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SSH Tectia

sshg3

sshg3 — Secure Shell terminal client - Generation 3

Synopsis

sshg3 [options...]
profile | [user@] host [#port]
[command]

Description

sshg3 (sshg3.exe on Windows) is a program for logging in to a remote machine and executing commands on a remote machine. sshg3 provides secure, encrypted communication channels between two hosts over an unsecured network. It can be used to replace the unsecured rlogin, rsh, and telnet programs. Also X11 connections and arbitrary TCP/IP ports can be forwarded over secure channels with sshg3.

To connect to a remote host using sshg3, give either the name of a connection profile defined in the ssh-broker-config.xml file (profile) or the IP address or DNS name of the remote host, optionally with the remote username and the port of the Secure Shell server ([user@]host[#port]). If no username is given, the local username is assumed. If no port is given, the default Secure Shell port 22 is assumed. The remote host must be running a Secure Shell version 2 server.

sshg3 launches ssh-broker-g3 as a transport. ssh-broker-g3 will ask for passwords or passphrases if they are needed for authentication. sshg3 uses the configuration specified in the ssh-broker-config.xml file.

When the user's identity has been accepted by the server, the server either executes the given command, or logs in to the machine and gives the user a normal shell. All communication with the remote command or shell will be automatically encrypted.

If no pseudo-tty has been allocated, the session is transparent and can be used to securely transfer binary data.

The session terminates when the command or shell on the remote machine exits and all X11 and TCP/IP connections have been closed. The exit status of the remote program is returned as the exit status of sshg3.

Agent Forwarding (Unix)

ssh-broker-g3 acts as an authentication agent, and the connection to the agent is automatically forwarded to the remote side unless disabled in the ssh-broker-config.xml file or on the sshg3 command line (with the -a option).

X11 Forwarding

If the user is using X11 (the DISPLAY environment variable is set), the connection to the X11 display can be automatically forwarded to the remote side in such a way that any X11 programs started from the shell (or command) will go through the encrypted channel, and the connection to the real X server will be made from the local machine. The user should not manually set DISPLAY. X11 connection forwarding can be allowed in the ssh-broker-config.xml file or on the sshg3 command line (with the +x option). By default, X11 forwarding is disabled.

The DISPLAY value set by sshg3 will point to the server machine, but with a display number greater than zero. This is normal, and happens because sshg3 creates a "proxy" X server on the server machine for forwarding the connections over the encrypted channel.

sshg3 will also automatically set up the Xauthority data on the server machine. For this purpose, it will generate a random authentication cookie, store it in the Xauthority data on the server, and verify that any forwarded connections carry this cookie and replace it with the real cookie when the connection is opened. The real authentication cookie is never sent to the server machine (and no cookies are sent in the plain).

TCP Port Forwarding

Forwarding of arbitrary TCP/IP connections over the secure channel can be specified either in the ssh-broker-config.xml file or on the sshg3 command line (with the -L and -R options).

Options

Command-line options override the settings in the ssh-broker-config.xml file if the same option has been configured in both places. The following options are available:

-a, --no-agent-forwarding

Disables authentication agent forwarding.

+a

Enables authentication agent forwarding. This is the default value.

-B, --batch-mode

Uses batch mode. Fails authentication if it requires user interaction on the terminal.

Using batch mode requires that you have previously saved the server host key on the client and set up a non-interactive method for user authentication (for example, host-based authentication or public-key authentication without a passphrase).

-D, --debug=LEVEL

Sets the debug level. LEVEL is a number from 0 to 99, where 99 specifies that all debug information should be displayed. This should be the first argument on the command line.

[Note]Note

Option -D only applies on Unix. On Windows, instead of this command line tool, use the Connection Broker debugging options -D, -l.

[Note]Note

The debug level can be set only when the sshg3 command starts the Connection Broker. This option has no effect in the command if the Connection Broker is already running.

-e, --escape-char=CHAR

Sets escape character (none: disabled, default: ~).

-f

Forks into background mode (Unix).

-g, --gateway

Gateways ports, which means that also other hosts may connect to locally forwarded ports. This option has to be specified before the "-L" option. Note the logic of + and - in this option.

