Bug 17623
| Summary: | date(1) -v doesn't handle time changes (DST) correctly | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Paul.Hernaus <paul.hernaus> |
| Component: | bin | Assignee: | freebsd-bugs (Nobody) <bugs> |
| Status: | Closed FIXED | ||
| Severity: | Affects Only Me | ||
| Priority: | Normal | ||
| Version: | 5.0-CURRENT | ||
| Hardware: | Any | ||
| OS: | Any | ||
Additional information: The documentation for the date command is also wrong because of this bug. It says: When a date is adjusted to a specific value or in units greater than hours, daylight savings time considerations are ignored. Adjustments in units of hours or less honor daylight saving time. So, assuming the current date is March 26, 0:30 and that the DST adjustment means that the clock goes forward at 01:00 to 02:00, using -v +1H will adjust the date to March 26, 2:30. Likewise, if the date is October 29, 0:30 and the DST adjustment means that the clock goes back at 02:00 to 01:00, using -v +3H will be nec- essary to reach October 29, 2:30. Looking at the code, it is obvious why the above is not the case. Hours are modified in the tm structure from localtime, instead of using the seconds-since-epoch and then converting it to printable time (as the bug originator pointed out). Another example of this bug in action: csdlap3$ date ; date -v+16H Sat Oct 26 15:44:58 CDT 2002 Sun Oct 27 07:44:58 CST 2002 This is also wrong (the second time should be 06:44:58 CST). I believe this was fixed in the set of commits of april 2000 on bin/date/vary.c Marc State Changed From-To: open->closed seemingly fixed in r59175; I can't reproduce |
Date adjustments with -v can result in an error because Daylight Savings Time is handled incorrectly. Fix: First convert the start date to UTC, then do the math, then convert back to the desired time zone, just like GNU date does. The correct result in this case would have been: [~] paul@itchy> date -v-39H Sun Mar 26 01:42:59 CET 2000 How-To-Repeat: [~] paul@itchy> date Mon Mar 27 17:42:55 CEST 2000 [~] paul@itchy> date -v-38H Sun Mar 26 03:42:59 CEST 2000 [~] paul@itchy> date -v-39H -39H: Cannot apply date adjustment usage: date [-nu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... [-f fmt date | [[[[[cc]yy]mm]dd]HH]MM[.ss]] [+format]