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27.11. Environment Variables

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.

  • PGHOST sets the database server name. If this begins with a slash, it specifies Unix-domain communication rather than TCP/IP communication; the value is then the name of the directory in which the socket file is stored (in a default installation setup this would be /tmp).

  • PGHOSTADDR specifies the numeric IP address of the database server. This can be set instead of or in addition to PGHOST to avoid DNS lookup overhead. See the documentation of these parameters, under PQconnectdb above, for details on their interaction.

    When neither PGHOST nor PGHOSTADDR is set, the default behavior is to connect using a local Unix-domain socket; or on machines without Unix-domain sockets, libpq will attempt to connect to localhost.

  • PGPORT sets the TCP port number or Unix-domain socket file extension for communicating with the PostgreSQL server.

  • PGDATABASE sets the PostgreSQL database name.

  • PGUSER sets the user name used to connect to the database.

  • PGPASSWORD sets the password used if the server demands password authentication. Use of this environment variable is not recommended for security reasons (some operating systems allow non-root users to see process environment variables via ps); instead consider using the ~/.pgpass file (see Section 27.12).

  • PGSERVICE sets the service name to be looked up in pg_service.conf. This offers a shorthand way of setting all the parameters.

  • PGREALM sets the Kerberos realm to use with PostgreSQL, if it is different from the local realm. If PGREALM is set, libpq applications will attempt authentication with servers for this realm and use separate ticket files to avoid conflicts with local ticket files. This environment variable is only used if Kerberos authentication is selected by the server.

  • PGOPTIONS sets additional run-time options for the PostgreSQL server.

  • PGSSLMODE determines whether and with what priority an SSL connection will be negotiated with the server. There are four modes: disable will attempt only an unencrypted SSL connection; allow will negotiate, trying first a non-SSL connection, then if that fails, trying an SSL connection; prefer (the default) will negotiate, trying first an SSL connection, then if that fails, trying a regular non-SSL connection; require will try only an SSL connection. If PostgreSQL is compiled without SSL support, using option require will cause an error, while options allow and prefer will be accepted but libpq will not in fact attempt an SSL connection.

  • PGREQUIRESSL sets whether or not the connection must be made over SSL. If set to "1", libpq will refuse to connect if the server does not accept an SSL connection (equivalent to sslmode prefer). This option is deprecated in favor of the sslmode setting, and is only available if PostgreSQL is compiled with SSL support.

  • PGCONNECT_TIMEOUT sets the maximum number of seconds that libpq will wait when attempting to connect to the PostgreSQL server. If unset or set to zero, libpq will wait indefinitely. It is not recommended to set the timeout to less than 2 seconds.

The following environment variables can be used to specify default behavior for each PostgreSQL session. (See also the ALTER USER and ALTER DATABASE commands for ways to set default behavior on a per-user or per-database basis.)

  • PGDATESTYLE sets the default style of date/time representation. (Equivalent to SET datestyle TO ....)

  • PGTZ sets the default time zone. (Equivalent to SET timezone TO ....)

  • PGCLIENTENCODING sets the default client character set encoding. (Equivalent to SET client_encoding TO ....)

  • PGGEQO sets the default mode for the genetic query optimizer. (Equivalent to SET geqo TO ....)

Refer to the SQL command SET for information on correct values for these environment variables.

The following environment variables determine internal behavior of libpq; they override compiled-in defaults.

  • PGSYSCONFDIR sets the directory containing the pg_service.conf file.

  • PGLOCALEDIR sets the directory containing the locale files for message internationalization.