+g

Does not gateway ports. Listens to tunneling connections originating only from the localhost. This is the default value. Note the logic of + and - in this option.

-l, --user=USERNAME

Logs in using this username.

-L [protocol/] [listen-address:] listen-port:dst-host:dst-port

Forwards a port on the local (client) host to a remote destination host and port.

This allocates a listener port (listen-port) on the local client. Whenever a connection is made to this listener, the connection is tunneled over Secure Shell to the remote server and another connection is made from the server to a specified destination host and port (dst-host:dst-port). The connection from the server onwards will not be secure, it is a normal TCP connection.

Giving the argument protocol enables protocol-specific forwarding. The protocols implemented are tcp (default, no special processing), ftp (temporary forwarding is created for FTP data channels, effectively securing the whole FTP session), and socks.

With the socks protocol, the syntax of the argument is "-L socks/[listen-address:]listen-port". When this is set, SSH Tectia Client will act as a SOCKS server for other applications, creating forwards as requested by the SOCKS transaction. This supports both SOCKS4 and SOCKS5.

If listen-address is given, only that interface on the client is listened. If it is omitted, all interfaces are listened.

-n

Redirects input from /dev/null (Unix).

-o option

Processes an option as if it was read from a SSH Tectia Client 4.x-style configuration file. The supported options are ForwardX11 and ForwardAgent (for example, -o "ForwardX11=yes").

-p, --port=PORT

Connects to this port on the remote host. A Secure Shell server must be listening on the same port.

-R [protocol/] [listen-address:] listen-port:dst-host:dst-port

Forwards a port on the remote (server) host to a destination host and port on the local side.

This allocates a listener port (listen-port) on the remote server. Whenever a connection is made to this listener, the connection is tunneled over Secure Shell to the local client and another connection is made from the client to a specified destination host and port (dst-host:dst-port). The connection from the client onwards will not be secure, it is a normal TCP connection.

Giving the argument protocol enables protocol-specific forwarding. The protocols implemented are tcp (default, no special processing) and ftp (temporary forwarding is created for FTP data channels, effectively securing the whole FTP session).

If listen-address is given, only that interface on the server is listened. If it is omitted, all interfaces are listened.

-s, --subsystem

Sets the executed command to be a subsystem rather than a shell executable.

-S, --no-session-channel

Does not request a session channel. This can be used with port-forwarding requests if a session channel (and tty) is not needed, or the server does not give one.

+S

Requests a session channel. This is the default value.

-t, --tty

Allocates a tty even if a command is given.

-v, --verbose

Uses verbose mode (equal to -D 2).

-w

Does not try an empty password.

+w, --try-empty-password

Tries an empty password.

+x, +X

Enables X11 connection forwarding.

-x, -X, --no-x11-forwarding

Disables X11 connection forwarding. This is the default value.

-z, --broker-log-file=FILE

Sets the Connection Broker log file to FILE. This option works only if ssh-broker-g3 gets started by this process).

--abort-on-failing-tunnel

Aborts if creating a tunnel listener fails (for example, if the port is already reserved).

--remote-environment name=value

When this option is used, the defined environment variables are passed to the server from the client side. The environment variables are applied on the server when requesting a command, shell or subsystem.

Note that the server can restrict the setting of environment variables.

You can also configure the environment variables to be passed to the server in the ssh-broker-config.xml configuration file with the <remote-environment> element in the default-settings and per profile. See remote-environment.

If the same variable is entered on the command-line client and configured in the ssh-broker-config.xml, the command-line version will be used.

--remote-environment-format name=value

The defined environment variables are passed to the server from the client side. The Connection Broker processes the value before sending it to the server.

You can use %U in the value to indicate a user name. The Connection Broker replaces the %U with the actual user name before sending it to the server.

For more information, see --remote-environment name=value.

--password= PASSWORD | file://PASSWORDFILE | extprog://PROGRAM

Sets user password that the client will send as a response to password authentication. The PASSWORD can be given directly as an argument to this option (not recommended), or a path to file containing the password can be given, or a path to a program or a script that outputs the password can be given.

