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

in.rlogind is invoked by inetd(1M) when a remote login connection is established, and executes the following protocol:

• 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. If an entry for the client exists in both /etc/hosts and /etc/hosts.equiv, a user logging in from the client is not prompted for a password. If the address is associated with a host for which no corresponding entry exists in /etc/hosts, the user is prompted for a password, regardless of whether or not an entry for the client is present in /etc/hosts.equiv. See hosts(4) and hosts.equiv(4).

Once the source port and address have been checked, in.rlogind allocates a pseudo-terminal and manipulates file descriptors so that the 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 -r.

The login process then proceeds with the pam(3PAM) authentication process. See SECURITY below. If automatic authentication fails, it reprompts the user to login.

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 program. In normal operation, a packet protocol is invoked to provide Ctrl-S and Ctrl-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(4).

rlogind and in.rlogind are IPv6-enabled. See ip6(7P).

in.rlogind uses pam(3PAM) for authentication, account management, and session management. The PAM configuration policy, listed through /etc/pam.conf, specifies the modules to be used for in.rlogind. Here is a partial pam.conf file with entries for the rlogin command using the "rhosts" and UNIX authentication modules, and the UNIX account, session management, and password management modules.

With this configuration, the server checks the client's source address. If an entry for the client exists in both /etc/hosts and /etc/hosts.equiv, a user logging in from the client is not prompted for a password. If the address is associated with a host for which no corresponding entry exists in /etc/hosts, the user is prompted for a password, regardless of whether or not an entry for the client is present in /etc/hosts.equiv. See hosts(4) and hosts.equiv(4).

If there are no entries for the rlogin 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. Removing the "pam_rhosts_auth.so.1" entry will disable the /etc/hosts.equiv and ~/.rhosts authentication protocol and the user would always be forced to type the password. The sufficient flag indicates that authentication through the pam_rhosts_auth.so.1 module is "sufficient" to authenticate the user. Only if this authentication fails is the next authentication module used.

See attributes(5) for descriptions of the following attributes:

login(1), rlogin(1), in.rshd(1M), inetd(1M), pam(3PAM), environ(4), hosts(4), hosts.equiv(4), inetd.conf(4), pam.conf(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)

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.

Hostname for your address unknown.

No entry in the host name database existed for the client's machine.

Try again.

A fork by the server failed.

/usr/bin/sh: ...

The user's login shell could not be started.

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

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

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).