rshd(8) System Manager's Manual rshd(8)
NAME
rshd - The remote shell server
SYNOPSIS
rshd [-aeln]
FLAGS
The addresses for the hostname are requested, verifying that the name and address correspond. Causes rshd to check for the /etc/nolo-
gin_{hostname} and /etc/nologin files. If either exists, rshd prints its contents and exits. Prevents the ruserok command from doing any
validation based on the user's .rhosts file, unless the user is the superuser. Disables transport-level, keep-alive messages.
SECURITY NOTE
This security-sensitive command uses the SIA (Security Integration Architecture) routine as an interface to the security mechanisms. See
the matrix.conf(4) reference page for more information.
DESCRIPTION
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: The server checks the client's source port. If the port is not in the range 512
to 1023, the server aborts the connection. The server reads bytes from the socket up to a null (` ') byte. The resultant string is
interpreted as an ASCII number, base 10. 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. The server checks the client's source address and requests the corre-
sponding 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 flag is given, the addresses for the hostname are requested, verifying that the name and address correspond. If address veri-
fication fails, the connection is aborted with the message Host address mismatch. 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. 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. 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 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 flag prevents ruserok(3) from doing any validation based
on the user's .rhosts file, unless the user is the superuser. If rshd was started with the -e flag, 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" message. 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 flag is present. The use of keep-alive messages allows sessions to be timed
out if the client crashes or becomes unreachable.
CAUTIONS
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.
DIAGNOSTICS
Except for the last diagnostic message listed, all diagnostic messages are returned on the initial socket, after which any network connec-
tions 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). The name of the user on the client's machine is longer than 16 characters. The
name of the user on the remote machine is longer than 16 characters. The command line passed exceeds the size of the argument list (as
configured into the system). No password file entry for the username existed. The server is currently not accepting connections. The
chdir command to the home directory failed. The authentication procedure previously described failed. The pipe needed for the stderr
option, but it was not created. 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 preceded by a flag byte.
FILES
Specifies the command path Stops logins. In a cluster, there is also /etc/nologin_{hostname}.
RELATED INFORMATION
Commands: rsh(1)
Functions: rcmd(3), ruserok(3) delim off
rshd(8)