INETD(8) OpenBSD System Manager's Manual INETD(8)
NAME
inetd - internet ``super-server''
SYNOPSIS
inetd [-d] [-R rate] [configuration file]
DESCRIPTION
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 fin-
ished, 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 option available for inetd:
-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 configu-
ration 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
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, sep-
arated by commas. Numeric IP addresses in dotted-quad notation can be
used as well as symbolic hostnames. Symbolic hostnames are looked up us-
ing 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 configu-
ration files (which have no host address specifiers) will be interpreted
in the traditional manner, with all services listened for on all local
addresses.
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''.
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. Exam-
ples might be ``tcp'' or ``udp''. RPC based services are specified with
the ``rpc/tcp'' or ``rpc/udp'' service type.
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 sock-
et. 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 ``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 excep-
tion; 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 op-
tional ``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.
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 eventual-
ly 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. identd(8) is usually the only stream
server marked as wait.
The user entry should contain the user name of the user as whom the serv-
er 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 associ-
ated 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 mid-
night, January 1, 1900). All of these services are TCP based. For de-
tails of these services, consult the appropriate RFC from the Network In-
formation 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.
BUGS
Host address specifiers, while they make conceptual sense for RPC ser-
vices, 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.)
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 modeled after that provided by SunOS 4.1.
OpenBSD 2.6 March 16, 1991