Linux: HOWTO get the number of CPUs
Harald Hoyer November 13, 2013 #linux #fedora$ getconf _NPROCESSORS_ONLN
returns the number of CPUs online.
Internally it is parsing
/sys/devices/system/cpu/online, which can have the contents: 0-3,5,7-9.
Better let getconf do all the counting for you.
This is very useful, if you want to optimize the number of threads.