nsswitch:名称解析服务

App->nsswitch->resolve_lib

libnss

/etc/nsswitch.conf主配置文件

# Example:

#passwd:    db files nisplus nis

#shadow:    db files nisplus nis

#group:     db files nisplus nis

passwd:     files

shadow:     files

group:      files

#hosts:     db files nisplus nis dns

hosts:      files dns

# Example - obey only what nisplus tells us...

#services:   nisplus [NOTFOUND=return] files

#networks:   nisplus [NOTFOUND=return] files

#protocols:  nisplus [NOTFOUND=return] files

#rpc:        nisplus [NOTFOUND=return] files

#ethers:     nisplus [NOTFOUND=return] files

#netmasks:   nisplus [NOTFOUND=return] files

nisplus返回值：

SUCCESS service ok,found name 服务正常，并且转到了值

NOTFOUND service ok,name not found 服务正常，名字没有转换到值

UNAVAAIL service not available 服务找不到，当UNACAAIL时 会找files

TRYAGAIN temporary service failure  临时性故障，再试一次

bootparams: nisplus [NOTFOUND=return] files

ethers:     files

netmasks:   files

networks:   files

protocols:  files

rpc:        files

services:   files

netgroup:   nisplus

publickey:  nisplus

automount:  files nisplus

aliases:    files nisplus

[[email protected] lib]# vim /etc/protocols

[[email protected] ~]# vim /etc/services

名称解析服务：

nsswitch调用/usr/lib里对应的库文件进行解析

getent获取nsswitch里某个库的所有条目

[[email protected] ~]# getent  passwd

[[email protected] ~]# getent passwd root

root:x:0:0:root:/root:/bin/bash

[[email protected] ~]# getent  hosts

127.0.0.1       localhost localhost.localdomain localhost4 localhost4.localdomain4

127.0.0.1       localhost localhost.localdomain localhost6 localhost6.localdomain6

[[email protected] ~]# getent hosts www.baidu.com 先到hosts里找如果没有再通过dns找

180.97.33.107   www.a.shifen.com www.baidu.com

180.97.33.108   www.a.shifen.com www.baidu.com