rshd.8c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 8C 代码 · 共 171 行

.\" SCCSID: @(#)rshd.8c	8.1	9/11/90
.TH rshd 8c
.SH Name
rshd \- remote shell server
.SH Syntax
.B /etc/rshd
.SH Description
.NXR "rshd server"
.NXS "remote shell server" "rshd server"
.NXAM "rcmd subroutine" "rshd server"
.NXAM "rsh program" "rshd server"
The
.PN rshd
command is the server for the 
.MS rcmd 3x 
routine and, consequently, for the
.MS rsh 1c 
program.  The server provides remote execution facilities
with authentication based on privileged port numbers.
.PP
The
.PN rshd
is invoked by 
.MS inetd 8c
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:
.NXR "rshd server" "protocol"
.IP 1)
The server checks the client's source port.
If the port is not in the range 0-1023, the server
aborts the connection.
.IP 2)
The server reads characters from the socket up
to a null (`\e0') byte.  The resultant string is
interpreted as an ASCII number, base 10.
.IP 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 
.BR 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.
.IP 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 connection.
For further information, see
.MS hosts 5 ,
.IP 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
.BR server 's
machine.
.IP 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
.BR client 's
machine.
.IP 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.  
.IP 8)
The
.PN rshd
command validates the user according to the following steps.
.NXR "rshd server" "validating users"
The remote user name is looked up in the password file
and a
.PN chdir
is performed to the user's home directory.  If either
the lookup or 
.PN chdir
fail, the connection is terminated.
If the user is not the superuser, (user id 0), the file
.PN /etc/hosts.equiv 
or 
.PN /etc/hosts.lpd 
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 
.PN .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 the lookup fails, the connection is terminated.
.IP 9)
A null byte is returned on the connection associated
with the
.B stderr 
and the command line is passed to the normal login
shell of the user.  The
shell inherits the network connections established
by
.PN rshd .
.SH Diagnostics
.NXR "rshd server" "diagnostics"
All diagnostic messages are returned on the connection
associated with the
.BR 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).
.PP
.B "locuser too long"
.br
The name of the user on the client's machine is
longer than 16 characters.
.PP
.B "remuser too long"
.br
The name of the user on the remote machine is
longer than 16 characters.
.PP
.B "command too long"
.br
The command line passed exceeds the size of the argument
list (as configured into the system).
.PP
.B "Hostname for your address unknown."
.br
No entry in the host name database existed for
the client's machine.
.PP
.B "Login incorrect."
.br
No password file entry for the user name existed.
.PP
.B "No remote directory."
.br
The 
.PN chdir
command to the home directory failed.
.PP
.B "Permission denied."
.br
The authentication procedure described above failed.
.PP
.B "Can't make pipe."
.br
The pipe needed for the 
.BR stderr 
was not created.
.PP
.B "Try again."
.br
A
.I fork
by the server failed.
.PP
.B "/bin/sh: ..."
.br
The user's login shell could not be started.
.SH Restrictions
.NXR "rshd server" "restricted"
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.
.SH See Also
rsh(1c), rcmd(3x), services(5), inetd(8c)