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adjtimexconfig(8) [debian man page]

ADJTIMEXCONFIG(8)					      System Manager's Manual						 ADJTIMEXCONFIG(8)

NAME
adjtimexconfig - find kernel clock variables and save for reboots SYNOPSIS
/sbin/adjtimexconfig DESCRIPTION
This script uses adjtimex(8) to find values for the kernel variables tick and frequency that will make the system clock approximately agree with the CMOS clock. It then saves these values in the configuration file /etc/default/adjtimex so the settings will be restored on every boot, when /etc/init.d/adjtimex runs. adjtimexconfig uses the drift rate recorded in /etc/adjtime to adjust the times it reads from the CMOS clock. If you find the CMOS clock has a systematic drift, read the clock(8) or hwclock(8) manual page, modify /etc/adjtime as required, and run adjtimexconfig again. AUTHOR
Michael Meskes <meskes@debian.org>. FILES
/etc/default/adjtimex /etc/init.d/adjtimex SEE ALSO
adjtimex(8), clock(8), hwclock(8), ntpd(8) April 27, 2003 ADJTIMEXCONFIG(8)

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ADJTIMEX(8)						      System Manager's Manual						       ADJTIMEX(8)

NAME
adjtimex - display or set the kernel time variables SYNOPSIS
adjtimex [option]... DESCRIPTION
This program gives you raw access to the kernel time variables. For a machine connected to the Internet, or equipped with a precision oscillator or radio clock, the best way to regulate the system clock is with ntpd(8). For a standalone or intermittently connected machine, you may use adjtimex instead to at least correct for systematic drift. Anyone may print out the time variables, but only the superuser may change them. If your computer can be connected to the net, you might run ntpd for at least several hours and use adjtimex --print to learn what values of tick and freq it settled on. Alternately, you could estimate values using the CMOS clock as a reference (see the --compare and --adjust switches). You could then add a line to rc.local invoking adjtimex to set those parameters each time you reboot. OPTIONS
Options may be introduced by either - or --, and unique abbreviations may be used. Here is a summary of the options, grouped by type. Explanations follow. Get/Set Kernel Time Parameters -p --print -t --tick val -f newfreq --frequency newfreq -o val --offset val -s adjustment --singleshot adjustment -m val --maxerr val -e val --esterror val -T val --timeconstant val -a[count] --adjust[=count] Estimate Systematic Drifts -c[count] --compare[=count] -i tim --interval tim -l file --logfile file -h timeserver --host timeserver -w --watch -r[file] --review[=file] -u --utc Informative Output --help -v --version -p, --print Print the current values of the kernel time variables. NOTE: The time is "raw", and may be off by up to one timer tick (10 msec). "status" gives the value of the time_status variable in the kernel. For Linux 1.0 and 1.2 kernels, the value is as follows: 0 clock is synchronized (so the kernel should periodically set the CMOS clock to match the system clock) 1 inserting a leap second at midnight 2 deleting a leap second at midnight 3 leap second in progress 4 leap second has occurred 5 clock not externally synchronized (so the kernel should leave the CMOS clock alone) For Linux 2.0 kernels, the value is a sum of these: 1 PLL updates enabled 2 PPS freq discipline enabled 4 PPS time discipline enabled 8 frequency-lock mode enabled 16 inserting leap second 32 deleting leap second 64 clock unsynchronized 128 holding frequency 256 PPS signal present 512 PPS signal jitter exceeded 1024 PPS signal wander exceeded 2048 PPS signal calibration error 4096 clock hardware fault -t val, --tick val Set the number of microseconds that should be added to the system time for each kernel tick interrupt. There are supposed to be 100 ticks per second, so val should be close to 10000. Increasing val by 1 speeds up the system clock by about 100 ppm, or 8.64 sec/day. tick must be in the range 9000...11000 on Intel systems, or 900...1100 on Alpha systems. -f newfreq, --frequency newfreq Set the system clock frequency offset to newfreq. newfreq can be negative or positive, and gives a much finer adjustment than the --tick switch. The value is scaled such that newfreq = 1<<16 speeds up the system clock by about 1 ppm, or .0864 sec/day. Thus, --tick 10000 --frequency 6553600 is about the same as --tick 10001 --frequency 0. newfreq must be in the