The clock time, sometimes called wall clock time, is the amount of time the
process takes
to run, and its value depends on the number of other processes being run on
the system.
The user CPU time is the CPU time attributed to user instructions.
The system CPU time is the CPU time attributed to the kernel when it executes
on behalf of the process.
Wall-clock time is the time that a clock on the wall (or a stopwatch in hand)
would measure as having elapsed between the start of the process and ‘now’.
从程序起点到现在的时间
The user-cpu time and system-cpu time are pretty much as you said - the amount
of time spent in user code and the amount of time spent in kernel code.
程序在系统code和用户code上运行的CPU时间
The units are seconds (and subseconds, which might be microseconds or
nanoseconds).
The wall-clock time is not the number of seconds that the process has spent on
the CPU; it is the elapsed time, including time spent waiting for its turn on
the CPU (while other processes get to run).
refs:
APUE