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5.1 The pg_hba.conf file

Client authentication is controlled by a configuration file, which traditionally is named ‘pg_hba.conf’ and is stored in the database cluster's data directory. (HBA stands for host-based authentication.) A default ‘pg_hba.conf’ file is installed when the data directory is initialized by initdb. It is possible to place the authentication configuration file elsewhere, however; see the hba_file configuration parameter.

The general format of the ‘pg_hba.conf’ file is a set of records, one per line. Blank lines are ignored, as is any text after the # comment character. Records cannot be continued across lines. A record is made up of a number of fields which are separated by spaces and/or tabs. Fields can contain white space if the field value is quoted. Quoting one of the keywords in a database or user name field (e.g., all or replication) makes the word lose its special character, and just match a database or user with that name.

Each record specifies a connection type, a client IP address range (if relevant for the connection type), a database name, a user name, and the authentication method to be used for connections matching these parameters. The first record with a matching connection type, client address, requested database, and user name is used to perform authentication. There is no “fall-through” or “backup”: if one record is chosen and the authentication fails, subsequent records are not considered. If no record matches, access is denied.

A record can have one of the seven formats

local      database  user  auth-method  [auth-options]
host       database  user  CIDR-address  auth-method  [auth-options]
hostssl    database  user  CIDR-address  auth-method  [auth-options]
hostnossl  database  user  CIDR-address  auth-method  [auth-options]
host       database  user  IP-address  IP-mask  auth-method  [auth-options]
hostssl    database  user  IP-address  IP-mask  auth-method  [auth-options]
hostnossl  database  user  IP-address  IP-mask  auth-method  [auth-options]

The meaning of the fields is as follows:

local

This record matches connection attempts using Unix-domain sockets. Without a record of this type, Unix-domain socket connections are disallowed.

host

This record matches connection attempts made using TCP/IP. host records match either SSL or non-SSL connection attempts.

Note: Remote TCP/IP connections will not be possible unless the server is started with an appropriate value for the listen_addresses configuration parameter, since the default behavior is to listen for TCP/IP connections only on the local loopback address localhost.

hostssl

This record matches connection attempts made using TCP/IP, but only when the connection is made with SSL encryption. To make use of this option the server must be built with SSL support. Furthermore, SSL must be enabled at server start time by setting the ssl configuration parameter (see section 3.8 Secure TCP/IP Connections with SSL for more information).

hostnossl

This record type has the opposite behavior of hostssl; it only matches connection attempts made over TCP/IP that do not use SSL.

database

Specifies which database name(s) this record matches. The value all specifies that it matches all databases. The value sameuser specifies that the record matches if the requested database has the same name as the requested user. The value samerole specifies that the requested user must be a member of the role with the same name as the requested database. (samegroup is an obsolete but still accepted spelling of samerole.) The value replication specifies that the record matches if a replication connection is requested (note that replication connections do not specify any particular database). Otherwise, this is the name of a specific PostgreSQL database. Multiple database names can be supplied by separating them with commas. A separate file containing database names can be specified by preceding the file name with @.

user

Specifies which database user name(s) this record matches. The value all specifies that it matches all users. Otherwise, this is either the name of a specific database user, or a group name preceded by +. (Recall that there is no real distinction between users and groups in PostgreSQL; a + mark really means “match any of the roles that are directly or indirectly members of this role”, while a name without a + mark matches only that specific role.) Multiple user names can be supplied by separating them with commas. A separate file containing user names can be specified by preceding the file name with @.

CIDR-address

Specifies the client machine IP address range that this record matches. This field contains an IP address in standard dotted decimal notation and a CIDR mask length. (IP addresses can only be specified numerically, not as domain or host names.) The mask length indicates the number of high-order bits of the client IP address that must match. Bits to the right of this must be zero in the given IP address. There must not be any white space between the IP address, the /, and the CIDR mask length. Instead of a CIDR-address, you can write samehost to match any of the server's own IP addresses, or samenet to match any address in any subnet that the server is directly connected to. Typical examples of a CIDR-address are 172.20.143.89/32 for a single host, or 172.20.143.0/24 for a small network, or 10.6.0.0/16 for a larger one. 0.0.0.0/0 (“all balls”) represents all addresses. To specify a single host, use a CIDR mask of 32 for IPv4 or 128 for IPv6. In a network address, do not omit trailing zeroes. An IP address given in IPv4 format will match IPv6 connections that have the corresponding address, for example 127.0.0.1 will match the IPv6 address ::ffff:127.0.0.1. An entry given in IPv6 format will match only IPv6 connections, even if the represented address is in the IPv4-in-IPv6 range. Note that entries in IPv6 format will be rejected if the system's C library does not have support for IPv6 addresses. This field only applies to host, hostssl, and hostnossl records.

