Configuring resolver nsswitch.conf file
Configuring the resolver with nsswitch.conf
The nsswitch.conf file tells the resolver library
which of the three possible methods to use to convert host names to IP addresses and back.
Here is a sample file, taken from a Linux machine:
# An example Name Service Switch config file.
# This file should be sorted with the most-used
# services at the beginning.
# The entry '[NOTFOUND=return]' means that the
# search for an entry should stop if the search
# in the previous entry turned up nothing. Note
# that if the search failed due to some other reason
# (like no NIS server responding) then the search
# continues with the next entry.
# Legal entries are:
# nisplus or nis+ Use NIS+ (NIS version 3)
# nis or yp Use NIS (NIS version 2), also called
# YP dns Use DNS (Domain Name Service)
# files Use the local files
# [NOTFOUND=return] Stop searching if not found
# so far
passwd: files nisplus nis
shadow: files nisplus nis
group: files nisplus nis
hosts: files nisplus nis dns
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
bootparams: nisplus [NOTFOUND=return] files
automount: files nisplus
aliases: files nisplus
We will study this file in more detail later, but for now, focus on the line marked
hosts: files nisplus nis dns This line tells the resolver library to first look in the /etc/hosts file (files), then try to contact an NIS+ server (nisplus), then an NIS server (nis), and finally to try the Domain Name Service.
The TCP/IP protocol library software that formats requests to be sent to the Domain Name Server
for hostname to Internet address conversion.