rshd(8c)rshd(8c)Namershd - remote shell server
Syntax
/etc/rshd
Description
The command is the server for the routine and, consequently, for the
program. The server provides remote execution facilities with authen‐
tication based on privileged port numbers.
The is invoked by when it receives a connection on the port indicated
in the cmd service specification. 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 0-1023, the server aborts the connection.
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 the server aborts the connec‐
tion. For further information, see
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 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 command validates the user according to the following steps.
The remote user name is looked up in the password file and a is
performed to the user's home directory. If either the lookup or
fail, the connection is terminated. If the user is not the
superuser, (user id 0), the file or is consulted for a list of
hosts considered equivalent. If the client's host name is in
this file, the authentication is considered successful. If the
lookup fails, or the user is the superuser, the file 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 the 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 estab‐
lished by
Diagnostics
All 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 com‐
mand execution).
locuser too long
The name of the user on the client's machine is longer than 16 charac‐
ters.
remuser too long
The name of the user on the remote machine is longer than 16 charac‐
ters.
command too long
The command line passed exceeds the size of the argument list (as con‐
figured 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.
No remote directory.
The command to the home directory failed.
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.
/bin/sh: ...
The user's login shell could not be started.
Restrictions
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.
See Alsorsh(1c), rcmd(3x), services(5), inetd(8c)rshd(8c)
