inetd - internet ``super-server''
inetd [-d] [-R rate] [configuration file]
inetd should be run at boot time by /etc/rc (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 options are as follows:
-d Turns on debugging.
-R rate
Specify the maximum number of times a service can be
invoked in
one minute; the default is 256.
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. The fields of the configuration file
are as follows:
service name
socket type
protocol
wait/nowait[.max]
user[.group] or user[:group]
server program
server program arguments
To specify a Sun-RPC based service, the entry would contain
these fields.
service name/version
socket type
rpc/protocol
wait/nowait[.max]
user[.group] or user[:group]
server program
server program arguments
For internet services, the first field of the line may also
have a host
address specifier prefixed to it, separated from the service
name by a
colon. If this is done, the string before the colon in the
first field
indicates what local address inetd should use when listening
for that
service. Multiple local addresses can be specified on the
same line,
separated by commas. Numeric IP addresses in dotted-quad
notation can be
used as well as symbolic hostnames. Symbolic hostnames are
looked up using
gethostbyname(). If a hostname has multiple address
mappings, inetd
creates a socket to listen on each address.
The single character ``*'' indicates INADDR_ANY, meaning
``all local
addresses''. To avoid repeating an address that occurs frequently, a
line with a host address specifier and colon, but no further
fields,
causes the host address specifier to be remembered and used
for all further
lines with no explicit host specifier (until another
such line or
the end of the file). A line
*:
is implicitly provided at the top of the file; thus, traditional configuration
files (which have no host address specifiers) will be
interpreted
in the traditional manner, with all services listened for on
all local
addresses. If the protocol is ``unix'', this value is ignored.
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''. For UNIX
domain sockets
this field specifies the path name of the socket.
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''. RPC based services are
specified with
the ``rpc/tcp'' or ``rpc/udp'' service type. ``tcp'' and
``udp'' will be
recognized as ``TCP or UDP over default IP version''. This
is currently
IPv4, but in the future it will be IPv6. If you need to
specify IPv4 or
IPv6 explicitly, use something like ``tcp4'' or ``udp6''. A
protocol of
``unix'' is used to specify a socket in the UNIX domain.
The wait/nowait entry is used to tell inetd if it should
wait for the
server program to return, or continue processing connections
on the socket.
If a datagram server connects to its peer, freeing the
socket so
inetd can receive 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 ``singlethreaded'' 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 256.
Stream servers are usually marked as ``nowait'' but if a
single server
process is to handle multiple connections, it may be marked
as ``wait''.
The master socket will then be passed as fd 0 to the server,
which will
then need to accept the incoming connection. The server
should eventually
time out and exit when no more connections are active.
inetd will
continue to listen on the master socket for connections, so
the server
should not close it when it exits.
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.
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.
IPv6 TCP/UDP behavior
If you wish to run a server for IPv4 and IPv6 traffic,
you'll need to run
two separate processes for the same server program, specified as two separate
lines in inetd.conf, for ``tcp4'' and ``tcp6''.
Under various combinations of IPv4/v6 daemon settings, inetd
will behave
as follows:
+o If you have only one server on ``tcp4'', IPv4 traffic
will be routed
to the server. IPv6 traffic will not be accepted.
+o If you have two servers on ``tcp4'' and ``tcp6'', IPv4
traffic will
be routed to the server on ``tcp4'', and IPv6 traffic
will go to
server on ``tcp6''.
+o If you have only one server on ``tcp6'', only IPv6 traffic will be
routed to the server.
comsat(8), fingerd(8), ftp-proxy(8), ftpd(8), identd(8),
rshd(8),
talkd(8), telnetd(8), tftpd(8)
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 added by
the KAME project in 1999.
Host address specifiers, while they make conceptual sense
for RPC services,
do not work entirely correctly. This is largely because the
portmapper interface does not provide a way to register different ports
for the same service on different local addresses. Provided
you never
have more than one entry for a given RPC service, everything
should work
correctly. (Note that default host address specifiers do
apply to RPC
lines with no explicit specifier.)
``rpc'' or ``tcpmux'' on IPv6 is not tested enough. Kerberos support on
IPv6 is not tested.
OpenBSD 3.6 March 16, 1991
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