INETD(8)

NAME
inetd - internet “super-server”

SYNOPSIS
inetd [-di] [-q queuelength] [configuration file]

DESCRIPTION
Inetd should be run at boot time by /etc/rc.local (see rc(8)). If your init(8) can respawn arbitrary daemons, inetd can be run from init instead; then init will restart it if it crashes. You must use the -i option to prevent inetd from backgrounding itself, or init will become confused.

When running, inetd listens for connections on certain internet sockets. When a connection is found on one of its sockets, it looks up what service the socket corresponds to, and invokes a program to service the request. After the program is finished, it will continue to listen on the socket, except in some special cases which will be described below. Essentially, inetd allows running one daemon to invoke several others, reducing load on the system.

  OPTIONS
The options available for inetd:

-d  Turns on several kinds of debugging and make inetd behave if run in a debugger. Also implies -i.

-i  Do not background; for running from init(8).

-q queuelength
    Sets the size of the socket listen queue to the specified value. Default is 128.

  CONFIGURATION
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[@hostname]
    socket type
    protocol
    wait/nowait[.max]
    user[.group]
    server program
    server program arguments

To specify an Sun-RPC based service, the entry would contain these fields.

    service name/version[@hostname]
    socket type
    rpc/protocol
    wait/nowait[.max]
    user[.group]
    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). When used to specify a Sun-RPC based service, this field is a valid RPC service name in the file /etc/rpc. The part on the right of the “/” is the RPC version number. This can simply be a single numeric argument or a range of versions. A range is bounded by the low version to the high version - “rusers/1-3”.

If a string of the form @hostname is appended to the service, it causes inetd to bind to the port for the service on only the specific IP address associated with hostname, instead of listening on all available addresses. This can be done as many times as desired for different addresses, which permits setting up ``virtually hosted'' services. Note, however, that while you can listen to as many specific addresses as you want, kernel restrictions prevent inetd from listening to the same port on a specific address and the general address at once. hostname should be a resolvable hostname or an IP address associated with one of the interfaces of the local system.

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”, both of which imply IPv4 for backward compatibility. The names “tcp4” and “udp4” specify IPv4 only. The names “tcp6” and “udp6” specify IPv6 only; inetd will reject / ignore packets from ipv4 clients. The names “tcp46” and “udp46” specify that the entry accepts both IPv4 and IPv6 connections via a wildcard PF_INET6 socket. Rpc based services are specified with the “rpc/tcp” or “rpc/udp” service type.

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 optional “max” suffix (separated from “wait” or “nowait” by a dot) specifies the maximum number of server instances that may be spawned from inetd within an interval of 60 seconds. When omitted, “max” defaults to 40.

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. An optional group name can be specified by appending a dot to the user name followed by the group name. This allows for servers to run with a different (primary) group id than specified in the password file. If a group is specified and user is not root, the supplementary groups associated with that user will still be set.

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.

  BUILTINS
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. Inetd creates a file /var/run/inetd.pid that contains its process identifier.

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. Support for Sun-RPC based services is modelled after that provided by SunOS 4.1. IPv6 support was developed by USAGI Project, based on Mauro Tortonesi <mauro@ferrara.linux.it>'s patch.