מתי עוברים לשעון חורף (ועוד כמה טיפים על אזורי זמן)
09/09/2023
מכונות יוניקס - ולכן גם לינוקס ומק, שומרות בסיס נתונים של אזורי זמן בתיקיה מיוחדת על המחשב שנקראת /usr/share/zoneinfo. הקבצים שם הם בינאריים שמתארים את ההפרש של אזור הזמן שמתאים לקובץ, וגם את כל השינויים באזור הזמן ובמיוחד בהיבט של מעבר בין שעון קיץ לחורף. בואו נצא לחקור קצת את הקבצים שם ולשחק עם אזורי זמן.
תחילה רשימת הקבצים בתיקייה, לפחות אצלי על המק:
$ ls -ld /usr/share/zoneinfo/
lrwxr-xr-x 1 root wheel 38 Apr 28 23:44 /usr/share/zoneinfo/ -> /var/db/timezone/tz/2023c.1.0/zoneinfo
$ ls -F /var/db/timezone/tz/2023c.1.0/zoneinfo/
+VERSION CET Eire GMT0 Japan Navajo Turkey leapseconds
Africa/ CST6CDT Etc/ Greenwich Kwajalein PRC UCT posixrules
America/ Canada/ Europe/ HST Libya PST8PDT US/ zone.tab
Antarctica/ Chile/ Factory Hongkong MET Pacific/ UTC
Arctic/ Cuba GB Iceland MST Poland Universal
Asia/ EET GB-Eire Indian/ MST7MDT Portugal W-SU
Atlantic/ EST GMT Iran Mexico/ ROC WET
Australia/ EST5EDT GMT+0 Israel NZ ROK Zulu
Brazil/ Egypt GMT-0 Jamaica NZ-CHAT Singapore iso3166.tab
ואנחנו רואים שהתיקיה מכילה קבצים ותיקיות, לפי המדינה והיבשת. אני לא בטוח למה לנו אין יבשת, אבל לפחות אנחנו לא היחידים. כשננסה להציג את תוכן הקובץ אנחנו עשויים להתאכזב שכן אלה קבצים בינאריים. אפשר להשתמש ב xxd:
$ xxd /usr/share/zoneinfo/Israel| head -4
00000000: 545a 6966 3200 0000 0000 0000 0000 0000 TZif2...........
00000010: 0000 0000 0000 0008 0000 0008 0000 0000 ................
00000020: 0000 0094 0000 0008 0000 0011 9e30 4588 .............0E.
00000030: c859 cf00 c8fa a600 c938 9c80 cce5 eb80 .Y.......8......
הפורמט מתואר בפירוט בתיעוד כאן. הדבר החשוב משם הוא לראות שקובץ כזה כולל הרבה מעבר להפרש השעות. הפקודה zdump מדפיסה את הזמן הנוכחי באזור זמן שמתאים לקובץ מהמאגר:
$ zdump Israel
Israel Fri Sep 8 14:14:43 2023 IDT
$ zdump Europe/Paris
Europe/Paris Fri Sep 8 13:15:03 2023 CEST
$ zdump Chile/Continental
Chile/Continental Fri Sep 8 08:15:45 2023 -03
ועם המתג המתאים היא יכולה להציג את השינויים שקובץ zoneinfo כולל, כלומר המעברים בין שעון חורף לקיץ. זה המצב אצלנו:
$ zdump -v Israel
Israel Fri Dec 13 20:45:52 1901 UTC = Fri Dec 13 23:06:32 1901 JMT isdst=0
Israel Sat Dec 14 20:45:52 1901 UTC = Sat Dec 14 23:06:32 1901 JMT isdst=0
Israel Mon Dec 31 21:39:19 1917 UTC = Mon Dec 31 23:59:59 1917 JMT isdst=0
Israel Mon Dec 31 21:39:20 1917 UTC = Mon Dec 31 23:39:20 1917 IST isdst=0
Israel Fri May 31 23:59:59 1940 UTC = Sat Jun 1 01:59:59 1940 IST isdst=0
Israel Sat Jun 1 00:00:00 1940 UTC = Sat Jun 1 03:00:00 1940 IDT isdst=1
Israel Mon Sep 30 23:59:59 1940 UTC = Tue Oct 1 02:59:59 1940 IDT isdst=1
Israel Tue Oct 1 00:00:00 1940 UTC = Tue Oct 1 02:00:00 1940 IST isdst=0
Israel Sat Nov 16 23:59:59 1940 UTC = Sun Nov 17 01:59:59 1940 IST isdst=0
Israel Sun Nov 17 00:00:00 1940 UTC = Sun Nov 17 03:00:00 1940 IDT isdst=1
Israel Sat Oct 31 23:59:59 1942 UTC = Sun Nov 1 02:59:59 1942 IDT isdst=1
Israel Sun Nov 1 00:00:00 1942 UTC = Sun Nov 1 02:00:00 1942 IST isdst=0
Israel Wed Mar 31 23:59:59 1943 UTC = Thu Apr 1 01:59:59 1943 IST isdst=0
Israel Thu Apr 1 00:00:00 1943 UTC = Thu Apr 1 03:00:00 1943 IDT isdst=1
Israel Sun Oct 31 23:59:59 1943 UTC = Mon Nov 1 02:59:59 1943 IDT isdst=1
Israel Mon Nov 1 00:00:00 1943 UTC = Mon Nov 1 02:00:00 1943 IST isdst=0
Israel Fri Mar 31 23:59:59 1944 UTC = Sat Apr 1 01:59:59 1944 IST isdst=0
