TimeZone.currentSystemDefault() returns wrong time zone on Linux

[NANDcs]

I'm on Ubuntu 24.04 noble with KDE 5.115.0 / Plasma 5.27.12 using library version 0.6.2.

Per the documentation for currentSystemDefault():

On Linux, this function queries the /etc/localtime symbolic link.

Looking at the /etc/localtime symlink:
localtime -> /usr/share/zoneinfo/America/New_York

However calling println(TimeZone.currentSystemDefault()) returns:
America/Los_Angeles

For context, last week I switched my time zone from Eastern to Pacific using the system settings. Switching it back fixes the system time in every other application except the KMP app I'm using (source code).

[dkhalanskyjb]

The call chain is, unconditionally, this:

• Try to acquire the name of the timezone:

  kotlinx-datetime/core/commonKotlin/src/TimeZone.kt

  Line 23 in e69f92f

  val (name, rules) = currentSystemDefaultZone()

• For that, look at the path of the current system timezone:

  kotlinx-datetime/core/linux/src/internal/TimeZoneNative.kt

  Line 16 in e69f92f

  val zonePath = currentSystemTimeZonePath ?: return "Z" to null

• For that, chase the symlinks of the /etc/localtime file:

  kotlinx-datetime/core/tzdbOnFilesystem/src/internal/TzdbOnFilesystem.kt

  Line 50 in e69f92f

  internal val currentSystemTimeZonePath get() = chaseSymlinks("/etc/localtime")

  , which should be /usr/share/zoneinfo/America/New_York.
• Then, take the part after zoneinfo/:

  kotlinx-datetime/core/tzdbOnFilesystem/src/internal/TzdbOnFilesystem.kt

  Lines 57 to 64 in e69f92f

  	internal fun Path.splitTimeZonePath(): Pair<Path, Path>? {
  	val i = components.indexOf("zoneinfo")
  	if (!isAbsolute || i == -1 || i == components.size - 1) return null
  	return Pair(
  	Path(true, components.subList(0, i + 1)),
  	Path(false, components.subList(i + 1, components.size))
  	)
  	}

  This gives you the name of the timezone: America/New_York.
• Return of("America/New_York"):

  kotlinx-datetime/core/commonKotlin/src/TimeZone.kt

  Line 25 in e69f92f

  of(name)

I highly doubt that America/New_York could be a symlink to America/Los_Angeles, so the procedure of chasing the symlinks should stop at /usr/share/America/New_York (it's a regular file and not a symlink on my system).

The only explanation I can find is that your KMP application runs in some containerized environment, which has its own /etc/localtime. Otherwise, there is just no place where our library could get America/Los_Angeles from, we don't have it hardcoded.

You can confirm this by checking the contents of /etc/localtime from inside your program using this code:

import kotlinx.cinterop.ByteVar
import kotlinx.cinterop.ExperimentalForeignApi
import kotlinx.cinterop.allocArray
import kotlinx.cinterop.memScoped
import kotlinx.cinterop.toKString
import platform.posix.PATH_MAX
import platform.posix.realpath

@OptIn(ExperimentalForeignApi::class)
fun getTimezoneSymlinkContents(): String? = memScoped {
    val buffer = allocArray<ByteVar>(PATH_MAX)
    return realpath("/etc/localtime", buffer)?.toKString()
}

[NANDcs]

Thanks for the extra context! I did look through some of the source for this library just to confirm, but yeah still confusing as to how it's getting the wrong value.

You can confirm this by checking the contents of /etc/localtime from inside your program using this code

I'm currently having trouble getting this code to run within my existing project (gradle/build errors) but I did try cloning the kmp-native-wizard project and putting it there. Here's what I got:

Code:

memScoped {
    val buffer = allocArray<ByteVar>(PATH_MAX)
    println(realpath("/etc/localtime", buffer)?.toKString())
}
println(TimeZone.currentSystemDefault())

Output:

/usr/share/zoneinfo/America/New_York
America/New_York

So in a fresh project everything works as expected. What's bizarre is that in my existing project it's still outputting the wrong time zone for the TimeZone.currentSystemDefault() call specifically (same machine, IDE, etc). I even tried printing out the symlink and raw file contents for /etc/localtime and it's different from the time zone call output.

Code:

println(File("/etc/localtime").readBytes().decodeToString())
println(Files.readSymbolicLink(Paths.get("/etc/localtime")))
println(TimeZone.currentSystemDefault())

Output:

[byte code containing "EST5EDT", which implies correct time zone]
/usr/share/zoneinfo/America/New_York
America/Los_Angeles

So there's clearly some weird disconnect between the symlink that JVM sees and what Kotlin Native sees in this context. Even weirder is that this issue occurs both when running the project within the IDE and when installing/running the app as a standalone package (on the same machine).

Based on your comments above and the call stack you've provided I'm leaning towards this being a general Kotlin Native/platform issue rather than an issue with the datetime library specifically. So maybe this issue is worth closing and/or moving to another repo.

[dkhalanskyjb]

What does java.time.ZoneId.systemDefault() return?

[NANDcs]

Ahhh there it is. ZoneId.systemDefault() also returns "America/Los_Angeles" and the user.timezone property is set to that as well. I see now that the JVM version of TimeZone.currentSystemDefault() just redirects to ZoneId.systemDefault() rather than reading from /etc/localtime.

[NANDcs]

Figured it out. The root issue was /etc/timezone, which is just a text file containing the time zone name, was set to LA. This file seems to take precedence over /etc/localtime in JVM. Here's an article that goes into more detail on how JVM detects system time: https://kaiwangchen.github.io/2018/09/30/java-timezone-revisited.html

I'll leave it up y'all, but I think this is worth mentioning in the documentation for TimeZone.currentSystemDefault().

Thanks for helping debug this.