rlogind

SYNOPSIS

rlogind [-alnQ]

DESCRIPTION

The rlogind(1) utility is the server for the rlogin(1) program. The server provides a remote login facility with authentication based on privileged port numbers from trusted hosts.

The following options are supported by rlogind(1):

-a: Ask host name for verification.
-l: Prevent any authentication based on the user's .rhosts file.
-n: Disable keep-alive messages.
-Q: Sets really quiet mode. Really quiet mode suppresses the entire login banner.

The rlogind(1) utility listens for service requests at the port indicated in the "login" service specification. When a service request is received, the following protocol is initiated:

The server checks the client's source port. If the port is not in the range 512-1023, the server aborts the connection.
The server checks the client's source address and requests the corresponding host name (see gethostbyaddr(3)), hosts(5), and named(1)). If the host name cannot be determined, the dot-notation representation of the host address is used. If the host name is in the same domain as the server (according to the last two components of the domain name), or if the -a option is given, the addresses for the host name are requested, verifying that the name and address correspond. Normal authentication is bypassed if the address verification fails.

After the source port and address have been checked, rlogind(1) proceeds with the authentication process described in rshd(1). It then allocates a pseudo terminal (see pty(1)), and manipulates file descriptors so that the subordinate (slave) half of the pseudo terminal becomes the stdin, stdout, and stderr for a login process. The login process is an instance of the login(1) program, invoked with the -f option if authentication has succeeded. If automatic authentication fails, the user is prompted to log in as if on a standard terminal line.

The parent of the login process manipulates the master side of the pseudo 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(1) 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. 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.

Transport-level keep-alive messages are enabled unless the -n option is present. The use of keep-alive messages allows sessions to be timed out if the client crashes or becomes unreachable.

Interix authentication

On traditional systems, a user can rlogin(1) from a system identified in the user's .rhosts file without providing a password. This is because on a traditional system, the rlogind(1) program is run as the superuser, and can take any login identity. This works on Interix if rlogind(1) runs as the SYSTEM user. If the daemon is running as a different user, the user's password must have been previously stored using the regpwd(1) utility.

If the iruserok(3) function reports that the host name and the host number do not match, the user is asked for a password.

(The test is done by converting the host number to a host name and then converting the host name to a host number. If the two host numbers do not match, the address might have been spoofed. A user can get similar results by using nslookup(1) to check both the host name and the host number.)

DIAGNOSTICS

All initial diagnostic messages are indicated by a leading byte with a value of 1, after which any network connections are closed. If there are no errors before login(1) is invoked, a null byte is returned as in indication of success.

Try again.: A fork(1) by the server failed.

FILES

The rlogin(1) and rlogind(1) programs make use of the following files, if they exist:

/etc/hosts.equiv: On the target system, this file contains the names of systems and users allowed to login. See hosts.equiv(5) for more information.
$HOME/.rhosts: On the target system, this file can contain the names of systems (and user names) allowed to login. See .rhosts(5) for more information.

BUGS

The authentication procedure used here assumes the integrity of each client computer and the connecting medium. This is insecure, but is useful in an "open" environment.

A facility to allow all data exchanges to be encrypted should be present.

A more extensible protocol should be used.