OSX: programmatically get uptime?

Question

Something similar to linux

cat /proc/uptime

which returns the uptime in seconds, and preferably not parsing uptime(1).

Answer 1

The Uptime article on Wikipedia has an interesting lead:

Using sysctl

There is also a method of using sysctl to call the system's last boot time: $ sysctl kern.boottime kern.boottime: { sec = 1271934886, usec = 667779 } Thu Apr 22 12:14:46 2010

Which references sysctl(8), which references sysctl(3).

Answer 2

There is a function UpTime declared in DriverServices.h. I believe this is equivalent to another function mach_absolute_time. Both seem to be undocumented.

Answer 3

Unfortunately the "sysctl kern.boottime" returns the seconds of the timestamp, not elapsed seconds.. Multiple calls do not increase the second count, but must be seconds from epoc of the boot date itself.