Meaning of Real, User and Sys time statistics

Under Linux, the time command is quite convenient to get the elapsed time taken by a command call. It is very simple to use: just type your command preceded by the time command itself. For instance:

The output looks like

In brief, Real refers to actual elapsed time including other processes that may be running at the same time; User and Sys refer to CPU time used only by the process (here the df command).

More precisely:

  • Real is wall clock time – time from start to finish of the call including time used by other processes and time the process spends blocked (for example if it is waiting for I/O to complete).
  • User is the actual CPU time used in executing the process. Other processes and time the process spends blocked do not count.

  • Sys is the amount of CPU time spent in the kernel within the process.

So, User + Sys is the actual CPU time used by your process

For more details, you can consult this quite precise description

https://stackoverflow.com/questions/556405/what-do-real-user-and-sys-mean-in-the-output-of-time1

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2 Responses to Meaning of Real, User and Sys time statistics

  1. coffee says:

    > time from start to finish of the call including including time used by other processes and time the process spends blocked
    There are two “including”.

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