usr.sbin/inetd/inetd.8

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.\"     from: @(#)inetd.8	8.3 (Berkeley) 4/13/94
.\" $FreeBSD$
.\"
.Dd May 14, 2020
.Dt INETD 8
.Os
.Sh NAME
.Nm inetd
.Nd internet
.Dq super-server
.Sh SYNOPSIS
.Nm
.Op Fl d
.Op Fl l
.Op Fl w
.Op Fl W
.Op Fl c Ar maximum
.Op Fl C Ar rate
.Op Fl a Ar address | hostname
.Op Fl p Ar filename
.Op Fl R Ar rate
.Op Fl s Ar maximum
.Op Ar configuration file
.Sh DESCRIPTION
The
.Nm
utility 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.
The server program is invoked with the service socket
as its standard input, output and error descriptors.
After the program is
finished,
.Nm
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 following options are available:
.Bl -tag -width indent
.It Fl d
Turn on debugging.
.It Fl l
Turn on logging of successful connections.
.It Fl w
Turn on TCP Wrapping for external services.
See the
.Sx "IMPLEMENTATION NOTES"
section for more information on TCP Wrappers support.
.It Fl W
Turn on TCP Wrapping for internal services which are built in to
.Nm .
.It Fl c Ar maximum
Specify the default maximum number of
simultaneous invocations of each service;
the default is unlimited.
May be overridden on a per-service basis with the "max-child"
parameter.
.It Fl C Ar rate
Specify the default maximum number of times a service can be invoked
from a single IP address in one minute; the default is unlimited.
May be overridden on a per-service basis with the
"max-connections-per-ip-per-minute" parameter.
.It Fl R Ar rate
Specify the maximum number of times a service can be invoked
in one minute; the default is 256.
A rate of 0 allows an unlimited number of invocations.
.It Fl s Ar maximum
Specify the default maximum number of
simultaneous invocations of each service from a single IP address;
the default is unlimited.
May be overridden on a per-service basis with the "max-child-per-ip"
parameter.
.It Fl a
Specify one specific IP address to bind to.
Alternatively, a hostname can be specified,
in which case the IPv4 or IPv6 address
which corresponds to that hostname is used.
Usually a hostname is specified when
.Nm
is run inside a
.Xr jail 8 ,
in which case the hostname corresponds to that of the
.Xr jail 8
environment.
.Pp
When the hostname specification is used
and both IPv4 and IPv6 bindings are desired,
one entry with the appropriate
.Em protocol
type for each binding
is required for each service in
.Pa /etc/inetd.conf .
For example,
a TCP-based service would need two entries,
one using
.Dq tcp4
for the
.Em protocol
and the other using
.Dq tcp6 .
See the explanation of the
.Pa /etc/inetd.conf
.Em protocol
field below.
.It Fl p
Specify an alternate file in which to store the process ID.
.El
.Pp
Upon execution,
.Nm
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.
There must be an entry for each field.
The
fields of the configuration file are as follows:
.Pp
.Bd -unfilled -offset indent -compact
service-name
socket-type
protocol
{wait|nowait}[/max-child[/max-connections-per-ip-per-minute[/max-child-per-ip]]]
user[:group][/login-class]
server-program
server-program-arguments
.Ed
.Pp
To specify an
.Tn "ONC RPC" Ns -based
service, the entry would contain these fields:
.Pp
.Bd -unfilled -offset indent -compact
service-name/version
socket-type
rpc/protocol
{wait|nowait}[/max-child[/max-connections-per-ip-per-minute[/max-child-per-ip]]]
user[:group][/login-class]
server-program
server-program-arguments
.Ed
.Pp
There are two types of services that
.Nm
can start: standard and TCPMUX.
A standard service has a well-known port assigned to it;
it may be a service that implements an official Internet standard or is a
.Bx Ns -specific
service.
As described in
.Tn RFC 1078 ,
TCPMUX services are nonstandard services that do not have a
well-known port assigned to them.
They are invoked from
.Nm
when a program connects to the
.Dq tcpmux
well-known port and specifies
the service name.
This feature is useful for adding locally-developed servers.
TCPMUX requests are only accepted when the multiplexor service itself
is enabled, above and beyond and specific TCPMUX-based servers; see the
discussion of internal services below.