Israel Sat Apr 1 00:00:00 1944 UTC = Sat Apr 1 03:00:00 1944 IDT isdst=1
Israel Tue Oct 31 23:59:59 1944 UTC = Wed Nov 1 02:59:59 1944 IDT isdst=1
Israel Wed Nov 1 00:00:00 1944 UTC = Wed Nov 1 02:00:00 1944 IST isdst=0
Israel Sun Apr 15 23:59:59 1945 UTC = Mon Apr 16 01:59:59 1945 IST isdst=0
Israel Mon Apr 16 00:00:00 1945 UTC = Mon Apr 16 03:00:00 1945 IDT isdst=1
Israel Wed Oct 31 23:59:59 1945 UTC = Thu Nov 1 02:59:59 1945 IDT isdst=1
Israel Thu Nov 1 00:00:00 1945 UTC = Thu Nov 1 02:00:00 1945 IST isdst=0
Israel Mon Apr 15 23:59:59 1946 UTC = Tue Apr 16 01:59:59 1946 IST isdst=0
Israel Tue Apr 16 00:00:00 1946 UTC = Tue Apr 16 03:00:00 1946 IDT isdst=1
Israel Thu Oct 31 23:59:59 1946 UTC = Fri Nov 1 02:59:59 1946 IDT isdst=1
Israel Fri Nov 1 00:00:00 1946 UTC = Fri Nov 1 02:00:00 1946 IST isdst=0
Israel Sat May 22 23:59:59 1948 UTC = Sun May 23 01:59:59 1948 IST isdst=0
Israel Sun May 23 00:00:00 1948 UTC = Sun May 23 04:00:00 1948 IDDT isdst=1
Israel Tue Aug 31 23:59:59 1948 UTC = Wed Sep 1 03:59:59 1948 IDDT isdst=1
Israel Wed Sep 1 00:00:00 1948 UTC = Wed Sep 1 03:00:00 1948 IDT isdst=1
Israel Sun Oct 31 23:59:59 1948 UTC = Mon Nov 1 02:59:59 1948 IDT isdst=1
Israel Mon Nov 1 00:00:00 1948 UTC = Mon Nov 1 02:00:00 1948 IST isdst=0
Israel Sat Apr 30 23:59:59 1949 UTC = Sun May 1 01:59:59 1949 IST isdst=0
Israel Sun May 1 00:00:00 1949 UTC = Sun May 1 03:00:00 1949 IDT isdst=1
Israel Mon Oct 31 23:59:59 1949 UTC = Tue Nov 1 02:59:59 1949 IDT isdst=1
Israel Tue Nov 1 00:00:00 1949 UTC = Tue Nov 1 02:00:00 1949 IST isdst=0
Israel Sat Apr 15 23:59:59 1950 UTC = Sun Apr 16 01:59:59 1950 IST isdst=0
Israel Sun Apr 16 00:00:00 1950 UTC = Sun Apr 16 03:00:00 1950 IDT isdst=1
Israel Thu Sep 14 23:59:59 1950 UTC = Fri Sep 15 02:59:59 1950 IDT isdst=1
Israel Fri Sep 15 00:00:00 1950 UTC = Fri Sep 15 02:00:00 1950 IST isdst=0
Israel Sat Mar 31 23:59:59 1951 UTC = Sun Apr 1 01:59:59 1951 IST isdst=0
Israel Sun Apr 1 00:00:00 1951 UTC = Sun Apr 1 03:00:00 1951 IDT isdst=1
Israel Sat Nov 10 23:59:59 1951 UTC = Sun Nov 11 02:59:59 1951 IDT isdst=1
Israel Sun Nov 11 00:00:00 1951 UTC = Sun Nov 11 02:00:00 1951 IST isdst=0
Israel Sat Apr 19 23:59:59 1952 UTC = Sun Apr 20 01:59:59 1952 IST isdst=0
Israel Sun Apr 20 00:00:00 1952 UTC = Sun Apr 20 03:00:00 1952 IDT isdst=1
Israel Sat Oct 18 23:59:59 1952 UTC = Sun Oct 19 02:59:59 1952 IDT isdst=1
Israel Sun Oct 19 00:00:00 1952 UTC = Sun Oct 19 02:00:00 1952 IST isdst=0
Israel Sat Apr 11 23:59:59 1953 UTC = Sun Apr 12 01:59:59 1953 IST isdst=0
Israel Sun Apr 12 00:00:00 1953 UTC = Sun Apr 12 03:00:00 1953 IDT isdst=1
Israel Sat Sep 12 23:59:59 1953 UTC = Sun Sep 13 02:59:59 1953 IDT isdst=1
Israel Sun Sep 13 00:00:00 1953 UTC = Sun Sep 13 02:00:00 1953 IST isdst=0
Israel Sat Jun 12 23:59:59 1954 UTC = Sun Jun 13 01:59:59 1954 IST isdst=0
Israel Sun Jun 13 00:00:00 1954 UTC = Sun Jun 13 03:00:00 1954 IDT isdst=1
Israel Sat Sep 11 23:59:59 1954 UTC = Sun Sep 12 02:59:59 1954 IDT isdst=1
Israel Sun Sep 12 00:00:00 1954 UTC = Sun Sep 12 02:00:00 1954 IST isdst=0
Israel Sat Jun 11 23:59:59 1955 UTC = Sun Jun 12 01:59:59 1955 IST isdst=0
Israel Sun Jun 12 00:00:00 1955 UTC = Sun Jun 12 03:00:00 1955 IDT isdst=1
Israel Sat Sep 10 23:59:59 1955 UTC = Sun Sep 11 02:59:59 1955 IDT isdst=1
