设置DNS方法--[ping: unknown host]

Linux下如果ping一个域名，出现如下状况：

#ping www.taobao.com

ping: unknown host www.taobao.com

那是因为系统没有设置DNS的缘故。在此场景下，任何通过域名的操作都会有问题。

[解决办法 ]

1、查看DNS设置

#cat /etc/resolv.conf

如果能看到 nameserver xxx.xxx.xxx.xxx

说明DNS已经设置，这时要考虑设置的DNS对否。

2、设置DNS

直接编辑 /etc/resolv.conf 即可

添加正确的DNS 地址.

如下：

nameserver xxx.xxx.xxx.xxx

很多应用软件会涉及到fqdn

如salt获取到的fqnd和host可能会不一样，两者有何区别？

THE FQDN

You can’t change the FQDN (as returned by hostname --fqdn) or the DNS domain name (as returned by dnsdomainname) with this command. The FQDN of

the system is the name that the resolver(3) returns for the host name.

Technically: The FQDN is the name gethostbyname(2) returns for the host name returned by gethostname(2). The DNS domain name is the part after

the first dot.

Therefore it depends on the configuration (usually in /etc/host.conf) how you can change it. Usually (if the hosts file is parsed before DNS or

NIS) you can change it in /etc/hosts.

If a machine has multiple network interfaces/addresses or is used in a mobile environment, then it may either have multiple FQDNs/domain names or

none at all. Therefore avoid using hostname --fqdn, hostname --domain and dnsdomainname. hostname --ip-address is subject to the same limitations

so it should be avoided as well.

FQDN = 简短的名字 + 域

如: hostname返回的结果是 dev-qa001 域为test.com 则fqdn为 dev-qa001.test.com

-f, --fqdn, --long

Display the FQDN (Fully Qualified Domain Name). A FQDN consists of a short host name and the DNS domain name. Unless you are using bind or

NIS for host lookups you can change the FQDN and the DNS domain name (which is part of the FQDN) in the /etc/hosts file. See the warnings in

section THE FQDN above, and avoid using this option; use hostname --all-fqdnsinstead.

返回hostname的命令

mportant; overflow: auto !important; font-size: 1em !important; background-color: rgb(255, 255, 255) !important;">hostname

返回域的命令

1	`dnsdomainname`

返回fqdn的命令

1	`hostname` `-f`

1	`hostname` `-f -v`

可以查看解析的详细过程

有时候这两个还不一样

hostname --all-fqdns 和 hostname -f

python中socket的库 socket.getfqdn() 这个方法是调用 hostname --all-fqdsn哦！ salt中可能会有坑(注意 minion端的/etc/hosts文件)

如何设置fqdn

优先的方法，方法一设置/etc/hosts

[root@CentOS-6-121 ~]# cat /etc/hosts | grep -i "Centos"

10.59.74.121 CentOS-6-121.test.com CentOS-6-121

第一列为IP 第二列为fqnd 第三列为主机名 (位置不能错误,否则结果不一致)

[root@CentOS-6-121 ~]# hostname  
CentOS-6-121
[root@CentOS-6-121 ~]# hostname -f
CentOS-6-121.test.com
[root@CentOS-6-121 ~]# dnsdomainname 
test.com

方法二：你配置了dns 通过dns查找

[root@CentOS-6-121 ~]# cat /etc/resolv.conf

search a.pa.com

但是你的dns一定要能解析你的fqdn,返回返回失效(你去除了hosts中的配置后)

[root@CentOS-6-121 ~]# hostname
CentOS-6-121
[root@CentOS-6-121 ~]# dnsdomainname 
dnsdomainname: Unknown host
[root@CentOS-6-121 ~]# hostname -f
hostname: Unknown host
[root@CentOS-6-121 ~]#