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. The entry
0.0.0.0
allows listening for all IPv4 addresses and
::
allows listening for all IPv6 addresses.
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. If the list is not empty, the server will start if it
can listen on at least one TCP/IP address. A warning will be
emitted for any TCP/IP address which cannot be opened.
The default value is localhost,
which allows only local TCP/IP “loopback” connections to be
made.
While client authentication (Chapter 21) allows fine-grained control
over who can access the server, listen_addresses
controls which interfaces accept connection attempts, which
can help prevent repeated malicious connection requests on
insecure network interfaces. 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.
When running a standby server, you must set this parameter to the same or higher value than on the primary server. Otherwise, queries will not be allowed in the standby server.
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, and no
new replication connections will be accepted.
The default value is three connections. The value must be less
than max_connections
.
This parameter can only be set at server start.
unix_socket_directories
(string
)
Specifies the directory of the Unix-domain socket(s) on which the server is to listen for connections from client applications. Multiple sockets can be created by listing multiple directories separated by commas. Whitespace between entries is ignored; surround a directory name with double quotes if you need to include whitespace or commas in the name. An empty value specifies not listening on any Unix-domain sockets, in which case only TCP/IP sockets can be used to connect to the server.
A value that starts with @
specifies that a
Unix-domain socket in the abstract namespace should be created
(currently supported on Linux only). In that case, this value
does not specify a “directory” but a prefix from which
the actual socket name is computed in the same manner as for the
file-system namespace. While the abstract socket name prefix can be
chosen freely, since it is not a file-system location, the convention
is to nonetheless use file-system-like values such as
@/tmp
.
The default value is normally
/tmp
, but that can be changed at build time.
On Windows, the default is empty, which means no Unix-domain socket is
created by default.
This parameter can only be set at server start.
In addition to the socket file itself, which is named
.s.PGSQL.
where
nnnn
nnnn
is the server's port number, an ordinary file
named .s.PGSQL.
will be
created in each of the nnnn
.lockunix_socket_directories
directories.
Neither file should ever be removed manually.
For sockets in the abstract namespace, no lock file is created.
unix_socket_group
(string
)
Sets the owning group of the Unix-domain socket(s). (The owning
user of the sockets 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 uses the default
group of the server user. This parameter can only be set at
server start.
This parameter is not supported on Windows. Any setting will be ignored. Also, sockets in the abstract namespace have no file owner, so this setting is also ignored in that case.
unix_socket_permissions
(integer
)
Sets the access permissions of the Unix-domain socket(s). Unix-domain
sockets use the usual Unix file system permission set.
The parameter value is expected to be a numeric mode
specified in the format 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, 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 21.
This parameter can only be set at server start.
This parameter is irrelevant on systems, notably Solaris as of Solaris
10, that ignore socket permissions entirely. There, one can achieve a
similar effect by pointing unix_socket_directories
to a
directory having search permission limited to the desired audience.
Sockets in the abstract namespace have no file permissions, so this setting is also ignored in that case.
bonjour
(boolean
)
Enables advertising the server's existence via Bonjour. The default is off. This parameter can only be set at server start.
bonjour_name
(string
)
Specifies the Bonjour service
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
)
Specifies the amount of time with no network activity after which
the operating system should send a TCP keepalive message to the client.
If this value is specified without units, it is taken as seconds.
A value of 0 (the default) selects the operating system's default.
This parameter is supported only on systems that support
TCP_KEEPIDLE
or an equivalent socket option, and on
Windows; on other systems, it must be zero.
In sessions connected via a Unix-domain socket, this parameter is
ignored and always reads as zero.
On Windows, setting a value of 0 will set this parameter to 2 hours, since Windows does not provide a way to read the system default value.
tcp_keepalives_interval
(integer
)
Specifies the amount of time after which a TCP keepalive message
that has not been acknowledged by the client should be retransmitted.
If this value is specified without units, it is taken as seconds.
A value of 0 (the default) selects the operating system's default.
This parameter is supported only on systems that support
TCP_KEEPINTVL
or an equivalent socket option, and on
Windows; on other systems, it must be zero.
In sessions connected via a Unix-domain socket, this parameter is
ignored and always reads as zero.
On Windows, setting a value of 0 will set this parameter to 1 second, since Windows does not provide a way to read the system default value.
tcp_keepalives_count
(integer
)
Specifies the number of TCP keepalive messages that can be lost before
the server's connection to the client is considered dead.
A value of 0 (the default) selects the operating system's default.
This parameter is supported only on systems that support
TCP_KEEPCNT
or an equivalent socket option;
on other systems, it must be zero.
In sessions connected via a Unix-domain socket, this parameter is
ignored and always reads as zero.