.Pp
The
.Em service-name
entry is the name of a valid service in
the file
.Pa /etc/services ,
or the specification of a
.Ux
domain socket (see below).
For
.Dq internal
services (discussed below), the service
name
should
be the official name of the service (that is, the first entry in
.Pa /etc/services ) .
When used to specify an
.Tn "ONC RPC" Ns -based
service, this field is a valid RPC service name listed 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 TCPMUX services, the value of the
.Em service-name
field consists of the string
.Dq tcpmux
followed by a slash and the
locally-chosen service name.
The service names listed in
.Pa /etc/services
and the name
.Dq help
are reserved.
Try to choose unique names for your TCPMUX services by prefixing them with
your organization's name and suffixing them with a version number.
.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.
TCPMUX services must use
.Dq stream .
.Pp
The
.Em protocol
must be a valid protocol or
.Dq unix .
Examples are
.Dq tcp
or
.Dq udp ,
both of which imply IPv4 for backward compatibility.
The names
.Dq tcp4
and
.Dq udp4
specify IPv4 only.
The names
.Dq tcp6
and
.Dq udp6
specify IPv6 only.
The names
.Dq tcp46
and
.Dq udp46
specify that the entry accepts both IPv4 and IPv6 connections
via a wildcard
.Dv AF_INET6
socket.
Rpc based services
are specified with the
.Dq rpc/tcp
or
.Dq rpc/udp
service type.
One can use specify IPv4 and/or IPv6 with the 4, 6 or 46 suffix, for example
.Dq rpc/tcp6
or
.Dq rpc/udp46 .
TCPMUX services must use
.Dq tcp ,
.Dq tcp4 ,
.Dq tcp6
or
.Dq tcp46 .
.Pp
The
.Em wait/nowait
entry specifies whether the server that is invoked by
.Nm
will take over
the socket associated with the service access point, and thus whether
.Nm
should wait for the server to exit before listening for new service
requests.
Datagram servers must use
.Dq wait ,
as they are always invoked with the original datagram socket bound
to the specified service address.
These servers must read at least one datagram from the socket
before exiting.
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;
it should read one datagram from the socket and create a new socket
connected to the peer.
It should fork, and the parent should then exit
to allow
.Nm
to check for new service requests to spawn new servers.
Datagram servers which process all incoming datagrams
on a socket and eventually time out are said to be
.Dq single-threaded .
The
.Xr comsat 8
and
.Xr talkd 8
utilities are examples of the latter type of
datagram server.
The
.Xr tftpd 8
utility is an example of a multi-threaded datagram server.
.Pp
Servers using stream sockets generally are multi-threaded and
use the
.Dq nowait
entry.
Connection requests for these services are accepted by
.Nm ,
and the server is given only the newly-accepted socket connected
to a client of the service.
Most stream-based services operate in this manner.
Stream-based servers that use
.Dq wait
are started with the listening service socket, and must accept
at least one connection request before exiting.
Such a server would normally accept and process incoming connection
requests until a timeout.
TCPMUX services must use
.Dq nowait .
.Pp
The maximum number of outstanding child processes (or
.Dq threads )
for a
.Dq nowait
service may be explicitly specified by appending a
.Dq /
followed by the number to the
.Dq nowait
keyword.
Normally
(or if a value of zero is specified) there is no maximum.
Otherwise,
once the maximum is reached, further connection attempts will be
queued up until an existing child process exits.
This also works
in the case of
.Dq wait
mode, although a value other than one (the
default) might not make sense in some cases.
You can also specify the maximum number of connections per minute
for a given IP address by appending
a
.Dq /
followed by the number to the maximum number of
outstanding child processes.
Once the maximum is reached, further
connections from this IP address will be dropped until the end of the
minute.
In addition, you can specify the maximum number of simultaneous
invocations of each service from a single IP address by appending a
.Dq /
followed by the number to the maximum number of outstanding child
processes.
Once the maximum is reached, further connections from this
IP address will be dropped.
.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.
The optional
.Em group
part separated by
.Dq \&:
allows a group name other
than the default group for this user to be specified.
The optional
.Em login-class
part separated by
.Dq /
allows specification of a login class other
than the default
.Dq daemon
login class.
