public class RCommandClient extends RExecClient
RExecClient,
from which it is derived, and implements the rcmd() facility that
first appeared in 4.2BSD Unix. rcmd() is the facility used by the rsh
(rshell) and other commands to execute a command on another machine
from a trusted host without issuing a password. The trust relationship
between two machines is established by the contents of a machine's
/etc/hosts.equiv file and a user's .rhosts file. These files specify
from which hosts and accounts on those hosts rcmd() requests will be
accepted. The only additional measure for establishing trust is that
all client connections must originate from a port between 512 and 1023.
Consequently, there is an upper limit to the number of rcmd connections
that can be running simultaneously. The required ports are reserved
ports on Unix systems, and can only be bound by a
process running with root permissions (to accomplish this rsh, rlogin,
and related commands usualy have the suid bit set). Therefore, on a
Unix system, you will only be able to successfully use the RCommandClient
class if the process runs as root. However, there is no such restriction
on Windows95 and some other systems. The security risks are obvious.
However, when carefully used, rcmd() can be very useful when used behind
a firewall.
As with virtually all of the client classes in org.apache.commons.net, this
class derives from SocketClient. But it overrides most of its connection
methods so that the local Socket will originate from an acceptable
rshell port. The way to use RCommandClient is to first connect
to the server, call the rcommand() method,
and then
fetch the connection's input, output, and optionally error streams.
Interaction with the remote command is controlled entirely through the
I/O streams. Once you have finished processing the streams, you should
invoke disconnect()
to clean up properly.
By default the standard output and standard error streams of the
remote process are transmitted over the same connection, readable
from the input stream returned by
getInputStream()
. However, it is
possible to tell the rshd daemon to return the standard error
stream over a separate connection, readable from the input stream
returned by getErrorStream()
. You
can specify that a separate connection should be created for standard
error by setting the boolean separateErrorStream
parameter of rcommand() to true .
The standard input of the remote process can be written to through
the output stream returned by
getOutputStream()
.
SocketClient,
RExecClient,
RLoginClient| Modifier and Type | Field and Description |
|---|---|
static int |
DEFAULT_PORT
The default rshell port.
|
static int |
MAX_CLIENT_PORT
The largest port number an rcmd client may use.
|
static int |
MIN_CLIENT_PORT
The smallest port number an rcmd client may use.
|
_errorStream_, NULL_CHAR_defaultPort_, _hostname_, _input_, _output_, _serverSocketFactory_, _socket_, _socketFactory_, _timeout_, connectTimeout, NETASCII_EOL| Constructor and Description |
|---|
RCommandClient()
The default RCommandClient constructor.
|
| Modifier and Type | Method and Description |
|---|---|
void |
connect(InetAddress host,
int port)
Opens a Socket connected to a remote host at the specified port and
originating from the current host at a port in a range acceptable
to the BSD rshell daemon.
|
void |
connect(InetAddress host,
int port,
InetAddress localAddr)
Opens a Socket connected to a remote host at the specified port and
originating from the specified local address using a port in a range
acceptable to the BSD rshell daemon.
|
void |
connect(InetAddress host,
int port,
InetAddress localAddr,
int localPort)
Opens a Socket connected to a remote host at the specified port and
originating from the specified local address and port.
|
void |
connect(String hostname,
int port)
Opens a Socket connected to a remote host at the specified port and
originating from the current host at a port in a range acceptable
to the BSD rshell daemon.
|
void |
connect(String hostname,
int port,
InetAddress localAddr)
Opens a Socket connected to a remote host at the specified port and
originating from the specified local address using a port in a range
acceptable to the BSD rshell daemon.
|
void |
connect(String hostname,
int port,
InetAddress localAddr,
int localPort)
Opens a Socket connected to a remote host at the specified port and
originating from the specified local address and port.
|
void |
rcommand(String localUsername,
String remoteUsername,
String command)
Same as
rcommand(localUsername, remoteUsername, command, false); |
void |
rcommand(String localUsername,
String remoteUsername,
String command,
boolean separateErrorStream)
Remotely executes a command through the rshd daemon on the server
to which the RCommandClient is connected.
