TIME_SECOND(9)

NAME
boottime, time_second, time_uptime - system time variables

SYNOPSIS
extern struct timeval boottime;
extern time_t time_uptime;
extern time_t time_second;

DESCRIPTION
The time_second variable is the system's “wall time” clock. It is set at boot by inittodr(9), and is updated by the settimeofday(2) system call and by periodic clock interrupts.

The boottime variable holds the system boot time. It is set from time at system boot, and is updated when the system time is adjusted with settimeofday(2).

The time_uptime variable is a monotonically increasing system clock. It is set from time_second at boot, and is updated by the periodic timer interrupt. (It is not updated by settimeofday(2).)

All of these variables contain times expressed in seconds and microseconds since midnight (0 hour), January 1, 1970.

Clock interrupts should be blocked when reading or writing time_second or time_uptime, because those variables are updated by hardclock(). boottime and runtime may be read and written without special precautions.

SEE ALSO
settimeofday(2), hardclock(9), hz(9), inittodr(9), microtime(9)