NAME
boottime,
mono_time, runtime,
time —
system time variables
SYNOPSIS
extern struct timeval boottime;
extern volatile struct timeval mono_time;
extern struct timeval runtime;
extern volatile struct timeval time;
DESCRIPTION
The time 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 runtime variable holds the time that the system switched to the current process. It is set after each context switch, and is updated when the system time is adjusted with settimeofday(2). Because runtime is used for system accounting, it is set with the high-resolution microtime(9) function, rather than being copied from time.
The mono_time variable is a monotonically increasing system clock. It is set from time 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 or mono_time, because those variables are updated by hardclock(9). Boottime and runtime may be read and written without special precautions.
SEE ALSO
settimeofday(2), hardclock(9), hz(9), inittodr(9), microtime(9)
BUGS
Runtime should not be updated when the system time is changed with settimeofday(2), because it is used for resource accounting.
The notion of having a single runtime variable obviously won't be appropriate in multiprocessor systems.