在/proc/[pid]/stat里有该进程的详细信息。其内容的解释可以在man 5 proc里查看（搜/stat）
相关部分如下：
(14) utime%lu
Amount of time that this process has been scheduled in user mode, measured
in clock ticks (divide by sysconf(_SC_CLK_TCK)). This includes guest
time, guest_time (time spent running a virtual CPU, see below), so that
applications that are not aware of the guest time field do not lose that
time from their calculations.
(15) stime %lu
Amount of time that this process has been scheduled in kernel mode, mea‐
sured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(16) cutime %ld
Amount of time that this process's waited-for children have been scheduled
in user mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).
(See also times(2).) This includes guest time, cguest_time (time spent
running a virtual CPU, see below).
(17) cstime %ld
Amount of time that this process's waited-for children have been scheduled
in kernel mode, measured in clock ticks (divide by sysconf(_SC_CLK_TCK)).一个进程里的所有线程的stat文件的内容都是一样的。
原文：https://unix.stackexchange.com/questions/132035/obtain-user-and-kernel-time-of-a-running-process