asp core 3.1 set global default timezone?

[EvgenyPrikhodko]

How to specify the global timzone?

[ericstj]

cc @safern @tarekgh @krwq

[tarekgh]

It has to be done through the User settings or the machine admin. We don't have API to set the default time zone on the machine because it need a specific privilege to do it which is turned off by default.

As user if you want to change the TZ from the settings you may follow the steps https://support.microsoft.com/en-us/help/4026213/windows-how-to-set-your-time-and-time-zone.

If you want to do it by APIs, you may consider pinvoke to https://docs.microsoft.com/en-us/windows/win32/api/timezoneapi/nf-timezoneapi-settimezoneinformation but you have to work getting the needed privlage before doing so or the API will fail.

[tarekgh]

Also, I want to point, changing the time zone by API would cause a problem if the change is not desired by the machine user which can affect many other running applications. So if you do that you have to be very careful and make sure will not cause any problem.

[EvgenyPrikhodko]

There is a backend API (asp netCore 3.1 + EFCore) works on centos-> kestrel -> nginx.
Backend run as service (deamon), OS timezone x, API time zone y.
How to run API timezone != TimezoneOS?

[tarekgh]

@EvgenyPrikhodko what is your scenario that need to run with different time zone than TimezoneOS? I am not familiar with what asp netcore3.1 + EFCore offering. CC @davidfowl if he knows more about that.

If you want to do that for testing purpose, one way to do it is using the Reflection to set the field https://source.dot.net/#System.Private.CoreLib/TimeZoneInfo.cs,65.

[EvgenyPrikhodko]

Thank you very much for the sample code, we will test it.

1. Can this Method be called once in Main for the entire Project?
2. Logic can reset again on Windows, no problem for Linux?

[tarekgh]

Can this Method be called once in Main for the entire Project?

Yes.

Logic can reset again on Windows, no problem for Linux?

Yes. When the time cross the year the rest will happen only on Windows.

But if anyone calls TimeZoneInfo.ClearCachedData the reset will happen on Windows and Linux. you may try to play with that to see the behavior.

[EvgenyPrikhodko]

Can this Method be called once in Main for the entire Project?

Yes.

Logic can reset again on Windows, no problem for Linux?

Yes. When the time cross the year the rest will happen only on Windows.

But if anyone calls TimeZoneInfo.ClearCachedData the reset will happen on Windows and Linux. you may try to play with that to see the behavior.

Thank you so much for your answers.

[tarekgh]

I want to emphasize you need to test this well with your scenario before you apply it. As I mentioned this is fragile and can break. The provided code is just example and not intended to be used in real product but it is your decision if you want to use it and depend on it.

[fukasawah]

This answer was very helpful to me.
I develop on Windows and run on Linux, and in both cases I needed to make TimeZoneInfo.Local behave like UTC time.

SetLocalTimeZone(TimeZoneInfo.CreateCustomTimeZone(
    "UTC-FOR-TEST", TimeZoneInfo.Utc.BaseUtcOffset, TimeZoneInfo.Utc.DisplayName, TimeZoneInfo.Utc.StandardName
));

However, if I call TimeZoneInfo.ConvertTime when datetime.Ticks==0, it calls ClearCachedData.

runtime/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs

Lines 605 to 613 in 215b39a

	public static DateTime ConvertTime(DateTime dateTime, TimeZoneInfo destinationTimeZone)
	{
	ArgumentNullException.ThrowIfNull(destinationTimeZone);
	// Special case to give a way clearing the cache without exposing ClearCachedData()
	if (dateTime.Ticks == 0)
	{
	ClearCachedData();
	}

It consumed a lot of time until I noticed this behavior...

[EvgenyPrikhodko]

please register my wish.
use-case
For example, I have an application that was written without timzone, I don't know what timezone hosting uses (azure, amazone, etc.).
Make dotnet myapp.dll --timezone "Morocco Standard Time"

[EvgenyPrikhodko]

@tarekgh Please consider my offer

[tarekgh]

This need to be turned into a proposal and logged a new issue as a request. The proposal has to be detailed for the behavior and if there is any needed new API. Here is some example #42109

[EvgenyPrikhodko]

Create

[PathogenDavid]

I'm a bit late, but if you only need Linux support for this, .NET respects the TZ environment variable as shown below:

The value of TZ can basically be any file under /usr/share/zoneinfo.

[SteveDesmond-ca]

This just saved me a ton of time zone logic code, thanks @PathogenDavid!

[tarekgh]

@PathogenDavid what is your scenario you want to use this for?

[PathogenDavid]

Replied on #42241