telnetd.1m (2010 09)

t
telnetd(1M) telnetd(1M)
NAME
telnetd - TELNET protocol server
SYNOPSIS
/usr/lbin/telnetd
[-A ] [-a authmode][
-b [bannerfile]] [-e][-f
][-n][-s][-t][-y
]
[
-z][-E
][-TCP_DELAY]
DESCRIPTION
The
telnetd daemon executes a server that supports the DARPA standard TELNET virtual terminal
protocol. The Internet daemon (inetd) executes
telnetd when it receives a service request at the port
listed in the services database for
telnet using the
tcp protocol (see inetd (1M) and services (4)).
telnetd operates by allocating a Telnet pseudo-terminal device (see tels (7)) for a client, then creating a
login process, which has the slave side of the Telnet pseudo-terminal as
stdin, stdout, and stderr.
telnetd manipulates the master side of the Telnet pseudo-terminal, implementing the TELNET proto-
col, and passing characters between the client and login process.
NOTE:
telnetd no longer uses pty (7) devices; instead it uses special devices created for TELNET
sessions only. For more information, see tels (7).
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 , and to receive terminal speed terminal
type , and authentication (if kerberos is enabled) information from the remote client. If the remote client
is ready, the remote terminal type is propagated in the environment of the created login process. The
pseudo-terminal allocated to the client is configured as a normal terminal for login, with the exception of
echoing characters (see tty (7)).
telnetd is willing to do: echo , binary , suppress go ahead , and timing mark .
telnetd is willing to have the remote client do: binary , flow control , terminal speed , terminal
type , suppress go ahead and authentication (if kerberos is enabled).
The flow control option permits applications running on a remote host to toggle the flow control on the
local host. To toggle flow control for a
telnet session programmatically, the application program must
first call the tcgetattr function to get the current termios settings. For example,
tcgetattr(filedes, &termios_p)
Then, the c_iflag of the termios structure must have IXON set(reset) to enable(disable) flow control.
Finally, the
tcsetattr function call can implement the change. For example,
tcsetattr(filedes, TCSANOW, &termios_p)
To toggle the flow control interactively, the user can issue a
stty command using the input options
-ixon to disable, or ixon to enable flow control. See the stty (1) manpage.
The terminal speed option permits applications running on a remote host to obtain the terminal speed of
the local host session using either ioctl or stty .
The
telnet server also supports the TAC User ID (also known as the TAC Access Control System, or
TACACS User ID) option using which, users telneting to two or more consenting hosts may avoid going
through a second login sequence. See the -t option below.
To start
telnetd from the Internet daemon, the configuration file /etc/inetd.conf must contain an
entry as follows:
telnet stream tcp nowait root /usr/lbin/telnetd telnetd
The above configuration applies only for the IPv4 environment. For telnetd to work in the IPv6
environment, the configuration file /etc/inetd.conf must contain a tcp6 entry as follows:
telnet stream tcp6 nowait root /usr/lbin/telnetd telnetd
NOTE: The tcp entry has changed to tcp6 to work in the IPv6 environment.
telnet uses the same files as rlogin to verify participating systems and authorized users,
hosts.equiv and .rhosts. (See hosts.equiv (4) and the HP-UX System Administrator’s Guide for
configuration details.)
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1