[Bookworm] Timezone setting is not propagated to containers

[vivekrnv]

Description

Timezone setting is expected to propagate to the containers. But after bookworm upgrade in SONiC, it is broken

202311

1. Set a new timezone: config clock timezone Asia/Pyongyang
2. Updated on host immediately:

timedatectl show
Timezone=Asia/Pyongyang
TimeUSec=Wed 2024-11-27 06:17:03 KST

3. config save & config reload for the change to be updated in the container.

docker exec eventd zdump /etc/localtime
/etc/localtime  Wed Nov 27 06:20:09 2024 KST

docker exec eventd cat /etc/timezone
Asia/Pyongyang

docker exec eventd date
Wed Nov 27 06:20:39 KST 2024

202405 and above:

config clock timezone Asia/Pyongyang

timedatectl show
Timezone=Asia/Pyongyang
TimeUSec=Wed 2024-11-27 06:37:01 KST

zdump /etc/localtime
/etc/localtime  Wed Nov 27 06:37:15 2024 KST

After config reload, containers are expected to have timezone change but it is not seen

docker exec eventd zdump /etc/localtime
/etc/localtime  Tue Nov 26 21:39:00 2024 UTC

docker exec eventd date
Tue Nov 26 21:39:09 UTC 2024

docker exec eventd cat /etc/timezone
Etc/UTC

cat /etc/timezone
Etc/UTC (Even on host, this file is not updated)

Triage

Issue lies in timedatectl command not updating /etc/timezone in systemd version used on bookworm
Ref: https://unix.stackexchange.com/questions/451709/timedatectl-set-timezone-doesnt-update-etc-timezone

/etc/timezone appears to be mostly Debian-specific (including derivatives). On Debian systems, timedatectl set-timezone also updates /etc/timezone, in version of systemd older than 252.6-1 (so until Debian 11 included).

This PR #14000 (Which fixes the timesync issue between host and container) uses /etc/timezone as reference to update the timezone in container.

[vivekrnv]

@nmoray can the logic be updated instead to use /etc/localtime directly from host instead of using /etc/timezone