Israel Sun Sep 11 00:00:00 1955 UTC = Sun Sep 11 02:00:00 1955 IST isdst=0
Israel Sat Jun 2 23:59:59 1956 UTC = Sun Jun 3 01:59:59 1956 IST isdst=0
Israel Sun Jun 3 00:00:00 1956 UTC = Sun Jun 3 03:00:00 1956 IDT isdst=1
Israel Sat Sep 29 23:59:59 1956 UTC = Sun Sep 30 02:59:59 1956 IDT isdst=1
Israel Sun Sep 30 00:00:00 1956 UTC = Sun Sep 30 02:00:00 1956 IST isdst=0
Israel Sat Apr 27 23:59:59 1957 UTC = Sun Apr 28 01:59:59 1957 IST isdst=0
Israel Sun Apr 28 00:00:00 1957 UTC = Sun Apr 28 03:00:00 1957 IDT isdst=1
Israel Sat Sep 21 23:59:59 1957 UTC = Sun Sep 22 02:59:59 1957 IDT isdst=1
Israel Sun Sep 22 00:00:00 1957 UTC = Sun Sep 22 02:00:00 1957 IST isdst=0
Israel Sat Jul 6 21:59:59 1974 UTC = Sat Jul 6 23:59:59 1974 IST isdst=0
Israel Sat Jul 6 22:00:00 1974 UTC = Sun Jul 7 01:00:00 1974 IDT isdst=1
Israel Sat Oct 12 20:59:59 1974 UTC = Sat Oct 12 23:59:59 1974 IDT isdst=1
Israel Sat Oct 12 21:00:00 1974 UTC = Sat Oct 12 23:00:00 1974 IST isdst=0
Israel Sat Apr 19 21:59:59 1975 UTC = Sat Apr 19 23:59:59 1975 IST isdst=0
Israel Sat Apr 19 22:00:00 1975 UTC = Sun Apr 20 01:00:00 1975 IDT isdst=1
Israel Sat Aug 30 20:59:59 1975 UTC = Sat Aug 30 23:59:59 1975 IDT isdst=1
Israel Sat Aug 30 21:00:00 1975 UTC = Sat Aug 30 23:00:00 1975 IST isdst=0
Israel Sat Aug 2 21:59:59 1980 UTC = Sat Aug 2 23:59:59 1980 IST isdst=0
Israel Sat Aug 2 22:00:00 1980 UTC = Sun Aug 3 01:00:00 1980 IDT isdst=1
Israel Sat Sep 13 21:59:59 1980 UTC = Sun Sep 14 00:59:59 1980 IDT isdst=1
Israel Sat Sep 13 22:00:00 1980 UTC = Sun Sep 14 00:00:00 1980 IST isdst=0
Israel Sat May 5 21:59:59 1984 UTC = Sat May 5 23:59:59 1984 IST isdst=0
Israel Sat May 5 22:00:00 1984 UTC = Sun May 6 01:00:00 1984 IDT isdst=1
Israel Sat Aug 25 21:59:59 1984 UTC = Sun Aug 26 00:59:59 1984 IDT isdst=1
Israel Sat Aug 25 22:00:00 1984 UTC = Sun Aug 26 00:00:00 1984 IST isdst=0
Israel Sat Apr 13 21:59:59 1985 UTC = Sat Apr 13 23:59:59 1985 IST isdst=0
Israel Sat Apr 13 22:00:00 1985 UTC = Sun Apr 14 01:00:00 1985 IDT isdst=1
Israel Sat Aug 31 20:59:59 1985 UTC = Sat Aug 31 23:59:59 1985 IDT isdst=1
Israel Sat Aug 31 21:00:00 1985 UTC = Sat Aug 31 23:00:00 1985 IST isdst=0
Israel Sat May 17 21:59:59 1986 UTC = Sat May 17 23:59:59 1986 IST isdst=0
Israel Sat May 17 22:00:00 1986 UTC = Sun May 18 01:00:00 1986 IDT isdst=1
Israel Sat Sep 6 20:59:59 1986 UTC = Sat Sep 6 23:59:59 1986 IDT isdst=1
Israel Sat Sep 6 21:00:00 1986 UTC = Sat Sep 6 23:00:00 1986 IST isdst=0
Israel Tue Apr 14 21:59:59 1987 UTC = Tue Apr 14 23:59:59 1987 IST isdst=0
Israel Tue Apr 14 22:00:00 1987 UTC = Wed Apr 15 01:00:00 1987 IDT isdst=1
Israel Sat Sep 12 20:59:59 1987 UTC = Sat Sep 12 23:59:59 1987 IDT isdst=1
Israel Sat Sep 12 21:00:00 1987 UTC = Sat Sep 12 23:00:00 1987 IST isdst=0
Israel Sat Apr 9 21:59:59 1988 UTC = Sat Apr 9 23:59:59 1988 IST isdst=0
Israel Sat Apr 9 22:00:00 1988 UTC = Sun Apr 10 01:00:00 1988 IDT isdst=1
Israel Sat Sep 3 20:59:59 1988 UTC = Sat Sep 3 23:59:59 1988 IDT isdst=1
Israel Sat Sep 3 21:00:00 1988 UTC = Sat Sep 3 23:00:00 1988 IST isdst=0
Israel Sat Apr 29 21:59:59 1989 UTC = Sat Apr 29 23:59:59 1989 IST isdst=0
Israel Sat Apr 29 22:00:00 1989 UTC = Sun Apr 30 01:00:00 1989 IDT isdst=1
Israel Sat Sep 2 20:59:59 1989 UTC = Sat Sep 2 23:59:59 1989 IDT isdst=1
Israel Sat Sep 2 21:00:00 1989 UTC = Sat Sep 2 23:00:00 1989 IST isdst=0
