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:

time df

The output looks like

real	0m3.905s
user	0m2.408s
sys	0m1.238s

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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