This parameter is not supported on Windows, and must be zero.
tcp_user_timeout
(integer
)
Specifies the amount of time that transmitted data may
remain unacknowledged before the TCP connection is forcibly closed.
If this value is specified without units, it is taken as milliseconds.
A value of 0 (the default) selects the operating system's default.
This parameter is supported only on systems that support
TCP_USER_TIMEOUT
; on other systems, it must be zero.
In sessions connected via a Unix-domain socket, this parameter is
ignored and always reads as zero.
This parameter is not supported on Windows, and must be zero.
client_connection_check_interval
(integer
)
Sets the time interval between optional checks that the client is still connected, while running queries. The check is performed by polling the socket, and allows long running queries to be aborted sooner if the kernel reports that the connection is closed.
This option is currently available only on systems that support the
non-standard POLLRDHUP
extension to the
poll
system call, including Linux.
If the value is specified without units, it is taken as milliseconds.
The default value is 0
, which disables connection
checks. Without connection checks, the server will detect the loss of
the connection only at the next interaction with the socket, when it
waits for, receives or sends data.
For the kernel itself to detect lost TCP connections reliably and within a known timeframe in all scenarios including network failure, it may also be necessary to adjust the TCP keepalive settings of the operating system, or the tcp_keepalives_idle, tcp_keepalives_interval and tcp_keepalives_count settings of PostgreSQL.
authentication_timeout
(integer
)
Maximum amount of time allowed to complete client authentication. If a
would-be client has not completed the authentication protocol in
this much time, the server closes the connection. This prevents
hung clients from occupying a connection indefinitely.
If this value is specified without units, it is taken as seconds.
The default is one minute (1m
).
This parameter can only be set in the postgresql.conf
file or on the server command line.
password_encryption
(enum
)
When a password is specified in CREATE ROLE or
ALTER ROLE, this parameter determines the
algorithm to use to encrypt the password. Possible values are
scram-sha-256
, which will encrypt the password with
SCRAM-SHA-256, and md5
, which stores the password
as an MD5 hash. The default is scram-sha-256
.
Note that older clients might lack support for the SCRAM authentication mechanism, and hence not work with passwords encrypted with SCRAM-SHA-256. See Section 21.5 for more details.
krb_server_keyfile
(string
)
Sets the location of the server's Kerberos key file. The default is
FILE:/usr/local/pgsql/etc/krb5.keytab
(where the directory part is whatever was specified
as sysconfdir
at build time; use
pg_config --sysconfdir
to determine that).
If this parameter is set to an empty string, it is ignored and a
system-dependent default is used.
This parameter can only be set in the
postgresql.conf
file or on the server command line.
See Section 21.6 for more information.
krb_caseins_users
(boolean
)
Sets whether 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, e.g., joe@
. 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
.
This feature is intended as a temporary measure until a complete solution is found. At that time, this option will be removed.
See Section 19.9 for more information about setting up SSL.
ssl
(boolean
)
Enables SSL connections.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is off
.
ssl_ca_file
(string
)
Specifies the name of the file containing the SSL server certificate
authority (CA).
Relative paths are relative to the data directory.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is empty, meaning no CA file is loaded,
and client certificate verification is not performed.
ssl_cert_file
(string
)
Specifies the name of the file containing the SSL server certificate.
Relative paths are relative to the data directory.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is server.crt
.
ssl_crl_file
(string
)
Specifies the name of the file containing the SSL client certificate
revocation list (CRL).
Relative paths are relative to the data directory.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is empty, meaning no CRL file is loaded (unless
ssl_crl_dir is set).
ssl_crl_dir
(string
)
Specifies the name of the directory containing the SSL client
certificate revocation list (CRL). Relative paths are relative to the
data directory. This parameter can only be set in
the postgresql.conf
file or on the server command
line. The default is empty, meaning no CRLs are used (unless
ssl_crl_file is set).
The directory needs to be prepared with the
OpenSSL command
openssl rehash
or c_rehash
. See
its documentation for details.
When using this setting, CRLs in the specified directory are loaded on-demand at connection time. New CRLs can be added to the directory and will be used immediately. This is unlike ssl_crl_file, which causes the CRL in the file to be loaded at server start time or when the configuration is reloaded. Both settings can be used together.
ssl_key_file
(string
)
Specifies the name of the file containing the SSL server private key.
Relative paths are relative to the data directory.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is server.key
.
ssl_ciphers
(string
)
Specifies a list of SSL cipher suites that are
allowed to be used by SSL connections. See the
ciphers
manual page in the OpenSSL package for the
syntax of this setting and a list of supported values. Only
connections using TLS version 1.2 and lower are affected. There is
currently no setting that controls the cipher choices used by TLS
version 1.3 connections. The default value is
HIGH:MEDIUM:+3DES:!aNULL
. The default is usually a
reasonable choice unless you have specific security requirements.
