host
Name of host to connect to.
If a host name looks like an absolute path name, it specifies Unix-domain communication rather than TCP/IP communication; the value is the name of the directory in which the socket file is stored. (On Unix, an absolute path name begins with a slash. On Windows, paths starting with drive letters are also recognized.) If the host name starts with
, it is taken as a Unix-domain socket in the abstract namespace (currently supported on Linux and Windows). The default behavior when
host
is not specified, or is empty, is to connect to a Unix-domain socket
in
/tmp
(or whatever socket directory was specified when
PostgreSQL
was built). On Windows, the default is to connect to
localhost
A comma-separated list of host names is also accepted, in which case each host name in the list is tried in order; an empty item in the list selects the default behavior as explained above. See
Section 32.1.1.3
for details.
hostaddr
Numeric IP address of host to connect to. This should be in the standard IPv4 address format, e.g.,
172.28.40.9
. If your machine supports IPv6, you can also use those addresses. TCP/IP communication is always used when a nonempty string is specified for this parameter. If this parameter is not specified, the value of
host
will be looked up to find the corresponding IP address — or, if
host
specifies an IP address, that value will be used directly.
Using
hostaddr
allows the application to avoid a host name look-up, which might be important in applications with time constraints. However, a host name is required for GSSAPI or SSPI authentication methods, as well as for
verify-full
SSL certificate verification. The following rules are used:
If
host
is specified without
hostaddr
, a host name lookup occurs. (When using
PQconnectPoll
, the lookup occurs when
PQconnectPoll
first considers this host name, and it may cause
PQconnectPoll
to block for a significant amount of time.)
If
hostaddr
is specified without
host
, the value for
hostaddr
gives the server network address. The connection attempt will fail if the authentication method requires a host name.
If both
host
and
hostaddr
are specified, the value for
hostaddr
gives the server network address. The value for
host
is ignored unless the authentication method requires it, in which case it will be used as the host name.
Note that authentication is likely to fail if
host
is not the name of the server at network address
hostaddr
. Also, when both
host
and
hostaddr
are specified,
host
is used to identify the connection in a password file (see
Section 32.16
).
A comma-separated list of
hostaddr
values is also accepted, in which case each host in the list is tried in order. An empty item in the list causes the corresponding host name to be used, or the default host name if that is empty as well. See
Section 32.1.1.3
for details.
Without either a host name or host address,
libpq
will connect using a local Unix-domain socket; or on Windows, it will attempt to connect to
localhost
port
Port number to connect to at the server host, or socket file name extension for Unix-domain connections.
If multiple hosts were given in the
host
or
hostaddr
parameters, this parameter may specify a comma-separated list of ports of the same length as the host list, or it may specify a single port number to be used for all hosts. An empty string, or an empty item in a comma-separated list, specifies the default port number established when
PostgreSQL
was built.
dbname
The database name. Defaults to be the same as the user name. In certain contexts, the value is checked for extended formats; see
Section 32.1.1
for more details on those.
user
PostgreSQL
user name to connect as. Defaults to be the same as the operating system name of the user running the application.
password
Password to be used if the server demands password authentication.
passfile
Specifies the name of the file used to store passwords (see
Section 32.16
). Defaults to
~/.pgpass
, or
%APPDATA%\postgresql\pgpass.conf
on Microsoft Windows. (No error is reported if this file does not exist.)
require_auth
Specifies the authentication method that the client requires from the server. If the server does not use the required method to authenticate the client, or if the authentication handshake is not fully completed by the server, the connection will fail. A comma-separated list of methods may also be provided, of which the server must use exactly one in order for the connection to succeed. By default, any authentication method is accepted, and the server is free to skip authentication altogether.
Methods may be negated with the addition of a
prefix, in which case the server must
not
attempt the listed method; any other method is accepted, and the server is free not to authenticate the client at all. If a comma-separated list is provided, the server may not attempt
any
of the listed negated methods. Negated and non-negated forms may not be combined in the same setting.
As a final special case, the
none
method requires the server not to use an authentication challenge. (It may also be negated, to require some form of authentication.)
