time indicates how long a UNIX command has run from start to end. It is used as a prefix of the command to be run.

time ls

time reports 3 timings:

  • the real elapsed time between the moment the command was issued and the moment the command ends

  • the user time which represents the CPU usage to execute the command

  • the system time which includes all calls to the operating systems (disk access, etc.) that stopped the execution of the command by the CPU.