IP-address

IP-mask

These fields can be used as an alternative to the CIDR-address notation. Instead of specifying the mask length, the actual mask is specified in a separate column. For example, 255.0.0.0 represents an IPv4 CIDR mask length of 8, and 255.255.255.255 represents a CIDR mask length of 32. These fields only apply to host, hostssl, and hostnossl records.

auth-method

Specifies the authentication method to use when a connection matches this record. The possible choices are summarized here; details are in section 5.3 Authentication methods.

trust

Allow the connection unconditionally. This method allows anyone that can connect to the PostgreSQL database server to login as any PostgreSQL user they wish, without the need for a password or any other authentication. See section 5.3.1 Trust authentication for details.

reject

Reject the connection unconditionally. This is useful for “filtering out” certain hosts from a group, for example a reject line could block a specific host from connecting, while a later line allows the remaining hosts in a specific network to connect.

md5

Require the client to supply an MD5-encrypted password for authentication. See section 5.3.2 Password authentication for details.

password

Require the client to supply an unencrypted password for authentication. Since the password is sent in clear text over the network, this should not be used on untrusted networks. See section 5.3.2 Password authentication for details.

gss

Use GSSAPI to authenticate the user. This is only available for TCP/IP connections. See section 5.3.3 GSSAPI authentication for details.

sspi

Use SSPI to authenticate the user. This is only available on Windows. See section 5.3.4 SSPI authentication for details.

krb5

Use Kerberos V5 to authenticate the user. This is only available for TCP/IP connections. See section 5.3.5 Kerberos authentication for details.

ident

Obtain the operating system user name of the client (for TCP/IP connections by contacting the ident server on the client, for local connections by getting it from the operating system) and check if it matches the requested database user name. See section 5.3.6 Ident-based authentication for details.

ldap

Authenticate using an LDAP server. See section 5.3.7 LDAP authentication for details.

radius

Authenticate using a RADIUS server. See section 5.3.8 RADIUS authentication for details.

cert

Authenticate using SSL client certificates. See section 5.3.9 Certificate authentication for details.

pam

Authenticate using the Pluggable Authentication Modules (PAM) service provided by the operating system. See section 5.3.10 PAM authentication for details.

auth-options

After the auth-method field, there can be field(s) of the form name=value that specify options for the authentication method. Details about which options are available for which authentication methods appear below.

Files included by @ constructs are read as lists of names, which can be separated by either whitespace or commas. Comments are introduced by #, just as in ‘pg_hba.conf’, and nested @ constructs are allowed. Unless the file name following @ is an absolute path, it is taken to be relative to the directory containing the referencing file.

Since the ‘pg_hba.conf’ records are examined sequentially for each connection attempt, the order of the records is significant. Typically, earlier records will have tight connection match parameters and weaker authentication methods, while later records will have looser match parameters and stronger authentication methods. For example, one might wish to use trust authentication for local TCP/IP connections but require a password for remote TCP/IP connections. In this case a record specifying trust authentication for connections from 127.0.0.1 would appear before a record specifying password authentication for a wider range of allowed client IP addresses.

The ‘pg_hba.conf’ file is read on start-up and when the main server process receives a SIGHUP signal. If you edit the file on an active system, you will need to signal the postmaster (using pg_ctl reload or kill -HUP) to make it re-read the file.

Tip: To connect to a particular database, a user must not only pass the ‘pg_hba.conf’ checks, but must have the CONNECT privilege for the database. If you wish to restrict which users can connect to which databases, it's usually easier to control this by granting/revoking CONNECT privilege than to put the rules in ‘pg_hba.conf’ entries.

Some examples of ‘pg_hba.conf’ entries are shown in section 5.1 The pg_hba.conf file. See the next section for details on the different authentication methods.

Example pg_hba.conf entries:

# Allow any user on the local system to connect to any
# database with any database user name using
# Unix-domain sockets (the default for local
# connections).
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
local   all             all                                     trust

# The same using local loopback TCP/IP connections.
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
host    all             all             127.0.0.1/32            trust

# The same as the previous line, but using a separate netmask column
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host all all 127.0.0.1 255.255.255.255 trust 

# Allow any user from any host with IP address 192.168.93.x to connect
# to database "postgres" as the same user name that ident reports for
# the connection (typically the operating system user name).
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
host    postgres        all             192.168.93.0/24         ident

# Allow any user from host 192.168.12.10 to connect to database
# "postgres" if the user's password is correctly supplied.
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
host    postgres        all             192.168.12.10/32        md5

# In the absence of preceding "host" lines, these two
# lines will reject all connections from 192.168.54.1
# (since that entry will be matched first), but allow
# Kerberos 5 connections from anywhere else on the
# Internet. The zero mask causes no bits of the host IP
# address to be considered, so it matches any host.
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
host    all             all             192.168.54.1/32         reject
host    all             all             0.0.0.0/0               krb5

# Allow users from 192.168.x.x hosts to connect to any
# database, if they pass the ident check. If, for
# example, ident says the user is "bryanh" and he
# requests to connect as PostgreSQL user "guest1", the
# connection is allowed if there is an entry in
# pg_ident.conf for map "omicron" that says "bryanh" is
# allowed to connect as "guest1".
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
host    all             all             192.168.0.0/16          ident map=omicron

# If these are the only three lines for local
# connections, they will allow local users to connect
# only to their own databases (databases with the same
# name as their database user name) except for
# administrators and members of role "support", who can
# connect to all databases. The file $PGDATA/admins
# contains a list of names of administrators. Passwords
# are required in all cases.
#
# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
local   sameuser        all                                     md5
local   all             @admins                                 md5
local   all             +support                                md5

# The last two lines above can be combined into a
# single line:
local   all             @admins,+support                        md5

# The database column can also use lists and file
# names:
local   db1,db2,@demodbs  all                                   md5