The following methods may be specified:
password
The server must request plaintext password authentication.
md5
The server must request MD5 hashed password authentication.
Warning
Support for MD5-encrypted passwords is deprecated and will be removed in a future release of
PostgreSQL
. Refer to
Section 20.5
for details about migrating to another password type.
gss
The server must either request a Kerberos handshake via
GSSAPI
or establish a
GSS
-encrypted channel (see also
gssencmode
).
sspi
The server must request Windows
SSPI
authentication.
scram-sha-256
The server must successfully complete a SCRAM-SHA-256 authentication exchange with the client.
oauth
The server must request an OAuth bearer token from the client.
none
The server must not prompt the client for an authentication exchange. (This does not prohibit client certificate authentication via TLS, nor GSS authentication via its encrypted transport.)
channel_binding
This option controls the client's use of channel binding. A setting of
require
means that the connection must employ channel binding,
prefer
means that the client will choose channel binding if available, and
disable
prevents the use of channel binding. The default is
prefer
if
PostgreSQL
is compiled with SSL support; otherwise the default is
disable
Channel binding is a method for the server to authenticate itself to the client. It is only supported over SSL connections with
PostgreSQL
11 or later servers using the
SCRAM
authentication method.
connect_timeout
Maximum time to wait while connecting, in seconds (write as a decimal integer, e.g.,
10
). Zero, negative, or not specified means wait indefinitely. This timeout applies separately to each host name or IP address. For example, if you specify two hosts and
connect_timeout
is 5, each host will time out if no connection is made within 5 seconds, so the total time spent waiting for a connection might be up to 10 seconds.
client_encoding
This sets the
client_encoding
configuration parameter for this connection. In addition to the values accepted by the corresponding server option, you can use
auto
to determine the right encoding from the current locale in the client (
LC_CTYPE
environment variable on Unix systems).
options
Specifies command-line options to send to the server at connection start. For example, setting this to
-c geqo=off
or
--geqo=off
sets the session's value of the
geqo
parameter to
off
. Spaces within this string are considered to separate command-line arguments, unless escaped with a backslash (
); write
\\
to represent a literal backslash. For a detailed discussion of the available options, consult
Chapter 19
application_name
Specifies a value for the
application_name
configuration parameter.
fallback_application_name
Specifies a fallback value for the
application_name
configuration parameter. This value will be used if no value has been given for
application_name
via a connection parameter or the
PGAPPNAME
environment variable. Specifying a fallback name is useful in generic utility programs that wish to set a default application name but allow it to be overridden by the user.
keepalives
Controls whether client-side TCP keepalives are used. The default value is 1, meaning on, but you can change this to 0, meaning off, if keepalives are not wanted. This parameter is ignored for connections made via a Unix-domain socket.
keepalives_idle
Controls the number of seconds of inactivity after which TCP should send a keepalive message to the server. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPIDLE
or an equivalent socket option is available, and on Windows; on other systems, it has no effect.
keepalives_interval
Controls the number of seconds after which a TCP keepalive message that is not acknowledged by the server should be retransmitted. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPINTVL
or an equivalent socket option is available, and on Windows; on other systems, it has no effect.
keepalives_count
Controls the number of TCP keepalives that can be lost before the client's connection to the server is considered dead. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPCNT
or an equivalent socket option is available; on other systems, it has no effect.
tcp_user_timeout
Controls the number of milliseconds that transmitted data may remain unacknowledged before a connection is forcibly closed. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket. It is only supported on systems where
TCP_USER_TIMEOUT
is available; on other systems, it has no effect.
replication
This option determines whether the connection should use the replication protocol instead of the normal protocol. This is what PostgreSQL replication connections as well as tools such as
pg_basebackup
use internally, but it can also be used by third-party applications. For a description of the replication protocol, consult
Section 54.4
The following values, which are case-insensitive, are supported:
true
on
yes
The connection goes into physical replication mode.
database
The connection goes into logical replication mode, connecting to the database specified in the
dbname
parameter.
false
off
no
The connection is a regular one, which is the default behavior.
