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onenetd(1) Network Tools onenetd(1)
NAME
onenetd - listen on a TCP port and launch a program to handle requests
SYNOPSIS
onenetd [options] ADDRESS PORT COMMAND ...
DESCRIPTION
onenetd binds a TCP socket to port PORT on IP address ADDRESS, listens
for and accepts connections, and spawns COMMAND with stdin and stdout
(and optionally stderr) connected to the accepted socket.
onenetd may be thought of as a minimal version of inetd, suitable only
for listening for "stream tcp nowait" services on a single port. The
idea is that multiple copies of onenetd will be run, one for each
service. The advantages of onenetd over inetd include:
o Connections may be refused with a fixed response after the
connection limit is reached.
o TCP_NODELAY may be set on a per-port basis.
o The address to bind to may be chosen arbitrarily, so it's easy
to make a service only listen on localhost, or run several
different services on the same port for different interface
addresses.
o Incoming connections may be logged to stderr.
Note that onenetd only handles TCP connections; it is not possible to
run UDP services (such as nmbd) from onenetd.
OPTIONS
ADDRESS
The hostname or IP address to bind() to. Specify 0 (or :: for
IPv6) to bind to all addresses.
PORT The service name or port number to bind() to. In order to bind
to a privileged port, onenetd must be initially run as root
(although you can use the -u etc. options to switch to another
user after the bind has been done). Specify 0 to bind to any
available port.
COMMAND ...
The command to execute, as well as its parameters (all
parameters given to onenetd after COMMAND are passed to COMMAND
as parameters). argv[0] for COMMAND will be set to COMMAND; if
you wish to specify a different argv[0], use the argv0 tool from
the freedt or daemontools packages.
-c N Limit the number of connections (and thus child processes) to N.
The default is 40.
-6 Bind to an IPv6 address. IPv6 sockets will also accept IPv4
connections, if bound to an appropriate address (e.g. ::).
-g GID After binding the TCP socket, setgid(GID). GID must be numeric.
-u UID After binding the TCP socket, setuid(UID). UID must be numeric.
-U After binding the TCP socket, setgid($GID) and setuid($UID).
$GID and $UID must be numeric. This is intended for use with
envuidgid (from daemontools or freedt).
-1 After binding the TCP socket, print the local port number to
stdout. You can use this when you've specified the local port
as 0 to find out what port has been chosen.
-b N Set the listen() backlog to N. Note that on many operating
systems, the listen backlog has an arbitrary limit, or may be
entirely ignored. The default is 10.
-D Set the TCP_NODELAY option on the accepted sockets. This causes
the operating system's TCP stack to avoid coalescing smaller
packets into larger ones, decreasing latency but reducing
throughput.
-Q Do not print any messages to stderr, except in the case of a
fatal error. This is the default.
-v Print messages to stderr indicating clients connecting and
disconnecting. These can be collected for logging purposes
using logger, multilog from daemontools, or dumblog from freedt.
-e Redirect the child's stderr to the socket. By default, only
stdin and stdout are redirected.
-h Print a brief usage message, then exit. The same message will be
shown if unknown or invalid arguments are passed.
-r MESSAGE
Normally once the number of active connections has passed the
limit set by -c, further connections will not be accepted until
the number of active connections has dropped again -- that is,
further connections will not be refused, but will not connect
until free connections are available. If -r is specified,
connections will be accepted and have the constant string
MESSAGE printed to them, then will be disconnected; this is done
inside the onenetd process without forking, so it does not use
up process slots. MESSAGE may contain \r, \n or \t to specify a
carriage return, newline or tab character.
EXIT CODE
onenetd returns 0 on success, or 20 on failure (for instance, invalid
arguments). Since onenetd is intended to run forever, the exit code is
generally not important, and stderr should be examined for diagnostic
messages if it exits unexpectedly.
ENVIRONMENT VARIABLES
Following D. J. Bernstein's UCSPI standard, onenetd sets several
variables in the child process's environment. These can be used for
logging or access control.
PROTO The string "TCP" for IPv4 connections, or "TCP6" for IPv6
connections.
TCPLOCALIP
The local address of the connected socket, as formatted by
inet_ntop (dotted quad for IPv4, hex for IPv6).
TCPLOCALPORT
The local port of the connected socket, as a decimal number.
TCPREMOTEIP
The remote address of the connected socket, as formatted by
inet_ntop.
TCPREMOTEPORT
The remote port of the connected socket, as a decimal number.
EXAMPLES
onenetd 0 echo cat
Simulate the standard inetd echo service.
onenetd -v 192.168.1.2 daytime date
Simulate the standard inetd daytime service on the interface
192.168.1.2, logging connections to stderr.
onenetd -1 ::1 0 myprog --my-arguments
Bind to a free port on the IPv6 localhost address, print the
port number chosen, and run "myprog --my-arguments" for
connections.
onenetd -v -c 5 -r '421 Server full\r\n' 0 21 /usr/sbin/ftpd -a
/home/ftp
Run an FTP service with a limit of five concurrent connections,
refusing any further connections with an appropriate FTP error
message. ftpd will be invoked as "/usr/sbin/ftpd -a /home/ftp".
envuidgid myuser onenetd -v -U 0 25098 myprog --my-arguments
Set user and group to that of myuser, and run "myprog --my-
arguments" for connections to port 25098 on any IPv4 interface.
AUTHOR
onenetd was written by Adam Sampson <ats@offog.org>.
SEE ALSO
inetd(8), argv0(8), envuidgid(8), softlimit(8), dumblog(8), logger(1),
sock(1).
Version 12 19th June 2014 onenetd(1)