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The Remote Command protocol enables an application to execute
commands on a remote host, with the output of the command returned
to the client. The SocketTools library actually implements three
related protocols: rexec, rshell and rlogin. The choice of
protocols is determined by the port that is selected when a
connection is established.
Rexec
The rexec protocol enables a client
application to execute a command on a remote host. Output from the
command is returned to the client and the connection is closed when
the command terminates. The client connects on port 512 and must
provide a user name and password to authenticate the session.
Rshell
The rshell protocol is similar to rexec in that it enables a client
to execute a command on a remote host. Output from the command is
returned to the client and the connection is closed when the
command terminates. The client connects on port 514 and must
provide a user name. The primary difference between the rexec and
rshell protocols is that rshell does not require a password.
Instead, it uses what is called "host equivalence" to determine if
the client is permitted to execute commands as that user. On a UNIX
based operating system, host equivalence is controlled by the
/etc/hosts.equiv and the .rhosts file in the user's home directory.
These files list the host names and user names which are permitted
to execute commands using the rshell protocol. Consult your
operating system manual pages for more information about how to
configure host equivalence.
Rlogin
The rlogin protocol is similar to Telnet in that it provides an
interactive terminal session. The connection is closed when the
user logs out or the shell process on the remote host is
terminated. The client connects on port 513 and must provide a user
name and terminal type. If there is an entry in the host
equivalence tables for the user and local host, then the client
will be automatically logged in and provided with a shell prompt.
If there is no host equivalence, the client will be prompted for a
password. The terminal emulation library can be used to provide
ANSI or DEC VT-220 emulation services if needed.
An important consideration when deciding whether to use rexec,
rshell or rlogin is how the server is configured and the type of
command being executed. If there is no entry for the local host in
the server's host equivalence tables, then the rexec command should
be used instead of rshell.
When using rexec or rshell, it is important to keep in mind that
although the command is executed with the privileges of the
specified user, that user is not actually logged in. The user's
login script is not executed and the program will not inherit the
user's normal environment as it would during an interactive
session. If you are connecting to a UNIX system, you should not
attempt to execute programs which try to put standard input into
raw mode; an example of this would be the vi editor. If you are
connecting to a Windows system, you should not execute a program
which uses a graphical interface. Only programs which read standard
input and write to standard output are suitable for use with rexec
or rshell.
The first step that your application must take is to initialize
the library and then establish a connection. The following
functions are available for use by your application:
RshInitialize
Initialize the library and load the Windows Sockets library for the
current process. This must be the first function call that the
application makes before calling the other Remote Command API
functions.
RshExecute
Execute the specified command on the remote host. The rshell or
rexec protocol is selected based on the port number that is
specified. Output from the command will be returned to the client
to be read. When the command terminates, the connection to the
server will be closed.
RshLogin
Establish an interactive login session which is similar to how the
Telnet protocol works. If there is no host equivalence with the
local host, you will be prompted for a password. Output from the
session will be returned to the client, and when the client logs
out the connection will be closed.
RshRead
Read the output generated by the command. Your application would
typically call this function in a loop until all of the data has
been read or an error occurs.
RshSearch
Search for a specific sequence of characters in the output returned
by the remote host. The function returns when the sequence is
encountered or when a timeout occurs. The data captured up to the
point where the character sequence was matched is returned to the
caller for processing.
RshDisconnect
Disconnect from the server and release the memory allocated for
that client session. After this function is called, the client
handle is no longer valid.
RshUninitialize
Unload the Windows Sockets library and release any resources that
have been allocated for the current process. This is the last
function call that the application should make prior to
terminating.
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