rshd - The remote shell server
-a The addresses for the hostname are requested, verifying that the name
and address correspond.
-e Causes rshd to check for the /etc/nologin_hostname and /etc/nologin
files. If either exists, rshd prints its contents and exits.
-l Prevents the ruserok command from doing any validation based on the
user's .rhosts file, unless the user is the superuser.
-n Disables transport-level, keep-alive messages.
The rshd daemon 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 rshd daemon listens for service requests at the port indicated in the
cmd service specification; see services(4). When a service request is
received, the following protocol is initiated:
1. The server checks the client's source port. If the port is not in the
range 512 to 1023, the server aborts the connection.
2. The server reads bytes from the socket up to a null (`\0') byte. The
resultant string is interpreted as an ASCII number, base 10.
3. If the number received in step 2 is nonzero, it is interpreted as the
port number of a secondary stream to be used for the stderr option. A
second connection is then created to the specified port on the
client's machine. The source port of this second connection is also
in the range 512 to 1023.
4. The server checks the client's source address and requests the
corresponding hostname (see gethostbyaddr(3), hosts(4), and named(8)).
If the hostname cannot be determined, the dot-notation representation
of the host address is used. If the hostname 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 hostname are
requested, verifying that the name and address correspond. If address
verification fails, the connection is aborted with the message Host
5. A null-terminated username of at most 16 bytes is retrieved on the
initial socket. This username is interpreted as the user identity on
the client 's machine.
6. A null-terminated username of at most 16 bytes is retrieved on the
initial socket. This username is interpreted as a user identity to
use on the server's machine.
7. 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.
8. The rshd daemon then validates the user using ruserok(3), which uses
the file /etc/hosts.equiv and the .rhosts file found in the user's
home directory. The -l option prevents ruserok(3) from doing any
validation based on the user's .rhosts file, unless the user is the
9. If rshd was started with the -e option, the user is not the superuser,
and either the /etc/nologin_hostname or /etc/nologin file exists, rshd
prints the contents of the first file found and aborts the connection.
If the file has a zero length, rshd prints a "logins disabled" mes-
10. 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.
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.
This security-sensitive command uses the SIA (Security Integration Archi-
tecture) routine as an interface to the security mechanisms. See the
matrix.conf(4) reference page for more information.
The authentication procedure used here assumes the integrity of each client
machine and the connecting medium. This is insecure, but is useful in an
Except for the last diagnostic message listed, 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 9 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's machine is longer than 16 charac-
Remuser too long.
The name of the user on the remote machine is longer than 16 charac-
Command too long.
The command line passed exceeds the size of the argument list (as con-
figured into the system).
No password file entry for the username existed.
The server is currently not accepting connections.
No remote directory.
The chdir command to the home directory failed.
The authentication procedure previously described failed.
Can't make pipe.
The pipe needed for the stderr option, but it was not created.
Can't fork; try again.
A fork by the server failed.
The user's login shell could not be started. This message is returned
on the connection associated with the stderr option, and is not pre-
ceded by a option byte.
Specifies the command path
Stops logins. In a cluster, there is also /etc/nologin_hostname.
Functions: rcmd(3), ruserok(3)