linux6重启后resolv中自动修改DNS信息实例分析

Linux 6的/etc/resolv.conf重启后修改的原因是因为如果NetworkManager服务在重启过程中自动启动，该服务会读取网卡信息。 NM_CONTROLLED和DNS配置，如果网卡中配置了NM_CONTROLLED=yes，如果网卡中配置了DNS，则将网卡中的DNS写入resolv.conf，如果网络如果没有配置DNS，则将空的DNS信息写入resolv.conf

如果重启时不希望/etc/resolv.conf被修改，请关闭NetworkManager服务服务 NetworkManager 停止
chkconfig --level 0123456 NetworkMan关闭
并修改网卡NM_CONTROLLED=no



即重启时，如果有Network Manager服务并且网卡配置了Network Manager服务，则该服务会根据网卡的DNS以及中的DNS配置修改/etc/resolv.conf

网卡。没有必要为每个网卡都配置IP。只要其中一台配置了DNS，因为DNS是共享的，所以必须在有IP的网卡上配置DNS。如果网卡很多但没有IP，即使配置了这些网卡，如果DNS不可用，重启后/etc/resolv.conf也不会获取到这个DNS


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故障现象1、/etc/resolv.conf中设置的nameserver信息丢失
[root@bsdb ~]# cat /etc/resolv.conf
#由NetworkManager生成
# 未找到域名服务器；尝试将 DNS 服务器放入您的
# ifcfg/etc/sysconfig/network-scripts 中的文件如下所示：
#
# DNS1=xxx.xxx.xxx.xxx
# DNS2=xxx.xxx。 xxx.xxx
# DOMAIN=lab.foo.com bar.foo.com

查看文件属性，发现文件被修改
[root@bsdb ~] #ll /etc/resolv.conf
-rw-r--r--. 1 root root 228 June 19 11:06 /etc/resolv.conf

发现文件修改时间和重启时间匹配
[root@bsdb ~]# last |grep restart
restart system boot 2.6.32-431.el6.x Tue Jun 19 11:06 - 11:27 (2+00:20)

检查网卡IP
[root @bsdb ~]# grep IPADDR /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network-scripts/ ifcfg-eth0:IPADDR=192.168.21.16
/etc/sysconfig /network-scripts/ifcfg-eth4:IPADDR=192.167.120.11

查看网卡的DNS信息，没有配置DNS
/>[root@bsdb ~]# grep DNS /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network-scripts/ifcfg-eth2:PEERDNS=yes
/etc /sysconfig/network-scripts/ifcfg-eth3:PEERDNS=yes
/etc/sysconfig/network-scripts/ifcfg-eth5:PEERDNS=yes
/etc/sysconfig/network-scripts/ifcfg-eth6 :PEERDNS=yes

检查网卡是否开启NetworkManager，即NM_CONTROLLED=yes
[root@bsdb ~]# grep NM_CONTROLLED /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network-scripts/ifcfg-eth0:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth2:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg -eth3:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth4:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth5:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth6:NM_CONTROLLED=yes

检查NetworkManager是否正在运行
[root@bsdb ~]# service NetworkManager status
NetworkManager (pid 6297) 正在运行...

操作系统版本
[oraprod@bsdb ~]$ cat /etc/issue
CentOS 版本 6.5（最终版）
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故障现象2、/etc/r中设置的nameserveresolv.conf已修改
[root@lmdb ~]# cat /etc/resolv.conf
#由NetworkManager生成
nameserver 192.168.30.50
nameserver 192.168.130.50

查看文件属性，发现文件被修改
[root@lmdb ~ ]# ll /etc/resolv.conf
-rw-r--r--。 1 root root 81 June 19 11:04 /etc/resolv.conf

发现文件修改时间和重启时间相符
[root@lmdb ~]# last |grep restart
reboot system boot 2.6.32-642.el6.x Tue Jun 19 11:04 - 10:09 (1+23:04)

查看网卡IP
[root@ lmdb ~]# grep IPADDR /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network-scripts/ifcfg-eth0:IPADDR=192.168.148.200
/etc/sysconfig/ network-scripts/ifcfg-eth2:IPADDR=192.168.130.200

检查网卡的DNS信息，配置DNS，为其中一个有IP的网卡配置DNS一
[ root@lmdb ~]# grep DNS /etc/sysconfig/network-scripts/ifcfg-eth*
/etc/sysconfig/network-scripts/ifcfg-eth0:PEERDNS=yes
/etc/sysconfig/network-scripts/ifcfg-eth2:DNS1=192.168.30.50
/etc/sysconfig/network-scripts/ifcfg-eth2:DNS2=192.168。 130.50
/etc/sysconfig/network-scripts/ifcfg-eth2:PEERDNS=yes
/etc/sysconfig/network-scripts/ifcfg-eth3:PEERDNS=yes
/etc/sysconfig/ network-scripts/ifcfg-eth4:PEERDNS= yes
/etc/sysconfig/network-scripts/ifcfg-eth5:PEERDNS=yes
/etc/sysconfig/network-scripts/ifcfg-eth6:PEERDNS= yes

检查网卡是否开启NetworkManager管理，即NM_CONTROLLED=yes
[root@lmdb ~]# grep NM_CONTROLLED /etc/sysconfig/network -scripts/ifcfg-eth *
/etc/sysconfig/network-scripts/ifcfg-eth0:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth2:NM_CONTROLLED=yes
/etc/sysconfig/ network-scripts/ifcfg-eth3:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ifcfg-eth4:NM_CONTROLLED=yes
/etc/sysconfig/network-scripts/ ifcfg-eth5:NM_CONTROLLED=是
/etc/sysconfig/network-scripts/ifcfg-eth6:NM_CONTROLLED=yes

检查NetworkManager是否正在运行
[root@lmdb ~]# service NetworkManager status
NetworkManager (pid 3173)正在运行...

操作系统版本
[root@lmdb ~]# cat /etc/issue
CentOS 版本 6.8（最终版）
\m 上的内核 \r