INETD(8) BSD System Managers Manual INETD(8)
inetd - internet super-server
inetd [-d] [-l] [-E] [-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 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 options are as follows:
-d Turns on debugging.
-E Prevents inetd from laundering the environment. Without this
option a selection of environent variables believed by the
authors to be harmful, including PATH, will be removed and not
inherited by services.
-l Turns on libwrap connection logging. Internal services cannot be
wrapped. When enabled, /usr/sbin/tcpd is silently not executed
even if present in /etc/inetd.conf.
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. The fields of the configuration file are as
user[.group] or user[:group]
server program arguments
To specify a Sun-RPC based service, the entry would contain these fields.
user[.group] or user[:group]
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 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. 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. Exam
ples might be unix, 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.
In addition to the protocol, the configuration file may specify the send
and receive socket buffer sizes for the listening socket. This is espe
cially useful for TCP as the window scale factor, which is based on the
receive socket buffer size, is advertised when the connection handshake
occurs, thus the socket buffer size for the server must be set on the
listen socket. By increasing the socket buffer sizes, better TCP perfor
mance may be realized in some situations. The socket buffer sizes are
specified by appending their values to the protocol specification as fol
A literal value may be specified, or modified using k to indicate kilo
bytes or m to indicate megabytes.
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 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 exception; it is a data
gram server that establishes pseudo-connections. It must be listed as
wait in order to avoid a race; the server reads the first packet, cre
ates 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 pro
cess 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 con
tinue 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, which is the name of the program. If the service
is provided internally, the word internal should take the place of this
inetd provides several trivial services internally by use of routines
within itself. These services are echo, discard, chargen (charac
ter generator), daytime (human readable time), and time (machine
readable time, in the form of the number of seconds since midnight, Jan
uary 1, 1900). All of these services are TCP based. For details of
these services, consult the appropriate RFC from the Network Information
inetd rereads its configuration file when it receives a hangup signal,
SIGHUP. Services may be added, deleted or modified when the configura
tion file is reread. inetd creates a file /var/run/inetd.pid that con
tains its process identifier.
Support for TCP wrappers is included with inetd to provide built-in tcpd-
like access control functionality. An external tcpd program is not
needed. You do not need to change the /etc/inetd.conf server-program
entry to enable this capability. inetd uses /etc/hosts.allow and
/etc/hosts.deny for access control facility configurations, as described
IPv6 TCP/UDP behavior
If you wish to run a server for IPv4 and IPv6 traffic, youll need to run
two separate processes for the same server program, specified as two sep
arate lines in inetd.conf, for tcp4 and tcp6.
Under various combinations of IPv4/v6 daemon settings, inetd will behave
If you have only one server on tcp4, IPv4 traffic will be routed to
the server. IPv6 traffic will not be accepted.
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
If you have only one server on tcp6, only IPv6 traffic will be
routed to the server.
The special tcp46 parameter can be used for obsolete servers which
require to receive IPv4 connections mapped in an IPv6 socket. Its
usage is discouraged.
fingerd(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.
Marco dItri ported this code from OpenBSD in summer 2002 and added
socket buffers tuning and libwrap support from the NetBSD source tree.
On Linux systems, the daemon cannot reload its configuration and needs to
be restarted when the host address for a service is changed between *
and a specific address.
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.)
rpc on IPv6 is not tested enough. Kerberos support on IPv6 is not
BSD March 16, 1991 BSD