inetd.8

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.\"     from: @(#)inetd.8	6.7 (Berkeley) 3/16/91
.\"	$Id: inetd.8,v 1.18 2000/07/30 23:56:58 dholland Exp $
.\"
.Dd August 22, 1999
.Dt INETD 8
.Os "Linux NetKit (0.17)"
.Sh NAME
.Nm inetd
.Nd internet
.Dq super-server
.Sh SYNOPSIS
.Nm inetd
.Op Fl di
.Op Fl q Ar queuelength
.Op Ar configuration file
.Sh DESCRIPTION
.Nm Inetd
should be run at boot time by
.Pa /etc/rc.local
(see
.Xr rc 8 ) .
If your 
.Xr init 8
can respawn arbitrary daemons,
.Nm inetd
can be run from init instead; then init will restart it if it crashes.
You must use the
.Fl i
option to prevent
.Nm inetd
from backgrounding itself, or init will become confused.
.Pp
When running,
.Nm 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,
.Nm inetd
allows running one daemon to invoke several others,
reducing load on the system.
.Ss OPTIONS
The options available for
.Nm inetd:
.Bl -tag -width Ds
.It Fl d
Turns on several kinds of debugging and make inetd behave if run in a 
debugger. Also implies
.Fl i .
.It Fl i
Do not background; for running from
.Xr init 8 .
.It Fl q Ar queuelength
Sets the size of the socket listen queue to the specified
value. Default is 128.
.El
.Ss CONFIGURATION
Upon execution,
.Nm inetd
reads its configuration information from a configuration
file which, by default, is
.Pa /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:
.Pp
.Bd -unfilled -offset indent -compact
service name[@hostname]
socket type
protocol
wait/nowait[.max]
user[.group]
server program
server program arguments
.Ed
.Pp
To specify an 
.Em Sun-RPC 
based service, the entry would contain these fields.
.Pp
.Bd -unfilled -offset indent -compact
service name/version[@hostname]
socket type
rpc/protocol
wait/nowait[.max]
user[.group]
server program
server program arguments
.Ed
.Pp
The
.Em service-name
entry is the name of a valid service in
the file
.Pa /etc/services .
For
.Dq internal
services (discussed below), the service
name
.Em must
be the official name of the service (that is, the first entry in
.Pa /etc/services ) . 
When used to specify a
.Em Sun-RPC
based service, this field is a valid RPC service name in
the file
.Pa /etc/rpc . 
The part on the right of the 
.Dq /
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 - 
.Dq rusers/1-3 .
.Pp
If a string of the form
.Em @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
.Em 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 
.Nm inetd
from listening to the same port on a specific address and the general
address at once.
.Em hostname
should be a resolvable hostname or an IP address associated with one
of the interfaces of the local system.

.Pp
The
.Em socket-type
should be one of
.Dq stream ,
.Dq dgram ,
.Dq raw ,
.Dq rdm ,
or
.Dq seqpacket ,
depending on whether the socket is a stream, datagram, raw,
reliably delivered message, or sequenced packet socket.
.Pp
The
.Em protocol
must be a valid protocol as given in
.Pa /etc/protocols .
Examples might be
.Dq tcp
or
.Dq udp .
Rpc based services are specified with the 
.Dq rpc/tcp
or 
.Dq rpc/udp 
service type.

.Pp
The
.Em wait/nowait
entry is applicable to datagram sockets only (other sockets should
have a
.Dq nowait
entry in this space).  If a datagram server connects
to its peer, freeing the socket so
.Nm inetd
can received further messages on the socket, it is said to be
a
.Dq multi-threaded
server, and should use the
.Dq nowait
entry.  For datagram servers which process all incoming datagrams
on a socket and eventually time out, the server is said to be
.Dq single-threaded
and should use a
.Dq wait
entry.
.Xr Comsat 8
.Pq Xr biff 1
and
.Xr talkd 8
are both examples of the latter type of
datagram server.
.Xr Tftpd 8
is an exception; it is a datagram server that establishes pseudo-connections.
It must be listed as
.Dq wait
in order to avoid a race;
the server reads the first packet, creates a new socket,
and then forks and exits to allow
.Nm inetd
to check for new service requests to spawn new servers.
The optional
.Dq max
suffix (separated from
.Dq wait
or
.Dq nowait
by a dot) specifies the maximum number of server instances that may be
spawned from
.Nm inetd
within an interval of 60 seconds. When omitted,
.Dq max
defaults to 40.
.Pp
The
.Em 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.
.Pp
The
.Em server-program
entry should contain the pathname of the program which is to be
executed by
.Nm inetd
when a request is found on its socket.  If
.Nm inetd
provides this service internally, this entry should
be
.Dq internal .
.Pp
The
.Em 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
.Dq internal
should take the place of this entry.
.Ss BUILTINS
.Nm Inetd
provides several
.Dq trivial
services internally by use of
routines within itself.  These services are
.Dq echo ,
.Dq discard ,
.Dq chargen
(character generator),
.Dq daytime
(human readable time), and
.Dq 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
.Tn RFC
from the Network Information Center.
.Pp
.Nm Inetd
rereads its configuration file when it receives a hangup signal,
.Dv SIGHUP .
Services may be added, deleted or modified when the configuration file
is reread.
.Nm Inetd
creates a file
.Em /var/run/inetd.pid
that contains its process identifier.
.Sh SEE ALSO
.Xr comsat 8 ,
.Xr fingerd 8 ,
.Xr ftpd 8 ,
.Xr rexecd 8 ,
.Xr rlogind 8 ,
.Xr rshd 8 ,
.Xr telnetd 8 ,
.Xr tftpd 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .
Support for
.Em Sun-RPC 
based services is modelled after that
provided by
.Em SunOS 4.1 .