ADDITIONAL SYSTEM INFORMATION :
Java Version: OpenJDK 17 & 21
OS: Debian GNU/Linux 12 (bookworm)

A DESCRIPTION OF THE PROBLEM :
In recent versions of Debian (starting with Debian 12), the system no longer relies on /etc/timezone for timezone management. Instead, Debian and systemd have transitioned to using /etc/localtime as the authoritative source for timezone data. However, OpenJDK still prioritizes /etc/timezone when determining the system timezone, leading to inconsistencies between the system's timezone and the default timezone for the JVM.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Set the system timezone using timedatectl: "sudo timedatectl set-timezone Europe/Paris"
2. Check /etc/localtime and /etc/timezone: "ls -l /etc/localtime; cat /etc/timezone"
    Observe that /etc/localtime points to /usr/share/zoneinfo/Europe/Paris, but /etc/timezone has not been updated.
3. Run a simple Java application and retrieve the default timezone:

    System.out.println(java.util.TimeZone.getDefault());
 
    Observe that the JVM reports the timezone from /etc/timezone

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Java should use /etc/localtime as the primary source for determining the system timezone, consistent with Debian’s new standard.
ACTUAL -
Java uses /etc/timezone, causing mismatches between the system timezone and the JVM timezone.

CUSTOMER SUBMITTED WORKAROUND :
Explicitly specifying the timezone with the "TZ" variable or "-Duser.timezone" JVM option.

or

Manually updating /etc/timezone after changing the systems timezone with "timedatectl":
timedatectl show --value --property=Timezone | sudo tee /etc/timezone

FREQUENCY : always