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clock_getres (2)

>> clock_getres (2) ( FreeBSD man: Системные вызовы )

clock_getres (2) ( Linux man: Системные вызовы )

clock_getres (3) ( Linux man: Библиотечные вызовы )

clock_getres (3) ( POSIX man: Библиотечные вызовы )

BSD mandoc

NAME



clock_gettime

 
clock_settime

 
clock_getres

 - get/set/calibrate date and time

LIBRARY

Lb libc

SYNOPSIS

#include <time.h>
int clock_gettime (clockid_t clock_id struct timespec *tp);
int clock_settime (clockid_t clock_id const struct timespec *tp);
int clock_getres (clockid_t clock_id struct timespec *tp);

DESCRIPTION

The clock_gettime ();
and clock_settime ();
system calls allow the calling process to retrieve or set the value used by a clock which is specified by Fa clock_id .

The Fa clock_id argument can be one of five values: CLOCK_REALTIME for time that increments as a wall clock should, CLOCK_MONOTONIC which increments in SI seconds, CLOCK_UPTIME which starts at zero when the kernel boots and increments monotonically in SI seconds while the machine is running, CLOCK_VIRTUAL for time that increments only when the CPU is running in user mode on behalf of the calling process, or CLOCK_PROF for time that increments when the CPU is running in user or kernel mode.

The structure pointed to by Fa tp is defined in #include <sys/timespec.h>
as:

struct timespec {
        time_t  tv_sec;         /* seconds */
        long    tv_nsec;        /* and nanoseconds */
};

Only the super-user may set the time of day. If the system securelevel is greater than 1 (see init(8)), the time may only be advanced. This limitation is imposed to prevent a malicious super-user from setting arbitrary time stamps on files. The system time can still be adjusted backwards using the adjtime(2) system call even when the system is secure.

The resolution (granularity) of a clock is returned by the clock_getres ();
system call. This value is placed in a (non-NULL) Fa *tp .