|
|
| Previous | Table of Contents | Next |
The sendmail daemon is the common Mail Transport Agent included with current versions of Unix. Because this program is a daemon, it listens for and accepts incoming e-mail connections from external systems. This daemon receives and subsequently delivers messages to local or remote users. sendmail is not intended to function as a user interface, but rather as the processing agent for user mail programs such as elm, pine, mailx, and mush.
The sendmail program functions in two modes: incoming and outgoing. It accepts mail from internal and external sources and processes it according to the rules found in the /etc/sendmail.cf configuration file. The format of and options for the /etc/sendmail.cf configuration file are far too complex to cover here.
The sendmail program is capable of accepting TCP/IP connections on port 25. The following output illustrates a connection to sendmail on this port.
nms% telnet nms 25 Trying 198.53.64.4 … Connected to nms. Escape character is `^]'. 220 nms.home.org Sendmail 4.1/ch-950121.1 ready at Sat, 26 Aug 95 11:28:36 EDT help 214-Commands: 214- HELO MAIL RCPT DATA RSET 214- NOOP QUIT HELP VRFY EXPN 214-For more info use "HELP >topic<". 214-smtp 214-To report bugs in the implementation contact Sun Microsystems 214-Technical Support. 214-For local information contact postmaster at this site. 214 End of HELP info quit 221 nms.home.org closing connection Connection closed by foreign host. nms%
The system administrator can test his or her configuration from the sendmail command directly. Unfortunately, this capability can also be used by the wily hacker to create a false mail message that looks like it came from somewhere else.
The getty daemon is responsible for providing a login prompt on terminals and on serial devices directly connected to the system; getty is also responsible for providing a login prompt on the console. The getty command is started by the init process, and is part of the login-<shell-<logout process. It is important to note that when you log in through Telnet, getty is not involved in the process. The Telnet server, telnetd, displays the login message and collects the user name from the user.
The rlogind daemon is the server side to the client rlogin program. It provides a remote login facility with authentication based on privileged port numbers and host name-user name pairs. rlogind is executed by the Internet daemon, inetd, when it receives a service request at the port indicated in the services database for login using the TCP/IP protocol.
The deliver daemon manages all mail delivery in the MMDF mail system. deliver does not deliver mail directly, but instead calls on MMDF channel programs to handle actual delivery. deliver’s actions are guided by the MMDF configuration file, /usr/mmdf/mmdftailor, and by command-line options. This daemon also maintains a cache of host information on a per-channel basis, so that mail for unavailable hosts can be skipped until the host is available.
The inetd daemon listens on multiple ports for incoming connection requests. When it receives a request, inetd spawns the appropriate server. The use of a “super-server” allows other servers to be spawned only when needed and to terminate when they have satisfied a particular request. The following servers are normally started by inetd: fingerd, ftpd, rexecd, rlogind, rshd, talkd, telnetd, and tftpd. inetd can also start several internal services: these are described in inetd.conf, which is typically found in the /etc directory. Do not arrange for inetd to start named, routed, rwhod, sendmail, pppd, or any NFS server.
The routed daemon is invoked by root at boot time to manage the Internet Routing Tables (usually during init 2). The routed daemon uses a variant of the Xerox NS Routing Information Protocol to maintain up-to-date kernel Routing Table entries. If the host is an internetwork router, routed periodically supplies copies of its Routing Tables to hosts and networks that are directly connected.
The nfsd daemon starts the NFS server daemons that handle client file system requests. The nfsd daemon is a user application entry point into the kernel-based NFS server. Depending on the option or options used, server daemons are started to handle:
The mountd daemon is an RPC server that responds to file system mount requests. It reads the file /etc/exports to determine which file systems are available to which machines and users. This daemon also provides information regarding clients with mounted file systems. This information can be printed using the showmount command.
The pcnfsd daemon is an RPC server that supports ONC clients on PC (DOS, OS/2, and Macintosh) systems. There are two implementations of the PC-NFS protocol: Version 1 and Version 2. Version 2 supports extended printing features. It reads the configuration file /etc/pcnfsd.conf if present, and then services RPC requests directed to program number 150001. Many releases of the pcnfsd daemon support both Version 1 and Version 2 of the pcnfsd protocol.
The statd and rpc.statd daemons are RPC servers that function as the RPC status monitor. It interacts with the lockd server to provide crash and recovery functions for the locking services on NFS. It is common to see either statd or rpc.statd but not both on your system.
The lockd daemon processes lock requests that are either sent locally by the kernel or remotely by another lock daemon. lockd forwards lock requests for remote data to the server site’s lock daemon. lockd then requests the status monitor daemon, statd or rpc.statd, for monitor service. The reply to the lock request will not be sent to the kernel until the status daemon and the server site’s lock daemon have replied.
| Previous | Table of Contents | Next |