2.11BSD/man/cat8/inetd.0
INETD(8) UNIX Programmer's Manual INETD(8)
NAME
inetd - internet ``super-server''
SYNOPSIS
inetd [-d] [-R _r_a_t_e] [_c_o_n_f_i_g_u_r_a_t_i_o_n _f_i_l_e]
DESCRIPTION
The inetd program should be run at boot time by /_e_t_c/_r_c (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. The server pro-
gram is invoked with the service socket as its standard
input, output and error descriptors. After the program is
finished, inetd 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 options available for inetd:
-d Turns on debugging.
-R _r_a_t_e Specifies the maximum number of times a service
can be invoked in one minute; the default is 1000.
Upon execution, inetd reads its configuration information
from a configuration file which, by default, is
/_e_t_c/_i_n_e_t_d._c_o_n_f. 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
There are two types of services that inetd can start: stan-
dard and TCPMUX. A standard service has a well-known port
assigned to it; it may be a service that implements an offi-
cial Internet standard or is a BSD-specific service. As
described in RFC 1078, TCPMUX services are nonstandard ser-
vices that do not have a well-known port assigned to them.
They are invoked from inetd when a program connects to the
``tcpmux'' well-known port and specifies the service name.
This feature is useful for adding locally-developed servers.
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INETD(8) UNIX Programmer's Manual INETD(8)
The _s_e_r_v_i_c_e-_n_a_m_e entry is the name of a valid service in the
file /_e_t_c/_s_e_r_v_i_c_e_s. For ``internal'' services (discussed
below), the service name must be the official name of the
service (that is, the first entry in /_e_t_c/_s_e_r_v_i_c_e_s). For
TCPMUX services, the value of the _s_e_r_v_i_c_e-_n_a_m_e field con-
sists of the string ``tcpmux'' followed by a slash and the
locally-chosen service name. The service names listed in
/_e_t_c/_s_e_r_v_i_c_e_s and the name ``help'' are reserved. Try to
choose unique names for your TCPMUX services by prefixing
them with your organization's name and suffixing them with a
version number.
The _s_o_c_k_e_t-_t_y_p_e should be one of ``stream'', ``dgram'',
``raw'', ``rdm'', or ``seqpacket'', depending on whether the
socket is a stream, datagram, raw, reliably delivered mes-
sage, or sequenced packet socket. TCPMUX services must use
``stream''.
NOTE: ``rdm'' and ``seqpacket'' are not supported in
2.11BSD.
The _p_r_o_t_o_c_o_l must be a valid protocol as given in
/_e_t_c/_p_r_o_t_o_c_o_l_s. Examples might be ``tcp'' or ``udp''.
TCPMUX services must use ``tcp''.
The _w_a_i_t/_n_o_w_a_i_t entry specifies whether the server that is
invoked by inetd will take over the socket associated with
the service access point, and thus whether inetd should wait
for the server to exit before listening for new service
requests. Datagram servers must use ``wait'', as they are
always invoked with the original datagram socket bound to
the specified service address. These servers must read at
least one datagram from the socket before exiting. 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; it should read one
datagram from the socket and create a new socket connected
to the peer. It should fork, and the parent should then
exit to allow inetd to check for new service requests to
spawn new servers. Datagram servers which process all
incoming datagrams on a socket and eventually time out are
said to be ``single-threaded''. Comsat(8), biff(1) and
talkd(8) are examples of the latter type of datagram server.
Tftpd(8) is an example of a multi-threaded datagram server.
Servers using stream sockets generally are multi-threaded
and use the ``nowait'' entry. Connection requests for these
services are accepted by inetd , and the server is given
only the newly-accepted socket connected to a client of the
service. Most stream-based services operate in this manner.
Stream-based servers that use ``wait'' are started with the
listening service socket, and must accept at least one
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INETD(8) UNIX Programmer's Manual INETD(8)
connection request before exiting. Such a server would nor-
mally accept and process incoming connection requests until
a timeout. TCPMUX services must use ``nowait''.
The _u_s_e_r 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 _s_e_r_v_e_r-_p_r_o_g_r_a_m 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 inter-
nally, this entry should be ``internal''.
The _s_e_r_v_e_r _p_r_o_g_r_a_m _a_r_g_u_m_e_n_t_s 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.
The inetd program provides several ``trivial'' services
internally by use of routines within itself. These services
are ``echo'', ``discard'', ``chargen'' (character genera-
tor), ``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.
The inetd program rereads its configuration file when it
receives a hangup signal, SIGHUP. Services may be added,
deleted or modified when the configuration file is reread.
TCPMUX
RFC 1078 describes the TCPMUX protocol: ``A TCP client con-
nects to a foreign host on TCP port 1. It sends the service
name followed by a carriage-return line-feed <CRLF>. The
service name is never case sensitive. The server replies
with a single character indicating positive (+) or negative
(-) acknowledgment, immediately followed by an optional mes-
sage of explanation, terminated with a <CRLF>. If the reply
was positive, the selected protocol begins; otherwise the
connection is closed.'' The program is passed the TCP con-
nection as file descriptors 0 and 1.
If the TCPMUX service name begins with a ``+'', inetd
returns the positive reply for the program. This allows you
to invoke programs that use stdin/stdout without putting any
special server code in them.
The special service name ``help'' causes inetd to list
TCPMUX services in _i_n_e_t_d._c_o_n_f.
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INETD(8) UNIX Programmer's Manual INETD(8)
EXAMPLES
Here are several example service entries for the various
types of services:
ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l
ntalk dgram udp wait root /usr/libexec/ntalkd ntalkd
tcpmux/+date stream tcp nowait guest /bin/date date
tcpmux/phonebook stream tcp nowait guest /usr/local/phonebook phonebook
ERROR MESSAGES
The inetd server logs error messages using syslog(3).
Important error messages and their explanations are:
_s_e_r_v_i_c_e/_p_r_o_t_o_c_o_l server failing (looping), service ter-
minated.
The number of requests for the specified service in the past
minute exceeded the limit. The limit exists to prevent a
broken program or a malicious user from swamping the system.
This message may occur for several reasons: 1) there are
lots of hosts requesting the service within a short time
period, 2) a 'broken' client program is requesting the ser-
vice too frequently, 3) a malicious user is running a pro-
gram to invoke the service in a 'denial of service' attack,
or 4) the invoked service program has an error that causes
clients to retry quickly. Use the -R option, as described
above, to change the rate limit. Once the limit is reached,
the service will be reenabled automatically in 10 minutes.
_s_e_r_v_i_c_e/_p_r_o_t_o_c_o_l: No such user '_u_s_e_r', service ignored
_s_e_r_v_i_c_e/_p_r_o_t_o_c_o_l: getpwnam: _u_s_e_r: No such user
No entry for _u_s_e_r exists in the _p_a_s_s_w_d file. The first mes-
sage occurs when inetd (re)reads the configuration file. The
second message occurs when the service is invoked.
_s_e_r_v_i_c_e: can't set uid _n_u_m_b_e_r
_s_e_r_v_i_c_e: can't set gid _n_u_m_b_e_r
The user or group ID for the entry's _u_s_e_r is invalid.
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. TCPMUX is based on
code and documentation by Mark Lottor.
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