[Caution]Caution

Supplying the password on the command line is not a secure option. For example, in a multi-user environment, the password given directly on the command line is trivial to recover from the process table. You should set up a more secure way to authenticate. For non-interactive batch jobs, it is more secure to use public-key authentication without a passphrase, or host-based authentication. At a minimum, use a file or a program to supply the password.

-V, --version

Displays program version and exits.

-h, --help

Displays a short summary of command-line options and exits.

The command can be either of the following:

remote_command [arguments] ...

Runs the command on a remote host.

-s service

Enables a service in remote server.

Escape Sequences

sshg3 supports escape sequences to manage a running session. For an escape sequence to take effect, it must be typed directly after a newline character (press Enter first). The escape sequences are not displayed on screen during typing.

The following escape sequences are supported:

~.

Terminates the connection.

~Ctrl-Z

Suspends the session.

~~

Sends the escape character literally.

~#

Lists forwarded connections.

~-

Disables the escape character irrevocably.

~?

Displays a summary of escape sequences.

~r

Initiates rekeying manually.

~s

Gives connection statistics, including server and client version, packets in, packets out, compression, key exchange algorithms, public-key algorithms, and symmetric ciphers.

~c

Gives statistics for individual channels (data window sizes etc). This is for debugging purposes.

~V

Dumps the client version number to stderr (useful for troubleshooting).

Environment Variables

Upon connection, the Secure Shell server will automatically set a number of environment variables that can be used by sshg3. The exact variables set depend on the Secure Shell server. The following variables can be used by sshg3:

DISPLAY

The DISPLAY variable indicates the location of the X11 server. It is automatically set by the server to point to a value of the form hostname:n where hostname indicates the host on which the server and the shell are running, and n is an integer greater than or equal to 1. sshg3 uses this special value to forward X11 connections over the secure channel.

The user should normally not set DISPLAY explicitly, as that will render the X11 connection unsecured (and will require the user to manually copy any required authorization cookies).

HOME

The user's home directory.

LOGNAME

Synonym for USER; set for compatibility with systems using this variable.

MAIL

The user's mailbox.

PATH

Set to the default PATH, depending on the operating system or, on some systems, /etc/environment or /etc/default/login.

SSH_SOCKS_SERVER

The address of the SOCKS server used by sshg3.

SSH2_AUTH_SOCK

If this exists, it is used to indicate the path of a Unix-domain socket used to communicate with the authentication agent (or its local representative).

SSH2_CLIENT

Identifies the client end of the connection. The variable contains three space-separated values: client IP address, client port number, and server port number.

SSH2_ORIGINAL_COMMAND

This will be the original command given to sshg3 if a forced command is run. It can be used, for example, to fetch arguments from the other end. This does not have to be a real command, it can be the name of a file, device, parameters or anything else.

SSH2_TTY

This is set to the name of the tty (path to the device) associated with the current shell or command. If the current session has no tty, this variable is not set.

TZ

The time-zone variable is set to indicate the present time zone if it was set when the server was started (the server passes the value to new connections).

USER

The name of the user.

For a list of varibles set by SSH Tectia Server, see the ssh-server-g3(8) man page.

Exit Values

On successful execution, sshg3 returns normally 0 (zero) as the exit value. If sshg3 encounters an error, you usually see the reason in an error message. In this case, the exit value is 1.

When executing remote commands, sshg3 exits with the status of the command run. On successful runs this is normally 0 (zero). The error code 127 is usually returned by the shell if the requested remote command is not found.

Examples

Connect as the local username to host remotehost, port 2222, and open shell:

$ sshg3 remotehost#2222

Connect to the host specified by the connection profile profile1 in the ssh-broker-config.xml file, and run the who command (and exit after running the command):

$ sshg3 profile1 who

Connect as user to host remotehost, and open a local port forwarding from port 143 on the client to port 143 on imapserver. Do not open shell. Also other hosts may connect to the local port. The connection from remotehost to imapserver will not be secured:

$ sshg3 -L 143:imapserver:143 -g -S user@remotehost

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