in.telnetd(1M)
NAME
in.telnetd, telnetd - DARPA TELNET protocol server
SYNOPSIS
/usr/sbin/in.telnetd
DESCRIPTION
in.telnetd is a server that supports the DARPA standard TEL-
NET virtual terminal protocol. in.telnetd is normally
invoked in the internet server (see inetd(1M)), for
requests to connect to the TELNET port as indicated by the
/etc/services file (see services(4)).
in.telnetd operates by allocating a pseudo-terminal device
for a client, then creating a login process which has the
slave side of the pseudo-terminal as its standard input,
output, and error. in.telnetd 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 starts up, in.telnetd sends TELNET
options to the client side indicating a willingness to do
remote echo of characters, and to suppress go ahead. The
pseudo-terminal allocated to the client is configured to
operate in "cooked" mode, and with XTABS, ICRNL and ONLCR
enabled. See termio(7I).
in.telnetd is willing to do: echo, binary, suppress go
ahead, and timing mark. in.telnetd is willing to have the
remote client do: binary, terminal type, terminal size,
logout option, and suppress go ahead.
in.telnetd also allows environment variables to be passed,
provided that the client negotiates this during the initial
option negotiation. The DISPLAY environment variable may be
sent this way, either by the TELNET general environment
passing methods, or by means of the XDISPLOC TELNET option.
DISPLAY can be passed in the environment option during the
same negotiation where XDISPLOC is used. Note that if you
use both methods, use the same value for both. Otherwise,
the results may be unpredictable.
These options are specified in Internet standards RFC 1096,
RFC 1408, RFC 1571, and RFC 1572.
The banner printed by in.telnetd is configurable. The
default is (more or less) equivalent to "`uname -sr`" and
will be used if no banner is set in /etc/default/telnetd.
To set the banner, add a line of the form
BANNER="..."
to /etc/default/telnetd. Nonempty banner strings are fed to
shells for evaluation. The default banner may be obtained by
BANNER="\\r\\n\\r\\n`uname -s` `uname -r`\\r\\n\\r\\n"
and no banner will be printed if /etc/default/telnetd con-
tains
BANNER=""
USAGE
telnetd and in.telnetd are IPv6-enabled. See ip6(7P).
SECURITY
in.telnetd uses pam(3PAM) for authentication, account
management, session management, and password management. The
PAM configuration policy, listed through /etc/pam.conf,
specifies the modules to be used for in.telnetd. Here is a
partial pam.conf file with entries for the telnet command
using the UNIX authentication, account management, session
management, and password management modules.
telnet auth requisite pam_authtok_get.so.1
telent auth required pam_dhkeys.so.1
telent auth required pam_unix_auth.so.1
telnet account requisite pam_roles.so.1
telnet account required pam_projects.so.1
telnet account required pam_unix_account.so.1
telnet session required pam_unix_session.so.1
telnet password required pam_dhkeys.so.1
telent password requisite pam_authtok_get.so.1
telnet password requisite pam_authtok_check.so.1
telnet password required pam_authtok_store.so.1
If there are no entries for the telnet service, then the
entries for the "other" service will be used. If multiple
authentication modules are listed, then the user may be
prompted for multiple passwords.
FILES
/etc/default/telnetd
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWtnetd |
|_____________________________|_____________________________|
SEE ALSO
telnet(1), inetd(1M), pam(3PAM), inetd.conf(4)pam.conf(4),
services(4), attributes(5), pam_authtok_check(5),
pam_authtok_get(5), pam_authtok_store(5), pam_dhkeys(5),
pam_passwd_auth(5), pam_unix(5), pam_unix_account(5),
pam_unix_auth(5), pam_unix_session(5), ip6(7P), termio(7I)
Alexander, S., TELNET Environment Option, RFC 1572, Network
Information Center, SRI International, Menlo Park, Calif.,
January 1994.
Borman, Dave, TELNET Environment Option, RFC 1408, Network
Information Center, SRI International, Menlo Park, Calif.,
January 1993.
Borman, Dave, TELNET Environment Option Interoperability
Issues, RFC 1571, Network Information Center, SRI Interna-
tional, Menlo Park, Calif., January 1994.
Crispin, Mark, TELNET Logout Option, RFC 727, Network Infor-
mation Center, SRI International, Menlo Park, Calif., April
1977.
Marcy, G., TELNET X Display Location Option. RFC 1096, Net-
work Information Center, SRI International, Menlo Park,
Calif., March 1989.
Postel, Jon, and Joyce Reynolds, TELNET Protocol Specifica-
tion, RFC 854, Network Information Center, SRI Interna-
tional, Menlo Park, Calif., May 1983.
Waitzman, D., TELNET Window Size Option, RFC 1073, Network
Information Center, SRI International, Menlo Park, Calif.,
October 1988.
NOTES
Some TELNET commands are only partially implemented.
Binary mode has no common interpretation except between
similar operating systems.
The terminal type name received from the remote client is
converted to lower case.
The packet interface to the pseudo-terminal should be used
for more intelligent flushing of input and output queues.
in.telnetd never sends TELNET go ahead commands.
The pam_unix(5) module might not be supported in a future
release. Similar functionality is provided by
pam_authtok_check(5), pam_authtok_get(5),
pam_authtok_store(5), pam_dhkeys(5), pam_passwd_auth(5),
pam_unix_account(5), pam_unix_auth(5), and
pam_unix_session(5).
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