CODEWITHSUNDEEP
linuxtimetimezone
sigidagi
sigidagi

Reputation: 864

why timestamps for two timezones with the same UTC offset are different?

Here is an example:

root@linux:~# timedatectl 
      Local time: Thu 2016-03-31 08:33:23 CEST
  Universal time: Thu 2016-03-31 06:33:23 UTC
        RTC time: n/a
       Time zone: Africa/Ceuta (CEST, +0200)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  Sun 2016-03-27 01:59:59 CET
                  Sun 2016-03-27 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  Sun 2016-10-30 02:59:59 CEST
                  Sun 2016-10-30 02:00:00 CET


root@linux:~# echo  $string
1970 01 01 0 0 0

root@linux:~# awk -v str="$string" 'BEGIN {print mktime(str)}'
0


root@linux:~# timedatectl set-timezone Europe/Berlin
root@linux:~# timedatectl 
      Local time: Thu 2016-03-31 08:59:01 CEST
  Universal time: Thu 2016-03-31 06:59:01 UTC
        RTC time: n/a
       Time zone: Europe/Berlin (CEST, +0200)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  Sun 2016-03-27 01:59:59 CET
                  Sun 2016-03-27 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  Sun 2016-10-30 02:59:59 CEST
                  Sun 2016-10-30 02:00:00 CET


root@linux:~# echo $string
1970 01 01 0 0 0

root@linux:~# awk -v str="$string" 'BEGIN {print mktime(str)}'
-3600

2 question: And why mktime output (when input 1970-01-01T00:00:00 ) for Europe/Berlin timezone is -1 hour?

Upvotes: 1

Views: 301

Answers (2)

Howard Hinnant
Howard Hinnant

Reputation: 219548

timedatectl (apparently) shows the current timezone rules in effect for the currently set timezone. However timezone rules change over time within the same timezone.

As of today, both Africa/Ceuta and Europe/Berlin have the same UTC offset, and follow the exact same rules for daylight savings. But they haven't always done so.

In 1970-01-01 Africa/Ceuta used a 0:00:00 UTC offset and did not use daylight saving.

In 1970-01-01 Europe/Berlin used a 1:00:00 UTC offset and did not use daylight saving.

It wasn't until 1986-03-30 01:00:00 UTC that Africa/Ceuta and Europe/Berlin adopted the same rules. Your computer knows this history, and accurately reflects it when doing conversions between UTC and local time for dates prior to 1986-03-30.

Upvotes: 1

Jeroen Evens
Jeroen Evens

Reputation: 125

they change to Summer and Winter-times at different dates, which is why the times might be different even though they have the same UTC offset

Upvotes: 0

Related Questions