1. Connect to an ESX host using an SSH client.
2. Log in with an user having administrative privileges.
3. To open up the ntpClient port in the internal ESX host firewall, run the commands:
   
   esxcfg-firewall -q ntpClient
   esxcfg-firewall -e ntpClient
   esxcfg-firewall -q ntpClient
   
   Note: The first line tells the status of the ntpClient port. The second line enables the ntpClient port. The third line shows you that it is open.
   
4. Now set the system time to the right time. If your ESX host has ntp access to the Internet, you can just issue the ntpdate command, with the -u switch, and point it at an ntp server. If your ESX host is blocked by your corporate firewall, you have to point it at an internal ntp server. If you do not have one, you have to set one up. Any of these ntpdate command should work:
   
   ntpdate -u pool.ntp.org
   ntpdate -u north-america.pool.ntp.org
   ntpdate -u 0.us.pool.ntp.org
   
   Or for example, if your internal ntp server was called ntp.yourdomain.com, you would issue the command:
   
   ntpdate -u ntp.yourdomain.com
   
   Note: Some programs react badly to sudden large changes in system time. For this reason, just updating and restarting ntpd as described below is preferred by some ntpd updates the system clock slowly for this reason.
   
   
5. Configure the ESX host as an ntp client. Make a backup copy of /etc/ntp.conf using the command:
   
   cp /etc/ntp.conf /etc/ntp.conf.bak.`date +%d%m%y`
   
6. Create a new ntp.conf file that contains this information:
   
   restrict 127.0.0.1
   server 0.us.pool.ntp.org
   server 1.us.pool.ntp.org
   server 2.us.pool.ntp.org
   server 3.us.pool.ntp.org
   server north-america.pool.ntp.org
   server pool.ntp.org
   server 127.127.1.0 # local clock
   fudge 127.127.1.0 stratum 10
   driftfile /var/lib/ntp/drift
   broadcastdelay 0.008
   
   Note: This ntp.conf assumes that the ESX host can send an ntp request out to the Internet. If you have outgoing ntp traffic blocked by your corporate firewall, you must instead set up an internal ntp server and make sure that it has access to the Internet so it can get an accurate time. While it is possible for you to configure one of your ESX hosts as an ntp server as well as a client, we recommend that ESX hosts be used solely as ESX hosts, and that they not be used for supporting IT infrastructure needs like ntp.
   
   If your corporate firewall has ntp access blocked to the Internet, then your ntp.conf file should contain something like this, under the assumption that you have an internal ntp server, which separately has Internet ntp access:
   
   restrict 127.0.0.1
   server ntp.yourdomain.com
   server 127.127.1.0 # local clock
   fudge 127.127.1.0 stratum 10
   driftfile /var/lib/ntp/drift
   broadcastdelay 0.008
   
   
7. Restart the ntpd service using any of these commands:
   
   service ntpd restart
   /etc/init.d/ntpd restart
   
   
8. Update the hardware clock with the current time of the system clock. Even though the system clock is updated from a known ntp server which has the right time and reconfigured ntp and restarted ntpd service, when the machine reboots, it sets its system clock based upon the time from the internal hardware clock.
   
   /sbin/hwclock --systohc

Related KB Articles

• Adjusting ESX Server Time Zone (1436)
• Using ESX as an NTP server (1002864)
• Installing and Configuring NTP on VMware ESX Server (1339)

Additional Information

• 日本語：ESX サーバでの NTP の構成ガイド （1033366）
• 简体中文: 在 ESX Server 上配置 NTP 指南 (2086210)