In physical or logical replication mode, only the simple query protocol can be used.
gssencmode
This option determines whether or with what priority a secure
GSS
TCP/IP connection will be negotiated with the server. There are three modes:
disable
only try a non-
GSSAPI
-encrypted connection
prefer
(default)
if there are
GSSAPI
credentials present (i.e., in a credentials cache), first try a
GSSAPI
-encrypted connection; if that fails or there are no credentials, try a non-
GSSAPI
-encrypted connection. This is the default when
PostgreSQL
has been compiled with
GSSAPI
support.
require
only try a
GSSAPI
-encrypted connection
gssencmode
is ignored for Unix domain socket communication. If
PostgreSQL
is compiled without GSSAPI support, using the
require
option will cause an error, while
prefer
will be accepted but
libpq
will not actually attempt a
GSSAPI
-encrypted connection.
sslmode
This option determines whether or with what priority a secure
SSL
TCP/IP connection will be negotiated with the server. There are six modes:
disable
only try a non-
SSL
connection
allow
first try a non-
SSL
connection; if that fails, try an
SSL
connection
prefer
(default)
first try an
SSL
connection; if that fails, try a non-
SSL
connection
require
only try an
SSL
connection. If a root CA file is present, verify the certificate in the same way as if
verify-ca
was specified
verify-ca
only try an
SSL
connection, and verify that the server certificate is issued by a trusted certificate authority (
CA
verify-full
only try an
SSL
connection, verify that the server certificate is issued by a trusted
CA
and that the requested server host name matches that in the certificate
See
Section 32.19
for a detailed description of how these options work.
sslmode
is ignored for Unix domain socket communication. If
PostgreSQL
is compiled without SSL support, using options
require
verify-ca
, or
verify-full
will cause an error, while options
allow
and
prefer
will be accepted but
libpq
will not actually attempt an
SSL
connection.
Note that if
GSSAPI
encryption is possible, that will be used in preference to
SSL
encryption, regardless of the value of
sslmode
. To force use of
SSL
encryption in an environment that has working
GSSAPI
infrastructure (such as a Kerberos server), also set
gssencmode
to
disable
requiressl
This option is deprecated in favor of the
sslmode
setting.
If set to 1, an
SSL
connection to the server is required (this is equivalent to
sslmode
require
).
libpq
will then refuse to connect if the server does not accept an
SSL
connection. If set to 0 (default),
libpq
will negotiate the connection type with the server (equivalent to
sslmode
prefer
). This option is only available if
PostgreSQL
is compiled with SSL support.
sslnegotiation
This option controls how SSL encryption is negotiated with the server, if SSL is used. In the default
postgres
mode, the client first asks the server if SSL is supported. In
direct
mode, the client starts the standard SSL handshake directly after establishing the TCP/IP connection. Traditional
PostgreSQL
protocol negotiation is the most flexible with different server configurations. If the server is known to support direct
SSL
connections then the latter requires one fewer round trip reducing connection latency and also allows the use of protocol agnostic SSL network tools. The direct SSL option was introduced in
PostgreSQL
version 17.
postgres
perform
PostgreSQL
protocol negotiation. This is the default if the option is not provided.
direct
start SSL handshake directly after establishing the TCP/IP connection. This is only allowed with
sslmode=require
or higher, because the weaker settings could lead to unintended fallback to plaintext authentication when the server does not support direct SSL handshake.
sslcompression
If set to 1, data sent over SSL connections will be compressed. If set to 0, compression will be disabled. The default is 0. This parameter is ignored if a connection without SSL is made.
SSL compression is nowadays considered insecure and its use is no longer recommended.
OpenSSL
1.1.0 disabled compression by default, and many operating system distributions disabled it in prior versions as well, so setting this parameter to on will not have any effect if the server does not accept compression.
PostgreSQL
14 disabled compression completely in the backend.