.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
entry lists the arguments to be passed to the
.Em server-program ,
starting with argv[0], which usually is the name of
the program.
If the service is provided internally, the
.Em service-name
of the service (and any arguments to it) or the word
.Dq internal
should take the place of this entry.
.Pp
Currently, the only internal service to take arguments is
.Dq auth .
Without options, the service will always return
.Dq ERROR\ : HIDDEN-USER .
The available arguments to this service that alter its behavior are:
.Bl -tag -width indent
.It Fl d Ar fallback
Provide a
.Ar fallback
username.
If the real
.Dq auth
service is enabled
(with the
.Fl r
option discussed below),
return this username instead of an error
when lookups fail
for either socket credentials or the username.
If the real
.Dq auth
service is disabled,
return this username for every request.
This is primarily useful when running this service on a NAT machine.
.It Fl g
Instead of returning
the user's name to the ident requester,
report a
username made up of random alphanumeric characters,
e.g.\&
.Dq c0c993 .
The
.Fl g
flag overrides not only the user names,
but also any fallback name,
.Pa .fakeid
or
.Pa .noident
files.
.It Fl t Xo
.Ar sec Ns Op . Ns Ar usec
.Xc
Specify a timeout for the service.
The default timeout is 10.0 seconds.
.It Fl r
Offer a real
.Dq auth
service, as per RFC 1413.
All the remaining flags apply only in this case.
.It Fl i
Return numeric user IDs instead of usernames.
.It Fl f
If the file
.Pa .fakeid
exists in the home directory of the identified user, report the username
found in that file instead of the real username.
If the username found in
.Pa .fakeid
is that of an existing user,
then the real username is reported.
If the
.Fl i
flag is also given then the username in
.Pa .fakeid
is checked against existing user IDs instead.
.It Fl F
same as
.Fl f
but without the restriction that the username in
.Pa .fakeid
must not match an existing user.
.It Fl n
If the file
.Pa .noident
exists in the home directory of the identified user, return
.Dq ERROR\ : HIDDEN-USER .
This overrides any
.Pa fakeid
file which might exist.
.It Fl o Ar osname
Use
.Ar osname
instead of the name of the system as reported by
.Xr uname 3 .
.El
.Pp
The
.Nm
utility also provides several other
.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 available in
both TCP and UDP versions; the UDP versions will refuse service if the
request specifies a reply port corresponding to any internal service.
(This is done as a defense against looping attacks; the remote IP address
is logged.)
For details of these services, consult the
appropriate
.Tn RFC
document.
.Pp
The TCPMUX-demultiplexing service is also implemented as an internal service.
For any TCPMUX-based service to function, the following line must be included
in
.Pa inetd.conf :
.Bd -literal -offset indent
tcpmux	stream	tcp	nowait	root	internal
.Ed
.Pp
When given the
.Fl l
option
.Nm
will log an entry to syslog each time a connection is accepted, noting the
service selected and the IP-number of the remote requester if available.
Unless otherwise specified in the configuration file,
and in the absence of the
.Fl W
and
.Fl w
options,
.Nm
will log to the
.Dq daemon
facility.
.Pp
The
.Nm
utility 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.
Except when started in debugging mode,
or configured otherwise with the
.Fl p
option,
.Nm
records its process ID in the file
.Pa /var/run/inetd.pid
to assist in reconfiguration.
.Sh IMPLEMENTATION NOTES
.Ss TCP Wrappers
When given the
.Fl w
option,
.Nm
will wrap all services specified as
.Dq stream nowait
or
.Dq dgram
except for
.Dq internal
services.
If the
.Fl W
option is given, such
.Dq internal
services will be wrapped.
If both options are given, wrapping for both
internal and external services will be enabled.
Either wrapping option
will cause failed connections to be logged to the
.Dq auth
syslog facility.
Adding the
.Fl l
flag to the wrapping options will include successful connections in the
logging to the
.Dq auth
facility.
.Pp
Note that
.Nm
only wraps requests for a
.Dq wait
service while no servers are available to service requests.
Once a
connection to such a service has been allowed,
.Nm
has no control
over subsequent connections to the service until no more servers
are left listening for connection requests.