Israel Sat Mar 24 21:59:59 1990 UTC = Sat Mar 24 23:59:59 1990 IST isdst=0
Israel Sat Mar 24 22:00:00 1990 UTC = Sun Mar 25 01:00:00 1990 IDT isdst=1
Israel Sat Aug 25 20:59:59 1990 UTC = Sat Aug 25 23:59:59 1990 IDT isdst=1
Israel Sat Aug 25 21:00:00 1990 UTC = Sat Aug 25 23:00:00 1990 IST isdst=0
Israel Sat Mar 23 21:59:59 1991 UTC = Sat Mar 23 23:59:59 1991 IST isdst=0
Israel Sat Mar 23 22:00:00 1991 UTC = Sun Mar 24 01:00:00 1991 IDT isdst=1
Israel Sat Aug 31 20:59:59 1991 UTC = Sat Aug 31 23:59:59 1991 IDT isdst=1
Israel Sat Aug 31 21:00:00 1991 UTC = Sat Aug 31 23:00:00 1991 IST isdst=0
Israel Sat Mar 28 21:59:59 1992 UTC = Sat Mar 28 23:59:59 1992 IST isdst=0
Israel Sat Mar 28 22:00:00 1992 UTC = Sun Mar 29 01:00:00 1992 IDT isdst=1
Israel Sat Sep 5 20:59:59 1992 UTC = Sat Sep 5 23:59:59 1992 IDT isdst=1
Israel Sat Sep 5 21:00:00 1992 UTC = Sat Sep 5 23:00:00 1992 IST isdst=0
Israel Thu Apr 1 21:59:59 1993 UTC = Thu Apr 1 23:59:59 1993 IST isdst=0
Israel Thu Apr 1 22:00:00 1993 UTC = Fri Apr 2 01:00:00 1993 IDT isdst=1
Israel Sat Sep 4 20:59:59 1993 UTC = Sat Sep 4 23:59:59 1993 IDT isdst=1
Israel Sat Sep 4 21:00:00 1993 UTC = Sat Sep 4 23:00:00 1993 IST isdst=0
Israel Thu Mar 31 21:59:59 1994 UTC = Thu Mar 31 23:59:59 1994 IST isdst=0
Israel Thu Mar 31 22:00:00 1994 UTC = Fri Apr 1 01:00:00 1994 IDT isdst=1
Israel Sat Aug 27 20:59:59 1994 UTC = Sat Aug 27 23:59:59 1994 IDT isdst=1
Israel Sat Aug 27 21:00:00 1994 UTC = Sat Aug 27 23:00:00 1994 IST isdst=0
Israel Thu Mar 30 21:59:59 1995 UTC = Thu Mar 30 23:59:59 1995 IST isdst=0
Israel Thu Mar 30 22:00:00 1995 UTC = Fri Mar 31 01:00:00 1995 IDT isdst=1
Israel Sat Sep 2 20:59:59 1995 UTC = Sat Sep 2 23:59:59 1995 IDT isdst=1
Israel Sat Sep 2 21:00:00 1995 UTC = Sat Sep 2 23:00:00 1995 IST isdst=0
Israel Thu Mar 14 21:59:59 1996 UTC = Thu Mar 14 23:59:59 1996 IST isdst=0
Israel Thu Mar 14 22:00:00 1996 UTC = Fri Mar 15 01:00:00 1996 IDT isdst=1
Israel Sun Sep 15 20:59:59 1996 UTC = Sun Sep 15 23:59:59 1996 IDT isdst=1
Israel Sun Sep 15 21:00:00 1996 UTC = Sun Sep 15 23:00:00 1996 IST isdst=0
Israel Thu Mar 20 21:59:59 1997 UTC = Thu Mar 20 23:59:59 1997 IST isdst=0
Israel Thu Mar 20 22:00:00 1997 UTC = Fri Mar 21 01:00:00 1997 IDT isdst=1
Israel Sat Sep 13 20:59:59 1997 UTC = Sat Sep 13 23:59:59 1997 IDT isdst=1
Israel Sat Sep 13 21:00:00 1997 UTC = Sat Sep 13 23:00:00 1997 IST isdst=0
Israel Thu Mar 19 21:59:59 1998 UTC = Thu Mar 19 23:59:59 1998 IST isdst=0
Israel Thu Mar 19 22:00:00 1998 UTC = Fri Mar 20 01:00:00 1998 IDT isdst=1
Israel Sat Sep 5 20:59:59 1998 UTC = Sat Sep 5 23:59:59 1998 IDT isdst=1
Israel Sat Sep 5 21:00:00 1998 UTC = Sat Sep 5 23:00:00 1998 IST isdst=0
Israel Thu Apr 1 23:59:59 1999 UTC = Fri Apr 2 01:59:59 1999 IST isdst=0
Israel Fri Apr 2 00:00:00 1999 UTC = Fri Apr 2 03:00:00 1999 IDT isdst=1
Israel Thu Sep 2 22:59:59 1999 UTC = Fri Sep 3 01:59:59 1999 IDT isdst=1
Israel Thu Sep 2 23:00:00 1999 UTC = Fri Sep 3 01:00:00 1999 IST isdst=0
Israel Thu Apr 13 23:59:59 2000 UTC = Fri Apr 14 01:59:59 2000 IST isdst=0
Israel Fri Apr 14 00:00:00 2000 UTC = Fri Apr 14 03:00:00 2000 IDT isdst=1
Israel Thu Oct 5 21:59:59 2000 UTC = Fri Oct 6 00:59:59 2000 IDT isdst=1
Israel Thu Oct 5 22:00:00 2000 UTC = Fri Oct 6 00:00:00 2000 IST isdst=0
Israel Sun Apr 8 22:59:59 2001 UTC = Mon Apr 9 00:59:59 2001 IST isdst=0
