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. 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 "loopback" connections to be made. 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 may be less if your kernel settings will not support it (as determined during initdb). This parameter can only be set at server start.

Increasing this parameter may cause PostgreSQL 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.

Determines the number of connection "slots" that are reserved for connections by PostgreSQL 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.

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.

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 selects the default group for the current user. This parameter can only be set at server start.

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 specification in the form 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 and 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 20.

This parameter can only be set at server start.

Specifies the Bonjour broadcast 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.

On systems that support the TCP_KEEPIDLE socket option, specifies the number of seconds between sending keepalives on an otherwise idle connection. A value of zero uses the system default. If TCP_KEEPIDLE is not supported, this parameter must be zero. This parameter is ignored for connections made via a Unix-domain socket.

On systems that support the TCP_KEEPINTVL socket option, specifies how long, in seconds, to wait for a response to a keepalive before retransmitting. A value of zero uses the system default. If TCP_KEEPINTVL is not supported, this parameter must be zero. This parameter is ignored for connections made via a Unix-domain socket.

On systems that support the TCP_KEEPCNT socket option, specifies how many keepalives may be lost before the connection is considered dead. A value of zero uses the system default. If TCP_KEEPCNT is not supported, this parameter must be zero. This parameter is ignored for connections made via a Unix-domain socket.

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 breaks 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 16.7 before using this. The default is off. This parameter can only be set at server start.

When a password is specified in CREATE USER or ALTER USER 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 20.2.3 for details. This parameter can only be set at server start.

Sets the Kerberos service name. See Section 20.2.3 for details. This parameter can only be set at server start.

Sets the host name part of the service principal. This, combined with krb_srvname, is used to generate the complete service principal, that is krb_srvname/krb_server_hostname@REALM. If not set, the default is the server host name. See Section 20.2.3 for details. This parameter can only be set at server start.

Sets whether Kerberos user names should be treated case-insensitively. The default is off (case sensitive). This parameter can only be set at server start.

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. The @ will be stripped off before the user name is looked up by the server.