Is hyper-threading enabled on a Linux system ?

When you need to know whether hyper-threading is enabled without the luxury to reboot the system (and consulting the BIOS), you can simply look at the output of /proc/cpuinfo and compare the siblings with the cpu cores fields.

Even though /proc/cpuinfo shows you all the logical CPUs (processor field) in the system, the siblings field holds the number of logical CPUs for the physical CPU this entry belongs to (including both the cores and the hyper-threaded LCPUs).

In other words, if you see: