Last update: 27-Jan-2014 05:31 UTC, John Hawkinson, <jhawk@MIT.EDU>
If you're not running Solaris 2.5.1 or later, it is likely that you will have problems; upgrading would be a really good plan.
We have a report that says starting with Solaris 2.6 we should leave dosynctodr alone. Here is the report.
Proper operation of ntp under Solaris may require setting the kernel variable dosynctodr to zero (meaning "do not synchronize the clock to the hardware time-of-day clock"). This can be done with the tickadj utility:
tickadj -sIf you prefer, it can also be done with the native Solaris kernel debugger:
echo dosynctodr/W0 | adb -k -w /dev/ksyms /dev/mem
Or, it can also be set by adding a line to /etc/system:
set dosynctodr = 0
Instead of the tick kernel variable, which many operating systems use to control microseconds added to the system time every clock tick (c.f. Dealing with Frequency Tolerance Violations), Solaris has the variables nsec_per_tick and usec_per_tick.
nsec_per_tick and usec_per_tick control the number of
nanoseconds and microseconds, respectively, added to the system clock
each clock interrupt. Enterprising souls may set these based on
information collected by ntpd in the
to correct for individual hardware variations.
On UltraSPARC systems, nsec_per_tick and usec_per_tick are ignored in favor of the cpu_tick_freq variable, which should be automatically be determined by the PROM in an accurate fashion.
In general, the same ntp binaries should not be used across multiple operating system releases. There is enough variation in the core operating system support for timekeeping that a rebuild of ntpd for the idiosyncracies of your specific operating system version is advisable.
It is recommended that ntp be started via a script like this one, installed in
/etc/init.d/ntpd with a symbol link from
However, in the case of certain notorious platforms, in particular Sun 4.1.1 systems, the performance can be improved by adjusting the values of certain kernel variables; in particular, tick and tickadj. The variable tick is the increment in microseconds added to the system time on each interval- timer interrupt, while the variable tickadj is used by the time adjustment code as a slew rate, in microseconds per tick. When the time is being adjusted via a call to the system routine adjtime(), the kernel increases or reduces tick by tickadj microseconds per tick until the specified adjustment has been completed. Unfortunately, in most Unix implementations the tick increment must be either zero or plus/minus exactly tickadj microseconds, meaning that adjustments are truncated to be an integral multiple of tickadj (this latter behaviour is a misfeature, and is the only reason the tickadj code needs to concern itself with the internal implementation of tickadj at all). In addition, the stock Unix implementation considers it an error to request another adjustment before a prior one has completed.
Thus, to make very sure it avoids problems related to the roundoff, the tickadj program can be used to adjust the values of tick and tickadj. This ensures that all adjustments given to adjtime() are an even multiple of tickadj microseconds and computes the largest adjustment that can be completed in the adjustment interval (using both the value of tick and the value of tickadj) so it can avoid exceeding this limit. It is important to note that not all systems will allow inspection or modification of kernel variables other than at system build time. It is also important to know that, with the current NTP tolerances, it is rarely necessary to make these changes, but in many cases they will substantially improve the general accuracy of the time service.
Unfortunately, the value of tickadj set by default is almost always too large for ntpd. NTP operates by continuously making small adjustments to the clock, usually at one-second intervals. If tickaj is set too large, the adjustments will disappear in the roundoff; while, if tickadj is too small, NTP will have difficulty if it needs to make an occasional large adjustment. While the daemon itself will read the kernel's values of these variables, it will not change the values, even if they are unsuitable. You must do this yourself before the daemon is started using the tickadj program included in the ./util directory of the distribution. Note that the latter program will also compute an optimal value of tickadj for NTP use based on the kernel's value of tick.
The tickadj program can reset several other kernel variables if asked. It can change the value of tick if asked. This is handy to compensate for kernel bugs which cause the clock to run with a very large frequency error, as with SunOS 4.1.1 systems. It can also be used to set the value of the kernel dosynctodr variable to zero. This variable controls whether to synchronize the system clock to the time-of-day clock, something you really don't want to be happen when ntpd is trying to keep it under control. In some systems, such as recent Sun Solaris kernels, the dosynctodr variable is the only one that can be changed by the tickadj program. In this and other modern kernels, it is not necessary to change the other variables in any case.
We have a report that says starting with Solaris 2.6 we should leave dosynctodr alone.
In order to maintain reasonable correctness bounds, as well as reasonably good accuracy with acceptable polling intervals, ntpd will complain if the frequency error is greater than 500 PPM. For machines with a value of tick in the 10-ms range, a change of one in the value of tick will change the frequency by about 100 PPM. In order to determine the value of tick for a particular CPU, disconnect the machine from all source s of time (dosynctodr = 0) and record its actual time compared to an outside source (eyeball-and-wristwatch will do) over a day or more. Multiply the time change over the day by 0.116 and add or subtract the result to tick, depending on whether the CPU is fast or slow. An example call to tickadj useful on SunOS 4.1.1 is:
tickadj -t 9999 -a 5 -swhich sets tick 100 PPM fast, tickadj to 5 microseconds and turns off the clock/calendar chip fiddle. This line can be added to the rc.local configuration file to automatically set the kernel variables at boot time.
All this stuff about diddling kernel variables so the NTP daemon will work is really silly. If vendors would ship machines with clocks that kept reasonable time and would make their adjtime() system call apply the slew it is given exactly, independent of the value of tickadj, all this could go away. This is in fact the case on many current Unix systems.
Solaris 2.6 adds support for kernel PLL timekeeping, but breaks this support in such a fashion that using it worse than not. This is SUN Bug ID 4095849, and it is not yet fixed as of June 1998.
On UltraSPARC systems, calculation of cpu_tick_freq is broken such that values that are off by significant amounts may be used instead. This unfortunately means that ntpd may have severe problems keeping synchronization. This is SUN Bug ID 4023118. Bryan Cantrill of Sun posted patchfreq, a workaround script, to comp.protocols.time.ntp in March of 1997.
Solaris 2.2 and later contain completely re-written clock code to
provide high resolution microsecond timers. A benefit of the
re-written clock code is that adjtime does not round off its
adjustments, so ntp does not have to compensate for this
rounding. Under Solaris 2.2 and later, ntp #define's
ADJTIME_IS_ACCURATE, and does not look for the tickadj
Solaris 2.1 contains fairly traditional clock code, with tick and tickadj.
Since settimeofday under Solaris 2.1 only sets the seconds part of timeval care must be used in starting xntpd. I suggest the following start up script:
tickadj -s -a 1000The first tickadj turns of the time of day clock and sets the tick adjust value to 1 millisecond. This will insure that an adjtime value of at most 2 seconds will complete in 20 seconds.
ntpdate -v server1 server2
ntpdate -v server1 server2
tickadj -a 200
The first ntpdate will set the time to within two seconds using settimeofday or it will adjust time using adjtime.
The first sleep insures the adjtime has completed for the first ntpdate.
The second ntpdate will use adjtime to set the time of day since the clock should be within 2 seconds of the correct time.
The second tickadj set the tick adjust system value to 5 microseconds.
The second sleeps insure that adjtime will complete before starting the next xntpd.
I tried running with a tickadj of 5 microseconds with out much success. 200 microseconds seems to work well.