usr.sbin/inetd/inetd.8

.\"	$NetBSD: inetd.8,v 1.37 2002/01/19 03:14:33 wiz Exp $
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.\"     from: @(#)inetd.8       8.4 (Berkeley) 6/1/94
.\"
.Dd March 10, 2001
.Dt INETD 8
.Os
.Sh NAME
.Nm inetd ,
.Nm inetd.conf
.Nd internet
.Dq super-server
.Sh SYNOPSIS
.Nm
.Op Fl d
.Op Fl l
.Op Ar configuration file
.Sh DESCRIPTION
.Nm
should be run at boot time by
.Pa /etc/rc
(see
.Xr 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,
.Nm
allows running one daemon to invoke several others,
reducing load on the system.
.Pp
The options available for
.\" Why doesn't just `.Nm :' work?
.Nm "" :
.Bl -tag -width Ds
.It Fl d
Turns on debugging.
.El
.Pp
.Bl -tag -width Ds
.It Fl l
Turns on libwrap connection logging.
.El
.Pp
Upon execution,
.Nm
reads its configuration information from a configuration
file which, by default, is
.Pa /etc/inetd.conf .
The path given for this configuration file must be absolute, unless
the
.Fl d
option is also given on the command line.
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 (except for one
special case, described below).
The fields of the configuration file are as follows:
.Pp
.Bd -unfilled -offset indent -compact
[addr:]service-name
socket-type
protocol[,sndbuf=size][,rcvbuf=size]
wait/nowait[:max]
user[:group]
server-program
server program arguments
.Ed
.Pp
To specify an
.Em Sun-RPC
based service, the entry would contain these fields.
.Pp
.Bd -unfilled -offset indent -compact
service-name/version
socket-type
rpc/protocol[,sndbuf=size][,rcvbuf=size]
wait/nowait[:max]
user[:group]
server-program
server program arguments
.Ed
.Pp
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
.Nm
should use when listening for that service, or the single character
.Dq \&*
to indicate
.Dv INADDR_ANY ,
meaning
.Sq 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
.Dl *:
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.
.Pp
The
.Em service-name
entry is the name of a valid service in
the file
.Pa /etc/services .
For
.Dq internal
services (discussed below), the service
name
.Em must
be the official name of the service (that is, the first entry in
.Pa /etc/services ) .
When used to specify a
.Em Sun-RPC
based service, this field is a valid RPC service name in
the file
.Pa /etc/rpc .
The part on the right of the
.Dq /
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 \-
.Dq rusers/1-3 .
.Pp
The
.Em socket-type
should be one of
.Dq stream ,
.Dq dgram ,
.Dq raw ,
.Dq rdm ,
or
.Dq seqpacket ,
depending on whether the socket is a stream, datagram, raw,
reliably delivered message, or sequenced packet socket.
.Pp
The
.Em protocol
must be a valid protocol as given in
.Pa /etc/protocols .
Examples might be
.Dq tcp
and
.Dq udp .
Rpc based services are specified with the
.Dq rpc/tcp
or
.Dq rpc/udp
service type.
.Dq tcp
and
.Dq udp
will be recognized as
.Dq TCP or UDP over default IP version .
It is currently IPv4, but in the future it will be IPv6.
If you need to specify IPv4 or IPv6 explicitly, use something like
.Dq tcp4
or
.Dq udp6 .
If you would like to enable special support for
.Xr faithd 8 ,
prepend a keyword
.Dq faith
into
.Em protocol ,
like
.Dq faith/tcp6 .
.Pp
In addition to the protocol, the configuration file may specify the
send and receive socket buffer sizes for the listening socket.
This is especially useful for
.Tn 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
.Tn TCP
performance may be realized in some situations.
The socket buffer sizes are specified by appending their values to
the protocol specification as follows:
.Bd -literal -offset indent
tcp,rcvbuf=16384
tcp,sndbuf=64k
tcp,rcvbuf=64k,sndbuf=1m
.Ed
.Pp
A literal value may be specified, or modified using
.Sq k
to indicate kilobytes or
.Sq m
to indicate megabytes.
Socket buffer sizes may be specified for all
services and protocols except for tcpmux services.
