Hesiod (name service)

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Hesiod (name service)

Hesiod is a name service for computers. It started in MIT’s Project Athena (1983–1991) and is named after the Greek poet Hesiod, who listed the names and origins of the gods in Theogony. Hesiod uses DNS to provide access to information that doesn’t change often, such as user accounts and other system data.

In Unix-like systems, Hesiod helps distribute data that would normally be kept in local files like /etc/passwd, /etc/group, and /etc/printcap. Instead of storing this data on every machine, Hesiod stores it in DNS records and lets clients query the DNS server for the needed information.

How it works:
- Hesiod uses the DNS HS class (not the usual IN) and stores data in TXT records.
- Records can be accessed by different keys, such as login name or UID. Example: foo.passwd.ns.example.net HS TXT "foo:x:100:10:Foo Bar:/home/foo:/bin/sh".
- A client can look up multiple records to access information in different ways.

Client setup (simplified):
- /etc/hesiod.conf: rhs=.example.net, lhs=.ns, classes=HS, IN
- DNS servers for Hesiod records are configured in /etc/resolv.conf.

Usage:
- hesinfo foo passwd returns a line like foo:x:100:10:Foo Bar:/home/foo:/bin/sh

Why Hesiod:
- It uses existing DNS infrastructure, making it easy to deploy across many machines.
- It centralizes information that would otherwise be kept locally on each machine.

See also: NSS, NIS, LDAP, Kerberos.