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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 specification; 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 cor‐
	  responding 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 iden‐
	  tity 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 iden‐
	  tity 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.	  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 perfor‐
	     mance 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 authenti‐
	     cation procedure described above failed.

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

     Logins not available right now.
	     The rsh(1) utility was attempted outside the allowed hours
	     defined in /etc/login.conf for the local user's login class.

     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 associated 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 use‐
     ful in an “open” environment.

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

     Post-PAM, FreeBSD also needs the following patch applied besides properly
     configuring .rhosts:

	   --- etc/pam.d/rsh.orig  Wed Dec 17 14:36:20 2003
	   +++ etc/pam.d/rsh	   Wed Dec 17 14:30:43 2003
	   @@ -9 +9 @@
	   -auth   required	   pam_rhosts.so   no_warn
	   +auth   required	   pam_rhosts.so   no_warn allow_root

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

BSD				 June 4, 1993				   BSD
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