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When I time a program on Ubuntu 10.4 I get output like:

real    0m14.581s
user    0m14.570s
sys     0m0.010s

What do these different categories mean?

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up vote 6 down vote accepted
man time

will give you the answer:

Real time and process time
   Real  time  is  defined  as time measured from some fixed point, either
   from a standard point in the past (see the description of the Epoch and
   calendar  time below), or from some point (e.g., the start) in the life
   of a process (elapsed time).

   Process time is defined as the amount of CPU time used  by  a  process.
   This  is  sometimes  divided into user and system components.  User CPU
   time is the time spent executing code in user mode.  System CPU time is
   the  time spent by the kernel executing in system mode on behalf of the
   process (e.g., executing system calls).  The  time(1)  command  can  be
   used  to determine the amount of CPU time consumed during the execution
   of a program.  A program can determine the amount of CPU  time  it  has
   consumed using times(2), getrusage(2), or clock(3).
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real time, here, is sometimes called "wall clock time." – mpez0 May 24 '10 at 11:00

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