CLOCK_GETTIME(2) MidnightBSD System Calls Manual CLOCK_GETTIME(2)

NAME

clock_gettime, clock_settime, clock_getres — get/set/calibrate date and time

LIBRARY

Standard C Library (libc, −lc)

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() allow the calling process to retrieve or set the value used by a clock which is specified by clock_id.

The 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 tp is defined in <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) *tp.

RETURN VALUES

Upon successful completion, the value 0 is returned; otherwise the value −1 is returned and the global variable errno is set to indicate the error.

ERRORS

The following error codes may be set in errno:

[EINVAL]

The clock_id argument was not a valid value.

[EFAULT]

The *tp argument address referenced invalid memory.

[EPERM]

A user other than the super-user attempted to set the time.

SEE ALSO

date(1), adjtime(2), ctime(3), timed(8)

STANDARDS

The clock_gettime(), clock_settime(), and clock_getres() system calls conform to IEEE Std 1003.1b-1993 (‘‘POSIX.1’’).

MidnightBSD 0.3 November 4, 2006 MidnightBSD 0.3