CPU user time system time

Clock Time (Wall Clock Time): It is the time that the clock passes from the start to the end of a process, which includes the time when the process is blocked and waiting.

   User CPU time: the time when the user processes run in user mode after obtaining CPU resources.

   System CPU time: the execution time in the kernel state after the user process obtains the CPU resources.

  The three statuses of a process are blocking, ready, and running.

  Clock time = blocking time + ready time + running time
  User CPU time = user space time in running state
  System CPU time = system space time in the running state.

  User CPU time + system CPU time = running time.