When a client application connects to the database server, it
specifies which PostgreSQL user name it
wants to connect as, much the same way one logs into a Unix computer
as a particular user. Within the SQL environment the active database
user name determines access privileges to database objects -- see
Chapter 4 for more information. Therefore, it is
essential to restrict which database users can connect.
Client authentication is controlled by the file
pg_hba.conf in the data directory, e.g.,
/usr/local/pgsql/data/pg_hba.conf.
(HBA stands for host-based authentication.) A default
pg_hba.conf file is installed when the data
directory is initialized by initdb.
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. 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. Records
cannot be continued across lines.
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 may have one of the three formats
local database user authentication-method [authentication-option]
host database user IP-address IP-mask authentication-method [authentication-option]
hostssl database user IP-address IP-mask authentication-method [authentication-option]
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 using TCP/IP networks.
Note that TCP/IP connections are disabled unless the server is
started with the -i option or the
tcpip_socket postgresql.conf
configuration parameter is enabled.
- hostssl
This record matches connection attempts using SSL over TCP/IP.
host records will match either SSL or
non-SSL connection attempts, but hostssl
records require SSL connections.
To be able make use of this option the server must be built
with SSL support enabled. Furthermore, SSL must be enabled by
enabling the option ssl in
postgresql.conf (see Section 3.4).
- database
Specifies which databases 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 samegroup specifies that
the requested user must a member of the group with the same
name as the requested database. Otherwise, this is the name of
a specific PostgreSQL database.
Multiple database names can be supplied by separating them with
commas. A file containing database names can be specified by
preceding the file name with @. The file must be in
the same directory as pg_hba.conf.
- user
Specifies which PostgreSQL users this record matches. The value
all specifies that it matches all users.
Otherwise, this is the name of a specific
PostgreSQL user. Multiple user names
can be supplied by separating them with commas. Group names can
be specified by preceding the group name with +. A
file containing user names can be specified by preceding the
file name with @. The file must be in the same
directory as pg_hba.conf.
- IP-address
IP-mask These two fields contain IP address/mask values in standard
dotted decimal notation. (IP addresses can only be specified
numerically, not as domain or host names.) Taken together they
specify the client machine IP addresses that this record
matches. The precise logic is that
must be zero for the record to match. (Of course IP addresses
can be spoofed but this consideration is beyond the scope of
PostgreSQL.)
These fields only apply to host and
hostssl records.
- authentication-method
Specifies the authentication method to use when connecting via
this record. The possible choices are summarized here; details
are in Section 6.2.
- trust
The connection is allowed unconditionally. This method
allows anyone that can connect to the
PostgreSQL database to login as
any PostgreSQL user they like,
without the need for a password. See Section 6.2.1 for details.
- reject
The connection is rejected unconditionally. This is useful for
"filtering out" certain hosts from a group.
- md5
Requires the client to supply an MD5 encrypted password for
authentication. This is the only method that allows encrypted
passwords to be stored in pg_shadow.
See Section 6.2.2 for details.
- crypt
Like md5 method but uses older crypt
encryption, which is needed for pre-7.2 clients.
md5 is preferred for 7.2 and later clients.
See Section 6.2.2 for details.
- password
Same as "md5", but the password is sent in clear text over the
network. This should not be used on untrusted networks.
See Section 6.2.2 for details.
- krb4
Kerberos V4 is used to authenticate the user. This is only
available for TCP/IP connections. See Section 6.2.3 for details.
- krb5
Kerberos V5 is used to authenticate the user. This is only
available for TCP/IP connections. See Section 6.2.3 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 the user is allowed to
connect as the requested database user by consulting the map
specified after the ident key word.
If you use the map sameuser, the user
names are assumed to be identical. If not, the map name is
looked up in the file pg_ident.conf
in the same directory as pg_hba.conf.
The connection is accepted if that file contains an
entry for this map name with the ident-supplied user name
and the requested PostgreSQL user
name.
For local connections, this only works on machines that
support Unix-domain socket credentials (currently
Linux, FreeBSD, NetBSD,
and BSD/OS).
See Section 6.2.4 below for details.
- pam
Authenticate using the Pluggable Authentication Modules
(PAM) service provided by the operating system. See Section 6.2.5 for details.
- authentication-option
The meaning of this optional field depends on the chosen
authentication method and is described in the next section.
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 connections but require a password for
remote TCP 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.
Important: Do not prevent the superuser from accessing the template1
database. Various utility commands need access to template1.
The pg_hba.conf file is read on start-up and when
the postmaster 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.
An example of a pg_hba.conf file is shown in
Example 6-1. See below for details on the
different authentication methods.
Example 6-1. An example pg_hba.conf file
# Allow any user on the local system to connect to any database under
# any user name using Unix-domain sockets (the default for local
# connections).
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
local all all trust
# The same using local loopback TCP/IP connections.
#
# 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 "template1" as the same user name that ident reports for
# the connection (typically the Unix user name).
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host template1 all 192.168.93.0 255.255.255.0 ident sameuser
# Allow a user from host 192.168.12.10 to connect to database
# "template1" if the user's password is correctly supplied.
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host template1 all 192.168.12.10 255.255.255.255 md5
# In the absence of preceding "host" lines, these two lines will
# reject all connection from 192.168.54.1 (since that entry will be
# matched first), but allow Kerberos V connections from anywhere else
# on the Internet. The zero mask means that no bits of the host IP
# address are considered so it matches any host.
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host all all 192.168.54.1 255.255.255.255 reject
host all all 0.0.0.0 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 IP-ADDRESS IP-MASK METHOD
host all all 192.168.0.0 255.255.0.0 ident 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 user name) except for administrators and
# members of group "support" who may connect to all databases. The file
# $PGDATA/admins contains a list of user names. Passwords are required in
# all cases.
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK 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, but not groups:
local db1,db2,@demodbs all md5
