Rolling back time Post: 18241

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Top Forums UNIX for Dummies Questions & Answers Rolling back time Post 18241 by Perderabo on Tuesday 26th of March 2002 08:31:31 AM

03-26-2002

Administrator Emeritus

Ideally, you want to set your system time to Zulu Time and then set your timezone variable so that your local software handles everything right for your locale. I would try hard for that solution. But in this thread we saw that peter.herlihy had a problem with an unusual timezone too. Most modern variants of unix now have very programmable timezone software. But some older versions only really support US timezones well.

It may be that if you use ntp to sync your clocks that you are left with no way to display the correct local time. If so, you may be forced to misalign your system clock. This is unfortunate, but it's what I would do if I were forced into it. If this is the case, you do do not want ntp.

When one of my system clocks is very far off for some odd reason, I do not patiently wait for ntp to correct the situation. I want instant gratification.

So to answer your original question, kill cron, then change the time, then restart cron. If cron sees the time change, it will catch up or stop running until it thinks it resyncs. Also be sure that no one is using "make". It's best to do this at a time when no one is using the system. If that's not possible, let the users know.

Perderabo

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LEARN ABOUT BSD

date

DATE(1) 						      General Commands Manual							   DATE(1)

NAME

       date - print and set the date

SYNOPSIS

       date [-nu] [-d dst] [-t timezone] [yymmddhhmm [.ss] ]

DESCRIPTION

       If  no arguments are given, the current date and time are printed.  Providing an argument will set the desired date; only the superuser can
       set the date.  The -d and -t flags set the kernel's values for daylight savings time and minutes west of GMT.  If dst is  non-zero,  future
       calls to gettimeofday(2) will return a non-zero tz_dsttime.  Timezone provides the number of minutes returned by future calls to gettimeof-
       day(2) in tz_minuteswest.  The -u flag is used to display or set the date in GMT (universal) time.  yy represents the last  two	digits	of
       the  year; the first mm is the month number; dd is the day number; hh is the hour number (24 hour system); the second mm is the minute num-
       ber; .ss is optional and represents the seconds.  For example:

	      date 8506131627

       sets the date to June 13 1985, 4:27 PM.	The year, month and day may be omitted; the default values will be the current ones.   The  system
       operates in GMT.  Date takes care of the conversion to and from local standard and daylight-saving time.

       If  timed(8)  is  running  to synchronize the clocks of machines in a local area network, date sets the time globally on all those machines
       unless the -n option is given.

FILES

       /usr/adm/wtmp to record time-setting.  In /usr/adm/messages, date records the name of the user setting the time.

SEE ALSO

       gettimeofday(2), utmp(5), timed(8),
       TSP: The Time Synchronization Protocol for UNIX 4.3BSD, R. Gusella and S. Zatti

DIAGNOSTICS

       Exit status is 0 on success, 1 on complete failure to set the date, and 2 on successfully setting the local date but failing globally.

       Occasionally, when timed synchronizes the time on many hosts, the setting of a new time value may require more  than  a	few  seconds.	On
       these occasions, date prints: `Network time being set'.	The message `Communication error with timed' occurs when the communication between
       date and timed fails.

BUGS

       The system attempts to keep the date in a format closely compatible with VMS.  VMS, however, uses local time (rather than GMT) and does not
       understand daylight-saving time.  Thus, if you use both UNIX and VMS, VMS will be running on GMT.

4th Berkeley Distribution					  March 24, 1987							   DATE(1)