Process time in unix environment

There are three metric values for the process time in the unix environment: 1. Wall Clock time: regards the process execution as a black box, and the difference between the start time and end time that humans perceive. 2. User CPU time: the CPU time used to execute User-state commands. 3. System CPU time: the kernel represents the CPU time spent during process execution. The combination of 2 and 3 is called the CPU time. in www.2cto.com shell, you can use time to measure the time spent on executing the process: Reference $ time-p curl facebook.com>/dev/null # deliberately access an inaccessible website to obtain: real 63.15 # Is Wall Clock Time. The process executes user 0.00 sys 0.01 in 63 seconds. # The user cpu time and sys cpu time are very short, indicating that most of the Time is spent on I/O waiting.