NTP_ADJTIME(2) | System Calls Manual | NTP_ADJTIME(2) |
ntp_adjtime
, ntp_gettime
—
#include <sys/time.h>
#include <sys/timex.h>
int
ntp_adjtime
(struct
timex *);
int
ntp_gettime
(struct
ntptimeval *);
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
ntp_adjtime
() system call is available only for the
super user. If the system call fails, the
ntp_adjtime
() function in the standard C library
will try to use the
clockctl(4) device if
present, thus making it possible for the NTP daemon to run as a
non-privileged user. If
clockctl(4) is not present,
ntp_adjtime
() returns
EPERM
.
The time offset and related variables which are set by
ntp_adjtime
() are used by
hardclock(9) 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 programs.
In the following, all variables that refer PPS are only relevant if the PPS_SYNC option (see options(4)) 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
():
ntp_adjtime
() call (write-only). Bitwise OR of the
following:
ntp_adjtime
() call, and increased by the kernel
once each second to reflect the maximum error bound growth
(read-write).ntp_adjtime
(), but unused by the kernel
(read-write).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 timespec time; /* current time (ro) */ long maxerror; /* maximum error (us) (ro) */ long esterror; /* estimated error (us) (ro) */ /* the following are placeholders for now */ long tai; /* TAI offset */ int time_state; /* time status */ };
These have the following meaning:
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:
J. Mogul, D. Mills, J. Brittenson, J. Stone, and U. Windl, Pulse-Per-Second API for UNIX-like Operating Systems, RFC 2783, March 2000.
December 8, 2015 | NetBSD 9.2 |