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My nsswitch file contains the following

hosts:          files dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

What is the meaning of the db value? For example in the protocols section I see db I assume this means so sort of database but where is this db? and is it just a plain text config file. If it is just a config file why wouldn't it just be files? And if it is a DB how do I edit it.

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db causes libnss_db to be used. That reads data from Berkeley DB files usually stored in /var/db (/var/lib/misc on Debian); this is typically faster than reading from plain text files, for large NSS databases.

You should be able to modify the databases with a Berkeley DB client, but they’re typically built wholesale from the relevant source data. In the configuration above, the data sources are text files in /etc, and these remain the reference; the DB file is a variant used for speed, built wholesale using makedb, and not intended as the primary storage. The text files here are /etc/protocols for protocols, /etc/services for services, /etc/ethers for Ethernet addresses, /etc/rpc for RPC program numbers.

It’s more common to see db used for the passwd and group databases, as a local cache for large, remotely-hosted user databases (typically using LDAP).

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