On Mon, 14 May 2007, Stuart Henderson wrote: > On 2007/05/13 23:06, John Nietzsche wrote: > > */5 * * * * /usr/sbin/rdate -4ncva > > -c corrects for leap seconds > > > */5 * * * * /usr/sbin/rdate -4cva gw | > > and here you do it again i.e. you are correcting time coming from a > source which is already corrected. > > I would really recommend against using rdate like this, it jumps the > clock. ntpd skews the clock (makes it run slightly fast or slow until > the time is correct), so you don't miss out on any seconds (which > sometimes skips cron jobs, makes logging more confusing, and can > cause a lot of trouble with some other applications).
While I agree with the advise, this is not true when the -a flag is given to rdate, in that case rdate uses adjtime(2). ntpd is of course much nicer, since its adjust the clock frequency as well, and poses a very light stress on the server: once time is synced, queries do not happen a lot. Not to speak of the ability to use time sensors and multiple time sources to provide redundancy. -Otto