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, applySocketAttributes, 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, verifyRemote
public 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) throws SocketException, IOException
_connectAction_()
is called to perform connection initialization
actions.connect
in class SocketClient
host
- 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(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, 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 SocketClient
host
- 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) throws SocketException, IOException, UnknownHostException
_connectAction_()
is called to perform connection initialization
actions.connect
in class SocketClient
hostname
- 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(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 SocketClient
hostname
- 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) throws IOException
rcommand(localUsername, remoteUsername, command, false);
localUsername
- the local userremoteUsername
- the remote usercommand
- the commandIOException
- on errorpublic 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.Copyright © 2001–2022 The Apache Software Foundation. All rights reserved.