The following environment variables can be used to select
default connection parameter values, which will be used by
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
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.
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 30.13).
PGPASSFILE specifies the name of the password file to use for lookups. If not set, it defaults to ~/.pgpass (see Section 30.13).
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.
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.
PGSSLKEY specifies the hardware token that stores the secret key for the client certificate. The value of this variable should consist of a colon-separated engine name (engines are OpenSSL loadable modules) and an engine-specific key identifier. If this is not set, the secret key must be kept in a file.
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.)
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.