|
disconnect, getErrorStream, getInputStream, getOutputStream, isRemoteVerificationEnabled, rexec, rexec, setRemoteVerificationEnabled_connectAction_, addProtocolCommandListener, connect, connect, createCommandSupport, fireCommandSent, fireReplyReceived, getCharset, getCharsetName, getCommandSupport, getConnectTimeout, getDefaultPort, getDefaultTimeout, getKeepAlive, getLocalAddress, getLocalPort, getProxy, getReceiveBufferSize, getRemoteAddress, getRemotePort, getSendBufferSize, getServerSocketFactory, getSoLinger, getSoTimeout, getTcpNoDelay, isAvailable, isConnected, removeProtocolCommandListener, setCharset, setConnectTimeout, setDefaultPort, setDefaultTimeout, setKeepAlive, setProxy, setReceiveBufferSize, setSendBufferSize, setServerSocketFactory, setSocketFactory, setSoLinger, setSoTimeout, setTcpNoDelay, verifyRemotepublic static final int DEFAULT_PORT
public static final int MIN_CLIENT_PORT
public static final int MAX_CLIENT_PORT
public RCommandClient()
DEFAULT_PORT .public void connect(InetAddress host, int port, InetAddress localAddr) throws SocketException, BindException, IOException
_connectAction_()
is called to perform connection initialization actions.host - The remote host.port - The port to connect to on the remote host.localAddr - The local address to use.SocketException - If the socket timeout could not be set.BindException - If all acceptable rshell ports are in use.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.public void connect(InetAddress host, int port) throws SocketException, IOException
_connectAction_()
is called to perform connection initialization actions.connect in class SocketClienthost - The remote host.port - The port to connect to on the remote host.SocketException - If the socket timeout could not be set.BindException - If all acceptable rshell ports are in use.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.public void connect(String hostname, int port) throws SocketException, IOException, UnknownHostException
_connectAction_()
is called to perform connection initialization actions.connect in class SocketClienthostname - The name of the remote host.port - The port to connect to on the remote host.SocketException - If the socket timeout could not be set.BindException - If all acceptable rshell ports are in use.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.UnknownHostException - If the hostname cannot be resolved.public void connect(String hostname, int port, InetAddress localAddr) throws SocketException, IOException
_connectAction_()
is called to perform connection initialization actions.hostname - The remote host.port - The port to connect to on the remote host.localAddr - The local address to use.SocketException - If the socket timeout could not be set.BindException - If all acceptable rshell ports are in use.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.public void connect(InetAddress host, int port, InetAddress localAddr, int localPort) throws SocketException, IOException, IllegalArgumentException
MIN_CLIENT_PORT and
MAX_CLIENT_PORT or an IllegalArgumentException will
be thrown.
Before returning, _connectAction_()
is called to perform connection initialization actions.connect in class SocketClienthost - The remote host.port - The port to connect to on the remote host.localAddr - The local address to use.localPort - The local port to use.SocketException - If the socket timeout could not be set.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.IllegalArgumentException - If an invalid local port number
is specified.public void connect(String hostname, int port, InetAddress localAddr, int localPort) throws SocketException, IOException, IllegalArgumentException, UnknownHostException
MIN_CLIENT_PORT and
MAX_CLIENT_PORT or an IllegalArgumentException will
be thrown.
Before returning, _connectAction_()
is called to perform connection initialization actions.connect in class SocketClienthostname - The name of the remote host.port - The port to connect to on the remote host.localAddr - The local address to use.localPort - The local port to use.SocketException - If the socket timeout could not be set.IOException - If the socket could not be opened. In most
cases you will only want to catch IOException since SocketException is
derived from it.UnknownHostException - If the hostname cannot be resolved.IllegalArgumentException - If an invalid local port number
is specified.public void rcommand(String localUsername, String remoteUsername, String command, boolean separateErrorStream) throws IOException
getInputStream() . Disconnecting
from the server or closing the process streams before reaching
end of file will not necessarily terminate the remote process.
If a separate error stream is requested, the remote server will
connect to a local socket opened by RCommandClient, providing an
independent stream through which standard error will be transmitted.
The local socket must originate from a secure port (512 - 1023),
and rcommand() ensures that this will be so.
RCommandClient will also do a simple security check when it accepts a
connection for this error stream. If the connection does not originate
from the remote server, an IOException will be thrown. This serves as
a simple protection against possible hijacking of the error stream by
an attacker monitoring the rexec() negotiation. You may disable this
behavior with
setRemoteVerificationEnabled()
.
localUsername - The user account on the local machine that is
requesting the command execution.remoteUsername - The account name on the server through which to
execute the command.command - The command, including any arguments, to execute.separateErrorStream - True if you would like the standard error
to be transmitted through a different stream than standard output.
False if not.IOException - If the rcommand() attempt fails. The exception
will contain a message indicating the nature of the failure.public void rcommand(String localUsername, String remoteUsername, String command) throws IOException
rcommand(localUsername, remoteUsername, command, false); localUsername - the local userremoteUsername - the remote usercommand - the commandIOException - on errorCopyright © 2001–2017 The Apache Software Foundation. All rights reserved.