.Pp
When wrapping is enabled, the
.Pa tcpd
daemon is not required, as that functionality is builtin.
For more information on TCP Wrappers, see the relevant documentation
.Pq Xr hosts_access 5 .
When reading that document, keep in mind that
.Dq internal
services have no associated daemon name.
Therefore, the service name
as specified in
.Pa inetd.conf
should be used as the daemon name for
.Dq internal
services.
.Ss TCPMUX
.Tn RFC 1078
describes the TCPMUX protocol:
``A TCP client connects to a foreign host on TCP port 1.
It sends the
service name followed by a carriage-return line-feed <CRLF>.
The
service name is never case sensitive.
The server replies with a
single character indicating positive (+) or negative (\-)
acknowledgment, immediately followed by an optional message of
explanation, terminated with a <CRLF>.
If the reply was positive,
the selected protocol begins; otherwise the connection is closed.''
The program is passed the TCP connection as file descriptors 0 and 1.
.Pp
If the TCPMUX service name begins with a
.Dq + ,
.Nm
returns the positive reply for the program.
This allows you to invoke programs that use stdin/stdout
without putting any special server code in them.
.Pp
The special service name
.Dq help
causes
.Nm
to list the TCPMUX services which are enabled in
.Pa inetd.conf .
.Ss IPsec
The implementation includes a tiny hack
to support IPsec policy settings for each socket.
A special form of comment line, starting with
.Dq Li #@ ,
is interpreted as a policy specifier.
Everything after the
.Dq Li #@
will be used as an IPsec policy string,
as described in
.Xr ipsec_set_policy 3 .
Each
policy specifier is applied to all the following lines in
.Pa inetd.conf
until the next policy specifier.
An empty policy specifier resets the IPsec policy.
.Pp
If an invalid IPsec policy specifier appears in
.Pa inetd.conf ,
.Nm
will provide an error message via the
.Xr syslog 3
interface and abort execution.
.Ss Ux Domain Sockets
In addition to running services on IP sockets,
.Nm
can also manage
.Ux
domain sockets.
To do this you specify a
.Em protocol
of
.Dq unix
and specify the
.Ux
domain socket as the
.Em service-name .
The
.Em service-type
may be
.Dq stream
or
.Dq dgram .
The specification of the socket must be
an absolute path name,
optionally prefixed by an owner and mode
of the form
.Em :user:group:mode: .
The specification:
.Pp
.Dl ":news:daemon:220:/var/run/sock"
.Pp
creates a socket owned
by user
.Dq news
in group
.Dq daemon
with permissions allowing only that user and group to connect.
The default owner is the user that
.Nm
is running as.
The default mode only allows the socket's owner to connect.
.Pp
.Sy WARNING :
while creating a
.Ux
domain socket,
.Nm
must change the ownership and permissions on the socket.
This can only be done securely if
the directory in which the socket is created
is writable only by root.
Do
.Em NOT
use
.Nm
to create sockets in world writable directories
such as
.Pa /tmp ;
use
.Pa /var/run
or a similar directory instead.
.Pp
Internal services may be run on
.Ux
domain sockets, in the usual way.
In this case
the name of the internal service
is determined using
the last component of the socket's pathname.
For example, specifying a socket named
.Pa /var/run/chargen
would invoke the
.Dq chargen
service when a connection is received on that socket.
.Sh "FILES"
.Bl -tag -width /var/run/inetd.pid -compact
.It Pa /etc/inetd.conf
configuration file
.It Pa /etc/netconfig
network configuration data base
.It Pa /etc/rpc
translation of service names to RPC program numbers
.It Pa /etc/services
translation of service names to port numbers
.It Pa /var/run/inetd.pid
the pid of the currently running
.Nm
.El
.Sh "EXAMPLES"
Here are several example service entries for the various types of services:
