20.1. 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 double-quoted. Quoting one of the keywords in a database, user, or address field (e.g., all or replication) makes the word lose its special meaning, and just match a database, user, or host 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
localdatabaseuserauth-method[auth-options] hostdatabaseuseraddressauth-method[auth-options] hostssldatabaseuseraddressauth-method[auth-options] hostnossldatabaseuseraddressauth-method[auth-options] hostdatabaseuserIP-addressIP-maskauth-method[auth-options] hostssldatabaseuserIP-addressIP-maskauth-method[auth-options] hostnossldatabaseuserIP-addressIP-maskauth-method[auth-options]
The meaning of the fields is as follows:
localThis record matches connection attempts using Unix-domain sockets. Without a record of this type, Unix-domain socket connections are disallowed.
hostThis record matches connection attempts made using TCP/IP.
hostrecords 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.hostsslThis 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 by setting the ssl configuration parameter (see Section 18.9 for more information). Otherwise, the
hostsslrecord is ignored except for logging a warning that it cannot match any connections.hostnosslThis record type has the opposite behavior of
hostssl; it only matches connection attempts made over TCP/IP that do not use SSL.databaseSpecifies which database name(s) this record matches. The value
allspecifies that it matches all databases. The valuesameuserspecifies that the record matches if the requested database has the same name as the requested user. The valuesamerolespecifies that the requested user must be a member of the role with the same name as the requested database. (samegroupis an obsolete but still accepted spelling ofsamerole.) Superusers are not considered to be members of a role for the purposes ofsameroleunless they are explicitly members of the role, directly or indirectly, and not just by virtue of being a superuser. The valuereplicationspecifies that the record matches if a physical 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@.userSpecifies which database user name(s) this record matches. The value
allspecifies 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.) For this purpose, a superuser is only considered to be a member of a role if they are explicitly a member of the role, directly or indirectly, and not just by virtue of being a superuser. 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@.addressSpecifies the client machine address(es) that this record matches. This field can contain either a host name, an IP address range, or one of the special key words mentioned below.
An IP address range is specified using standard numeric notation for the range's starting address, then a slash (
/) and a CIDR mask length. The mask length indicates the number of high-order bits of the client IP address that must match. Bits to the right of this should be zero in the given IP address. There must not be any white space between the IP address, the/, and the CIDR mask length.Typical examples of an IPv4 address range specified this way are
172.20.143.89/32for a single host, or172.20.143.0/24for a small network, or10.6.0.0/16for a larger one. An IPv6 address range might look like::1/128for a single host (in this case the IPv6 loopback address) orfe80::7a31:c1ff:0000:0000/96for a small network.0.0.0.0/0represents all IPv4 addresses, and::0/0represents all IPv6 addresses. To specify a single host, use a mask length of 32 for IPv4 or 128 for IPv6. In a network address, do not omit trailing zeroes.An entry given in IPv4 format will match only IPv4 connections, and 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.
You can also write
allto match any IP address,samehostto match any of the server's own IP addresses, orsamenetto match any address in any subnet that the server is directly connected to.If a host name is specified (anything that is not an IP address range or a special key word is treated as a host name), that name is compared with the result of a reverse name resolution of the client's IP address (e.g., reverse DNS lookup, if DNS is used). Host name comparisons are case insensitive. If there is a match, then a forward name resolution (e.g., forward DNS lookup) is performed on the host name to check whether any of the addresses it resolves to are equal to the client's IP address. If both directions match, then the entry is considered to match. (The host name that is used in
pg_hba.confshould be the one that address-to-name resolution of the client's IP address returns, otherwise the line won't be matched. Some host name databases allow associating an IP address with multiple host names, but the operating system will only return one host name when asked to resolve an IP address.)A host name specification that starts with a dot (
.) matches a suffix of the actual host name. So.example.comwould matchfoo.example.com(but not justexample.com).When host names are specified in
pg_hba.conf, you should make sure that name resolution is reasonably fast. It can be of advantage to set up a local name resolution cache such asnscd. Also, you may wish to enable the configuration parameterlog_hostnameto see the client's host name instead of the IP address in the log.This field only applies to
host,hostssl, andhostnosslrecords.Note
Users sometimes wonder why host names are handled in this seemingly complicated way, with two name resolutions including a reverse lookup of the client's IP address. This complicates use of the feature in case the client's reverse DNS entry is not set up or yields some undesirable host name. It is done primarily for efficiency: this way, a connection attempt requires at most two resolver lookups, one reverse and one forward. If there is a resolver problem with some address, it becomes only that client's problem. A hypothetical alternative implementation that only did forward lookups would have to resolve every host name mentioned in
pg_hba.confduring every connection attempt. That could be quite slow if many names are listed. And if there is a resolver problem with one of the host names, it becomes everyone's problem.Also, a reverse lookup is necessary to implement the suffix matching feature, because the actual client host name needs to be known in order to match it against the pattern.
