[ntp:questions] ntpdate -b replacement

Spoon devnull at localhost.com
Fri Mar 30 08:31:56 UTC 2007

Hello everyone,

ntpdate -b means:
     Force the time to be stepped using the settimeofday() system call, 
rather than slewed (default) using the adjtime() system call. This 
option should be used when called from a startup file at boot time.

This page mentions the ntpd alternative:
-b 	 always step 	 ntpd -q -x

ntpd -x means
     Normally, the time is slewed if the offset is less than the step 
threshold, which is 128 ms by default, and stepped if above the 
threshold. This option sets the threshold to 600 s, which is well within 
the accuracy window to set the clock manually. Note: Since the slew rate 
of typical Unix kernels is limited to 0.5 ms/s, each second of 
adjustment requires an amortization interval of 2000 s. Thus, an 
adjustment as much as 600 s will take almost 14 days to complete. This 
option can be used with the -g and -q options. See the tinker command 
for other options. Note: The kernel time discipline is disabled with 
this option.

This seems to be the *opposite* of -b because the threshold to step the 
clock is raised. If I understand correctly, ntpd -x will not set the 
clock unless it is wrong by more than 10 minutes. If it wrong by less 
than 10 minutes, it will slew.

If the intent is to always step the time, wouldn't it be better to use 
tinker step to set step to a small (but non-zero) value?

e.g. tinker step 0.001


More information about the questions mailing list