Amazon Elastic Compute Cloud
User Guide for Windows Instances

Setting the Time for a Windows Instance

A consistent and accurate time reference is crucial for many server tasks and processes. Most system logs include a time stamp that you can use to determine when problems occur and in what order the events take place. If you use the AWS CLI or an AWS SDK to make requests from your instance, these tools sign requests on your behalf. If your instance's date and time are not set correctly, the date in the signature may not match the date of the request, and AWS rejects the request. We recommend that you use Coordinated Universal Time (UTC) for your Windows instances. However, you can use a different time zone if you want.

Changing the Time Zone

Windows instances are set to the UTC time zone by default. you can change the time to correspond to your local time zone or a time zone for another part of your network.

To change the time zone on an instance

  1. From your instance, open a Command Prompt window.

  2. Identify the time zone to use on the instance. To get a list of time zones, use the following command: tzutil /l. This command returns a list of all available time zones, using the following format:

    display name time zone ID
  3. Locate the time zone ID to assign to the instance.

  4. Assign the time zone to the instance by using the following command:

    tzutil /s "Pacific Standard Time"

    The new time zone should take effect immediately.

Configuring Network Time Protocol (NTP)

Amazon provides the Amazon Time Sync Service, which is accessible from all EC2 instances, and is also used by other AWS services. We recommend that you configure your instance to use the Amazon Time Sync Service. This service uses a fleet of satellite-connected and atomic reference clocks in each AWS Region to deliver accurate current time readings of the Coordinated Universal Time (UTC) global standard. The Amazon Time Sync Service automatically smooths any leap seconds that are added to UTC. This service is available at the IP address for any instance running in a VPC, and your instance does not require internet access to use it. Starting with the August 2018 release, Windows AMIs use the Amazon Time Sync Service by default.

To verify the NTP configuration

  1. From your instance, open a Command Prompt window.

  2. Get the current NTP configuration by typing the following command:

    w32tm /query /configuration

    This command returns the current configuration settings for the Windows instance.

  3. (Optional) Get the status of the current configuration by typing the following command:

    w32tm /query /status

    This command returns information such as the last time the instance synced with the NTP server and the poll interval.

To change the NTP server to use the Amazon Time Sync Service

  1. From the Command Prompt window, run the following command:

    w32tm /config /manualpeerlist: /syncfromflags:manual /update
  2. Verify your new settings by using the following command:

    w32tm /query /configuration

    In the output that's returned, verify that NtpServer displays the IP address.

You can change the instance to use a different set of NTP servers if you need to. For example, if you have Windows instances that do not have internet access, you can configure them to use an NTP server located within your private network. Your instance's security group must allow outbound UDP traffic on port 123 (NTP).

To change the NTP servers

  1. From the Command Prompt window, run the following command:

    w32tm /config /manualpeerlist:comma-delimited list of NTP servers /syncfromflags:manual /update

    Where comma-delimited list of NTP servers is the list of NTP servers for the instance to use.

  2. Verify your new settings by using the following command:

    w32tm /query /configuration

Default Network Time Protocol (NTP) Settings for Amazon Windows AMIs

Amazon Machine Images (AMIs) generally adhere to the out-of-the-box defaults except in cases where changes are required to function on EC2 infrastructure. The following settings have been determined to work well in a virtualized environment, as well as to keep any clock drift to within one second of accuracy:

  • Update Interval – governs how frequently the time service will adjust system time towards accuracy. AWS configures the update interval to occur once every two minutes.

  • NTP Server – starting with the August 2018 release, AMIs will now use the Amazon Time Sync Service by default. This time service is accessible from any EC2 Region at the endpoint. Additionally, the 0x9 flag indicates that the time service is acting as a client, and to use SpecialPollInterval to determine how frequently to check in with the configured time server.

  • Type – "NTP" means that the service acts as a standalone NTP client instead of acting as part of a domain.

  • Enabled and InputProvider – the time service is enabled and provides time to the operating system.

  • Special Poll Interval – checks against the configured NTP Server every 900 seconds, or 15 minutes.

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Configuring Time Settings for Windows Server 2008 and later

When you change the time on a Windows instance, you must ensure that the time persists through system restarts. Otherwise, when the instance restarts, it reverts back to using UTC time. For Windows Server 2008 and later, you can persist your time setting by adding a RealTimeIsUniversal registry key.

To set the RealTimeIsUniversal registry key

  1. From the instance, open a Command Prompt window.

  2. Use the following command to add the registry key:

    reg add "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation" /v RealTimeIsUniversal /d 1 /t REG_DWORD /f
  3. If you are using a Windows Server 2008 AMI (not Windows Server 2008 R2) that was created before February 22, 2013, we recommend updating to the latest AWS Windows AMI. If you are using an AMI running Windows Server 2008 R2 (not Windows Server 2008), you must verify that the Microsoft hotfix KB2922223 is installed. If this hotfix is not installed, we recommend updating to the latest AWS Windows AMI.

  4. (Optional) Verify that the instance saved the key successfully using the following command:

    reg query "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation" /s

    This command returns the subkeys for the TimeZoneInformation registry key. You should see the RealTimeIsUniversal key at the bottom of the list, similar to the following:

    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation Bias REG_DWORD 0x1e0 DaylightBias REG_DWORD 0xffffffc4 DaylightName REG_SZ @tzres.dll,-211 DaylightStart REG_BINARY 00000300020002000000000000000000 StandardBias REG_DWORD 0x0 StandardName REG_SZ @tzres.dll,-212 StandardStart REG_BINARY 00000B00010002000000000000000000 TimeZoneKeyName REG_SZ Pacific Standard Time DynamicDaylightTimeDisabled REG_DWORD 0x0 ActiveTimeBias REG_DWORD 0x1a4 RealTimeIsUniversal REG_DWORD 0x1

For more information about how the Windows operating system coordinates and manages time, including the addition of a leap second, see the following documentation: