♦) What do 'real', 'user' and 'sys' mean in the output of time?
One of these things is not like the other. Real refers to actual
elapsed time; User and Sys refer to CPU time used only by the process.
1) Real is wall clock time - time from start to finish of the call.
This is all elapsed time including time slices
used by other processes and time the process spends blocked
(for example if it is waiting for I/O to complete). In simple words this is the time which your wall clock registers.
2)User is the amount of CPU time spent in user-mode code (outside the
kernel) within the process. This is only actual
CPU time used in executing the process. Other
processes and time the process spends blocked do not count towards this figure.
3)Sys is the amount of CPU time spent in the kernel within the process.
This means executing CPU time spent in system calls
within the kernel,as opposed to library code, which
is still running in user-space. Like 'user', this is only CPU time used by the
process.