Israel Sun Apr 8 23:00:00 2001 UTC = Mon Apr 9 02:00:00 2001 IDT isdst=1
Israel Sun Sep 23 21:59:59 2001 UTC = Mon Sep 24 00:59:59 2001 IDT isdst=1
Israel Sun Sep 23 22:00:00 2001 UTC = Mon Sep 24 00:00:00 2001 IST isdst=0
Israel Thu Mar 28 22:59:59 2002 UTC = Fri Mar 29 00:59:59 2002 IST isdst=0
Israel Thu Mar 28 23:00:00 2002 UTC = Fri Mar 29 02:00:00 2002 IDT isdst=1
Israel Sun Oct 6 21:59:59 2002 UTC = Mon Oct 7 00:59:59 2002 IDT isdst=1
Israel Sun Oct 6 22:00:00 2002 UTC = Mon Oct 7 00:00:00 2002 IST isdst=0
Israel Thu Mar 27 22:59:59 2003 UTC = Fri Mar 28 00:59:59 2003 IST isdst=0
Israel Thu Mar 27 23:00:00 2003 UTC = Fri Mar 28 02:00:00 2003 IDT isdst=1
Israel Thu Oct 2 21:59:59 2003 UTC = Fri Oct 3 00:59:59 2003 IDT isdst=1
Israel Thu Oct 2 22:00:00 2003 UTC = Fri Oct 3 00:00:00 2003 IST isdst=0
Israel Tue Apr 6 22:59:59 2004 UTC = Wed Apr 7 00:59:59 2004 IST isdst=0
Israel Tue Apr 6 23:00:00 2004 UTC = Wed Apr 7 02:00:00 2004 IDT isdst=1
Israel Tue Sep 21 21:59:59 2004 UTC = Wed Sep 22 00:59:59 2004 IDT isdst=1
Israel Tue Sep 21 22:00:00 2004 UTC = Wed Sep 22 00:00:00 2004 IST isdst=0
Israel Thu Mar 31 23:59:59 2005 UTC = Fri Apr 1 01:59:59 2005 IST isdst=0
Israel Fri Apr 1 00:00:00 2005 UTC = Fri Apr 1 03:00:00 2005 IDT isdst=1
Israel Sat Oct 8 22:59:59 2005 UTC = Sun Oct 9 01:59:59 2005 IDT isdst=1
Israel Sat Oct 8 23:00:00 2005 UTC = Sun Oct 9 01:00:00 2005 IST isdst=0
Israel Thu Mar 30 23:59:59 2006 UTC = Fri Mar 31 01:59:59 2006 IST isdst=0
Israel Fri Mar 31 00:00:00 2006 UTC = Fri Mar 31 03:00:00 2006 IDT isdst=1
Israel Sat Sep 30 22:59:59 2006 UTC = Sun Oct 1 01:59:59 2006 IDT isdst=1
Israel Sat Sep 30 23:00:00 2006 UTC = Sun Oct 1 01:00:00 2006 IST isdst=0
Israel Thu Mar 29 23:59:59 2007 UTC = Fri Mar 30 01:59:59 2007 IST isdst=0
Israel Fri Mar 30 00:00:00 2007 UTC = Fri Mar 30 03:00:00 2007 IDT isdst=1
Israel Sat Sep 15 22:59:59 2007 UTC = Sun Sep 16 01:59:59 2007 IDT isdst=1
Israel Sat Sep 15 23:00:00 2007 UTC = Sun Sep 16 01:00:00 2007 IST isdst=0
Israel Thu Mar 27 23:59:59 2008 UTC = Fri Mar 28 01:59:59 2008 IST isdst=0
Israel Fri Mar 28 00:00:00 2008 UTC = Fri Mar 28 03:00:00 2008 IDT isdst=1
Israel Sat Oct 4 22:59:59 2008 UTC = Sun Oct 5 01:59:59 2008 IDT isdst=1
Israel Sat Oct 4 23:00:00 2008 UTC = Sun Oct 5 01:00:00 2008 IST isdst=0
Israel Thu Mar 26 23:59:59 2009 UTC = Fri Mar 27 01:59:59 2009 IST isdst=0
Israel Fri Mar 27 00:00:00 2009 UTC = Fri Mar 27 03:00:00 2009 IDT isdst=1
Israel Sat Sep 26 22:59:59 2009 UTC = Sun Sep 27 01:59:59 2009 IDT isdst=1
Israel Sat Sep 26 23:00:00 2009 UTC = Sun Sep 27 01:00:00 2009 IST isdst=0
Israel Thu Mar 25 23:59:59 2010 UTC = Fri Mar 26 01:59:59 2010 IST isdst=0
Israel Fri Mar 26 00:00:00 2010 UTC = Fri Mar 26 03:00:00 2010 IDT isdst=1
Israel Sat Sep 11 22:59:59 2010 UTC = Sun Sep 12 01:59:59 2010 IDT isdst=1
Israel Sat Sep 11 23:00:00 2010 UTC = Sun Sep 12 01:00:00 2010 IST isdst=0
Israel Thu Mar 31 23:59:59 2011 UTC = Fri Apr 1 01:59:59 2011 IST isdst=0
Israel Fri Apr 1 00:00:00 2011 UTC = Fri Apr 1 03:00:00 2011 IDT isdst=1
Israel Sat Oct 1 22:59:59 2011 UTC = Sun Oct 2 01:59:59 2011 IDT isdst=1
Israel Sat Oct 1 23:00:00 2011 UTC = Sun Oct 2 01:00:00 2011 IST isdst=0
Israel Thu Mar 29 23:59:59 2012 UTC = Fri Mar 30 01:59:59 2012 IST isdst=0
