What do 'real', 'user' and 'sys' mean in the output of time(1)?

Question

$ time foo
real        0m0.003s
user        0m0.000s
sys         0m0.004s
$

What do \'real\', \'user\' and \'sys\' mean in the output of time?

Answer 1

I want to mention some other scenario when the real-time is much much bigger than user + sys. I've created a simple server which respondes after a long time

real 4.784
user 0.01s
sys  0.01s

the issue is that in this scenario the process waits for the response which is not on the user site nor in the system.

Something similar happens when you run the find command. In that case, the time is spent mostly on requesting and getting a response from SSD.