Kernel has a sys_tz and FAT based file systems have a new mount option to control time zone of FAT file systems: tz=UTC.

The default for most FAT volumes is the local time (i. e. tz=UTC not used in mount options). In local time mode, kernel uses sys_tz kernel variable.

But sys_tz is not set, so all FAT based file systems are mounted with the time zone equal to UTC. It causes "several hours off" effect.

As far as I see, the only user space utility capable to set the sys_tz is the hwclock utility. But hwclock does not work as expected:

"hwclock --systz --utc" does nothing useful.

"hwclock --systz --localtime" sets sys_tz variable correctly but also reads hwclock and sets system clock, exactly as "hwclock --localtime --hctosys". It is not wanted in most cases.

Work-around:
hwclock --systz --localtime
hwclock --hctosys --utc
With exception of time race while called, it does what most people expect.

Correct fix:
It is mis-design of --systz. --systz either should not include --hctosys and set only sys_tz or --systz --utc should do something useful: set sys_tz to the correct time zone.

Note: other distributions probably have the same problem.