If security is not a primary concern, compression can improve throughput if the network is the bottleneck. Disabling compression can improve response time and throughput if CPU performance is the limiting factor.
sslcert
This parameter specifies the file name of the client SSL certificate, replacing the default
~/.postgresql/postgresql.crt
. This parameter is ignored if an SSL connection is not made.
sslkey
This parameter specifies the location for the secret key used for the client certificate. It can either specify a file name that will be used instead of the default
~/.postgresql/postgresql.key
, or it can specify a key obtained from an external
engine
(engines are
OpenSSL
loadable modules). An external engine specification should consist of a colon-separated engine name and an engine-specific key identifier. This parameter is ignored if an SSL connection is not made.
sslkeylogfile
This parameter specifies the location where
libpq
will log keys used in this SSL context. This is useful for debugging
PostgreSQL
protocol interactions or client connections using network inspection tools like
Wireshark
. This parameter is ignored if an SSL connection is not made, or if
LibreSSL
is used (
LibreSSL
does not support key logging). Keys are logged using the
NSS
format.
Warning
Key logging will expose potentially sensitive information in the keylog file. Keylog files should be handled with the same care as
sslkey
files.
sslpassword
This parameter specifies the password for the secret key specified in
sslkey
, allowing client certificate private keys to be stored in encrypted form on disk even when interactive passphrase input is not practical.
Specifying this parameter with any non-empty value suppresses the
Enter PEM pass phrase:
prompt that
OpenSSL
will emit by default when an encrypted client certificate key is provided to
libpq
If the key is not encrypted this parameter is ignored. The parameter has no effect on keys specified by
OpenSSL
engines unless the engine uses the
OpenSSL
password callback mechanism for prompts.
There is no environment variable equivalent to this option, and no facility for looking it up in
.pgpass
. It can be used in a service file connection definition. Users with more sophisticated uses should consider using
OpenSSL
engines and tools like PKCS#11 or USB crypto offload devices.
sslcertmode
This option determines whether a client certificate may be sent to the server, and whether the server is required to request one. There are three modes:
disable
A client certificate is never sent, even if one is available (default location or provided via
sslcert
).
allow
(default)
A certificate may be sent, if the server requests one and the client has one to send.
require
The server
must
request a certificate. The connection will fail if the client does not send a certificate and the server successfully authenticates the client anyway.
Note
sslcertmode=require
doesn't add any additional security, since there is no guarantee that the server is validating the certificate correctly; PostgreSQL servers generally request TLS certificates from clients whether they validate them or not. The option may be useful when troubleshooting more complicated TLS setups.
sslrootcert
This parameter specifies the name of a file containing SSL certificate authority (
CA
) certificate(s). If the file exists, the server's certificate will be verified to be signed by one of these authorities. The default is
~/.postgresql/root.crt
The special value
system
may be specified instead, in which case the trusted CA roots from the SSL implementation will be loaded. The exact locations of these root certificates differ by SSL implementation and platform. For
OpenSSL
in particular, the locations may be further modified by the
SSL_CERT_DIR
and
SSL_CERT_FILE
environment variables.
Note
When using
sslrootcert=system
, the default
sslmode
is changed to
verify-full
, and any weaker setting will result in an error. In most cases it is trivial for anyone to obtain a certificate trusted by the system for a hostname they control, rendering
verify-ca
and all weaker modes useless.
The magic
system
value will take precedence over a local certificate file with the same name. If for some reason you find yourself in this situation, use an alternative path like
sslrootcert=./system
instead.
sslcrl
This parameter specifies the file name of the SSL server certificate revocation list (CRL). Certificates listed in this file, if it exists, will be rejected while attempting to authenticate the server's certificate. If neither
sslcrl
nor
sslcrldir
is set, this setting is taken as
~/.postgresql/root.crl
sslcrldir
This parameter specifies the directory name of the SSL server certificate revocation list (CRL). Certificates listed in the files in this directory, if it exists, will be rejected while attempting to authenticate the server's certificate.
The directory needs to be prepared with the
OpenSSL
command
openssl rehash
or
c_rehash
. See its documentation for details.
Both
sslcrl
and
sslcrldir
can be specified together.
sslsni
If set to 1 (default), libpq sets the TLS extension
Server Name Indication
SNI
) on SSL-enabled connections. By setting this parameter to 0, this is turned off.
