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5.3.6.2 Ident Authentication over Local Sockets

On systems supporting SO_PEERCRED requests for Unix-domain sockets (currently Linux, FreeBSD, NetBSD, OpenBSD, BSD/OS, and Solaris), ident authentication can also be applied to local connections. PostgreSQL uses SO_PEERCRED to find out the operating system name of the connected client process. In this case, no security risk is added by using ident authentication; indeed it is a preferable choice for local connections on such systems.

On systems without SO_PEERCRED requests, ident authentication is only available for TCP/IP connections. As a work-around, it is possible to specify the localhost address 127.0.0.1 and make connections to this address. This method is trustworthy to the extent that you trust the local ident server.