The first of the commands examined here falls into the set called the r-commands. These are the rlogin, rcp, and rsh/rcmd commands. They are called the r-commands because they all start with the letter "r". The successful use of these commands in this article is dependent upon the user and host equiv being properly configured. Most users have difficulty with these commands because their network admin has not properly configured the host and user equiv.

rlogin

The rlogin command connects you local session to a remote session on a different host. To initiate a remote terminal session, use the following command:

	[Syntax]
	rlogin [-8DEKLdx] [-e char] [-k realm] [-l username] host
  

For example:

	[2]<[email protected]># rlogin telnet.submental.org

	Last login: Tue Feb 16 00:54:53 from 207.202.64.115
	Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
	The Regents of the University of California.  All rights reserved.

	FreeBSD 2.2.7-RELEASE (SubMental) #0: Wed Jul 22 08:48:29 GMT 1998
        
	[3]<[email protected]>#
  

The terminal type of the remote connection is the same as the terminal type that is in use for the current connection, unless modified by the user's startup files. All of the character echoing is done done at the remote site, so except for delays, the use of rlogin is transparent to the user. Termination of the connection is made either by logging out of the remote host, or through the termination character, which is ~. (tilde period).

rcp

The rcp or "Remote Copy" command enables the user to copy a file from one host to another. Each file or directory argument is either a remote filename of the form 'rhost:path', or a local filename (containing no `:` characters, or a `/` before any `:`).

	[Syntax]
	rcp [ -p ] file1 file2
	rcp [ -p ] [ -r ] file ..... directory
  

The following is an example of copying a file from the local host to the remote system:

	[2]<[email protected]># rcp test.new infected:test.new
	[2]<[email protected]>#
  

When the filename, as shown in the example, does not begin with a (/), the file is copied in a directory relative to your home directory on the remote system. The rcp command behaves like like the cp command in that the file could be called by a different name on the remote system.

If the -r option is specified and any of the source files are directories, rcp copies each subtree rooted at that name; in this case, the destination must be a directory. By default, the mode and owner of file2 are preserved if the file already existed; otherwise, the mode of the source file modified by the umask on the destination host is used.

The -p option causes `rcp` to attempt to preserve (duplicate) in it copies the modification times and modes of the source file, ignoring the umask.

rsh

rsh is to execute a command on a remote system. Interactive commands are not good candidates for this type of execution.

Typically, the system that use rsh for remote execution are BSD-based Unix systems. rsh works by connecting to the specified hostname and executing the specified remote command to its standard output, and the standard error of the remote command to its standard error. Interrupt, quit, and terminate signals are propagated to the remote commands; rsh is normally terminated when the remote command does.

	[Syntax]
	rsh [-Kdnx] [-t timeout] [-k realm] [-l username] host [command]
  

The execution of a command involves entering the name of the host where the command is to be executed and the name of the command. Running rsh with no command argument has the effect of logging you into the remote system by using rlogin. The following examples illustrate using rsh to execute commands:

	[2]<[email protected]># rsh infected date
	Tue Feb 23 21:37:54 GMT 1999
	[2]<[email protected]># rsh infected hostname 
	infected.org
	[2]<[email protected]># 
  

There are only two options to rsh:

	-l username
  

Use username as the remote username instead of your local username. In the absence of this option, the remote username is the same as your local username.

	-n
  

Redirect the input of rsh to /dev/null. You sometimes need this option to avoid unfortunate interactions between rsh and the shell that invokes it. If, for example, you are running rsh and start an rsh in the background without redirecting its input away from the terminal, it will block even if no reads are posted by the remote command. Using the -n option prevents this.

Virtually any command can be executed on the remote system. Commands that rely upon terminal characteristics or a level of user interaction, however, are not good candidates for the use of rsh.

Hopefully this explained the r* commands well enough for you to make use of them. For more information, please read the appropriate man pages.

Greg Munker

Return to Issue #3