.Pp
The
.Em wait/nowait
entry is used to tell
.Nm
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
.Nm
can receive further messages on the socket, it is said to be
a
.Dq multi-threaded
server, and should use the
.Dq nowait
entry.
For datagram servers which process all incoming datagrams
on a socket and eventually time out, the server is said to be
.Dq single-threaded
and should use a
.Dq wait
entry.
.Xr comsat 8
.Pq Xr biff 1
and
.Xr talkd 8
are both examples of the latter type of
datagram server.
.Xr tftpd 8
is an exception; it is a datagram server that establishes pseudo-connections.
It must be listed as
.Dq wait
in order to avoid a race;
the server reads the first packet, creates a new socket,
and then forks and exits to allow
.Nm
to check for new service requests to spawn new servers.
The optional
.Dq max
suffix (separated from
.Dq wait
or
.Dq nowait
by a dot or a colon) specifies the maximum number of server instances that may
be spawned from
.Nm
within an interval of 60 seconds.
When omitted,
.Dq max
defaults to 40.
.Pp
Stream servers are usually marked as
.Dq nowait
but if a single server process is to handle multiple connections, it may be
marked as
.Dq 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.
.Nm
will continue to
listen on the master socket for connections, so the server should not close
it when it exits.
.Xr identd 8
is usually the only stream server marked as wait.
.Pp
The
.Em 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.
Optionally, a group can be specified by appending a colon to the user name,
followed by the group name (it is possible to use a dot (``.'') in lieu of a
colon, however this feature is provided only for backward compatibility).
This allows for servers to run with a different (primary) group id than
specified in the password file.
If a group is specified and
.Em user
is not root, the supplementary groups associated with that user will still be
set.
.Pp
The
.Em server-program
entry should contain the pathname of the program which is to be
executed by
.Nm
when a request is found on its socket.
If
.Nm
provides this service internally, this entry should
be
.Dq internal .
.Pp
The
.Em 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
.Dq internal
should take the place of this entry.
.Ss Internal Services
.Nm
provides several
.Qq trivial
services internally by use of routines within itself.
These services are
.Qq echo ,
.Qq discard ,
.Qq chargen
(character generator),
.Qq daytime
(human readable time), and
.Qq time
(machine readable time,
in the form of the number of seconds since midnight, January 1, 1900 GMT).
For details of these services, consult the appropriate
.Tn RFC .
.Pp
TCP services without official port numbers can be handled with the
RFC1078-based tcpmux internal service.
TCPmux listens on port 1 for requests.
When a connection is made from a foreign host, the service name
requested is passed to TCPmux, which performs a lookup in the
service name table provided by
.Pa /etc/inetd.conf
and returns the proper entry for the service.
TCPmux returns a negative reply if the service doesn't exist,
otherwise the invoked server is expected to return the positive
reply if the service type in
.Pa /etc/inetd.conf
file has the prefix
.Qq tcpmux/ .
If the service type has the
prefix
.Qq tcpmux/+ ,
TCPmux will return the positive reply for the
process; this is for compatibility with older server code, and also
allows you to invoke programs that use stdin/stdout without putting any
special server code in them.
Services that use TCPmux are
.Qq nowait
because they do not have a well-known port nubmer and hence cannot listen
for new requests.
.Pp
.Nm
rereads its configuration file when it receives a hangup signal,
.Dv SIGHUP .
Services may be added, deleted or modified when the configuration file
is reread.
.Nm
creates a file
.Em /var/run/inetd.pid
that contains its process identifier.
.Ss libwrap
Support for
.Tn TCP
wrappers is included with
.Nm
to provide internal tcpd-like access control functionality.
An external tcpd program is not needed.
You do not need to change the
.Pa /etc/inetd.conf
server-program entry to enable this capability.
.Nm
uses
.Pa /etc/hosts.allow
and
.Pa /etc/hosts.deny
for access control facility configurations, as described in
.Xr hosts_access 5 .
.Ss IPsec
The implementation includes a tiny hack to support IPsec policy settings for
each socket.
A special form of the comment line, starting with
.Dq Li "#@" ,
is used as a policy specifier.
The content of the above comment line will be treated as a IPsec policy string,
as described in
.Xr ipsec_set_policy 3 .