Israel Fri Mar 30 00:00:00 2012 UTC = Fri Mar 30 03:00:00 2012 IDT isdst=1
Israel Sat Sep 22 22:59:59 2012 UTC = Sun Sep 23 01:59:59 2012 IDT isdst=1
Israel Sat Sep 22 23:00:00 2012 UTC = Sun Sep 23 01:00:00 2012 IST isdst=0
Israel Thu Mar 28 23:59:59 2013 UTC = Fri Mar 29 01:59:59 2013 IST isdst=0
Israel Fri Mar 29 00:00:00 2013 UTC = Fri Mar 29 03:00:00 2013 IDT isdst=1
Israel Sat Oct 26 22:59:59 2013 UTC = Sun Oct 27 01:59:59 2013 IDT isdst=1
Israel Sat Oct 26 23:00:00 2013 UTC = Sun Oct 27 01:00:00 2013 IST isdst=0
Israel Thu Mar 27 23:59:59 2014 UTC = Fri Mar 28 01:59:59 2014 IST isdst=0
Israel Fri Mar 28 00:00:00 2014 UTC = Fri Mar 28 03:00:00 2014 IDT isdst=1
Israel Sat Oct 25 22:59:59 2014 UTC = Sun Oct 26 01:59:59 2014 IDT isdst=1
Israel Sat Oct 25 23:00:00 2014 UTC = Sun Oct 26 01:00:00 2014 IST isdst=0
Israel Thu Mar 26 23:59:59 2015 UTC = Fri Mar 27 01:59:59 2015 IST isdst=0
Israel Fri Mar 27 00:00:00 2015 UTC = Fri Mar 27 03:00:00 2015 IDT isdst=1
Israel Sat Oct 24 22:59:59 2015 UTC = Sun Oct 25 01:59:59 2015 IDT isdst=1
Israel Sat Oct 24 23:00:00 2015 UTC = Sun Oct 25 01:00:00 2015 IST isdst=0
Israel Thu Mar 24 23:59:59 2016 UTC = Fri Mar 25 01:59:59 2016 IST isdst=0
Israel Fri Mar 25 00:00:00 2016 UTC = Fri Mar 25 03:00:00 2016 IDT isdst=1
Israel Sat Oct 29 22:59:59 2016 UTC = Sun Oct 30 01:59:59 2016 IDT isdst=1
Israel Sat Oct 29 23:00:00 2016 UTC = Sun Oct 30 01:00:00 2016 IST isdst=0
Israel Thu Mar 23 23:59:59 2017 UTC = Fri Mar 24 01:59:59 2017 IST isdst=0
Israel Fri Mar 24 00:00:00 2017 UTC = Fri Mar 24 03:00:00 2017 IDT isdst=1
Israel Sat Oct 28 22:59:59 2017 UTC = Sun Oct 29 01:59:59 2017 IDT isdst=1
Israel Sat Oct 28 23:00:00 2017 UTC = Sun Oct 29 01:00:00 2017 IST isdst=0
Israel Thu Mar 22 23:59:59 2018 UTC = Fri Mar 23 01:59:59 2018 IST isdst=0
Israel Fri Mar 23 00:00:00 2018 UTC = Fri Mar 23 03:00:00 2018 IDT isdst=1
Israel Sat Oct 27 22:59:59 2018 UTC = Sun Oct 28 01:59:59 2018 IDT isdst=1
Israel Sat Oct 27 23:00:00 2018 UTC = Sun Oct 28 01:00:00 2018 IST isdst=0
Israel Thu Mar 28 23:59:59 2019 UTC = Fri Mar 29 01:59:59 2019 IST isdst=0
Israel Fri Mar 29 00:00:00 2019 UTC = Fri Mar 29 03:00:00 2019 IDT isdst=1
Israel Sat Oct 26 22:59:59 2019 UTC = Sun Oct 27 01:59:59 2019 IDT isdst=1
Israel Sat Oct 26 23:00:00 2019 UTC = Sun Oct 27 01:00:00 2019 IST isdst=0
Israel Thu Mar 26 23:59:59 2020 UTC = Fri Mar 27 01:59:59 2020 IST isdst=0
Israel Fri Mar 27 00:00:00 2020 UTC = Fri Mar 27 03:00:00 2020 IDT isdst=1
Israel Sat Oct 24 22:59:59 2020 UTC = Sun Oct 25 01:59:59 2020 IDT isdst=1
Israel Sat Oct 24 23:00:00 2020 UTC = Sun Oct 25 01:00:00 2020 IST isdst=0
Israel Thu Mar 25 23:59:59 2021 UTC = Fri Mar 26 01:59:59 2021 IST isdst=0
Israel Fri Mar 26 00:00:00 2021 UTC = Fri Mar 26 03:00:00 2021 IDT isdst=1
Israel Sat Oct 30 22:59:59 2021 UTC = Sun Oct 31 01:59:59 2021 IDT isdst=1
Israel Sat Oct 30 23:00:00 2021 UTC = Sun Oct 31 01:00:00 2021 IST isdst=0
Israel Thu Mar 24 23:59:59 2022 UTC = Fri Mar 25 01:59:59 2022 IST isdst=0
Israel Fri Mar 25 00:00:00 2022 UTC = Fri Mar 25 03:00:00 2022 IDT isdst=1
Israel Sat Oct 29 22:59:59 2022 UTC = Sun Oct 30 01:59:59 2022 IDT isdst=1
Israel Sat Oct 29 23:00:00 2022 UTC = Sun Oct 30 01:00:00 2022 IST isdst=0
Israel Thu Mar 23 23:59:59 2023 UTC = Fri Mar 24 01:59:59 2023 IST isdst=0
Israel Fri Mar 24 00:00:00 2023 UTC = Fri Mar 24 03:00:00 2023 IDT isdst=1
