systemd-userdbd.service, systemd-userdbd - JSON User/Group Record Query Multiplexer/NSS Compatibility

systemd-userdbd is a system service that multiplexes user/group lookups to all local services that
       provide JSON user/group record definitions to the system. In addition it synthesizes JSON user/group
       records from classic UNIX/glibc NSS user/group records in order to provide full backwards compatibility.
       It may also pick up statically defined JSON user/group records from files in /etc/userdb/, /run/userdb/,
       /run/host/userdb/ and /usr/lib/userdb/ with the ".user" extension.

       Most of systemd-userdbd's functionality is accessible through the userdbctl(1) command.

       The user and group records this service provides access to follow the JSONUserRecords[1] and JSONGroupRecord[2] definitions. This service implements the User/GroupRecordLookupAPIviaVarlink[3], and
       multiplexes access other services implementing this API, too. It is thus both server and client of this
       API.

       This service provides three distinct Varlink[4] services: io.systemd.Multiplexer provides a single,
       unified API for querying JSON user and group records. Internally it talks to all other user/group record
       services running on the system in parallel and forwards any information discovered. This simplifies
       clients substantially since they need to talk to a single service only instead of all of them in
       parallel.  io.systemd.NameServiceSwitch provides compatibility with classic UNIX/glibc NSS user records,
       i.e. converts structpasswd and structgroup records as acquired with APIs such as getpwnam(1) to JSON
       user/group records, thus hiding the differences between the services as much as possible.
       io.systemd.DropIn makes JSON user/group records from the aforementioned drop-in directories available.

       systemd-userdbd.service, systemd-userdbd - JSON User/Group Record Query Multiplexer/NSS Compatibility

        1. JSON User Records
           https://systemd.io/USER_RECORD

        2. JSON Group Record
           https://systemd.io/GROUP_RECORD

        3. User/Group Record Lookup API via Varlink
           https://systemd.io/USER_GROUP_API

        4. Varlink
           https://varlink.org/

systemd 257.7                                                                         SYSTEMD-USERDBD.SERVICE(8)

systemd(1), nss-systemd(8), userdbctl(1), systemd-homed.service(8)

       systemd-userdbd.service

       /usr/lib/systemd/systemd-userdbd