The Server Name Indication can be used by SSL-aware proxies to route connections without having to decrypt the SSL stream. (Note that unless the proxy is aware of the PostgreSQL protocol handshake this would require setting
sslnegotiation
to
direct
.) However,
SNI
makes the destination host name appear in cleartext in the network traffic, so it might be undesirable in some cases.
requirepeer
This parameter specifies the operating-system user name of the server, for example
requirepeer=postgres
. When making a Unix-domain socket connection, if this parameter is set, the client checks at the beginning of the connection that the server process is running under the specified user name; if it is not, the connection is aborted with an error. This parameter can be used to provide server authentication similar to that available with SSL certificates on TCP/IP connections. (Note that if the Unix-domain socket is in
/tmp
or another publicly writable location, any user could start a server listening there. Use this parameter to ensure that you are connected to a server run by a trusted user.) This option is only supported on platforms for which the
peer
authentication method is implemented; see
Section 20.9
ssl_min_protocol_version
This parameter specifies the minimum SSL/TLS protocol version to allow for the connection. Valid values are
TLSv1
TLSv1.1
TLSv1.2
and
TLSv1.3
. The supported protocols depend on the version of
OpenSSL
used, older versions not supporting the most modern protocol versions. If not specified, the default is
TLSv1.2
, which satisfies industry best practices as of this writing.
ssl_max_protocol_version
This parameter specifies the maximum SSL/TLS protocol version to allow for the connection. Valid values are
TLSv1
TLSv1.1
TLSv1.2
and
TLSv1.3
. The supported protocols depend on the version of
OpenSSL
used, older versions not supporting the most modern protocol versions. If not set, this parameter is ignored and the connection will use the maximum bound defined by the backend, if set. Setting the maximum protocol version is mainly useful for testing or if some component has issues working with a newer protocol.
min_protocol_version
Specifies the minimum protocol version to allow for the connection. The default is to allow any version of the
PostgreSQL
protocol supported by libpq, which currently means
3.0
. If the server does not support at least this protocol version the connection will be closed.
The current supported values are
3.0
3.2
, and
latest
. The
latest
value is equivalent to the latest protocol version supported by the libpq version being used, which is currently
3.2
max_protocol_version
Specifies the protocol version to request from the server. The default is to use version
3.0
of the
PostgreSQL
protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use
PQfullProtocolVersion
to find out which exact protocol version was negotiated.
The current supported values are
3.0
3.2
, and
latest
. The
latest
value is equivalent to the latest protocol version supported by the libpq version being used, which is currently
3.2
krbsrvname
Kerberos service name to use when authenticating with GSSAPI. This must match the service name specified in the server configuration for Kerberos authentication to succeed. (See also
Section 20.6
.) The default value is normally
postgres
, but that can be changed when building
PostgreSQL
via the
--with-krb-srvnam
option of
configure
. In most environments, this parameter never needs to be changed. Some Kerberos implementations might require a different service name, such as Microsoft Active Directory which requires the service name to be in upper case (
POSTGRES
).
gsslib
GSS library to use for GSSAPI authentication. Currently this is disregarded except on Windows builds that include both GSSAPI and SSPI support. In that case, set this to
gssapi
to cause libpq to use the GSSAPI library for authentication instead of the default SSPI.
gssdelegation
Forward (delegate) GSS credentials to the server. The default is
which means credentials will not be forwarded to the server. Set this to
to have credentials forwarded when possible.
scram_client_key
The base64-encoded SCRAM client key. This can be used by foreign-data wrappers or similar middleware to enable pass-through SCRAM authentication. See
Section F.38.1.10
for one such implementation. It is not meant to be specified directly by users or client applications.
scram_server_key
The base64-encoded SCRAM server key. This can be used by foreign-data wrappers or similar middleware to enable pass-through SCRAM authentication. See
Section F.38.1.10
for one such implementation. It is not meant to be specified directly by users or client applications.
