path: root/upstream/debian-bookworm/man8/inetd.8

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.\"     from: @(#)inetd.8	6.7 (Berkeley) 3/16/91
.\"
.Dd $Mdocdate: February 10 2020 $
.Dt INETD 8
.Os
.Sh NAME
.Nm inetd ,
.Nm inetd.conf
.Nd internet super-server
.Sh SYNOPSIS
.Nm inetd
.Op Fl d
.Op Fl E
.Op Fl i
.Op Fl l
.Op Fl q Ar length
.Op Fl R Ar rate
.Op Ar configuration_file
.Sh DESCRIPTION
.Nm inetd
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 inetd
allows running one daemon to invoke several others,
reducing load on the system.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl d
Turns on debugging.
.It Fl E
Prevents
.Nm inetd
from laundering the environment.  Without this option a selection of
potentially harmful environment variables, including
.Pa PATH ,
will be removed and not inherited by services.
.It Fl i
Makes the program not daemonize itself.
.It Fl l
Turns on libwrap connection logging and access control.
Internal services cannot be wrapped.  When enabled,
.Pa /usr/sbin/tcpd
is silently not executed even if present in
.Pa /etc/inetd.conf
and instead libwrap is called directly by inetd.
.It Fl q Ar length
Specify the length of the
.Xr listen 2
connections queue; the default is 128.
.It Fl R Ar rate
Specify the maximum number of times a service can be invoked
in one minute; the default is 256.
If a service exceeds this limit,
.Nm
will log the problem
and stop servicing requests for the specific service for ten minutes.
See also the wait/nowait configuration fields below.
.El
.Pp
Upon execution,
.Nm inetd
reads its configuration information from a configuration
file which, by default, is
.Pa /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
.Dq #
at the beginning
of a line.
The fields of the configuration file are as follows:
.Bd -unfilled -offset indent
service name
socket type
protocol[,sndbuf=size][,rcvbuf=size]
wait/nowait[.max]
user[.group] or user[:group]
server program
server program arguments
.Ed
.Pp
To specify a Sun-RPC
based service, the entry would contain these fields.
.Bd -unfilled -offset indent
service name/version
socket type
rpc/protocol[,sndbuf=size][,rcvbuf=size]
wait/nowait[.max]
user[.group] or 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.
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
.Fn getaddrinfo .
If a hostname has multiple address mappings, inetd creates a socket
to listen on each address.
.Pp
The single character
.Dq \&*
indicates
.Dv INADDR_ANY ,
meaning
.Dq 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.
If the protocol is
.Dq unix ,
this value is ignored.
.Pp
The
.Em service name
entry is the name of a valid service in
the file
.Pa /etc/services
or a port number.
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 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 .
For
.Ux Ns -domain
sockets this field specifies the path name of the socket.
.Pp
The
.Em socket type
should be one of
.Dq stream
or
.Dq dgram ,
depending on whether the socket is a stream or datagram socket.
.Pp
The
.Em protocol
must be a valid protocol as given in
.Pa /etc/protocols or
.Dq unix .
Examples might be
.Dq tcp
or
.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 both IPv4 and IPv6.
If you need to specify IPv4 or IPv6 explicitly, use something like
.Dq tcp4
or
.Dq udp6 .
A
.Em protocol
of
.Dq unix
is used to specify a socket in the
.Ux Ns -domain .
.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.
.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 inetd
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.
The optional
.Dq max
suffix (separated from
.Dq wait
or
.Dq nowait
by a dot) specifies the maximum number of times a service can be invoked
in one minute; the default is 256.
If a service exceeds this limit,
.Nm
will log the problem
and stop servicing requests for the specific service for ten minutes.
See also the
.Fl R
option above.
.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.
.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.
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.
.Pp
The
.Em server program
entry should contain the pathname of the program which is to be
executed by
.Nm inetd
when a request is found on its socket.
If
.Nm inetd
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.
.Pp
.Nm inetd
provides several
.Dq trivial
services internally by use of routines within itself.
These services are
.Dq echo ,
.Dq discard ,
.Dq chargen
(character generator),
.Dq daytime
(human readable time), and
.Dq 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.
.Pp
.Nm inetd
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.
.Ss libwrap
Support for
.Tn TCP
wrappers is included with
.Nm
to provide built-in 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 IPv6 TCP/UDP behavior
The default is to run two servers: one for IPv4 and one for IPv6 traffic.
If you have different requirements then you may specify one or two
separate lines in
.Pa inetd.conf ,
for
.Dq tcp4
and
.Dq tcp6 .
.Pp
Under various combinations 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 the server on
.Dq tcp6 ,
which is identical to the default behaviour when only
.Dq tcp
is specified.
.It
If you have only one server on
.Dq tcp6 ,
only IPv6 traffic will be routed to the server.
.Pp
The special
.Dq tcp46
parameter can be used for obsolete servers which require to receive IPv4
connections mapped in an IPv6 socket. Its usage is discouraged.
.El
.Sh FILES
.Bl -tag -width /etc/inetd.conf -compact
.It Pa /etc/inetd.conf
.El
.Sh SEE ALSO
.Xr fingerd 8 ,
.Xr ftpd 8 ,
.Xr identd 8 ,
.Xr talkd 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .
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.
.Pp
Marco d'Itri ported this code from OpenBSD in summer 2002 and added
socket buffers tuning and libwrap support from the NetBSD source tree.
.Sh BUGS
On Linux systems, the daemon cannot reload its configuration and needs
to be restarted when the host address for a service is changed between
.Dq \&*
and a specific address.
.Pp
Server programs used with
.Dq dgram
.Dq udp
.Dq nowait
must read from the network socket, or
.Nm inetd
will spawn processes until the maximum is reached.
.Pp
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.)