The rshd(1) server is the server for the rcmd(3)
routine and, consequently, for the rsh(1) program. The
server provides remote execution facilities with authentication
based on privileged port numbers from trusted hosts.
The following options are supported by rshd(1):
-a
Ask host name for verification.
-l
Prevent any authentication based on the user's .rhosts
file.
-n
Disable keep-alive messages.
-L
Log successful accesses very verbosely.
The rshd(1) server listens for service requests at the
port indicated in the "cmd" 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 ends the connection.
The server reads characters from the socket up to a null ('\0')
byte. The resultant string is interpreted as an ASCII number, base
10.
If the number received in step 2 is non-zero, it is interpreted
as the port number of a secondary stream to be used for the
stderr. A second connection is then created to the specified
port on the client computer. The source port of this second
connection is also in the range 512-1023.
The server checks the client's source address and requests the
corresponding host name (see gethostbyaddr(3)). 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. If
address verification fails, the connection is ended with the
message, "Host address mismatch."
A null terminated user name of at most 128 characters is
retrieved on the initial socket. This user name is interpreted as
the user identity on the client computer.
A null terminated user name of at most 128 characters is
retrieved on the initial socket. This user name is interpreted as a
user identity to use on the server computer.
A null terminated command to be passed to a shell is retrieved
on the initial socket. The length of the command is limited by the
upper bound on the size of the system's argument list.
The rshd(1) utility then validates the user using
iruserok(3), which uses the file
/etc/hosts.equiv and the .rhosts file found in the
user's home directory. If the daemon is not running as the
SYSTEM user, the password of the user account used to run the
daemon must have been previously stored using the regpwd(1)
utility. The -l option prevents ruserok(3) from doing any
validation based on the user's .rhosts file, unless the user
is the superuser. If the iruserok(3) function reports that the
address might have been spoofed, the connection is refused.
The file /etc/nologinexists.
A null byte is returned on the initial socket and the command line
is passed to the normal login shell of the user. The shell inherits
the network connections established by rshd(1).
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.
The -L option causes all successful accesses to be logged
to syslogd(1) as messages.
On traditional systems, a user can run rsh(1) from a
system identified in the user's .rhosts file without
providing a password. This is because on a traditional system, the
rshd(1) program is run as the superuser, and can take any
login identity. On Interix, this is not possible. Instead, the user
must run the regpwd(1) utility on th host to store the
user's password before running rsh.
Except for the last diagnostic message listed in this section,
all diagnostic messages are returned on the initial socket, after
which any network connections are closed. An error is indicated by
a leading byte with a value of 1 (0 is returned in step 10 above
upon successful completion of all the steps prior to the execution
of the login shell).
Locuser too long.
The name of the user on the client computer is longer than 128
characters.
Ruser too long.
The name of the user on the remote computer is longer than 128
characters.
Command too long.
The command line passed exceeds the size of the argument list
(as configured into the system).
Remote directory.
The chdir(1) command to the home directory failed.
Permission denied.
The authentication procedure described above failed or there is
no password file entry for the specified user.
Can't make pipe.
The pipe needed for the stderr, was not created.
Can't fork; try again.
A fork(1) by the server failed.
<shellname>: ...
The user's login shell could not be started. This message is
returned on the connection associated with the stderr, and
is not preceded by a flag byte.
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 (such as Telnet) should be used.