The connection service file allows libpq connection parameters to be associated with a single service name. That service name can then be specified by a libpq connection, and the associated settings will be used. This allows connection parameters to be modified without requiring a recompile of the libpq application. The service name can also be specified using the PGSERVICE environment variable.
The connection service file can be a per-user service file at ~/.pg_service.conf or the location specified by the environment variable PGSERVICEFILE, or it can be a system-wide file at etc/pg_service.conf or in the directory specified by the environment variable PGSYSCONFDIR. If service definitions with the same name exist in the user and the system file, the user file takes precedence.
The file uses an "INI file" format where the section name is the service name and the parameters are connection parameters; see Section 31.1.2 for a list. For example:
# comment [mydb] host=somehost port=5433 user=admin
An example file is provided at share/pg_service.conf.sample.