.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)rlogind.8c	6.3 (Berkeley) 5/24/86
.\"
.TH KRLOGIND 8C "Kerberos Version 5.0" "MIT Project Athena"
.SH NAME
krlogind \- remote login server
.SH SYNOPSIS
.B /etc/rlogind
[
.B \-kr54cpPe
]
.SH DESCRIPTION
.I Krlogind
is the server for the 
.IR rlogin (1C)
program.  The server is 
based on rlogind(8C) but uses kerberos authentication.
.PP
The 
.I krlogind
server is invoked by \fIinetd(8c)\fP when it receives a
connection on the port indicated in /etc/inetd.conf.  A typical
/etc/inetd.conf configuration line for \fIkrlogind\fP might be:

klogin	stream	tcp	nowait	root	/krb5/sbin/krlogind krlogind -e5c

When a service request is received, the following protocol is initiated:

.IP 1)
Check authentication.
.IP 2)
Check authorization via the access-control files \fI.k5login\fP, \fI.klogin\fP 
and \fI.rhosts\fP in the user's home directory.
.IP 3)
Prompt for password if any checks fail and the \fI-p\fP option was supplied.
.PP
If the authentication succeeds, login the user by calling the accompanying 
login.krb5 or /bin/login, according to the definition of 
DO_NOT_USE_K_LOGIN.  
.PP 
The configuration of \fIkrlogind\fP is done
by command line arguments passed by inetd.  The options are:
.IP \fB\-5\fP 10
Allow Kerberos5 authentication with the \fI.k5login\fP access control file
to be trusted.  If this authentication system is used by the client and the
authorization check is passed, then the user is allowed to log in.

.IP \fB\-4\fP 
Allow Kerberos4 authentication with the \fI.klogin\fP access control file
to be trusted.  If this authentication system is used by the client and the
authorization check is passed, then the user is allowed to log in.

.IP \fB\-k\fP 
Allow Kerberos5 and Kerberos4 as acceptable authentication
mechanisms.  This is the same as including \fB\-4\fP and \fB\-5\fP.

.IP \fB\-r\fP 
Trust the remote hostname as an authentication system using the 
 \fI.rhosts\fP authorization list.  This option may
be desupported in future version of klogind.

.IP \fB\-p\fP
 If all other authorization checks fail, prompt the user
for a password If this option is not included, access is denied
without successful authentication and authorization using one of the
previous mechanisms.

.IP \fB\-P\fP
Prompt the user for a password.
If the -P option is passed, then the password is verified in addition
to all other checks.

.IP \fB\-e\fP
Create an encrypted session. 

.IP \fB\-c\fP 
Require Kerberos5 clients to present a cryptographic
checksum of initial connection information like the name of the user
that the client is trying to access in the initial authenticator.
This checksum provides additionl security by preventing an attacker
from changing the initial connection information.  To benefit from
this security, only Kerberos5 should be trusted; Kerberos4 and rhosts
authentication do not include this checksum.  If this option is
specified, older Kerberos5 clients that do not send a checksum in the
authenticator will not be able to authenticate to this server.  This
option is mutually exclusive with the \fB-i\fP option.

	If neither the \fB-c\fP or \fB-i\fP options are specified,then
checksums are validated if presented.  Since it is difficult to remove
a checksum from an authenticator without making the authenticator
invalid, this default mode is almost as significant of a security
improvement as \fB-c\fP if new clients are used.  It has the additional
advantage of backwards compatability with some clients.
Unfortunately, clients before Kerberos V5, Beta5, generate invalid
checksums; if these clients are used, the \fB-i\fP option must be
used.

.IP \fB\-i\fP 
Ignore authenticator checksums if provided.  This option
ignore authenticator checksusm presented by current Kerberos clients
to protect initial connection information; it is the opposite of
\fB-c\fP.  This option is provided because some older
clients--particularly clients predating the release of Kerberos V5
Beta5 (May 1995)--present bogus checksums that prevent Kerberos
authentication from succeeding in the default mode.


.PP
If the
~/.rhosts check is to be used, then the program verifies that the
client is connecting from a privileged port, before allowing login.

.PP The parent of the login process manipulates the master side of the
pseduo terminal, operating as an intermediary between the login
process and the client instance of the .I rlogin(1C) program.  In
normal operation, the packet protocol described in .IR pty (4) is
invoked to provide ^S/^Q type facilities and propagate interrupt
signals to the remote programs.  The login process propagates the
client terminal's baud rate and terminal type, as found in the
environment variable, ``TERM''; see .IR environ (7).  The screen or
window size of the terminal is requested from the client, and window
size changes from the client are propagated to the pseudo terminal.

.PP .I Krlogind supports three options which are used for testing
purposes:

.IP \fB\-S\ srvtab\fP 10
Set the \fIsrvtab\fP file to use.

.IP \fB\-M\ realm\fP
Set the Kerberos realm to use.

.IP \fB\-L\ login\fP
Set the login program to use.  This option only has an effect if
DO_NOT_USE_K_LOGIN was not defined when
.I krlogind
was compiled.
.SH DIAGNOSTICS
All diagnostic messages are returned on the connection
associated with the
.BR stderr ,
after which any network connections are closed.
An error is indicated by a leading byte with a value of 1.
.PP
.B ``Try again.''
.br
A
.I fork
by the server failed.
.PP
.B ``/bin/sh: ...''
.br
The user's login shell could not be started.
.SH SEE ALSO
rlogind(8C), rlogin(1C)
.SH BUGS
A more extensible protocol should be used.