range -6553600...6553600, allowing maximum adjustments of plus or minus 100 ppm. -s adj, --singleshot adj Slew the system clock by adj usec. (Its rate is changed temporarily by about 1 part in 2000.) -o adj, --offset adj Add a time offset of adj usec. The kernel code adjusts the time gradually by adj, notes how long it has been since the last time offset, and then adjusts the frequency offset to correct for the apparent drift. adj must be in the range -512000...512000. -m val, --maxerror val Set maximum error (usec). -e val, --esterror val Set estimated error (usec). The maximum and estimated error are not used by the kernel. They are merely made available to user processes via the adjtimex(2) system call. -t val, --timeconstant val Set phase locked loop (PLL) time constant. val determines the bandwidth or "stiffness" of the PLL. The effective PLL time constant will be a multiple of (1 << val). For room-temperature quartz oscillators, David Mills recommends the value 2, which corresponds to a PLL time constant of about 900 sec and a maximum update interval of about 64 sec. The maximum update interval scales directly with the time constant, so that at the maximum time constant of 6, the update interval can be as large as 1024 sec. Values of val between zero and 2 give quick convergence; values between 2 and 6 can be used to reduce network load, but at a modest cost in accuracy. -c[count], --compare[=count] Periodically compare the system clock with the CMOS clock. After the first two calls, print values for tick and frequency offset that would bring the system clock into approximate agreement with the CMOS clock. CMOS clock readings are adjusted for systematic drift using using the correction in /etc/adjtime -- see hwclock(8). The interval between comparisons is 10 seconds, unless changed by the --interval switch. The optional argument is the number of comparisons. (If the argument is supplied, the "=" is required.) -a[count], --adjust[=count] By itself, same as --compare, except the recommended values are actually installed after every other comparison. With --review, the tick and frequency are set to the least-squares estimates. (In the latter case, any count value is ignored.) -i tim, --interval tim Set the interval in seconds between clock comparisons for the --compare and --adjust options. -u, --utc The CMOS clock is set to UTC (universal time) rather than local time. -l[file], --log[=file] Save the current values of the system and CMOS clocks, and optionally a reference time, to file (default /var/log/clocks.log). The reference time is taken from a network timeserver (see the --host switch) or supplied by the user (see the --watch switch). -h timeserver, --host timeserver Use ntpdate to query the given timeserver for the current time. This will fail if timeserver is not running a Network Time Protocol (NTP) server, or if that server is not synchronized. Implies --log. -w, --watch Ask for a keypress when the user knows the time, then ask what that time was, and its approximate accuracy. Implies --log. -r[file], --review[=file] Review the clock log file (default /var/log/clocks.log) and estimate, if possible, the rates of the CMOS and system clocks. Calculate least-squares rates using all suitable log entries. Suggest corrections to adjust for systematic drift. With --adjust, the frequency and tick are set to the suggested values. (The CMOS clock correction is not changed.) -h, --help Print the program options. -v, --version Print the program version. EXAMPLES
If your system clock gained 8 seconds in 24 hours, you could set the tick to 9999, and then it would lose 0.64 seconds a day (that is, 1 tick unit = 8.64 seconds per day). To correct the rest of the error, you could set the frequency offset to (1<<16)*0.64/.0864 = 485452. Thus, putting the following in rc.local would approximately correct the system clock: adjtimex --tick 9999 --freq 485452 NOTES
adjtimex adjusts only the system clock -- the one that runs while the computer is powered up. To set or regulate the CMOS clock, see hwclock(8). AUTHORS
Steven S. Dick <ssd@nevets.oau.org>, Jim Van Zandt <jrv@vanzandt.mv.com>. SEE ALSO
date(1L), gettimeofday(2), settimeofday(2), hwclock(8), ntpdate(8), ntpd(8), /usr/src/linux/include/linux/timex.h, /usr/src/linux/include/linux/sched.h, /usr/src/linux/kernel/time.c, /usr/src/linux/kernel/sched.c October 24, 1998 ADJTIMEX(8)
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