Israel Sat Oct 28 22:59:59 2023 UTC = Sun Oct 29 01:59:59 2023 IDT isdst=1
Israel Sat Oct 28 23:00:00 2023 UTC = Sun Oct 29 01:00:00 2023 IST isdst=0
Israel Thu Mar 28 23:59:59 2024 UTC = Fri Mar 29 01:59:59 2024 IST isdst=0
Israel Fri Mar 29 00:00:00 2024 UTC = Fri Mar 29 03:00:00 2024 IDT isdst=1
Israel Sat Oct 26 22:59:59 2024 UTC = Sun Oct 27 01:59:59 2024 IDT isdst=1
Israel Sat Oct 26 23:00:00 2024 UTC = Sun Oct 27 01:00:00 2024 IST isdst=0
Israel Thu Mar 27 23:59:59 2025 UTC = Fri Mar 28 01:59:59 2025 IST isdst=0
Israel Fri Mar 28 00:00:00 2025 UTC = Fri Mar 28 03:00:00 2025 IDT isdst=1
Israel Sat Oct 25 22:59:59 2025 UTC = Sun Oct 26 01:59:59 2025 IDT isdst=1
Israel Sat Oct 25 23:00:00 2025 UTC = Sun Oct 26 01:00:00 2025 IST isdst=0
Israel Thu Mar 26 23:59:59 2026 UTC = Fri Mar 27 01:59:59 2026 IST isdst=0
Israel Fri Mar 27 00:00:00 2026 UTC = Fri Mar 27 03:00:00 2026 IDT isdst=1
Israel Sat Oct 24 22:59:59 2026 UTC = Sun Oct 25 01:59:59 2026 IDT isdst=1
Israel Sat Oct 24 23:00:00 2026 UTC = Sun Oct 25 01:00:00 2026 IST isdst=0
Israel Thu Mar 25 23:59:59 2027 UTC = Fri Mar 26 01:59:59 2027 IST isdst=0
Israel Fri Mar 26 00:00:00 2027 UTC = Fri Mar 26 03:00:00 2027 IDT isdst=1
Israel Sat Oct 30 22:59:59 2027 UTC = Sun Oct 31 01:59:59 2027 IDT isdst=1
Israel Sat Oct 30 23:00:00 2027 UTC = Sun Oct 31 01:00:00 2027 IST isdst=0
Israel Thu Mar 23 23:59:59 2028 UTC = Fri Mar 24 01:59:59 2028 IST isdst=0
Israel Fri Mar 24 00:00:00 2028 UTC = Fri Mar 24 03:00:00 2028 IDT isdst=1
Israel Sat Oct 28 22:59:59 2028 UTC = Sun Oct 29 01:59:59 2028 IDT isdst=1
Israel Sat Oct 28 23:00:00 2028 UTC = Sun Oct 29 01:00:00 2028 IST isdst=0
Israel Thu Mar 22 23:59:59 2029 UTC = Fri Mar 23 01:59:59 2029 IST isdst=0
Israel Fri Mar 23 00:00:00 2029 UTC = Fri Mar 23 03:00:00 2029 IDT isdst=1
Israel Sat Oct 27 22:59:59 2029 UTC = Sun Oct 28 01:59:59 2029 IDT isdst=1
Israel Sat Oct 27 23:00:00 2029 UTC = Sun Oct 28 01:00:00 2029 IST isdst=0
Israel Thu Mar 28 23:59:59 2030 UTC = Fri Mar 29 01:59:59 2030 IST isdst=0
Israel Fri Mar 29 00:00:00 2030 UTC = Fri Mar 29 03:00:00 2030 IDT isdst=1
Israel Sat Oct 26 22:59:59 2030 UTC = Sun Oct 27 01:59:59 2030 IDT isdst=1
Israel Sat Oct 26 23:00:00 2030 UTC = Sun Oct 27 01:00:00 2030 IST isdst=0
Israel Thu Mar 27 23:59:59 2031 UTC = Fri Mar 28 01:59:59 2031 IST isdst=0
Israel Fri Mar 28 00:00:00 2031 UTC = Fri Mar 28 03:00:00 2031 IDT isdst=1
Israel Sat Oct 25 22:59:59 2031 UTC = Sun Oct 26 01:59:59 2031 IDT isdst=1
Israel Sat Oct 25 23:00:00 2031 UTC = Sun Oct 26 01:00:00 2031 IST isdst=0
Israel Thu Mar 25 23:59:59 2032 UTC = Fri Mar 26 01:59:59 2032 IST isdst=0
Israel Fri Mar 26 00:00:00 2032 UTC = Fri Mar 26 03:00:00 2032 IDT isdst=1
Israel Sat Oct 30 22:59:59 2032 UTC = Sun Oct 31 01:59:59 2032 IDT isdst=1
Israel Sat Oct 30 23:00:00 2032 UTC = Sun Oct 31 01:00:00 2032 IST isdst=0
Israel Thu Mar 24 23:59:59 2033 UTC = Fri Mar 25 01:59:59 2033 IST isdst=0
Israel Fri Mar 25 00:00:00 2033 UTC = Fri Mar 25 03:00:00 2033 IDT isdst=1
Israel Sat Oct 29 22:59:59 2033 UTC = Sun Oct 30 01:59:59 2033 IDT isdst=1
Israel Sat Oct 29 23:00:00 2033 UTC = Sun Oct 30 01:00:00 2033 IST isdst=0
Israel Thu Mar 23 23:59:59 2034 UTC = Fri Mar 24 01:59:59 2034 IST isdst=0
Israel Fri Mar 24 00:00:00 2034 UTC = Fri Mar 24 03:00:00 2034 IDT isdst=1