This parameter can only be set in the
postgresql.conf
file or on the server command
line.
Explanation of the default value:
HIGH
Cipher suites that use ciphers from HIGH
group (e.g.,
AES, Camellia, 3DES)
MEDIUM
Cipher suites that use ciphers from MEDIUM
group
(e.g., RC4, SEED)
+3DES
The OpenSSL default order for
HIGH
is problematic because it orders 3DES
higher than AES128. This is wrong because 3DES offers less
security than AES128, and it is also much slower.
+3DES
reorders it after all other
HIGH
and MEDIUM
ciphers.
!aNULL
Disables anonymous cipher suites that do no authentication. Such cipher suites are vulnerable to MITM attacks and therefore should not be used.
Available cipher suite details will vary across
OpenSSL versions. Use the command
openssl ciphers -v 'HIGH:MEDIUM:+3DES:!aNULL'
to
see actual details for the currently installed
OpenSSL version. Note that this list is
filtered at run time based on the server key type.
ssl_prefer_server_ciphers
(boolean
)
Specifies whether to use the server's SSL cipher preferences, rather
than the client's.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is on
.
Older PostgreSQL versions do not have this setting and always use the client's preferences. This setting is mainly for backward compatibility with those versions. Using the server's preferences is usually better because it is more likely that the server is appropriately configured.
ssl_ecdh_curve
(string
)
Specifies the name of the curve to use in ECDH key
exchange. It needs to be supported by all clients that connect.
It does not need to be the same curve used by the server's Elliptic
Curve key.
This parameter can only be set in the postgresql.conf
file or on the server command line.
The default is prime256v1
.
OpenSSL names for the most common curves
are:
prime256v1
(NIST P-256),
secp384r1
(NIST P-384),
secp521r1
(NIST P-521).
The full list of available curves can be shown with the command
openssl ecparam -list_curves
. Not all of them
are usable in TLS though.
ssl_min_protocol_version
(enum
)
Sets the minimum SSL/TLS protocol version to use. Valid values are
currently: TLSv1
, TLSv1.1
,
TLSv1.2
, TLSv1.3
. Older
versions of the OpenSSL library do not
support all values; an error will be raised if an unsupported setting
is chosen. Protocol versions before TLS 1.0, namely SSL version 2 and
3, are always disabled.
The default is TLSv1.2
, which satisfies industry
best practices as of this writing.
This parameter can only be set in the postgresql.conf
file or on the server command line.
ssl_max_protocol_version
(enum
)
Sets the maximum SSL/TLS protocol version to use. Valid values are as for ssl_min_protocol_version, with addition of an empty string, which allows any protocol version. The default is to allow any version. Setting the maximum protocol version is mainly useful for testing or if some component has issues working with a newer protocol.
This parameter can only be set in the postgresql.conf
file or on the server command line.
ssl_dh_params_file
(string
)
Specifies the name of the file containing Diffie-Hellman parameters
used for so-called ephemeral DH family of SSL ciphers. The default is
empty, in which case compiled-in default DH parameters used. Using
custom DH parameters reduces the exposure if an attacker manages to
crack the well-known compiled-in DH parameters. You can create your own
DH parameters file with the command
openssl dhparam -out dhparams.pem 2048
.
This parameter can only be set in the postgresql.conf
file or on the server command line.
ssl_passphrase_command
(string
)
Sets an external command to be invoked when a passphrase for decrypting an SSL file such as a private key needs to be obtained. By default, this parameter is empty, which means the built-in prompting mechanism is used.
The command must print the passphrase to the standard output and exit
with code 0. In the parameter value, %p
is
replaced by a prompt string. (Write %%
for a
literal %
.) Note that the prompt string will
probably contain whitespace, so be sure to quote adequately. A single
newline is stripped from the end of the output if present.
The command does not actually have to prompt the user for a passphrase. It can read it from a file, obtain it from a keychain facility, or similar. It is up to the user to make sure the chosen mechanism is adequately secure.
This parameter can only be set in the postgresql.conf
file or on the server command line.
ssl_passphrase_command_supports_reload
(boolean
)
This parameter determines whether the passphrase command set by
ssl_passphrase_command
will also be called during a
configuration reload if a key file needs a passphrase. If this
parameter is off (the default), then
ssl_passphrase_command
will be ignored during a
reload and the SSL configuration will not be reloaded if a passphrase
is needed. That setting is appropriate for a command that requires a
TTY for prompting, which might not be available when the server is
running. Setting this parameter to on might be appropriate if the
passphrase is obtained from a file, for example.
This parameter can only be set in the postgresql.conf
file or on the server command line.