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RSHD(8)                   BSD System Manager's Manual                  RSHD(8)

NAME
     rshd -- remote shell server

SYNOPSIS
     rshd [-aDLln]

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

     The rshd utility listens for service requests at the port indicated in the ``cmd'' service specifica-tion; specification;
     tion; see services(5).  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 512-1023, the server
          aborts the connection.

     2.   The server reads characters from the socket up to a NUL (`\0') byte.  The resultant string is
          interpreted as an ASCII number, base 10.

     3.   If the number received in step 2 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 512-1023.

     4.   The server checks the client's source address and requests the corresponding host name (see
          gethostbyaddr(3), hosts(5) and named(8)).  If the hostname cannot be determined or the hostname
          and address do not match after verification, the dot-notation representation of the host address
          is used.

     5.   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.

     6.   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.

     7.   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.

     8.   The rshd utility 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 option prevents ruserok(3) from
          doing any validation based on the user's .rhosts file, unless the user is the superuser.

     9.   If the file /etc/nologin exists and the user is not the superuser, the connection is closed.

     10.  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 rshd.

     The options are as follows:

     -a      This flag is ignored, and is present for compatability purposes.

     -D      Sets the TCP_NODELAY socket option, which improves the performance of small back-to-back writes
             at the expense of additional network traffic.

     -L      Causes all successful accesses to be logged to syslogd(8) as auth.info messages.

     -l      Do not use the user's .rhosts file for authentication, unless the user is the superuser.

     -n      Turn off transport level keepalive messages.  This will prevent sessions from timing out if the
             client crashes or becomes unreachable.

FILES
     /etc/hosts
     /etc/hosts.equiv
     /etc/login.conf
     $HOME/.rhosts

     /etc/pam.conf     rshd uses /etc/pam.conf entries with service name ``rsh''.  Authentication modules
                       requiring passwords (such as pam_unix) are not supported.

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 10 above upon successful completion of all the steps prior to the execution of the
     login shell).

     Locuser too long.
             The name of the user on the client's machine is longer than 16 characters.

     Ruser too long.
             The name of the user on the remote machine is longer than 16 characters.

     Command too long.
             The command line passed exceeds the size of the argument list (as configured into the system).

     Login incorrect.
             No password file entry for the user name existed or the authentication procedure described
             above failed.

     Remote directory.
             The chdir(2) function to the home directory failed.

     Can't make pipe.
             The pipe needed for the stderr, was not created.

     Can't fork; try again.
             A fork(2) by the server failed.

     <shellname>: ...
             The user's login shell could not be started.  This message is returned on the connection asso-ciated associated
             ciated with the stderr, and is not preceded by a flag byte.

SEE ALSO
     rlogin(1), rsh(1), gethostbyaddr(3), rcmd(3), ruserok(3), auth.conf(5), hosts(5), hosts.equiv(5),
     login.conf(5), services(5), named(8), rlogind(8), syslogd(8)

HISTORY
     IPv6 support was added by WIDE/KAME project.

BUGS
     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.

     A facility to allow all data exchanges to be encrypted should be present.

     A more extensible protocol (such as Telnet) should be used.

BSD                              June 4, 1993                              BSD

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