UNIX System Administration Handbook - Evi Nemeth [494]
rpc.nisd: NIS+ server
rpc.nisd is the NIS+ counterpart of ypserv. It runs on all NIS+ servers. If invoked with the -B option, rpc.nisd automatically forks rpc.nisd_resolv, which permits the use of DNS through NIS+.
See Chapter 16 for more information about DNS.
28.8 INTERNET DAEMONS
We define “Internet daemons” very loosely to mean daemons that use Internet protocols to handle requests. Many Internet daemons actually spend the majority of their time servicing local requests.
talkd: network chat service
Connection requests from the talk program are handled by talkd. When it receives a request, talkd negotiates with the other machine to set up a network connection between the two users who have executed talk.
talk comes in two flavors: the original (at port 517) and a newer one from 4.3BSD (ntalk, at port 518). ntalk is not backward compatible and will not accept connections from talk clients. Although 4.3BSD was released in 1986, many systems still use the “older” version of talk (15 years later!).
comsat: notify users of new mail
comsat notifies users that new mail has arrived. When it receives an indication that a user has new mail and /etc/utmp shows that the user is logged on, comsat checks to see whether notifications have been enabled with biffy.6 If so, comsat prints the beginning of the mail message on the user’s terminal. In modern times, most users access their mail from a PC-based mail client by using IMAP or POP; comsat has nothing to do with that procedure.
sendmail: transport electronic mail
sendmail’s tasks include accepting messages from users and remote sites, rewriting addresses, expanding aliases, and transferring mail across the Internet. sendmail is an important and very complex daemon. Refer to Chapter 19, Electronic Mail, for the complete scoop.
snmpd: provide remote network management service
snmpd responds to requests that use the Simple Network Management Protocol (SNMP) protocol. SNMP standardizes some common network management operations. See page 640 for more information about SNMP.
rwhod: maintain remote user list
rwhod is a leftover from “the early days” (the 1980s) and maintains information about the users that are logged in to machines on the network. rwhod collects this information for the local machine and broadcasts it; when it receives information from other hosts, it verifies that the information is reasonable and then puts it in the file /var/spool/rwho/whod.hostname, where hostname is the name of the host that sent the information. The programs rwho and ruptime refer to these files.
By default, rwhod broadcasts every three minutes, so the information reported by rwho and ruptime is only approximately correct. rwhod is very inefficient, so unless you have network bandwidth to burn and actually use the information, you should turn it off.
ftpd: file transfer server
ftpd is the daemon that handles requests from ftp, the Internet file transfer program. Many sites disable it, either because it is a resource hog or because they are worried about security. ftpd can be set up to allow anyone to transfer files to and from your machine.
See page 696 for more information about ftpd.
popper: basic mailbox server
The popper daemon implements the Post Office Protocol (POP). This protocol is commonly used by non-UNIX systems to receive electronic mail.
imapd: deluxe mailbox server
The imapd daemon implements the Internet Mail Access Protocol, IMAP, which is a more festive and featureful alternative to POP. It allows PC-based users (or UNIX users with IMAP-enabled mail readers) to access their email from a variety of locations, with mail folders being stored on the UNIX server. Check out www.imap.org for more information about IMAP.
rlogind: remote login server
rlogind is responsible for handling remote logins. When invoked by inetd, it tries to automatically authenticate the remote user by examining /etc/hosts.equiv