```
On each segment host, log in as root and edit the /etc/ntp.conf file. Set the first server parameter to point to the master host, and the second server parameter to point to the standby master host. For example:
```
server mdw prefer
server smdw
```
On the standby master host, log in as root and edit the /etc/ntp.conf file. Set the first server parameter to point to the primary master host, and the second server parameter to point to your data center's NTP time server. For example:
```
server mdw prefer
server 10.6.220.20
```
On the master host, use the NTP daemon synchronize the system clocks on all Greenplum hosts. For example, using gpssh:
```
# gpssh -f hostfile_gpssh_allhosts -v -e 'ntpd'
```