17.3. Connections and Authentication

Specifies the TCP/IP address(es) on which the server is to listen for connections from client applications. The value takes the form of a comma-separated list of host names and/or numeric IP addresses. The special entry * corresponds to all available IP interfaces. The entry 0.0.0.0 allows listening for all IPv4 addresses and :: allows listening for all IPv6 addresses. If the list is empty, the server does not listen on any IP interface at all, in which case only Unix-domain sockets can be used to connect to it. The default value is localhost, which allows only local TCP/IP "loopback" connections to be made. While client authentication (Chapter 18) allows fine-grained control over who can access the server, listen_addresses controls which interfaces accept connection attempts, which can help prevent repeated malicious connection requests on insecure network interfaces. This parameter can only be set at server start.

The TCP port the server listens on; 5432 by default. Note that the same port number is used for all IP addresses the server listens on. This parameter can only be set at server start.

Determines the maximum number of concurrent connections to the database server. The default is typically 100 connections, but might be less if your kernel settings will not support it (as determined during initdb). This parameter can only be set at server start.

In the case of the Coordinator, this parameter determines how many connections can each Coordinator accept.

In the case of the Datanode, number of connection to each Datanode may become as large as max_connections multiplied by the number of Coordinators.

Increasing this parameter might cause Coordinator or Datanode to request more System V shared memory or semaphores than your operating system's default configuration allows. See Section 16.4.1 for information on how to adjust those parameters, if necessary.

When running a standby server, you must set this parameter to the same or higher value than on the master server. Otherwise, queries will not be allowed in the standby server.

Determines the number of connection "slots" that are reserved for connections by Coordinator or Datanode superusers. At most max_connections connections can ever be active simultaneously. Whenever the number of active concurrent connections is at least max_connections minus superuser_reserved_connections, new connections will be accepted only for superusers, and no new replication connections will be accepted.

The default value is three connections. The value must be less than the value of max_connections. This parameter can only be set at server start.

Specifies the directory of the Unix-domain socket on which the server is to listen for connections from client applications. The default is normally /tmp, but can be changed at build time. This parameter can only be set at server start.

In addition to the socket file itself, which is named .s.PGSQL.nnnn where nnnn is the server's port number, an ordinary file named .s.PGSQL.nnnn.lock will be created in the unix_socket_directory directory. Neither file should ever be removed manually.

This parameter is irrelevant on Windows, which does not have Unix-domain sockets.

Sets the owning group of the Unix-domain socket. (The owning user of the socket is always the user that starts the server.) In combination with the parameter unix_socket_permissions this can be used as an additional access control mechanism for Unix-domain connections. By default this is the empty string, which uses the default group of the server user. This parameter can only be set at server start.

This parameter is irrelevant on Windows, which does not have Unix-domain sockets.

Sets the access permissions of the Unix-domain socket. Unix-domain sockets use the usual Unix file system permission set. The parameter value is expected to be a numeric mode specified in the format accepted by the chmod and umask system calls. (To use the customary octal format the number must start with a 0 (zero).)

The default permissions are 0777, meaning anyone can connect. Reasonable alternatives are 0770 (only user and group, see also unix_socket_group) and 0700 (only user). (Note that for a Unix-domain socket, only write permission matters, so there is no point in setting or revoking read or execute permissions.)

This access control mechanism is independent of the one described in Chapter 18.

This parameter can only be set at server start.

This parameter is irrelevant on Windows, which does not have Unix-domain sockets.

Enables advertising the server's existence via Bonjour. The default is off. This parameter can only be set at server start.

Specifies the Bonjour service name. The computer name is used if this parameter is set to the empty string '' (which is the default). This parameter is ignored if the server was not compiled with Bonjour support. This parameter can only be set at server start.

Specifies the number of seconds before sending a keepalive packet on an otherwise idle connection. A value of 0 uses the system default. This parameter is supported only on systems that support the TCP_KEEPIDLE or TCP_KEEPALIVE symbols, and on Windows; on other systems, it must be zero. In sessions connected via a Unix-domain socket, this parameter is ignored and always reads as zero.

Specifies the number of seconds between sending keepalives on an otherwise idle connection. A value of 0 uses the system default. This parameter is supported only on systems that support the TCP_KEEPINTVL symbol, and on Windows; on other systems, it must be zero. In sessions connected via a Unix-domain socket, this parameter is ignored and always reads as zero.

Specifies the number of keepalive packets to send on an otherwise idle connection. A value of 0 uses the system default. This parameter is supported only on systems that support the TCP_KEEPCNT symbol; on other systems, it must be zero. In sessions connected via a Unix-domain socket, this parameter is ignored and always reads as zero.

Maximum time to complete client authentication, in seconds. If a would-be client has not completed the authentication protocol in this much time, the server closes the connection. This prevents hung clients from occupying a connection indefinitely. The default is one minute (1m). This parameter can only be set in the postgresql.conf file or on the server command line.

Enables SSL connections. Please read Section 16.9 before using this. The default is off. This parameter can only be set at server start. SSL communication is only possible with TCP/IP connections.

Specifies how much data can flow over an SSL-encrypted connection before renegotiation of the session keys will take place. Renegotiation decreases an attacker's chances of doing cryptanalysis when large amounts of traffic can be examined, but it also carries a large performance penalty. The sum of sent and received traffic is used to check the limit. If this parameter is set to 0, renegotiation is disabled. The default is 512MB.

Specifies a list of SSL ciphers that are allowed to be used on secure connections. See the openssl manual page for a list of supported ciphers.

When a password is specified in CREATE USER or ALTER ROLE without writing either ENCRYPTED or UNENCRYPTED, this parameter determines whether the password is to be encrypted. The default is on (encrypt the password).

Sets the location of the Kerberos server key file. See Section 18.3.5 or Section 18.3.3 for details. This parameter can only be set in the postgresql.conf file or on the server command line.

Sets the Kerberos service name. See Section 18.3.5 for details. This parameter can only be set in the postgresql.conf file or on the server command line.

Sets whether Kerberos and GSSAPI user names should be treated case-insensitively. The default is off (case sensitive). This parameter can only be set in the postgresql.conf file or on the server command line.

This parameter enables per-database user names. It is off by default. This parameter can only be set in the postgresql.conf file or on the server command line.

If this is on, you should create users as username@dbname. When username is passed by a connecting client, @ and the database name are appended to the user name and that database-specific user name is looked up by the server. Note that when you create users with names containing @ within the SQL environment, you will need to quote the user name.

With this parameter enabled, you can still create ordinary global users. Simply append @ when specifying the user name in the client, e.g. joe@. The @ will be stripped off before the user name is looked up by the server.

db_user_namespace causes the client's and server's user name representation to differ. Authentication checks are always done with the server's user name so authentication methods must be configured for the server's user name, not the client's. Because md5 uses the user name as salt on both the client and server, md5 cannot be used with db_user_namespace.