operating-system User Space and Kernel Space Exam CPU time spent on one process

Example

Use time command.

time ./perl-timeout-example 100.100.100

We could not ping the desired address!

real    0m5.0013s
user    0m0.004s
sys     0m0.008s

• Real: Total time from start to finish of the call, including the CPU time spent on other processes.
• User: The amount of CPU time spent in user space.
• Sys: The amount of CPU time spent in the kernel space.

Normally, user + sys is the total CPU time spent on such process. It is smaller than real. But in multicore CPU, user + sys is the total CPU time spent on this process. It could be large than real.