service
Service name to use for additional parameters. It specifies a service name in
pg_service.conf
that holds additional connection parameters. This allows applications to specify only a service name so connection parameters can be centrally maintained. See
Section 32.17
target_session_attrs
This option determines whether the session must have certain properties to be acceptable. It's typically used in combination with multiple host names to select the first acceptable alternative among several hosts. There are six modes:
any
(default)
any successful connection is acceptable
read-write
session must accept read-write transactions by default (that is, the server must not be in hot standby mode and the
default_transaction_read_only
parameter must be
off
read-only
session must not accept read-write transactions by default (the converse)
primary
server must not be in hot standby mode
standby
server must be in hot standby mode
prefer-standby
first try to find a standby server, but if none of the listed hosts is a standby server, try again in
any
mode
load_balance_hosts
Controls the order in which the client tries to connect to the available hosts and addresses. Once a connection attempt is successful no other hosts and addresses will be tried. This parameter is typically used in combination with multiple host names or a DNS record that returns multiple IPs. This parameter can be used in combination with
target_session_attrs
to, for example, load balance over standby servers only. Once successfully connected, subsequent queries on the returned connection will all be sent to the same server. There are currently two modes:
disable
(default)
No load balancing across hosts is performed. Hosts are tried in the order in which they are provided and addresses are tried in the order they are received from DNS or a hosts file.
random
Hosts and addresses are tried in random order. This value is mostly useful when opening multiple connections at the same time, possibly from different machines. This way connections can be load balanced across multiple
PostgreSQL
servers.
While random load balancing, due to its random nature, will almost never result in a completely uniform distribution, it statistically gets quite close. One important aspect here is that this algorithm uses two levels of random choices: First the hosts will be resolved in random order. Then secondly, before resolving the next host, all resolved addresses for the current host will be tried in random order. This behaviour can skew the amount of connections each node gets greatly in certain cases, for instance when some hosts resolve to more addresses than others. But such a skew can also be used on purpose, e.g. to increase the number of connections a larger server gets by providing its hostname multiple times in the host string.
When using this value it's recommended to also configure a reasonable value for
connect_timeout
. Because then, if one of the nodes that are used for load balancing is not responding, a new node will be tried.
oauth_issuer
The HTTPS URL of a trusted issuer to contact if the server requests an OAuth token for the connection. This parameter is required for all OAuth connections; it should exactly match the
issuer
setting in
the server's HBA configuration
As part of the standard authentication handshake,
libpq
will ask the server for a
discovery document:
a URL providing a set of OAuth configuration parameters. The server must provide a URL that is directly constructed from the components of the
oauth_issuer
, and this value must exactly match the issuer identifier that is declared in the discovery document itself, or the connection will fail. This is required to prevent a class of
"mix-up attacks"
on OAuth clients.
You may also explicitly set
oauth_issuer
to the
/.well-known/
URI used for OAuth discovery. In this case, if the server asks for a different URL, the connection will fail, but a
custom OAuth flow
may be able to speed up the standard handshake by using previously cached tokens. (In this case, it is recommended that
oauth_scope
be set as well, since the client will not have a chance to ask the server for a correct scope setting, and the default scopes for a token may not be sufficient to connect.)
libpq
currently supports the following well-known endpoints:
Warning
Issuers are highly privileged during the OAuth connection handshake. As a rule of thumb, if you would not trust the operator of a URL to handle access to your servers, or to impersonate you directly, that URL should not be trusted as an
oauth_issuer
oauth_client_id
An OAuth 2.0 client identifier, as issued by the authorization server. If the
PostgreSQL
server
requests an OAuth token
for the connection (and if no
custom OAuth hook
is installed to provide one), then this parameter must be set; otherwise, the connection will fail.
oauth_client_secret
The client password, if any, to use when contacting the OAuth authorization server. Whether this parameter is required or not is determined by the OAuth provider; "public" clients generally do not use a secret, whereas "confidential" clients generally do.
oauth_scope
The scope of the access request sent to the authorization server, specified as a (possibly empty) space-separated list of OAuth scope identifiers. This parameter is optional and intended for advanced usage.
Usually the client will obtain appropriate scope settings from the
PostgreSQL
server. If this parameter is used, the server's requested scope list will be ignored. This can prevent a less-trusted server from requesting inappropriate access scopes from the end user. However, if the client's scope setting does not contain the server's required scopes, the server is likely to reject the issued token, and the connection will fail.
The meaning of an empty scope list is provider-dependent. An OAuth authorization server may choose to issue a token with "default scope", whatever that happens to be, or it may reject the token request entirely.