{"Entry":{"collection":"conn","key":"sslnegotiation","name":"sslnegotiation","aliases":["PGSSLNEGOTIATION","sslnegotiation"],"metadata":{"aliases":["PGSSLNEGOTIATION","sslnegotiation"],"category":"TLS","content_hash":"f39e52605ee426560b2a0ed3aaf85f72cc83a7380f57fa491217c19c6f543e51","derived_content_hash":"8e1eeb8e806343ddb3b695ff0d4ca622d54588fc8234eb6efd337872d6acd1fd","documentation_refresh":{"batch":"20261113","original_source_rev":"","versions":{"17":"17.12","18":"18.7","19":"19rc2"}},"imported_at":"2026-09-30T00:40:35.149361+08:00","name":"sslnegotiation","name_zh":"","slug":"sslnegotiation","summary":"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."}},"Definition":{"Collection":"conn","Key":"sslnegotiation","SourceDatabase":"center","Version":"18","SourceTable":"connection_parameter","SourceKey":"sslnegotiation","SourceRevision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","Facts":{"comparison_data":{"compiled_default_expression":"DefaultSSLNegotiation","default_evidence":["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. 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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.","documented":true,"environment":"PGSSLNEGOTIATION","keyword":"sslnegotiation"},"comparison_hash":"689f6cf691345735854fbeef2bdc05e6e429ffdf8aaab4d9b03c3cc187c1c304","default_evidence":["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. 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The direct SSL option was introduced in PostgreSQL version 17."],"description_zh":"如果使用 SSL，此选项控制如何与服务器协商 SSL 加密。在默认的 postgres 模式下，客户端会先询问服务器是否支持 SSL；在 direct 模式下，客户端会在建立 TCP/IP 连接后直接开始标准 SSL 握手。传统的 PostgreSQL 协议协商能兼容更多不同的服务器配置；如果已知服务器支持直接 SSL 连接，则后一种方式可以减少一次往返，从而降低连接延迟，也允许使用与协议无关的 SSL 网络工具。直接 SSL 选项是在 PostgreSQL 17 中引入的。 postgres 执行 PostgreSQL 协议协商。如果未提供该选项，这是默认值。 direct 在建立 TCP/IP 连接后直接开始 SSL 握手。仅当 sslmode=require 或更高时才允许使用该模式，因为更弱的设置可能在服务器不支持直接 SSL 握手时导致意外回退到明文认证。","description_zh_html":"\u003cp\u003e连接参数 sslnegotiation。\u003c/p\u003e\u003ch3\u003e同版本中文手册定义\u003c/h3\u003e\u003cdd\u003e\u003cp\u003e\n        如果使用 SSL，此选项控制如何与服务器协商 SSL 加密。在默认的 \u003ccode class=\"literal\"\u003epostgres\u003c/code\u003e 模式下，客户端会先询问服务器是否支持 SSL；在 \u003ccode class=\"literal\"\u003edirect\u003c/code\u003e 模式下，客户端会在建立 TCP/IP 连接后直接开始标准 SSL 握手。传统的 \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 协议协商能兼容更多不同的服务器配置；如果已知服务器支持直接 \u003cacronym class=\"acronym\"\u003eSSL\u003c/acronym\u003e 连接，则后一种方式可以减少一次往返，从而降低连接延迟，也允许使用与协议无关的 SSL 网络工具。直接 SSL 选项是在 \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 17 中引入的。\n       \u003c/p\u003e\u003cdiv class=\"variablelist\"\u003e\u003cdl class=\"variablelist\"\u003e\u003cdt\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003epostgres\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\u003cdd\u003e\u003cp\u003e\n           执行 \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 协议协商。如果未提供该选项，这是默认值。\n          \u003c/p\u003e\u003c/dd\u003e\u003cdt\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003edirect\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\u003cdd\u003e\u003cp\u003e\n           在建立 TCP/IP 连接后直接开始 SSL 握手。仅当 \u003ccode class=\"literal\"\u003esslmode=require\u003c/code\u003e 或更高时才允许使用该模式，因为更弱的设置可能在服务器不支持直接 SSL 握手时导致意外回退到明文认证。\n          \u003c/p\u003e\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e\u003c/dd\u003e\u003cp\u003e\u003ca href=\"/zh/docs/18/libpq-connect.html#LIBPQ-CONNECT-SSLNEGOTIATION\"\u003e查看完整中文手册与上下文\u003c/a\u003e。\u003c/p\u003e","documented":true,"environment":[{"description":"PGSSLNEGOTIATION behaves the same as the sslnegotiation connection parameter.","name":"PGSSLNEGOTIATION","source_url":"/docs/18/libpq-envars.html"}],"facts":[{"label":"Client library","value":"libpq 18.6"},{"label":"Manual definition","value":"Documented"},{"label":"Source environment fallback","value":"PGSSLNEGOTIATION"},{"label":"Compiled fallback expression","value":"DefaultSSLNegotiation"}],"facts_zh":[{"label":"客户端库","value":"libpq 18.6"},{"label":"手册定义","value":"手册已记载"},{"label":"源码中的环境变量回退","value":"PGSSLNEGOTIATION"},{"label":"编译时回退表达式","value":"DefaultSSLNegotiation"}],"keyword":"sslnegotiation","manual_html":"\u003cdiv\u003e\u003cdl class=\"variablelist\"\u003e\u003cdt id=\"LIBPQ-CONNECT-SSLNEGOTIATION\"\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003esslnegotiation\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eThis option controls how SSL encryption is negotiated with the server, if SSL is used. 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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. 