lt_hba.conf File
Client authentication is controlled by a configuration file,
which traditionally is named
lt_hba.conf and is stored in the database
cluster's data directory.
(HBA stands for host-based authentication.) A default
lt_hba.conf file is installed when the data
directory is initialized by lt_initdb. It is
possible to place the authentication configuration file elsewhere,
however; see the hba_file configuration parameter.
The general format of the lt_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 several 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.
host
This record matches connection attempts made using TCP/IP.
host records match
SSL or non-SSL connection
attempts.
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 17.9 for more information).
Otherwise, the hostssl record is ignored except for
logging a warning that it cannot match any connections.
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.)
Superusers are not considered to be members of a role for the
purposes of samerole unless they are explicitly
members of the role, directly or indirectly, and not just by
virtue of being a superuser.
The value replication specifies 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 LightDB 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 LightDB; 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
172.20.143.89/32 for a single host, or
172.20.143.0/24 for a small network, or
10.6.0.0/16 for a larger one.
An IPv6 address range might look like ::1/128
for a single host (in this case the IPv6 loopback address) or
fe80::7a31:c1ff:0000:0000/96 for a small
network.
0.0.0.0/0 represents all
IPv4 addresses, and ::0/0 represents
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 all to match any IP address,
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.
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 lt_hba.conf should 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.com would match
foo.example.com (but not just
example.com).
When host names are specified
in lt_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
as nscd. Also, you may wish to enable the
configuration parameter log_hostname to see
the client's host name instead of the IP address in the log.
These fields do not apply to local records.
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
lt_hba.conf during 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-mask
These two fields can be used as an alternative to the
IP-address/mask-length
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 do not apply to local records.
auth-methodSpecifies the authentication method to use when a connection matches this record. The possible choices are summarized here; details are in Section 19.3. All the options are lower case and treated case sensitively.
trustAllow the connection unconditionally. This method allows anyone that can connect to the LightDB database server to login as any LightDB user they wish, without the need for a password or any other authentication. See Section 19.4 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.
scram-sha-256Perform SCRAM-SHA-256 authentication to verify the user's password. See Section 19.5 for details.
md5Perform SCRAM-SHA-256 or MD5 authentication to verify the user's password. See Section 19.5 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 19.5 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 19.6 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 19.7 for details.
certAuthenticate using SSL client certificates. See Section 19.8 for details.
pamAuthenticate using the Pluggable Authentication Modules (PAM) service provided by the operating system. See Section 19.9 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.
In addition to the method-specific options listed below, there is one
method-independent authentication option clientcert, which
can be specified in any hostssl record.
This option can be set to verify-ca or
verify-full. Both options require the client
to present a valid (trusted) SSL certificate, while
verify-full additionally enforces that the
cn (Common Name) in the certificate matches
the username or an applicable mapping.
This behavior is similar to the cert authentication
method (see Section 19.8) but enables pairing
the verification of client certificates with any authentication
method that supports hostssl entries.
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
lt_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 lt_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 lt_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 lt_ctl reload, calling the SQL function
pg_reload_conf(), or using kill
-HUP) to make it re-read the file.
The system view
pg_hba_file_rules
can be helpful for pre-testing changes to the lt_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.
To connect to a particular database, a user must not only pass the
lt_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 lt_hba.conf entries.
Some examples of lt_hba.conf entries are shown in
Example 19.1. See the next section for details on the
different authentication methods.
Example 19.1. Example lt_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 three lines will # reject all connections from 192.168.54.1 (since that entry will be # matched first). The zero mask causes no bits of the host IP address to # be considered, so it matches any host. but only from 192.168.12.10. # # TYPE DATABASE USER ADDRESS METHOD host all all 192.168.54.1/32 reject # 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 LightDB user "guest1", the # connection is allowed if there is an entry in lt_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 # $LTDATA/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