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MICROTIME(9) FreeBSD Kernel Developer's Manual MICROTIME(9) NAME microuptime, getmicrouptime, nanouptime, getnanouptime, nsecuptime, getnsecuptime, getuptime, nanoruntime, getnsecruntime, microtime, getmicrotime, nanotime, getnanotime, gettime, microboottime, nanoboottime - get the time SYNOPSIS #include <sys/time.h> void microuptime(struct timeval *tv); void getmicrouptime(struct timeval *tv); void nanouptime(struct timespec *ts); void getnanouptime(struct timespec *ts); uint64_t nsecuptime(void); uint64_t getnsecuptime(void); time_t getuptime(void); void nanoruntime(struct timespec *ts); uint64_t getnsecruntime(void); void microtime(struct timeval *tv); void getmicrotime(struct timeval *tv); void nanotime(struct timespec *ts); void getnanotime(struct timespec *ts); time_t gettime(void); void microboottime(struct timeval *tv); void nanoboottime(struct timespec *ts); DESCRIPTION The kernel has three clocks and a variety of interfaces for reading them. The uptime clock measures the time elapsed since the system booted. It begins at zero and advances monotonically. The uptime clock may be read with the following functions: Name Output Format Source microuptime() struct timeval hardware getmicrouptime() struct timeval timestamp nanouptime() struct timespec hardware getnanouptime() struct timespec timestamp nsecuptime() uint64_t hardware getnsecuptime() uint64_t timestamp getuptime() time_t timestamp The runtime clock measures the time elapsed since the system booted, less any time the system is suspended or hibernating. It begins at zero and normally advances monotonically, but pauses while the system is suspended or hibernating. The runtime clock may be read with the following functions: Name Output Format Source nanoruntime() struct timespec hardware getnsecruntime() uint64_t timestamp The UTC clock measures the time elapsed since Jan 1 1970 00:00:00 (the Unix Epoch). The clock normally advances monotonically, but jumps when a process calls clock_settime(2) or settimeofday(2). The UTC clock may be read with the following functions: Name Output Format Source microtime() struct timeval hardware getmicrotime() struct timeval timestamp nanotime() struct timespec hardware getnanotime() struct timespec timestamp gettime() time_t timestamp The kernel also maintains a boot timestamp. It is the moment on the UTC clock when the system booted. The timestamp jumps when a process calls clock_settime(2) or settimeofday(2). The boot timestamp may be read with the following functions: Name Output Format Source microboottime() struct timeval timestamp nanoboottime() struct timespec timestamp Functions that source from the hardware provide the most precise result possible. Functions that source from a timestamp provide a far less precise result, but do so very quickly. On most platforms, timestamps are updated approximately 100 times per second. CONTEXT These functions may be called during autoconf, from process context, or from any interrupt context. RETURN VALUES nsecuptime(), getnsecuptime(), and getnsecruntime() return a count of nanoseconds. getuptime() and gettime() return a count of seconds. ERRORS These functions are always successful, and no return value is reserved to indicate an error. CODE REFERENCES sys/kern/kern_tc.c SEE ALSO clock_settime(2), settimeofday(2), timeradd(3), hardclock(9), hz(9), inittodr(9), tc_init(9) FreeBSD 14.1-RELEASE-p8 December 28, 2022 FreeBSD 14.1-RELEASE-p8