Hesiod Jonathan Reed

What is Hesiod? The Hesiod Name Service is an important component of Athena. Used transparently by Athena, user rarely interacts with it directly. An extension to the DNS system. Greek poet ca. ~700B.C., who documented the names of the Gods and the myths surrounding them.

Some Background on DNS DNS is the Domain Name System that converts hostnames (web.mit.edu) to IP addresses ( ) In the past, one file (/etc/hosts) was used to map a hostname to an IP address. The file had to exist on each machine that wanted the ability to use hostnames. Maintaining hundreds of /etc/hosts files (even with tools such as Sun’s NIS/YP that automated the process) became prohibitive as the internet grew. DNS was conceived to provide a centralized service that machines could query to convert a hostname to an IP address. All the local machine needs to know was the IP address of a DNS server.

DNS is a Network Not all DNS servers are identical. DNS servers usually only contain information for their local domains. When they receive a query for a host outside of their domain, they often ask other DNS servers to find that information for them.

More than just IP addresses In order to be able to log into a machine, you need an entry in the /etc/passwd file. When you’ve got 10 machines, and 5 users, having an entry for each user in each /etc/passwd file isn’t that bad. If scaled to Project Athena, however, it would be impossible to maintain. The developers of Project Athena needed a name server to store information such as passwd entries, printer entries, and other information. Sun’s Yellow Pages (YP, a/k/a NIS) was used by many sites for this purpose, but it was proprietary. The source code for BIND (Berkeley Internet Name Daemon), a popular DNS package, was freely available, so it was decided that Hesiod would be based on the DNS service.

DNS Records DNS is essentially a database stored in a text file. This text file contains records of a certain type. – “A” records indicate a host – “CNAME” indicates an alias – “PTR” records indicate a pointer (for reverse lookups) – “MX” records indicate a “Mail eXchanger” (mail server) – “NS” records indicate a “Name Server” – “TXT” records indicate a record to be treated as regular ASCII text Hesiod uses TXT records to store the information.

Hesiod Names Hesiod names consist of a HesiodName and a HesiodType HesiodNames can be anything, but there are fixed HesiodTypes: –passwd, pobox, uid, gid, group, grplist, filsys, cluster, sloc, service, pcap

hesinfo The hesinfo command is used to query the hesiod servers. Usage: hesinfo HesiodName HesiodType athena% hesinfo $USER passwd will display your /etc/passwd entry.

hes The “ hes ” command, in the consult locker, can take a HesiodName as an argument, and iterate through all possible HesiodTypes and return any results. It returns nothing if there are no matches.

So Hesiod is just DNS? Basically. You can even use standard DNS query tools to lookup Hesiod information. (But you really should use the hesinfo command) – You need to provide special options to the DNS query tools, since you’re looking for TXT records, not A or PTR records – HesiodName.HesiodType.ns.athena.mit.edu athena% host -t txt jdreed.passwd.ns.athena.mit.edu

Types to care about Cluster information (CLUSTER): – tells the machine the highest possible athena version it can have: syslib on Athena Suns syscontrol/sysprefix on Athena Linux boxes – Also sets things like default printers Filesystem (FILSYS): – Can be AFS, NFS, or ERR. – ERR means the account is deactivated – NFS means they’re NFS lockers (really old users, or some course lockers) so AFS commands (like fs ) won’t work. Login Information (PASSWD) – what an entry in /etc/passwd would look like