Multiple IPsec policy strings may be specified by using a semicolon
as a separator.
If conflicting policy strings are found in a single line,
the last string will take effect.
A
.Li "#@"
line affects all of the following lines in
.Pa /etc/inetd.conf ,
so you may want to reset the IPsec policy by using a comment line containing
only
.Li "#@"
.Pq with no policy string .
.Pp
If an invalid IPsec policy string appears in
.Pa /etc/inetd.conf ,
.Nm
logs an error message using
.Xr syslog 3
and terminates itself.
.Ss IPv6 TCP/UDP behavior
If you wish to run a server for IPv4 and IPv6 traffic,
you'll need to run two separate process for the same server program,
specified as two separate lines on
.Pa /etc/inetd.conf ,
for
.Dq tcp4
and
.Dq tcp6 .
.Dq tcp
means TCP on top of currently-default IP version,
which is, at this moment, IPv4.
.Pp
Under various combination of IPv4/v6 daemon settings,
.Nm
will behave as follows:
.Bl -bullet -compact
.It
If you have only one server on
.Dq tcp4 ,
IPv4 traffic will be routed to the server.
IPv6 traffic will not be accepted.
.It
If you have two servers on
.Dq tcp4
and
.Dq tcp6 ,
IPv4 traffic will be routed to the server on
.Dq tcp4 ,
and IPv6 traffic will go to server on
.Dq tcp6 .
.It
If you have only one server on
.Dq tcp6 ,
only IPv6 traffic will be routed to the server.
The kernel may route to the server IPv4 traffic as well,
under certain configuration.
See
.Xr ip6 4
for details.
.El
.Sh FILES
.Bl -tag -width /etc/hosts.allow -compact
.It Pa /etc/inetd.conf
configuration file for all
.Nm
provided services
.It Pa /etc/services
service name to protocol and port number mappings.
.It Pa /etc/protocols
protocol name to protocol number mappings
.It Pa /etc/rpc
.Tn Sun-RPC
service name to service number mappings.
.It Pa /etc/hosts.allow
explicit remote host access list.
.It Pa /etc/hosts.deny
explicit remote host denial of service list.
.El
.Sh SEE ALSO
.Xr hosts_access 5 ,
.Xr hosts_options 5 ,
.Xr protocols 5 ,
.Xr rpc 5 ,
.Xr services 5 ,
.Xr comsat 8 ,
.Xr fingerd 8 ,
.Xr ftpd 8 ,
.Xr rexecd 8 ,
.Xr rlogind 8 ,
.Xr rshd 8 ,
.Xr telnetd 8 ,
.Xr tftpd 8
.Rs
.%A J. Postel
.%R RFC
.%N 862
.%D May 1983
.%T "Echo Protocol"
.Re
.Rs
.%A J. Postel
.%R RFC
.%N 863
.%D May 1983
.%T "Discard Protocol"
.Re
.Rs
.%A J. Postel
.%R RFC
.%N 864
.%D May 1983
.%T "Character Generator Protocol"
.Re
.Rs
.%A J. Postel
.%R RFC
.%N 867
.%D May 1983
.%T "Daytime Protocol"
.Re
.Rs
.%A J. Postel
.%A K. Harrenstien
.%R RFC
.%N 868
.%D May 1983
.%T "Time Protocol"
.Re
.Rs
.%A M. Lottor
.%R RFC
.%N 1078
.%D November 1988
.%T "TCP port service Multiplexer (TCPMUX)"
.Re
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .
Support for
.Em Sun-RPC
based services is modeled after that
provided by SunOS 4.1.
Support for specifying the socket buffer sizes was added in
.Nx 1.4 .
In November 1996, libwrap support was added to provide
internal tcpd-like access control functionality;
libwrap is based on Wietse Venema's tcp_wrappers.
IPv6 support and IPsec hack was made by KAME project, in 1999.
.Sh BUGS
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.)
.Pp
.Dq tcpmux
on IPv6 is not tested enough.
.Sh SECURITY CONSIDERATIONS
Enabling the
.Dq echo ,
.Dq discard ,
and
.Dq chargen
built-in trivial services is not recommended because remote
users may abuse these to cause a denial of network service to
or from the local host.