没有任何理由为成功百胜更新导致后续wget的失败？ [英] Is there any reason for a successful yum update to cause a subsequent wget to fail?

问题描述

我正在为CentOS 6.4的机器一个bash安装脚本。在一个全新的安装我运行到这似乎是重复性的问题，但情况是不同寻常的。

I'm working on a bash setup script for CentOS 6.4 machines. On a brand new install I'm running into an issue that seems to be reproducible, but the scenario is unusual.

设置脚本用root身份运行。第一步是运行不带选项的yum更新：

The setup script is run with root. The first step is to run yum update with no options:

yum update

这以零退出code成功完成。下一步骤是检索EPEL转速使用wget：

This completes successfully with a zero exit code. The next step is to retrieve the EPEL rpm using wget:

wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm

然而，这是一贯的每个这是从运行时解析主机名时没有一个干净的安装CentOS的：

However, this is consistently failing when resolving the host name every time this is run from a clean CentOS install:

wget: unable to resolve host address "dl.fedoraproject.org"

在自然而在命令行中相继执行这些命令，任何问题都遇到了和wget能够获取EPEL转：

When executing these commands in succession from the command line however, no issues are encountered and wget is able to retrieve the EPEL rpm:

sudo yum update
sudo wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm

这有什么yum的更新，可能导致DNS查询，而无需先退出脚本失败过程中发生？如果我第一次失败后，重新运行该脚本，它通过对第二次左右。

Is there anything that happens during the yum update that could cause the DNS lookup to fail without exiting the script first? If I rerun the script after the first failure, it passes on the second time around.

推荐答案

在住域名的时间的下一个实例之前，在系统上或缓存DNS服务器上过期这是可能的wget 并解决域名从权威的服务器失败的一次新的尝试。请参见 http://en.wikipedia.org/wiki/Time_to_live#DNS_records 。当然，这也有可能是缓存DNS服务器将无法访问。

It's possible when the Time to Live of the domain name expires on the system or on a cache DNS server before the next instance of wget and the next attempt to resolve the domain name from the authorative server fails. See http://en.wikipedia.org/wiki/Time_to_live#DNS_records. Of course it's also possible that the cache DNS server becomes inaccessible.

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