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     boottime, time_second, time_uptime - system time variables


     #include <sys/time.h>

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


     The boottime variable holds the system boot time.

     The time_second variable is the system’s “wall time” clock to the second.

     The time_uptime variable is the number of seconds since boot.

     The bintime(9), getbintime(9), microtime(9), getmicrotime(9),
     nanotime(9), and getnanotime(9) functions can be used to get the current
     time more accurately and in an atomic manner.  Similarly, the The
     binuptime(9), getbinuptime(9), microuptime(9), getmicrouptime(9),
     nanouptime(9), and getnanouptime(9) functions can be used to get the time
     elapse since boot more accurately and in an atomic manner.  The boottime
     variable may be read and written without special precautions.


     clock_settime(2), ntp_adjtime(2), settimeofday(2), bintime(9),
     binuptime(9), getbintime(9), getbinuptime(9), getmicrotime(9),
     getmicrouptime(9), getnanotime(9), getnanouptime(9), microtime(9),
     microuptime(9), nanotime(9), nanouptime(9)

     Poul-Henning Kamp, "Timecounters: Efficient and precise timekeeping in
     SMP kernels", Proceedings of EuroBSDCon 2002, Amsterdam,

     Marshall Kirk McKusick and George V. Neville-Neil, The Design and
     Implementation of the FreeBSD Operating System, Addison-Wesley,
     57-61,65-66, July 2004.