Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

FreeBSD 11.0 - man page for ntp_gettime (freebsd section 2)

NTP_ADJTIME(2)						      BSD System Calls Manual						    NTP_ADJTIME(2)

NAME
ntp_adjtime, ntp_gettime -- Network Time Protocol (NTP) daemon interface system calls
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/timex.h> int ntp_adjtime(struct timex *); int ntp_gettime(struct ntptimeval *);
DESCRIPTION
The two system calls ntp_adjtime() and ntp_gettime() are the kernel interface to the Network Time Protocol (NTP) daemon ntpd(8). The ntp_adjtime() function is used by the NTP daemon to adjust the system clock to an externally derived time. The time offset and related variables which are set by ntp_adjtime() are used by hardclock() to adjust the phase and frequency of the phase- or frequency-lock loop (PLL resp. FLL) which controls the system clock. The ntp_gettime() function provides the time, maximum error (sync distance) and estimated error (dispersion) to client user application pro- grams. In the following, all variables that refer PPS are only relevant if the PPS_SYNC option is enabled in the kernel. ntp_adjtime() has as argument a struct timex * of the following form: struct timex { unsigned int modes; /* clock mode bits (wo) */ long offset; /* time offset (us) (rw) */ long freq; /* frequency offset (scaled ppm) (rw) */ long maxerror; /* maximum error (us) (rw) */ long esterror; /* estimated error (us) (rw) */ int status; /* clock status bits (rw) */ long constant; /* pll time constant (rw) */ long precision; /* clock precision (us) (ro) */ long tolerance; /* clock frequency tolerance (scaled * ppm) (ro) */ /* * The following read-only structure members are implemented * only if the PPS signal discipline is configured in the * kernel. */ long ppsfreq; /* pps frequency (scaled ppm) (ro) */ long jitter; /* pps jitter (us) (ro) */ int shift; /* interval duration (s) (shift) (ro) */ long stabil; /* pps stability (scaled ppm) (ro) */ long jitcnt; /* jitter limit exceeded (ro) */ long calcnt; /* calibration intervals (ro) */ long errcnt; /* calibration errors (ro) */ long stbcnt; /* stability limit exceeded (ro) */ }; The members of this struct have the following meanings when used as argument for ntp_adjtime(): modes Defines what settings should be changed with the current ntp_adjtime() call (write-only). Bitwise OR of the following: MOD_OFFSET set time offset MOD_FREQUENCY set frequency offset MOD_MAXERROR set maximum time error MOD_ESTERROR set estimated time error MOD_STATUS set clock status bits MOD_TIMECONST set PLL time constant MOD_CLKA set clock A MOD_CLKB set clock B offset Time offset (in microseconds), used by the PLL/FLL to adjust the system time in small increments (read-write). freq Frequency offset (scaled ppm) (read-write). maxerror Maximum error (in microseconds). Initialized by an ntp_adjtime() call, and increased by the kernel once each second to reflect the maximum error bound growth (read-write). esterror Estimated error (in microseconds). Set and read by ntp_adjtime(), but unused by the kernel (read-write). status System clock status bits (read-write). Bitwise OR of the following: STA_PLL Enable PLL updates (read-write). STA_PPSFREQ Enable PPS freq discipline (read-write). STA_PPSTIME Enable PPS time discipline (read-write). STA_FLL Select frequency-lock mode (read-write). STA_INS Insert leap (read-write). STA_DEL Delete leap (read-write). STA_UNSYNC Clock unsynchronized (read-write). STA_FREQHOLD Hold frequency (read-write). STA_PPSSIGNAL PPS signal present (read-only). STA_PPSJITTER PPS signal jitter exceeded (read-only). STA_PPSWANDER PPS signal wander exceeded (read-only). STA_PPSERROR PPS signal calibration error (read-only). STA_CLOCKERR Clock hardware fault (read-only). constant PLL time constant, determines the bandwidth, or ``stiffness'', of the PLL (read-write). precision Clock precision (in microseconds). In most cases the same as the kernel tick variable (see hz(9)). If a precision clock counter or external time-keeping signal is available, it could be much lower (and depend on the state of the signal) (read-only). tolerance Maximum frequency error, or tolerance of the CPU clock oscillator (scaled ppm). Ordinarily a property of the architecture, but could change under the influence of external time-keeping signals (read-only). ppsfreq PPS frequency offset produced by the frequency median filter (scaled ppm) (read-only). jitter PPS jitter measured by the time median filter in microseconds (read-only). shift Logarithm to base 2 of the interval duration in seconds (PPS, read-only). stabil PPS stability (scaled ppm); dispersion (wander) measured by the frequency median filter (read-only). jitcnt Number of seconds that have been discarded because the jitter measured by the time median filter exceeded the limit MAXTIME (PPS, read-only). calcnt Count of calibration intervals (PPS, read-only). errcnt Number of calibration intervals that have been discarded because the wander exceeded the limit MAXFREQ or where the calibration interval jitter exceeded two ticks (PPS, read-only). stbcnt Number of calibration intervals that have been discarded because the frequency wander exceeded the limit MAXFREQ/4 (PPS, read- only). After the ntp_adjtime() call, the struct timex * structure contains the current values of the corresponding variables. ntp_gettime() has as argument a struct ntptimeval * with the following members: struct ntptimeval { struct timeval time; /* current time (ro) */ long maxerror; /* maximum error (us) (ro) */ long esterror; /* estimated error (us) (ro) */ }; These have the following meaning: time Current time (read-only). maxerror Maximum error in microseconds (read-only). esterror Estimated error in microseconds (read-only).
RETURN VALUES
ntp_adjtime() and ntp_gettime() return the current state of the clock on success, or any of the errors of copyin(9) and copyout(9). ntp_adjtime() may additionally return EPERM if the user calling ntp_adjtime() does not have sufficient permissions. Possible states of the clock are: TIME_OK Everything okay, no leap second warning. TIME_INS ``insert leap second'' warning. At the end of the day, a leap second will be inserted after 23:59:59. TIME_DEL ``delete leap second'' warning. At the end of the day, second 23:59:59 will be skipped. TIME_OOP Leap second in progress. TIME_WAIT Leap second has occurred within the last few seconds. TIME_ERROR Clock not synchronized.
ERRORS
The ntp_adjtime() system call may return EPERM if the caller does not have sufficient permissions.
SEE ALSO
options(4), ntpd(8), hardclock(9), hz(9) http://www.bipm.fr/enus/5_Scientific/c_time/time_1.html http://www.boulder.nist.gov/timefreq/general/faq.htm ftp://time.nist.gov/pub/leap-seconds.list
BUGS
Take note that this API is extremely complex and stateful. Users should not attempt modification without first reviewing the ntpd(8) sources in depth.
BSD
July 13, 2005 BSD