klogind - remote login server
klogind [ -rcpPef ] [[ -w[ip|maxhostlen[,[no]striplocal ]] ] [ -D port
Klogind is the server for the rlogin(1) program. The server is based
on rlogind(8) but uses Kerberos authentication.
The klogind server is invoked by inetd(8) when it receives a connection
on the port indicated in /etc/inetd.conf. A typical /etc/inetd.conf
configuration line for klogind might be:
klogin stream tcp nowait root /usr/sbin/klogind klogind -e5c
When a service request is received, the following protocol is
1) Check authentication.
2) Check authorization via the access-control files .k5login and
.klogin in the user’s home directory.
3) Prompt for password if any checks fail and the -p option was
If the authentication succeeds, login the user by calling the
klogind allows Kerberos V5 authentication with the .k5login access
control file to be trusted. If this authorization check is passed,
then the user is allowed to log in. If the user has no .k5login file,
the login will be authorized if the results of krb5_aname_to_localname
conversion matches the account name. Unless special rules are
configured, this will be true if and only if the Kerberos principal of
the connecting user is in the default local realm and the principal
portion matches the account name.
The configuration of klogind is done by command line arguments passed
by inetd. The options are:
-P Prompt the user for a password. If the -P option is passed,
then the password is verified in addition to all other checks.
-e Create an encrypted session.
-c Require Kerberos V5 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. If
this option is specified, older Kerberos V5 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 -i option.
If neither the -c or -i 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 -c 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 -i option must be used.
-i 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
-c. 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.
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 rlogin(1) program. In normal operation,
the packet protocol described in 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
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.
Klogind supports the following options to control the form of the
hostname passed to login(1):
Controls the form of the remote hostname passed to login(1).
Specifying ip results in the numeric IP address always being
passed to login(1). Specifying a number, maxhostlen, sets the
maximum length of the hostname passed to login(1) before it will
be passed as a numeric IP address. If maxhostlen is 0, then the
system default, as determined by the utmp or utmpx structures,
is used. The nostriplocal and striplocal options, which must be
preceded by a comma, control whether or not the local host
domain is stripped from the remote hostname. By default, the
equivalent of striplocal is in effect.
Klogind supports five options which are used for testing purposes:
-S keytab Set the keytab file to use.
-M realm Set the Kerberos realm to use.
-L login Set the login program to use. This option only has an effect
if DO_NOT_USE_K_LOGIN was not defined when klogind was
-D port Run in standalone mode, listening on port. The daemon will
exit after one connection and will not background itself.
-f Allows for standalone daemon operation. A new child is
started for each incoming connection and waits for it to
finish before accepting the next connection. This
automagically figures out which port to bind to if no port is
All diagnostic messages are returned on the connection associated with
the stderr, after which any network connections are closed. An error
is indicated by a leading byte with a value of 1.
A fork by the server failed.
The user’s login shell could not be started.
A more extensible protocol should be used.