On a Debian 9 machine:
patate:~> TZ=UTC date; TZ=UTC0 date
Sun Aug 12 03:02:35 CEST 2018
Sun Aug 12 01:02:35 UTC 2018
The first line is based on the /usr/share/zoneinfo/UTC file according
to strace, but this is wrong as CEST is not UTC. The file is:
-rw-r--r-- 1 root root 2971 2018-05-15 10:01:38 /usr/share/zoneinfo/UTC
which doesn't seem to be the original one. I assume that it got
corrupted via a write to /etc/localtime, but /etc/localtime is
a symlink to /usr/share/zoneinfo/Etc/UTC, which is itself a
symlink to /usr/share/zoneinfo/UTC.
Now, could the write to /etc/localtime be regarded as a bug?
Probably not, because /etc/localtime is a config file, and one
is allowed to write to config files under /etc.
In short, having a symlink from a file under /etc to a file from
a package does not seem to be correct.
BTW, on https://www.virtualmin.com/node/15246 someone mentioned
another issue with a symlink: "It's not really wise to make
/etc/localtime a symlink. That used to be the standard behavior for
Linux in the past, but then someone realized that /usr/share/zoneinfo
could be on a different volume that's not always mounted, and we
definitely don't want to be without /etc/localtime, [...]"
-- System Information:
Debian Release: 9.5
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 4.9.0-7-amd64 (SMP w/16 CPU cores)
Locale: LANG=POSIX, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=POSIX
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages tzdata depends on:
ii debconf [debconf-2.0] 1.5.61
tzdata recommends no packages.
tzdata suggests no packages.
-- no debconf information