The Name Service Switch configuration file is at /etc/nssswitch.conf. In this file will be lines that list the database name followed by one or more words. In this example, this line tells the system to first use the /etc/hosts file for IP address to hostname resolution, and then use DNS second. If you were to issue command ping -c4 example.com, first the /etc/hosts file would be checked for a line that contains the IP address of example.com.
hosts: files dns
In this example, the passwd command will first check the /etc/passwd file, and then sss. As an example, if the passwd user1 command is used to update the password for user1, first the /etc/passwd file will be checked for a record for user1, and then use SSSD second.
passwd: files sss
Notice in this prior examples, that instead of /etc/hosts and /etc/passwd being listed, just the word files was used. When the word files is used, following are the paths to the files that are used.
aliases /etc/aliases ethers /etc/ethers group /etc/group hosts /etc/hosts initgroups /etc/group netgroup /etc/netgroup networks /etc/networks passwd /etc/passwd protocols /etc/protocols publickey /etc/publickey rpc /etc/rpc services /etc/services shadow /etc/shadow