linux bash命令hwclock输出含义

Question

我在主机中使用hwclock命令，然后我会得到以下内容

hwclock
Fri 22 Nov 2019 10:42:56 AM CST  -0.062877 seconds

但是我不知道-0.062877秒是什么意思

Answer 1

0.062877秒是在shell上发出命令的时间与读取硬件时钟的时间之间的时间差。

$ time sudo hwclock
Thu Nov 21 21:08:24 2019  -0.710984 seconds

real    0m0.719s
user    0m0.004s
sys 0m0.005s
$ time sudo hwclock
Thu Nov 21 21:08:32 2019  -0.775224 seconds

real    0m0.783s
user    0m0.002s
sys 0m0.006s
$ time sudo hwclock
Thu Nov 21 21:08:39 2019  -0.467983 seconds

real    0m0.475s
user    0m0.003s
sys 0m0.006s
[sharad@sharad-singla ~]$


$ time sudo hwclock -D
hwclock from util-linux-ng 2.17.2
Using /dev interface to clock.
Last drift adjustment done at 1574399257 seconds after 1969
Last calibration done at 1474351262 seconds after 1969
Hardware clock is on UTC time
Assuming hardware clock is kept in UTC time.
Waiting for clock tick...
...got clock tick
Time read from Hardware Clock: 2019/11/22 05:12:25
Hw clock time : 2019/11/22 05:12:25 = 1574399545 seconds since 1969
Thu Nov 21 21:12:25 2019  -0.721502 seconds

real    0m0.729s
user    0m0.005s
sys 0m0.004s
$

参考：

• https://www.softprayog.in/tutorials/hwclock-the-hardware-clock-query-and-set-program
• http://man7.org/linux/man-pages/man8/hwclock.8.html