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telnetd(8)
NAME
  telnetd - The DARPA telnet protocol server daemon

SYNOPSIS
  telnetd [-debug | debug6 [port]] [-D modifier...] [-n] [-x] [-K] [-d auth |
  enc]

OPTIONS
  -debug|debug6 [port]
      Starts telnetd manually, rather than through inetd, on alternate TCP
      port number port (if specified). It either creates an IPv4 socket
      (-debug) or IPv6 socket (-debug6).

  -D modifier ...
      Prints out debugging information.	 This allows telnetd to print out
      debugging information to the connection, allowing the user to see what
      telnetd is doing. Valid values for modifier are:

      options Prints information about negotiation of telnet options.

      report  Prints the same information as options, along with additional
	      processing information.

      netdata Displays the data stream received by telnetd.

      ptydata Displays data written to the pty.

      exercise
	      Not yet implemented.

  -n  Disables reverse lookups of remote host names. This option can prevent
      login delays and timeouts in an environment where host name resolution
      is sluggish.

  -x  Encrypts the data transmitted between the local host and the remote
      host. This option requires that the local and remote hosts be
      configured to use Kerberos authentication in the same or trusting
      Kerberos realms.

  -K  Specifies that only Kerberos authenticated connections will be
      accepted. This option requires that the local and remote hosts be
      configured to use Kerberos authentication in the same or trusting
      Kerberos realms.

  -d [auth | enc]
      Enables authentication (auth) or encryption (enc) debugging.

DESCRIPTION
  The telnetd daemon is a server that supports the DARPA (Defense Advanced
  Research Projects Agency) standard telnet virtual terminal protocol. The
  telnetd daemon is invoked by the Internet server (see inetd(8)) normally
  for requests to connect to the telnet port as indicated by the
  /etc/services file (see services(4)). Either the -debug option (for IPv4
  sockets) or -debug6 option (for IPv6 sockets) may be used, to start up
  telnetd manually.  If the daemon is started up this way, port may be
  specified to run telnetd on an alternate TCP port number.

  The telnetd daemon operates by allocating a pseudoterminal device (see
  pty(7)) for a client, then creating a login process that has the slave side
  of the pseudoterminal as stdin, stdout, and stderr.  The telnetd daemon
  manipulates the master side of the pseudo-terminal, implementing the telnet
  protocol and passing characters between the remote client and the login
  process.

  When a telnet session is started up, telnetd sends telnet options to the
  client side, indicating a willingness to do remote echo of characters, to
  suppress go ahead, to do remote flow control, and to receive terminal type
  information, terminal speed information, and window size information from
  the remote client. If the remote client is willing, the remote terminal
  type is propagated in the environment of the created login process. The
  pseudoterminal allocated to the client is configured to operate in cooked
  mode, and with XTABS and CRMOD enabled (see tty(7)).

  The telnetd daemon is willing to do: echo, binary, suppress go ahead, and
  timing mark.	The telnetd daemon is willing to have the remote client do:
  line mode, binary, terminal type, terminal speed, window size, toggle flow
  control, environment, X display location, and suppress go ahead.

  The telnetd daemon never sends telnet go ahead commands.

  Note that binary mode has no common interpretation except between similar
  operating systems (Unix-compatible systems in this case).

  Note also that the terminal type name received from the remote client is
  converted to lowercase.

  The telnet command uses the default Type-of-Service value recommended by
  RFC1060, which is as follows:

  telnet
      Low delay

  You can configure this value by specifying it in the /etc/iptos file. For
  more information, see iptos(4).

  By default, the telnetd daemon starts the login dialog using the login
  string specified in the message field of the /etc/gettydefs file. If you
  want to use a customized banner, create an /etc/issue.net or /etc/issue
  file. The telnetd daemon reads the file that exists and writes its contents
  over a new telnet connection prior to starting the login dialog. If both
  files exist, only the /etc/issue.net file is used.

SECURE CONNECTION
  The telnetd daemon can use a secure connection. A secure connection is one
  where the telnetd daemon authenticates a user by using Kerberos. Kerberos
  is a client/server application that authenticate the client, server, and
  user, encrypt data, and ensure data integrity and nonrepudiation.  See your
  system administrator to determine if your system is running Kerberos. See
  Security Administration for more information about Kerberos.

  Kerberos authenticates by using secret-key cryptography and tickets between
  Kerberos clients and Kerberos server in the same or trusting Kerberos
  realms. Once authenticated by Kerberos, users receive a Kerberos Ticket
  Granting Ticket (TGT). Users with a valid TGT are not prompted for a
  username or password when the remote host is in the same or trusting
  Kerberos realm.

CAUTIONS
  Some telnet commands are only partially implemented.

  Because of bugs in the original 4.2BSD telnet command, telnetd performs
  some dubious protocol exchanges to try to discover if the remote client is,
  in fact, a 4.2BSD telnet.

FILES
  /usr/sbin/telnetd
      Specifies the command path.

  /etc/issue.net
      Specifies the path name for the network issue identification file.

  /etc/issue
      Specifies the path name for the issue identification file.

SEE ALSO
  Commands: telnet(1)

  Files: iptos(4), issue(4), issue.net(4)

  Guides: Security Administration

Index for Section 8

Alphabetical listing for T

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