Israel Sat Oct 28 22:59:59 2034 UTC = Sun Oct 29 01:59:59 2034 IDT isdst=1
Israel Sat Oct 28 23:00:00 2034 UTC = Sun Oct 29 01:00:00 2034 IST isdst=0
Israel Thu Mar 22 23:59:59 2035 UTC = Fri Mar 23 01:59:59 2035 IST isdst=0
Israel Fri Mar 23 00:00:00 2035 UTC = Fri Mar 23 03:00:00 2035 IDT isdst=1
Israel Sat Oct 27 22:59:59 2035 UTC = Sun Oct 28 01:59:59 2035 IDT isdst=1
Israel Sat Oct 27 23:00:00 2035 UTC = Sun Oct 28 01:00:00 2035 IST isdst=0
Israel Thu Mar 27 23:59:59 2036 UTC = Fri Mar 28 01:59:59 2036 IST isdst=0
Israel Fri Mar 28 00:00:00 2036 UTC = Fri Mar 28 03:00:00 2036 IDT isdst=1
Israel Sat Oct 25 22:59:59 2036 UTC = Sun Oct 26 01:59:59 2036 IDT isdst=1
Israel Sat Oct 25 23:00:00 2036 UTC = Sun Oct 26 01:00:00 2036 IST isdst=0
Israel Thu Mar 26 23:59:59 2037 UTC = Fri Mar 27 01:59:59 2037 IST isdst=0
Israel Fri Mar 27 00:00:00 2037 UTC = Fri Mar 27 03:00:00 2037 IDT isdst=1
Israel Sat Oct 24 22:59:59 2037 UTC = Sun Oct 25 01:59:59 2037 IDT isdst=1
Israel Sat Oct 24 23:00:00 2037 UTC = Sun Oct 25 01:00:00 2037 IST isdst=0
Israel Mon Jan 18 03:14:07 2038 UTC = Mon Jan 18 05:14:07 2038 IST isdst=0
Israel Tue Jan 19 03:14:07 2038 UTC = Tue Jan 19 05:14:07 2038 IST isdst=0
או בהשוואה למקומות שכבר לא מזיזים את השעון:
$ zdump -v /usr/share/zoneinfo/America/Bogota
/usr/share/zoneinfo/America/Bogota Fri Dec 13 20:45:52 1901 UTC = Fri Dec 13 15:49:36 1901 BMT isdst=0
/usr/share/zoneinfo/America/Bogota Sat Dec 14 20:45:52 1901 UTC = Sat Dec 14 15:49:36 1901 BMT isdst=0
/usr/share/zoneinfo/America/Bogota Mon Nov 23 04:56:15 1914 UTC = Sun Nov 22 23:59:59 1914 BMT isdst=0
/usr/share/zoneinfo/America/Bogota Mon Nov 23 04:56:16 1914 UTC = Sun Nov 22 23:56:16 1914 -05 isdst=0
/usr/share/zoneinfo/America/Bogota Sun May 3 04:59:59 1992 UTC = Sat May 2 23:59:59 1992 -05 isdst=0
/usr/share/zoneinfo/America/Bogota Sun May 3 05:00:00 1992 UTC = Sun May 3 01:00:00 1992 -04 isdst=1
/usr/share/zoneinfo/America/Bogota Sun Feb 7 03:59:59 1993 UTC = Sat Feb 6 23:59:59 1993 -04 isdst=1
/usr/share/zoneinfo/America/Bogota Sun Feb 7 04:00:00 1993 UTC = Sat Feb 6 23:00:00 1993 -05 isdst=0
/usr/share/zoneinfo/America/Bogota Mon Jan 18 03:14:07 2038 UTC = Sun Jan 17 22:14:07 2038 -05 isdst=0
/usr/share/zoneinfo/America/Bogota Tue Jan 19 03:14:07 2038 UTC = Mon Jan 18 22:14:07 2038 -05 isdst=0
אז עכשיו שאנחנו מבינים את בסיס הנתונים של אזורי הזמן בואו נסכם בכמה טריקים שיכולים לעזור לנו כשמדברים עם אנשים מכל העולם. הטריק הראשון הוא שבשביל לראות את השעה במקום מסוים אפשר להשתמש ב zdump:
$ zdump /usr/share/zoneinfo/America/Bogota
/usr/share/zoneinfo/America/Bogota Fri Sep 8 06:22:09 2023 -05
ואפשר גם להשתמש רק בשם של אזור הזמן בלי הנתיב המלא:
$ zdump America/Bogota
America/Bogota Fri Sep 8 06:22:28 2023 -05
ואפילו אם אין לכם את zdump על המחשב תוכלו להשתמש ב date ולהעביר את אזור הזמן בתור משתנה סביבה:
$ TZ=America/Bogota date
Fri Sep 8 06:23:15 -05 2023
הטריק השני הוא שבשביל לזהות מתי פעם הבאה צריך להזיז את השעון כל מה שצריך זה לחפש שורות בקובץ אזור הזמן:
zdump -v Israel| grep 2023|grep isdst=1
Israel Fri Mar 24 00:00:00 2023 UTC = Fri Mar 24 03:00:00 2023 IDT isdst=1
Israel Sat Oct 28 22:59:59 2023 UTC = Sun Oct 29 01:59:59 2023 IDT isdst=1
ואנחנו רואים שב 2023 מזיזים את השעון פעמיים, פעם אחת ב 24/3 זה היה המעבר לשעון קיץ, ופעם שניה תהיה ב 29/10 כשנעבור לשעון חורף.