ntpd 同步后执行脚本答案

【问题标题】：Execute script after ntpd syncntpd 同步后执行脚本
【发布时间】：2015-01-22 01:36:21
【问题描述】：

我有 raspbian 的树莓派。我想在时间与 ntpd 同步后立即执行一个脚本，我的脚本需要正确的日期时间。我该怎么做？

【问题讨论】：

【解决方案1】：

正确的做法是使用ntp-wait。 ntp-wait 是为这种情况量身定做的。这是手册页：

ntp-wait(1)                     User Commands                    ntp-wait(1)

NAME
       ntp-wait - Wait for ntpd to stabilize the system clock

SYNOPSIS
       ntp-wait [-flag [value]]... [--opt-name [[=| ]value]]...

       All arguments must be options.

DESCRIPTION
       will  send  at  most  num-tries queries to sleeping for secs-between-
       tries after each status return that says has not yet produced a  syn‐
       chronized and stable system clock.

       will do this quietly, unless the v flag is provided.

OPTIONS
       -n num-tries, --=num-tries
              Number  of  times to check ntpd.  This option takes an integer
              number as its argument.  The default num-tries for this option
              is:
                   100

              The  maximum  number  of times we will check ntpd to see if it
              has been able to synchronize and stabilize the system clock.

       -s secs-between-tries, --=secs-between-tries
              How long to sleep between tries.  This option takes an integer
              number  as  its  argument.  The default secs-between-tries for
              this option is:
                   6

              We will sleep for @file{secs-between-tries} after  each  query
              of ntpd that returns "the time is not yet stable".

       -v, -- Be verbose.

              By  default,  ntp-wait  is silent.  With this option, ntp-wait
              will provide status information.

       -?, --help
              Display usage information and exit.

       -!, --more-help
              Pass the extended usage information through a pager.

       - [{v|c|n}], --version[={v|c|n}]
              Output version of program and exit.  The default mode is  `v',
              a  simple version.  The `c' mode will print copyright informa‐
              tion and `n' will print the full copyright notice.


EXIT STATUS
       One of the following exit values will be returned:

       0      Successful program execution.

       1      The operation failed or the command syntax was not valid.

【讨论】：

如果 ntp-wait 有类似 -n 0 的选项（永远等待），我希望它更好读取代码会与大数字混淆并计算 secs*tries 以确保它没有任何意义......我会抱怨定制西装不合身:)

【解决方案2】：

假设您有一个有权调用 ntpdate 的用户（换句话说，谁可以调整系统的时间），您可以使用以下脚本，我在下面的示例中使用 ntp 服务器“0.ca. pool.ntp.org"

#!/bin/bash

NEEDS_SYNC=1
while [ "$NEEDS_SYNC" -ne "0" ]; do
    ntpdate -t 4     0.ca.pool.ntp.org
    NEEDS_SYNC=$?    # If this variable is set ot 0, time sync worked
    sleep 2
done

# RUN THE SCRIPT THT NEEDS ntp SYNC'D TIME HERE

请注意，您可能需要安装包“ntpdate”才能使其正常工作。

【讨论】：

我不懂$？部分 $ 是什么？
抱歉，很难搜索 $？在谷歌，但我终于想通了，$？是命令退出状态
我刚看到你的问题，抱歉。我很高兴听到你想通了。对，美元？保存 ntpdate 的退出状态，仅在有效设置日期时返回零。