I have made a small patch to "cron" that lets people choose between
localtime and gmtime for their crontab entries. The choice is made
depending on the setting of an environment variable in the crontab file.
The cost is a factor 2 for the tiny amount of work that cron does when
it checks all the crontab entries every minute.

I finally got tired of having to use local daylight saving time for
crontabs after seeing my nightly statistics-gathering scripts having
to deal with 23 hour days, 25 hour days, some scripts running twice
the same night, or not running at all, etc.

Here is a sample crontab that will send mail to the crontab owner
every day at 12:00 GMT, and at 12:00 in the local timezone.

00 12 * * *     echo localtime
CRONTAB_UTC=1
00 12 * * *     echo gmtime

Setting CRONTAB_UTC=0 will turn off the flag for later entries.

I have only tested this on FreeBSD 3.0, FreeBSD 3.3, and Linux RedHat 6.1
but it should work on any system that uses Vixie cron.

To install the patch in the cron source:
On FreeBSD, cd to /usr/src/usr.sbin/cron/ and do "patch -p0"
On RedHat, cd to /usr/src/redhat/SOURCES/vixie-cron-* and do "patch -p1"
(with this patch file as the input of course).

                        Happy hacking,

                                Bjorn Danielsson  <bd@sunet.se>


*** lib/entry.c~	Sat Aug 28 03:17:00 1999
--- lib/entry.c	Sun Oct 31 19:00:43 1999
***************
*** 312,316 ****
  	e->envp = env_set(e->envp, envstr);
  #endif
! 
  	Debug(DPARS, ("load_entry()...about to parse command\n"))
  
--- 312,319 ----
  	e->envp = env_set(e->envp, envstr);
  #endif
! 	{
! 	  char *utc = env_get("CRONTAB_UTC", e->envp);
! 	  if (utc && atoi(utc)) { e->flags |= CRONTAB_UTC; }
! 	}
  	Debug(DPARS, ("load_entry()...about to parse command\n"))
  
*** cron/cron.h~	Sat Aug 28 03:17:00 1999
--- cron/cron.h	Sun Oct 31 19:06:00 1999
***************
*** 173,176 ****
--- 173,177 ----
  #define	DOW_STAR	0x02
  #define	WHEN_REBOOT	0x04
+ #define	CRONTAB_UTC	0x08
  } entry;
  
*** cron/cron.c~	Sat Aug 28 03:17:00 1999
--- cron/cron.c	Sun Dec 12 16:26:59 1999
***************
*** 169,173 ****
--- 169,175 ----
  	register user		*u;
  	register entry		*e;
+ 	register int		utcflag = 0;
  
+  again:
  	/* make 0-based values out of these so we can use them as indicies
  	 */
***************
*** 189,192 ****
--- 191,195 ----
  	for (u = db->head;  u != NULL;  u = u->next) {
  		for (e = u->crontab;  e != NULL;  e = e->next) {
+ 		  if ((e->flags & CRONTAB_UTC) == utcflag) {
  			Debug(DSCH|DEXT, ("user [%s:%d:%d:...] cmd=\"%s\"\n",
  					  env_get("LOGNAME", e->envp),
***************
*** 202,206 ****
--- 205,218 ----
  				job_add(e, u);
  			}
+ 		  }
  		}
+ 	}
+ 	/* run the above code once again, but now with utcflag non-zero and
+ 	 * tm set to GMT instead of local time.
+ 	 */
+ 	if (!utcflag) {
+ 	  utcflag = CRONTAB_UTC;
+ 	  tm = gmtime(&TargetTime);
+ 	  goto again;
  	}
  }