boottime, time_second, time_uptime — system time variables

       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
       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.

       boottime, time_second, time_uptime — system time variables

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”, ProceedingsofEuroBSDCon2002,Amsterdam, /usr/share/doc/papers/timecounter.ascii.gz.

       Marshall Kirk McKusick and George V. Neville-Neil, TheDesignandImplementationoftheFreeBSDOperatingSystem, Addison-Wesley, 57-61,65-66, July 2004.

Debian                                         September 17, 2004                                        TIME(9)

#include<sys/time.h>externstructtimevalboottime;
       externtime_ttime_second;
       externtime_ttime_uptime;