rexecd.8c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 8C 代码 · 共 121 行

.\" SCCSID: @(#)rexecd.8c	8.1	9/11/90
.TH rexecd 8c
.SH Name
rexecd \- remote execution server
.SH Syntax
.B /etc/rexecd
.SH Description
.NXR "rexecd server"
.NXAM "rexec subroutine" "rexecd server"
.NXR "rexecd server" "protocol"
The
.PN rexecd
command is the server for the 
.MS rexec 3x
routine.  The server provides remote execution facilities
with authentication based on usernames and encrypted
passwords.
.PP
The
.PN rexecd
command is invoked by 
.MS inetd 8c
when it receives a connection on the port indicated in
the ``exec'' service specification.  For further information, see
.MS services 5 .
When a service request is received the following protocol
is initiated:
.IP 1) 3
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 2)
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.
.IP 3)
A null terminated username of at most 16 characters
is retrieved on the initial socket.
.IP 4)
A null terminated password of at most
16 characters is retrieved on the initial socket.  
.IP 5)
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.  
.IP 6)
The
.PN rexecd
command then validates the user as is done at login time
and, if the authentication was successful, changes
to the user's home directory, and establishes the user
and group protections of the user.
If any of these steps fail the connection is
aborted with a diagnostic message returned.
.IP 7)
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 rexecd .
.SH 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 7 above upon successful completion
of all the steps prior to the command execution).
.PP
.B "username too long"
.br
The name is
longer than 16 characters.
.PP
.B "password too long"
.br
The password 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 "Login incorrect"
.br
No password file entry for the username existed.
.PP
.B "Password incorrect"
.br
The wrong was password supplied.
.PP
.B "No remote directory"
.br
The 
.PN chdir
command to the home directory failed.
.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 "rexecd server" "restricted"
Indicating ``Login incorrect'' as opposed to ``Password incorrect''
is a security breach which allows people to probe a system for users
with null passwords.
.SH See Also
inetd(8c)