Note that this behavior is consistent with other popular implementations of host name-based access control, such as the Apache HTTP Server and TCP Wrappers.
IP-addressIP-maskThese two fields can be used as an alternative to the
IP-address/mask-lengthnotation. Instead of specifying the mask length, the actual mask is specified in a separate column. For example,255.0.0.0represents an IPv4 CIDR mask length of 8, and255.255.255.255represents a CIDR mask length of 32.These fields only apply to
host,hostssl, andhostnosslrecords.auth-methodSpecifies the authentication method to use when a connection matches this record. The possible choices are summarized here; details are in Section 20.3. All the options are lower case and treated case sensitively, so even acronyms like
ldapmust be specified as lower case.trustAllow 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 20.3.1 for details.
rejectReject the connection unconditionally. This is useful for “filtering out” certain hosts from a group, for example a
rejectline could block a specific host from connecting, while a later line allows the remaining hosts in a specific network to connect.scram-sha-256Perform SCRAM-SHA-256 authentication to verify the user's password. See Section 20.3.2 for details.
md5Perform SCRAM-SHA-256 or MD5 authentication to verify the user's password. See Section 20.3.2 for details.
passwordRequire 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 20.3.2 for details.
gssUse GSSAPI to authenticate the user. This is only available for TCP/IP connections. See Section 20.3.3 for details.
sspiUse SSPI to authenticate the user. This is only available on Windows. See Section 20.3.4 for details.
identObtain the operating system user name of the client by contacting the ident server on the client and check if it matches the requested database user name. Ident authentication can only be used on TCP/IP connections. When specified for local connections, peer authentication will be used instead. See Section 20.3.5 for details.
peerObtain the client's operating system user name from the operating system and check if it matches the requested database user name. This is only available for local connections. See Section 20.3.6 for details.
ldapAuthenticate using an LDAP server. See Section 20.3.7 for details.
radiusAuthenticate using a RADIUS server. See Section 20.3.8 for details.
certAuthenticate using SSL client certificates. See Section 20.3.9 for details.
pamAuthenticate using the Pluggable Authentication Modules (PAM) service provided by the operating system. See Section 20.3.10 for details.
bsdAuthenticate using the BSD Authentication service provided by the operating system. See Section 20.3.11 for details.
auth-optionsAfter the
auth-methodfield, there can be field(s) of the formname=valuethat specify options for the authentication method. Details about which options are available for which authentication methods appear below.In addition to the method-specific options listed below, there is one method-independent authentication option
clientcert, which can be specified in anyhostsslrecord. When set to1, this option requires the client to present a valid (trusted) SSL certificate, in addition to the other requirements of the authentication method.
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, calling the SQL function pg_reload_conf(), or using kill -HUP) to make it re-read the file.
Note
The preceding statement is not true on Microsoft Windows: there, any changes in the pg_hba.conf file are immediately applied by subsequent new connections.
The system view pg_hba_file_rules can be helpful for pre-testing changes to the pg_hba.conf file, or for diagnosing problems if loading of the file did not have the desired effects. Rows in the view with non-null error fields indicate problems in the corresponding lines of 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 Example 20.1. See the next section for details on the different authentication methods.
Example 20.1. 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 ADDRESS METHOD local all all trust # The same using local loopback TCP/IP connections. # # TYPE DATABASE USER 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 # The same over IPv6. # # TYPE DATABASE USER ADDRESS METHOD host all all ::1/128 trust # The same using a host name (would typically cover both IPv4 and IPv6). # # TYPE DATABASE USER ADDRESS METHOD host all all localhost 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 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 ADDRESS METHOD host postgres all 192.168.12.10/32 scram-sha-256 # Allow any user from hosts in the example.com domain to connect to # any database if the user's password is correctly supplied. # # Require SCRAM authentication for most users, but make an exception # for user 'mike', who uses an older client that doesn't support SCRAM # authentication. # # TYPE DATABASE USER ADDRESS METHOD host all mike .example.com md5 host all all .example.com scram-sha-256 # 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 GSSAPI 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 ADDRESS METHOD host all all 192.168.54.1/32 reject host all all 0.0.0.0/0 gss # 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 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 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