The GNU C library contains an NSS module for the Hesiod name service.

Hesiod is a general name service for a variety of applications and is

based on the Berkeley Internet Name Daemon (BIND).

Introduction

============

The Hesiod NSS module implements access to all relevant standard

Hesiod types, which means that Hesiod can be used for the `group',

`passwd' and `services' databases.  There is however a restriction.

In the same way that it is impossible to use `gethostent()' to iterate

over all the data provided by DNS, it is not possible to scan the

entire Hesiod database by means of `getgrent()', `getpwent()' and

`getservent()'.  Besides, Hesiod only provides support for looking up

services by name and not for looking them up by port.  In essence this

means that the Hesiod name service is only consulted as a result of

one of the following function calls:

  * getgrname(), getgrgid()

  * getpwname(), getpwuid()

  * getservbyname()

and their reentrant counterparts.

Configuring your systems

========================

Configuring your systems to make use the Hesiod name service requires

one or more of the following steps, depending on whether you are

already running Hesiod in your network.

Configuring NSS

---------------

First you should modify the file `/etc/nsswitch.conf' to tell

NSS for which database you want to use the Hesiod name service.  If

you want to use Hesiod for all databases it can handle your

configuration file could look like this:

  # /etc/nsswitch.conf

  #

  # Example configuration of GNU Name Service Switch functionality.

  #

  passwd:	  db files hesiod

  group:	  db files hesiod

  shadow:	  db files

  hosts:	  files dns

  networks:	  files dns

  protocols:	  db files

  services:	  db files hesiod

  ethers:	  db files

  rpc:		  db files

For more information on NSS, please refer to the `The GNU C Library

Reference Manual'.

Configuring Hesiod

------------------

Next, you will have to configure Hesiod.  If you are already running

Hesiod in your network, you probably already have a file named

`hesiod.conf' on your machines (probably as `/etc/hesiod.conf' or

`/usr/local/etc/hesiod.conf').  The Hesiod NSS module looks for

`/etc/hesiod.conf' by default.  If there is no configuration file you

will want to create your own.  It should look something like:

  rhs=.your.domain

  lhs=.ns

  classes=in,hs

The optional classes settings specifies which DNS classes Hesiod

should do lookups in.  Possible values are IN (the preferred class)

and  HS (the deprecated class, still used by some sites).

You may specify both classes separated by a comma to try one class

first and then the other if no entry is available in the first

class.  The default value of the classes variable is `IN,HS'.

The value of rhs can be overridden by the environment variable

`HES_DOMAIN'.

Configuring your name servers

-----------------------------

In addition, if you are not already running Hesiod in your network,

you need to create Hesiod information on your central name servers.

You need to run `named' from BIND 4.9 or higher on these servers, and

make them authoritative for the domain `ns.your.domain' with a line in

`/etc/named.boot' reading something like:

  primary         ns.your.domain          named.hesiod

or if you are using the new BIND 8.1 or higher add something to

`/etc/named.conf' like:

  zone "ns.your.domain" {

          type master;

          file "named.hesiod";

  };

Then in the BIND working directory (usually `/var/named') create the

file `named.hesiod' containing data that looks something like:

  ; SOA and NS records.

  @       IN      SOA     server1.your.domain admin-address.your.domain (

                  40000           ; serial - database version number

                  1800            ; refresh - sec servers

                  300             ; retry - for refresh

                  3600000         ; expire - unrefreshed data

                  7200 )          ; min

                  NS      server1.your.domain

                  NS      server2.your.domain

  ; Actual Hesiod data.

  libc.group      TXT     "libc:*:123:gnu,gnat"

  123.gid         CNAME   libc.group

  gnu.passwd      TXT     "gnu:*:4567:123:GNU:/home/gnu:/bin/bash"

  456.uid         CNAME   mark.passwd

  nss.service     TXT     "nss tcp 789 switch sw "

  nss.service     TXT     "nss udp 789 switch sw"

where `libc' is an example of a group, `gnu' an example of an user,

and `nss' an example of a service.  Note that the format used to

describe services differs from the format used in `/etc/services'.

For more information on `named' refer to the `Name Server Operations

Guide for BIND' that is included in the BIND distribution.

Security

========

Note that the information stored in the Hesiod database in principle

is publicly available.  Care should be taken with including vulnerable

information like encrypted passwords in the Hesiod database.  There

are some ways to improve security by using features provided by

`named' (see the discussion about `secure zones' in the BIND

documentation), but one should keep in mind that Hesiod was never

intended to distribute passwords.  In the origional design

authenticating users was the job of the Kerberos service.

More information

================

For more information on the Hesiod name service take a look at some of

the papers in ftp://athena-dist.mit.edu:/pub/ATHENA/usenix and the

documentation that accompanies the source code for the Hesiod name

service library in ftp://athena-dist.mit.edu:/pub/ATHENA/hesiod.

There is a mailing list at MIT for Hesiod users, hesiod@mit.edu.  To

get yourself on or off the list, send mail to hesiod-request@mit.edu.