rshd(1M) (TCP/IP) rshd(1M)
NAME
rshd - remote shell server
SYNOPSIS
in.rshd host.port
DESCRIPTION
rshd is the server for the rsh(1) program. The server provides
remote execution facilities with authentication based on privileged
port numbers.
rshd is invoked by inetd(1M) each time a shell service is requested,
and executes the following protocol:
1) The server checks the client's source port. If the port is not
in the range 0-1023, the server aborts the connection. The
clients host address (in hex) and port number (in decimal) are
the argument passed to rshd.
2) The server reads characters 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 1 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's machine. The source port of this second
connection is also in the range 0-1023.
4) The server checks the client's source address. If the address
is associated with a host for which no corresponding entry
exists in the host name data base [see hosts(4)], the server
aborts the connection.
5) A null terminated user name of at most 16 characters is
retrieved on the initial socket. This user name is interpreted
as a user identity to use on the server's machine.
6) A null terminated user name of at most 16 characters is
retrieved on the initial socket. This user name is interpreted
as the user identity on the client'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) rshd then validates the user according to the following steps.
The remote user name is looked up in the password file and a
chdir is performed to the user's home directory. If the lookup
or fails, the connection is terminated. If the chdir fails, it
does a chdir to / (root). If the user is not the super-user,
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(user ID 0), the file /etc/hosts.equiv is consulted for a list
of hosts considered equivalent. If the client's host name is
present in this file, the authentication is considered
successful. If the lookup fails, or the user is the super-
user, then the file .rhosts in the home directory of the remote
user is checked for the machine name and identity of the user
on the client's machine. If this lookup fails, the connection
is terminated.
9) A null byte is returned on the connection associated with the
stderr and the command line is passed to the normal login shell
of the user. The shell inherits the network connections
established by rshd.
FILES
/etc/hosts.equiv
SEE ALSO
rsh(1)
DIAGNOSTICS
The following 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 (0
is returned in step 9 above upon successful completion of all the
steps prior to the command execution).
locuser too long
The name of the user on the client's machine is longer than 16
characters.
remuser too long
The name of the user on the remote machine is longer than 16
characters.
command too long
The command line passed exceeds the size of the argument list
(as configured into the system).
Hostname for your address unknown.
No entry in the host name database existed for the client's
machine.
Login incorrect.
No password file entry for the user name existed.
Permission denied.
The authentication procedure described above failed.
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rshd(1M) (TCP/IP) rshd(1M)
Can't make pipe.
The pipe needed for the stderr was not created.
Try again.
A fork by the server failed.
NOTES
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.
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