AVM has a daylight saving time problem with their FRITZ!Box and FRITZ!Fon products

My FRITZ!Box 7390 synchronises properly with the NTP servers, but it does not take the DST ("daylight saving time", in German: "Sommerzeit") into account, that started last night over here in Germany (e.g.).

When I log in to my box, it shows the date (day and time) like this:

$ telnet fritz.box
# date
Sun Mar 25 10:05:09 CET 2012

It should show this instead:

Sun Mar 25 11:05:09 CEST 2012

The time itself is alright, just the DST is not.

On the IP-Phone-Forum there are currently 2 threads dealing with the issue:

• one on its "FRITZ!Box Fon: Internet" subforum: "[Fritz!Box 7390] Umstellung auf Sommerzeit erfolgte nicht",
• one on its "Fritz!Mini, M2, MT-C, MT-D, MT-F, C3" subforum: "Keine autom. Aktualisierung auf Sommerzeit?"; here I found the most thorough description of the situation: "Es ist ein Problem mit der Zeitzone".

Another look inside the box:

# ls -l /etc/TZ
lrwxrwxrwx    1 root     root             7 Mar  2 16:01 /etc/TZ -> /var/TZ
# ls -l /var/TZ
lrwxrwxrwx    1 root     root            19 Mar 25 11:01 /var/TZ -> /etc/default.049/TZ
# ls -l /etc/default.049/TZ
-rwxrwxrwx    1 root     root            45 Mar  2 16:01 /etc/default.049/TZ
# cat /etc/default.049/TZ
CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00

The TZ file looks like it's writable, but it's on a read-only filesystem.

The constituents of "M3.5.0" mean this:

• The "3" means the 3rd month of the year.
• The "0" means the 0th day of the week, i.e. the Sunday.
• The "5" means neither the 1st through 4th, but the last Sunday.

Looks like AVM's software has a problem with determining the right date for the last Sunday of March in 2012.

On my blog in German I am referring to an article in a German magazine, that shows how and where to change the timezone "manually". (Somebody on the IP-Phone-Forum quoted that article, and that's how I found it.) My fix for 2012: replace that "5" by "4"!

Update 2012-03-26: AVM look like they don't want to announce a fix for this problem within the next couple of days [Link].

Update 2012-03-28: AVM provide a "Labor" firmware update.

A heise Netze article (in German) on the topic [link].