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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.","BodyHTML":"\u003cdiv\u003e\u003cdl\u003e\u003cdt id=\"LIBPQ-CONNECT-SSLNEGOTIATION\"\u003e\u003cspan\u003e\u003ccode\u003esslnegotiation\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eThis option controls how SSL encryption is negotiated with the server, if SSL is used. In the default \u003ccode\u003epostgres\u003c/code\u003e mode, the client first asks the server if SSL is supported. In \u003ccode\u003edirect\u003c/code\u003e mode, the client starts the standard SSL handshake directly after establishing the TCP/IP connection. Traditional \u003cspan\u003ePostgreSQL\u003c/span\u003e 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 \u003cspan\u003ePostgreSQL\u003c/span\u003e version 17.\u003c/p\u003e\n\u003cdiv\u003e\n\u003cdl\u003e\n\u003cdt\u003e\u003cspan\u003e\u003ccode\u003epostgres\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\n\u003cdd\u003e\n\u003cp\u003eperform \u003cspan\u003ePostgreSQL\u003c/span\u003e protocol negotiation. This is the default if the option is not provided.\u003c/p\u003e\n\u003c/dd\u003e\n\u003cdt\u003e\u003cspan\u003e\u003ccode\u003edirect\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\n\u003cdd\u003e\n\u003cp\u003estart SSL handshake directly after establishing the TCP/IP connection. This is only allowed with \u003ccode\u003esslmode=require\u003c/code\u003e or higher, because the weaker settings could lead to unintended fallback to plaintext authentication when the server does not support direct SSL handshake.\u003c/p\u003e\n\u003c/dd\u003e\n\u003c/dl\u003e\n\u003c/div\u003e\n\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e","SourceRevision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","ContentHash":"87412d33c9615c26aebed19bf1b7818facac0a0369d1ae047f0f355a0a63fd7a","Payload":{"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."],"manual_html":"\u003cdiv\u003e\u003cdl class=\"variablelist\"\u003e\u003cdt id=\"LIBPQ-CONNECT-SSLNEGOTIATION\"\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003esslnegotiation\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eThis option controls how SSL encryption is negotiated with the server, if SSL is used. In the default \u003ccode class=\"literal\"\u003epostgres\u003c/code\u003e mode, the client first asks the server if SSL is supported. In \u003ccode class=\"literal\"\u003edirect\u003c/code\u003e mode, the client starts the standard SSL handshake directly after establishing the TCP/IP connection. Traditional \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 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 \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e version 17.\u003c/p\u003e\n\u003cdiv class=\"variablelist\"\u003e\n\u003cdl class=\"variablelist\"\u003e\n\u003cdt\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003epostgres\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\n\u003cdd\u003e\n\u003cp\u003eperform \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e protocol negotiation. This is the default if the option is not provided.\u003c/p\u003e\n\u003c/dd\u003e\n\u003cdt\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003edirect\u003c/code\u003e\u003c/span\u003e\u003c/dt\u003e\n\u003cdd\u003e\n\u003cp\u003estart SSL handshake directly after establishing the TCP/IP connection. This is only allowed with \u003ccode class=\"literal\"\u003esslmode=require\u003c/code\u003e or higher, because the weaker settings could lead to unintended fallback to plaintext authentication when the server does not support direct SSL handshake.\u003c/p\u003e\n\u003c/dd\u003e\n\u003c/dl\u003e\n\u003c/div\u003e\n\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e","related":[{"label":"Connection service file","url":"/docs/18/libpq-pgservice.html"},{"label":"Password file","url":"/docs/18/libpq-pgpass.html"},{"label":"All libpq environment variables","url":"/docs/18/libpq-envars.html"}],"sections":[{"paragraphs":["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."],"title":"Default resolution and service-file precedence"},{"paragraphs":["PGSSLNEGOTIATION behaves the same as the sslnegotiation connection parameter."],"title":"Environment variable evidence"}],"tables":[{"columns":[{"key":"name","label":"Variable"},{"key":"description","label":"Documented behavior"}],"key":"environment","rows":[{"description":"PGSSLNEGOTIATION behaves the same as the sslnegotiation connection parameter.","name":{"text":"PGSSLNEGOTIATION","url":"/docs/18/libpq-envars.html"}}],"title":"Environment fallback"}]}},"RequestedLocale":"en","Fallback":false,"Versions":["17","18","19","20"],"Locales":["en","zh-Hans"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}