conch Man page

CONCH(1) BSD General Commands Manual CONCH(1)

NAME

conch — Conch SSH client

SYNOPSIS

conch [-AaCfINnrsTtVvx] [-c cipher_spec] [-e escape_char] [-i identity_file] [-K connection_spec] [-L port:host:hostport] [-l user] [-m mac_spec] [-o openssh_option] [-p port] [-R port:host:hostport] [user@] hostname [command]

DESCRIPTION

conch is a SSHv2 client for logging into a remote machine and executing
commands. It provides encrypted and secure communications across a pos‐
sibly insecure network. Arbitrary TCP/IP ports can also be forwarded
over the secure connection.

conch connects and logs into hostname (as user or the current username).
The user must prove her/his identity through a public-key or a password.
Alternatively, if a connection is already open to a server, a new shell
can be opened over the connection without having to reauthenticate.

If command is specified, command is executed instead of a shell. If the
-s option is given, command is treated as an SSHv2 subsystem name.

Authentication
Conch supports the public-key, keyboard-interactive, and password authen‐
tications.

The public-key method allows the RSA or DSA algorithm to be used. The
client uses his/her private key, $HOME/.ssh/id_rsa or $HOME/.ssh/id_dsa
to sign the session identifier, known only by the client and server. The
server checks that the matching public key is valid for the user, and
that the signature is correct.

If public-key authentication fails, conch can authenticate by sending an
encrypted password over the connection.

Connection sharing
conch has the ability to multiplex multiple shells, commands and TCP/IP
ports over the same secure connection. To disable multiplexing for a
connection, use the -I flag.

The -K option determines how the client connects to the remote host. It
is a comma-separated list of the methods to use, in order of preference.
The two connection methods are ‘unix’ (for connecting over a multiplexed
connection) and ‘direct’ (to connect directly). To disable connecting
over a multiplexed connection, do not include ‘unix’ in the preference
list.

As an example of how connection sharing works, to speed up CVS over SSH:

conch –noshell –fork -l cvs_user cvs_host
set CVS_RSH=conch

Now, when CVS connects to cvs_host as cvs_user, instead of making a new
connection to the server, conch will add a new channel to the existing
connection. This saves the cost of repeatedly negotiating the cryptogra‐
phy and authentication.

The options are as follows:

-A Enables authentication agent forwarding.

-a Disables authentication agent forwarding (default).

-C Enable compression.

-c cipher_spec
Selects encryption algorithms to be used for this connection, as
a comma-separated list of ciphers in order of preference. The
list that conch supports is (in order of default preference):
aes256-ctr, aes256-cbc, aes192-ctr, aes192-cbc, aes128-ctr,
aes128-cbc, cast128-ctr, cast128-cbc, blowfish-ctr, blowfish,
idea-ctr, idea-cbc, 3des-ctr, 3des-cbc.

-e ch | ^ch | none
Sets the escape character for sessions with a PTY (default: ‘~’).
The escape character is only recognized at the beginning of a
line (after a newline). The escape character followed by a dot
(‘.’) closes the connection; followed by ^Z suspends the connec‐
tion; and followed by the escape character sends the escape char‐
acter once. Setting the character to “none” disables any
escapes.

-f Fork to background after authentication.

-I Do not allow connection sharing over this connection.

-i identity_spec
The file from which the identity (private key) for RSA or DSA
authentication is read. The defaults are $HOME/.ssh/id_rsa and
$HOME/.ssh/id_dsa. It is possible to use this option more than
once to use more than one private key.

-K connection_spec
Selects methods for connection to the server, as a comma-sepa‐
rated list of methods in order of preference. See Connection
sharing for more information.

-L port:host:hostport
Specifies that the given port on the client host is to be for‐
warded to the given host and port on the remote side. This allo‐
cates a socket to listen to port on the local side, and when con‐
nections are made to that socket, they are forwarded over the
secure channel and a connection is made to host port hostport
from the remote machine. Only root can forward privieged ports.

-l user
Log in using this username.

-m mac_spec
Selects MAC (message authentication code) algorithms, as a comma-
separated list in order of preference. The list that conch sup‐
ports is (in order of preference): hmac-sha2-512, hmac-sha2-256,
hmac-sha1, hmac-md5.

-N Do not execute a shell or command.

-n Redirect input from /dev/null.

-o openssh_option
Ignored OpenSSH options.

-p port
The port to connect to on the server.

-R port:host:hostport
Specifies that the given port on the remote host is to be for‐
warded to the given host and port on the local side. This allo‐
cates a socket to listen to port on the remote side, and when
connections are made to that socket, they are forwarded over the
secure channel and a connection is made to host port hostport
from the client host. Only root can forward privieged ports.

-s Reconnect to the server if the connection is lost.

-s Invoke command (mandatory) as a SSHv2 subsystem.

-T Do not allocate a TTY.

-t Allocate a TTY even if command is given.

-V Display version number only.

-v Log to stderr.

-x Disable X11 connection forwarding (default).

AUTHOR

Written by Paul Swartz .

REPORTING BUGS

To report a bug, visit http://twistedmatrix.com/bugs/

COPRYRIGHT

Copyright © 2002-2008 Twisted Matrix Laboratories.
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

SEE ALSO

ssh

BSD May 22, 2004 BSD