通过 ifcfg-eth0 管理 /etc/resolv.conf

2018-09-10 分类：System 标签：Network

kickstart 装机 post-inst 阶段配置网卡，还要一同配置 /etc/resolv.conf

后来用户要增加新的 search DOMAIN 或修改 DNS IP

这样要修改 两处 配置信息，有点麻烦。

干脆把 /etc/resolv.conf 配置并入 ifcfg-eth0 ：

ifcfg-eth0	/etc/resolv.conf
PEERDNS=yes
DNS1=1.1.1.1	nameserver 1.1.1.1
DNS2=8.8.8.8	nameserver 8.8.8.8
DOMAIN='example.com example-inc.com'	search example.com example-inc.com

• PEERDNS=yes 选项配置 ifcfg-eth0 的 DNS1，DNS2 为 /etc/resolv.conf 的 nameserver
• DOMAIN='example.com ...' 选项配置 /etc/resolv.conf 的默认搜索域 search 字段

官方文档对 PEERDNS=yes 的介绍：

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/s1-networkscripts-interfaces

PEERDNS=answer

where answer is one of the following:

• yes — Modify /etc/resolv.conf if the DNS directive is set, if using DHCP, or if using Microsoft’s RFC 1877 IPCP extensions with PPP. In all cases yes is the default.
• no — Do not modify /etc/resolv.conf.

DNS{1,2}=address

where address is a name server address to be placed in /etc/resolv.conf provided that the PEERDNS directive is not set to no.

How can I add additional search domains to the resolv.conf created by dhclient in CentOS

多个搜索域一定要用 “引号” 包裹，不然无法更新 /etc/resolv.conf 的 search 字段。

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
NAME=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
HWADDR=90:bd:11:1a:2a:b2
IPADDR=10.16.5.1
PREFIX=24
GATEWAY=10.16.5.254
# config /etc/resolv.conf
PEERDNS=yes
DNS1=1.1.1.1
DNS2=8.8.8.8
DOMAIN='example.com example-inc.com'    # <-- 多个搜索域要用 "引号" 包裹

# service network restart
Restarting network (via systemctl):                        [  OK  ]

# cat /etc/resolv.conf
# nameserver 1.1.1.1
# nameserver 8.8.8.8
# search example.com
nameserver 1.1.1.1
nameserver 8.8.8.8
search example.com example-inc.com

修改 /etc/resolv.conf 文件是 /etc/sysconfig/network-scripts/ifup-post 脚本：

# fgrep -w DOMAIN /etc/sysconfig/network-scripts/*
/etc/sysconfig/network-scripts/ifup-post:    if [ -n "${DOMAIN}" ] && ! grep -q "^search.*${DOMAIN}.*$" /etc/resolv.conf ||
/etc/sysconfig/network-scripts/ifup-post:                        if [ -n "${DOMAIN}" ]; then
/etc/sysconfig/network-scripts/ifup-post:            if [ -n "${DOMAIN}" ]; then
/etc/sysconfig/network-scripts/ifup-post:                echo "search ${DOMAIN}${search_str}" >> "${tmp_file}"

修改 search 字段对应的 shell 代码：

while read line; do
    case ${line} in

        # Skip nameserver entries when at least one DNS option was given
        # (at this stage we know that we have to update all the nameserver
        # enries anyway -- see below), or copy them if we are changing just
        # the 'search' field in /etc/resolv.conf:
        nameserver*)
            if [[ "${grep_regexp}" != ".*" ]]; then
                continue
            else
                echo "${line}" >> "${tmp_file}"
            fi
            ;;

        domain* | search*)
            if [ -n "${DOMAIN}" ]; then
                read search value < <(echo ${line})
                search_str+=" ${value}"
            else
                echo "${line}" >> "${tmp_file}"
            fi
            ;;

        # Keep the rest of the /etc/resolv.conf as it was:
        *)
            echo "${line}" >> "${tmp_file}"
            ;;
    esac
done < /etc/resolv.conf

# Insert the domain into 'search' field:
if [ -n "${DOMAIN}" ]; then
    echo "search ${DOMAIN}${search_str}" >> "${tmp_file}"
fi

本文标题	通过 ifcfg-eth0 管理 /etc/resolv.conf
原始链接	https://lvii.github.io/system/2018-09-10-generate-resolv.conf-by-ifcfg-eth0/