sslnegotiation

Reading PostgreSQL 18.6.

Description

This option controls how SSL encryption is negotiated with the server, if SSL is used. In the default postgres mode, the client first asks the server if SSL is supported. In direct mode, the client starts the standard SSL handshake directly after establishing the TCP/IP connection. Traditional PostgreSQL protocol negotiation is the most flexible with different server configurations. If the server is known to support direct SSL connections then the latter requires one fewer round trip reducing connection latency and also allows the use of protocol agnostic SSL network tools. The direct SSL option was introduced in PostgreSQL version 17.

Client library: libpq 18.6
Manual definition: Documented
Source environment fallback: PGSSLNEGOTIATION
Compiled fallback expression: DefaultSSLNegotiation

Usage

sslnegotiation

Default resolution and service-file precedence

The following environment variables can be used to select default connection parameter values, which will be used by PQconnectdb , PQsetdbLogin and PQsetdb if no value is directly specified by the calling code. These are useful to avoid hard-coding database connection information into simple client applications, for example.

Service names can be defined in either a per-user service file or a system-wide file. If the same service name exists in both the user and the system file, the user file takes precedence. By default, the per-user service file is named ~/.pg_service.conf . On Microsoft Windows, it is named %APPDATA%\postgresql\.pg_service.conf (where %APPDATA% refers to the Application Data subdirectory in the user's profile). A different file name can be specified by setting the environment variable PGSERVICEFILE . The system-wide file is named pg_service.conf . By default it is sought in the etc directory of the PostgreSQL installation (use pg_config --sysconfdir to identify this directory precisely). Another directory, but not a different file name, can be specified by setting the environment variable PGSYSCONFDIR .

Connection parameters obtained from a service file are combined with parameters obtained from other sources. A service file setting overrides the corresponding environment variable, and in turn can be overridden by a value given directly in the connection string. For example, using the above service file, a connection string service=mydb port=5434 will use host somehost , port 5434 , user admin , and other parameters as set by environment variables or built-in defaults.

Environment variable evidence

PGSSLNEGOTIATION behaves the same as the sslnegotiation connection parameter.

Environment fallback

Variable	Documented behavior
PGSSLNEGOTIATION	PGSSLNEGOTIATION behaves the same as the sslnegotiation connection parameter.

Manual definition

sslnegotiation

This option controls how SSL encryption is negotiated with the server, if SSL is used. In the default postgres mode, the client first asks the server if SSL is supported. In direct mode, the client starts the standard SSL handshake directly after establishing the TCP/IP connection. Traditional PostgreSQL protocol negotiation is the most flexible with different server configurations. If the server is known to support direct SSL connections then the latter requires one fewer round trip reducing connection latency and also allows the use of protocol agnostic SSL network tools. The direct SSL option was introduced in PostgreSQL version 17.

postgres: perform PostgreSQL protocol negotiation. This is the default if the option is not provided.
direct: start SSL handshake directly after establishing the TCP/IP connection. This is only allowed with sslmode=require or higher, because the weaker settings could lead to unintended fallback to plaintext authentication when the server does not support direct SSL handshake.

Related entries

Documentation and source

Source build

Version: 18.6
Build: https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2
Source fingerprint: ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8

Compare versions

PostgreSQL 17 → 18: unchanged.

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

Export JSON · Back to Connection Parameters · Recorded in PostgreSQL 17 through 20; the first sample is not necessarily its introduction.