PostgreSQL 8.4.12 Documentation
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# 18.3. Connections and Authentication

## 18.3.1. Connection Settings

`listen_addresses` (`string`)

  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.

`port` (`integer`)

  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.

`max_connections` (`integer`)

  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.

  Increasing this parameter might cause PostgreSQL to request more System V shared memory or semaphores than your operating system's default configuration allows. See Section 17.4.1 for information on how to adjust those parameters, if necessary.

`superuser_reserved_connections` (`integer`)

  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.

`unix_socket_directory` (`string`)

  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.

`unix_socket_group` (`string`)

  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.

`unix_socket_permissions` (`integer`)

  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 19.

  This parameter can only be set at server start.

`bonjour_name` (`string`)

  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.

`tcp_keepalives_idle` (`integer`)

  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.

`tcp_keepalives_interval` (`integer`)

  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.

`tcp_keepalives_count` (`integer`)

  On systems that support the `TCP_KEEPCNT` socket option, specifies how many keepalives can 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.

## 18.3.2. Security and Authentication

`authentication_timeout` (`integer`)

  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.

`ssl` (`boolean`)

  Enables SSL connections. Please read Section 17.8 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.

`ssl_renegotiation_limit` (`integer`)

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

  > Note: SSL libraries from before November 2009 are insecure when using SSL renegotiation, due to a vulnerability in the SSL protocol. As a stop-gap fix for this vulnerability, some vendors also shipped SSL libraries incapable of doing renegotiation. If any of these libraries are in use on the client or server, SSL renegotiation should be disabled.

`ssl_ciphers` (`string`)

  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. This parameter is unavailable unless the server is compiled with support for SSL.

`password_encryption` (`boolean`)

  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).

`krb_server_keyfile` (`string`)

  Sets the location of the Kerberos server key file. See Section 19.3.5 or Section 19.3.3 for details. This parameter can only be set in the `postgresql.conf` file or on the server command line.

`krb_srvname` (`string`)

  Sets the Kerberos service name. See Section 19.3.5 for details. This parameter can only be set in the `postgresql.conf` file or on the server command line.

`krb_caseins_users` (`boolean`)

  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.

`db_user_namespace` (`boolean`)

  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.

  `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`.

  > Note: This feature is intended as a temporary measure until a complete solution is found. At that time, this option will be removed.

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