.Bd -literal
# The first four launch the relevant daemon when a connection on a port
# as defined by /etc/services is opened.
ftp          stream  tcp   nowait root  /usr/libexec/ftpd        ftpd -l
ntalk        dgram   udp   wait   root  /usr/libexec/ntalkd      ntalkd
telnet       stream  tcp6  nowait root  /usr/libexec/telnetd  telnetd
shell        stream  tcp46  nowait root  /usr/libexec/rshd rshd

# Let the system respond to date requests via tcpmux
tcpmux/+date stream  tcp   nowait guest /bin/date                date

# Let people access the system phonebook via tcpmux
tcpmux/phonebook stream tcp nowait guest /usr/local/bin/phonebook phonebook

# Make kernel statistics accessible
rstatd/1-3   dgram   rpc/udp wait root  /usr/libexec/rpc.rstatd  rpc.rstatd

# Use netcat as a one-shot HTTP proxy with nc (from freebsd-tips fortune)
http         stream  tcp   nowait nobody /usr/bin/nc nc -N dest-ip 80

# Set up a unix socket at /var/run/echo that echo's back whatever is written
# to it.
/var/run/echo stream unix  nowait root  internal

# Run chargen for IPsec Authentication Headers
#@ ipsec ah/require
chargen      stream  tcp   nowait root  internal
#@
.Ed
.Sh "ERROR MESSAGES"
The
.Nm
server
logs error messages using
.Xr syslog 3 .
Important error messages and their explanations are:
.Pp
.Bl -ohang -compact
.It Xo
.Ar service Ns / Ns Ar protocol
.No "server failing (looping), service terminated."
.Xc
The number of requests for the specified service in the past minute
exceeded the limit.
The limit exists to prevent a broken program
or a malicious user from swamping the system.
This message may occur for several reasons:
.Bl -enum -offset indent
.It
There are many hosts requesting the service within a short time period.
.It
A broken client program is requesting the service too frequently.
.It
A malicious user is running a program to invoke the service in
a denial-of-service attack.
.It
The invoked service program has an error that causes clients
to retry quickly.
.El
.Pp
Use the
.Fl R Ar rate
option,
as described above, to change the rate limit.
Once the limit is reached, the service will be
reenabled automatically in 10 minutes.
.Pp
.It Xo
.Ar service Ns / Ns Ar protocol :
.No \&No such user
.Ar user ,
.No service ignored
.Xc
.It Xo
.Ar service Ns / Ns Ar protocol :
.No getpwnam :
.Ar user :
.No \&No such user
.Xc
No entry for
.Ar user
exists in the
.Xr passwd 5
database.
The first message
occurs when
.Nm
(re)reads the configuration file.
The second message occurs when the
service is invoked.
.Pp
.It Xo
.Ar service :
.No can't set uid
.Ar uid
.Xc
.It Xo
.Ar service :
.No can't set gid
.Ar gid
.Xc
The user or group ID for the entry's
.Ar user
field is invalid.
.Pp
.It "setsockopt(SO_PRIVSTATE): Operation not supported"
The
.Nm
utility attempted to renounce the privileged state associated with a
socket but was unable to.
.Pp
.It Xo unknown
.Ar rpc/udp
or
.Ar rpc/tcp
.Xc
No entry was found for either
.Ar udp
or
.Ar tcp
in the
.Xr netconfig 5
database.
.Pp
.It Xo unknown
.Ar rpc/udp6
or
.Ar rpc/tcp6
.Xc
No entry was found for either
.Ar udp6
or
.Ar tcp6
in the
.Xr netconfig 5
database.
.El
.Sh SEE ALSO
.Xr nc 1 ,
.Xr ipsec_set_policy 3 ,
.Xr hosts_access 5 ,
.Xr hosts_options 5 ,
.Xr login.conf 5 ,
.Xr netconfig 5 ,
.Xr passwd 5 ,
.Xr rpc 5 ,
.Xr services 5 ,
.Xr comsat 8 ,
.Xr fingerd 8 ,
.Xr ftpd 8 ,
.Xr rlogind 8 ,
.Xr rpcbind 8 ,
.Xr rshd 8 ,
.Xr talkd 8 ,
.Xr telnetd 8 ,
.Xr tftpd 8
.Rs
.%A Michael C. St. Johns
.%T Identification Protocol
.%O RFC1413
.Re
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.3 .
TCPMUX is based on code and documentation by Mark Lottor.
Support for
.Tn "ONC RPC"
based services is modeled after that
provided by
.Tn SunOS
4.1.
The IPsec hack was contributed by the KAME project in 1999.
The
.Fx
TCP Wrappers support first appeared in
.Fx 3.2 .