INETD(8)

NAME
inetd - internet “super-server”

SYNOPSIS
inetd [-d] [configuration file]

DESCRIPTION
Inetd should be run at boot time by /etc/rc.local (see rc(8)). It then listens for connections on certain internet sockets. When a connection is found on one of its sockets, it decides what service the socket corresponds to, and invokes a program to service the request. After the program is finished, it continues to listen on the socket (except in some cases which will be described below). Essentially, inetd allows running one daemon to invoke several others, reducing load on the system.

The option available for inetd:

-d  Turns on debugging.

Upon execution, inetd reads its configuration information from a configuration file which, by default, is /etc/inetd.conf. There must be an entry for each field of the configuration file, with entries for each field separated by a tab or a space. Comments are denoted by a ``#'' at the beginning of a line. There must be an entry for each field. The fields of the configuration file are as follows:

    service name
    socket type
    protocol
    wait/nowait
    user
    server program
    server program arguments

The service-name entry is the name of a valid service in the file /etc/services. For “internal” services (discussed below), the service name must be the official name of the service (that is, the first entry in /etc/services).

The socket-type should be one of “stream”, “dgram”, “raw”, “rdm”, or “seqpacket”, depending on whether the socket is a stream, datagram, raw, reliably delivered message, or sequenced packet socket.

The protocol must be a valid protocol as given in /etc/protocols. Examples might be “tcp” or “udp”.

The wait/nowait entry is applicable to datagram sockets only (other sockets should have a “nowait” entry in this space). If a datagram server connects to its peer, freeing the socket so inetd can received further messages on the socket, it is said to be a “multi-threaded” server, and should use the “nowait” entry. For datagram servers which process all incoming datagrams on a socket and eventually time out, the server is said to be “single-threaded” and should use a “wait” entry. Comsat(8) (biff(1)) and talkd(8) are both examples of the latter type of datagram server. Tftpd(8) is an exception; it is a datagram server that establishes pseudo-connections. It must be listed as “wait” in order to avoid a race; the server reads the first packet, creates a new socket, and then forks and exits to allow inetd to check for new service requests to spawn new servers.

The user entry should contain the user name of the user as whom the server should run. This allows for servers to be given less permission than root.

The server-program entry should contain the pathname of the program which is to be executed by inetd when a request is found on its socket. If inetd provides this service internally, this entry should be “internal”.

The server program arguments should be just as arguments normally are, starting with argv[0], which is the name of the program. If the service is provided internally, the word “internal” should take the place of this entry.

Inetd provides several “trivial” services internally by use of routines within itself. These services are “echo”, “discard”, “chargen” (character generator), “daytime” (human readable time), and “time” (machine readable time, in the form of the number of seconds since midnight, January 1, 1900). All of these services are tcp based. For details of these services, consult the appropriate RFC from the Network Information Center.

Inetd rereads its configuration file when it receives a hangup signal, SIGHUP. Services may be added, deleted or modified when the configuration file is reread.

SEE ALSO
comsat(8), fingerd(8), ftpd(8), rexecd(8), rlogind(8), rshd(8), telnetd(8), tftpd(8)

HISTORY
The inetd command appeared in 4.3BSD.