NAME
adjtimex - tune kernel clock SYNOPSIS
#include
int adjtimex(struct timex *buf); DESCRIPTION Linux uses David L. Mills' clock adjustment algorithm (see RFC 1305). The system call adjtimex() reads and optionally sets adjustment parame‐ ters for this algorithm. It takes a pointer to a timex structure, updates kernel parameters from field values, and returns the same structure with current kernel values. This structure is declared as follows: struct timex { int modes; /* mode selector */ long offset; /* time offset (usec) */ long freq; /* frequency offset (scaled ppm) */ long maxerror; /* maximum error (usec) */ long esterror; /* estimated error (usec) */ int status; /* clock command/status */ long constant; /* pll time constant */ long precision; /* clock precision (usec) (read-only) */ long tolerance; /* clock frequency tolerance (ppm)
(read-only) */
struct timeval time; /* current time (read-only) */ long tick; /* usecs between clock ticks */ }; The modes field determines which parameters, if any, to set. It may
contain a bitwise-or combination of zero or more of the following bits:
#define ADJOFFSET 0x0001 /* time offset */
#define ADJFREQUENCY 0x0002 /* frequency offset */
#define ADJMAXERROR 0x0004 /* maximum time error */
#define ADJESTERROR 0x0008 /* estimated time error */
#define ADJSTATUS 0x0010 /* clock status */
#define ADJTIMECONST 0x0020 /* pll time constant */
#define ADJTICK 0x4000 /* tick value */
#define ADJOFFSETSINGLESHOT 0x8001 /* old-fashioned adjtime() */ Ordinary users are restricted to a zero value for mode. Only the supe‐ ruser may set any parameters. RETURN VALUE On success, adjtimex() returns the clock state:
#define TIMEOK 0 /* clock synchronized */
#define TIMEINS 1 /* insert leap second */
#define TIMEDEL 2 /* delete leap second */
#define TIMEOOP 3 /* leap second in progress */
#define TIMEWAIT 4 /* leap second has occurred */
#define TIMEBAD 5 /* clock not synchronized */
On failure, adjtimex() returns -1 and sets errno. ERRORS EFAULT buf does not point to writable memory. EINVAL An attempt is made to set buf.offset to a value outside the
range -131071 to +131071, or to set buf.status to a value other than those listed above, or to set buf.tick to a value outside the range 900000/HZ to 1100000/HZ, where HZ is the system timer interrupt frequency. EPERM buf.mode is nonzero and the caller does not have sufficient privilege. Under Linux the CAPSYSTIME capability is required. CONFORMING TO
adjtimex() is Linux-specific and should not be used in programs intended to be portable. See adjtime(3) for a more portable, but less flexible, method of adjusting the system clock. SEE ALSO settimeofday(2), adjtime(3), capabilities(7), time(7) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2004-05-27 ADJTIMEX(2)