使用 ps 命令查看进程启动的精确时间和启动后所流逝的时间

       lstart      STARTED   time the command started.  See also bsdstart, start, start_time, and stime.
       etime       ELAPSED   elapsed time since the process was started, in the form [[DD-]hh:]mm:ss.

查看 nginx 进程启动的精确时间和启动后所流逝的时间：

[root@iZ25p102vo3Z ~]# ps -eo pid,lstart,etime,cmd | grep nginx
16968 Fri Mar  4 16:04:27 2016 41-21:14:04 nginx: master process /usr/sbin/nginx
17826 Fri Mar  4 22:53:51 2016 41-14:24:40 nginx: worker process
18312 Fri Apr 15 13:18:31 2016       00:00 grep --color=auto nginx