NAME¶
rlogind —
remote login server
SYNOPSIS¶
DESCRIPTION¶
Rlogind 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.
Options supported by
rlogind:
- -a
- This option exists for compatibility with historical
systems.
- -f
- Disable the Nagle algorithm. This is only needed to work
around some broken operating systems.
- -h
- Permit use of superuser
“.rhosts” files.
- -l
- Prevent any authentication based on the user's
“.rhosts” file. If the user is logging in as
the superuser and the -h option is used,
“.rhosts” processing is still enabled.
- -L
- Prevent any authentication based on
“.rhosts” or
“hosts.equiv” information.
- -n
- Disable keep-alive messages.
The -h, -l, and -L flags are not used if PAM (Pluggable Authentication Module)
support is in use.
The
-h and
-l options should also not be
trusted without verifying that they work as expected with the particular
version of libc installed on your system (and should be tested again after any
libc update) because some versions of libc may not honor the internal flags
used by
rlogind. As the
-L option bypasses
the libc functions entirely, it is not subject to this problem.
Also note that the design of the
.rhosts system is COMPLETELY
INSECURE except on a carefully firewalled private network. Always use the
-L option under all other circumstances. Also, since
rlogind does not encrypt communications, it should not, in
general, be used at all. Consider
ssh(8).
Rlogind listens for service requests at the port indicated in
the ``login'' service specification; see
services(5). 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(8)). If the
hostname cannot be determined, the dot-notation representation of the host
address is used. The addresses for the hostname are requested, verifying
that the name and address correspond. Normal authentication is bypassed if
the address verification fails.
Once the source port and address have been checked,
rlogind
proceeds with the authentication process described in
rshd(8). It then allocates a pseudo terminal (see
pty(4)), 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
-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 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.
Transport-level keepalive messages are enabled unless the
-n
option is present. The use of keepalive messages allows sessions to be timed
out if the client crashes or becomes unreachable.
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 is invoked, a null byte is returned as in
indication of success.
- Try
again.
- A fork by the server failed.
SEE ALSO¶
login(1),
ruserok(3),
rshd(8)
BUGS¶
The authentication procedure used here assumes the integrity of each client
machine 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.
HISTORY¶
The
rlogind command appeared in
4.2BSD.