rshd(1M) rshd(1M)
NAME
rshd, in.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 con-
nection.
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.
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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 superuser, (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 superuser, 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.
DIAGNOSTICS
The following diagnostic messages are returned on the connection asso-
ciated 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.
Can't make pipe.
The pipe needed for the stderr was not created.
Try again.
A fork by the server failed.
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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.
FILES
/etc/hosts.equiv
SEE ALSO
rsh(1).
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