NetBSD/libexec/rexecd/rexecd.8

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.\"     from: @(#)rexecd.8	8.3 (Berkeley) 6/1/94
.\"
.Dd June 1, 1994
.Dt REXECD 8
.Os
.Sh NAME
.Nm rexecd
.Nd remote execution server
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm
is the server for the
.Xr rexec 3
routine.
The server provides remote execution facilities with authentication
based on user names and passwords.
.Pp
.Nm
listens for service requests at the port indicated in
the ``exec'' service specification; see
.Xr services 5 .
When a service request is received the following protocol
is initiated:
.Bl -enum
.It
The server reads characters from the socket up to a NUL
.Pq Ql \e0
byte.
The resultant string is interpreted as an
.Tn ASCII
number, base 10.
.It
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
.Em stderr .
A second connection is then created to the specified
port on the client's machine.
.It
A NUL terminated user name of at most 16 characters
is retrieved on the initial socket.
.It
A NUL terminated, unencrypted password of at most
16 characters is retrieved on the initial socket.
.It
A NUL 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.
.It
.Nm
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.
.It
A NUL byte is returned on the initial socket and the command line
is passed to the normal login shell of the user.
The shell inherits the network connections established by
.Nm "" .
.El
.Sh DIAGNOSTICS
Except for the last one listed below,
all diagnostic messages are returned on the initial socket,
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
.Bl -tag -width Ds
.It Sy username too long
The name is
longer than 16 characters.
.It Sy password too long
The password is longer than 16 characters.
.It Sy command too long
The command line passed exceeds the size of the argument
list (as configured into the system).
.It Sy Login incorrect.
No password file entry for the user name existed.
.It Sy Password incorrect.
The wrong password was supplied.
.ne 1i
.It Sy \&No remote directory.
The
.Xr chdir 2
to the home directory failed.
.It Sy Try again.
A
.Xr fork 2
by the server failed.
.It Sy <shellname>: ...
The user's login shell could not be started.
This message is returned
on the connection associated with the
.Em stderr ,
and is not preceded by a flag byte.
.El
.Sh SEE ALSO
.Xr rexec 3
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Sh BUGS
Indicating ``Login incorrect'' as opposed to ``Password incorrect''
is a security breach which allows people to probe a system for users
with null passwords.
.Pp
A facility to allow all data and password exchanges to be encrypted should be
present.
.Sh SECURITY CONSIDERATIONS
As the passwords exchanged by the client and
.Nm
are not encrypted, it is
.Em strongly
recommended that this service is not enabled.