Install libnss-db by entering the following commands in the terminal:
sudo apt update sudo apt install libnss-db
NSS module for using Berkeley Databases as a naming service
nss_db is a set of C library extensions which allow Berkeley Databases to be used as a primary source of aliases, ethers, groups, hosts, networks, protocol, users, RPCs, services, and shadow passwords (instead of or in addition to using flat files or NIS). Install nss_db if your flat name service files are too large and lookups are slow.