rshd(8) 						      System Manager's Manual							   rshd(8)

NAME

       rshd - The remote shell server

SYNOPSIS

       rshd [-aeln]

FLAGS

       The  addresses  for  the  hostname  are requested, verifying that the name and address correspond.  Causes rshd to check for the /etc/nolo-
       gin_{hostname} and /etc/nologin files.  If either exists, rshd prints its contents and exits.  Prevents the ruserok command from doing  any
       validation based on the user's .rhosts file, unless the user is the superuser.  Disables transport-level, keep-alive messages.

SECURITY NOTE

       This  security-sensitive  command  uses the SIA (Security Integration Architecture) routine as an interface to the security mechanisms. See
       the matrix.conf(4) reference page for more information.

DESCRIPTION

       The rshd daemon is the server for the rcmd(3) routine and, consequently, for the rsh(1) program.   The  server  provides  remote  execution
       facilities with authentication based on privileged port numbers from trusted hosts.

       The  rshd  daemon  listens  for	service  requests at the port indicated in the cmd service specification; see services(4).  When a service
       request is received, the following protocol is initiated: The server checks the client's source port.  If the port is not in the range  512
       to  1023,  the  server  aborts  the  connection.  The server reads bytes from the socket up to a null (`') byte.  The resultant string is
       interpreted as an ASCII number, base 10.  If the number received in step 2 is nonzero, it is interpreted as the port number of a  secondary
       stream  to  be  used for the stderr option.  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 512 to 1023.  The server checks the client's source address	and  requests  the  corre-
       sponding hostname (see gethostbyaddr(3), hosts(4), and named(8)).  If the hostname cannot be determined, the dot-notation representation of
       the host address is used.  If the hostname is in the same domain as the server (according to the last two components of the  domain  name),
       or if the -a flag is given, the addresses for the hostname are requested, verifying that the name and address correspond.  If address veri-
       fication fails, the connection is aborted with the message Host address mismatch.  A null-terminated  username  of  at  most  16  bytes	is
       retrieved  on  the initial socket.  This username is interpreted as the user identity on the client 's machine.	A null-terminated username
       of at most 16 bytes is retrieved on the initial socket.	This username is interpreted as a user identity to use on the server's machine.  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.  The  rshd  daemon  then  validates  the  user	using  ruserok(3),  which  uses  the  file
       /etc/hosts.equiv  and the .rhosts file found in the user's home directory.  The -l flag prevents ruserok(3) from doing any validation based
       on the user's .rhosts file, unless the user is the superuser.  If rshd was started with the -e flag, the user is  not  the  superuser,  and
       either the /etc/nologin_{hostname} or /etc/nologin file exists, rshd prints the contents of the first file found and aborts the connection.
       If the file has a zero length, rshd prints a "logins disabled" message.	A null 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 rshd.

       Transport-level, keep-alive messages are enabled unless the -n flag is present.	The use of keep-alive messages allows sessions to be timed
       out if the client crashes or becomes unreachable.

CAUTIONS

       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.

DIAGNOSTICS

       Except  for the last diagnostic message listed, all diagnostic messages are returned on the initial socket, after which any network connec-
       tions 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 execution of the login shell).  The name of the user on the client's machine is longer than 16 characters.  The
       name of the user on the remote machine is longer than 16 characters.  The command line passed exceeds the size of  the  argument  list  (as
       configured  into  the  system).	 No password file entry for the username existed.  The server is currently not accepting connections.  The
       chdir command to the home directory failed.  The authentication procedure previously described failed.  The  pipe  needed  for  the  stderr
       option,	but  it  was not created.  A fork by the server failed.  The user's login shell could not be started.  This message is returned on
       the connection associated with the stderr option, and is not preceded by a flag byte.

FILES

       Specifies the command path Stops logins.  In a cluster, there is also /etc/nologin_{hostname}.

RELATED INFORMATION

       Commands:  rsh(1)

       Functions:  rcmd(3), ruserok(3) delim off

																	   rshd(8)