term% cat index.txt SSH(1) General Commands Manual SSH(1)
NAME
ssh, sshnet, scp, sshserve - secure login and file copy from/to Unix or
Plan 9
SYNOPSIS
ssh [ -CfiImPpRrw ] [ -A authlist ] [ -c cipherlist ] [ -[lu] user ]
[user@]host [ cmd [ args ... ]]
sshnet [ -A authlist ] [ -c cipherlist ] [ -m mtpt ] [ -s service ]
[user@]host
scp [host:]file [host:]file
scp [host:]file ... [host:]dir
aux/sshserve [ -p ] address
DESCRIPTION
Ssh allows authenticated login over an encrypted channel to hosts that
support the ssh protocol (see the RFCs listed below for encryption and
authentication details).
Ssh takes the host name of the machine to connect to as its mandatory
argument. It may be specified as a domain name or an IP address. Nor‐
mally, login is attempted using the user name from /dev/user.
Command-line options are:
-C force input to be read in cooked mode: ``line at a time'' with
local echo.
-f enable agent forwarding. With this flag, ssh uses SSH's agent
forwarding protocol to allow programs running on the remote
server to interact with factotum(4) to perform RSA authentica‐
tion.
-i force interactive mode. In interactive mode, ssh prompts for
passwords and confirmations of new host keys when necessary.
(In non-interactive mode, password requests are rejected and un‐
recognized host keys are cause for disconnecting.) By default,
ssh runs in interactive mode only when its input file descriptor
is /dev/cons.
-I force non-interactive mode.
-m disable the control-\ menu, described below.
-p force pseudoterminal request. The ssh protocol, grounded in
Unix tradition, differentiates between connections that request
controlling pseudoterminals and those that do not. By default,
ssh requests a pseudoterminal only when no command is given.
-P force no pseudoterminal request.
-r strip carriage returns.
-R put the allocated pseudoterminal, if any, in raw mode.
-w notify the remote side whenever the window changes size.
-[lu] user
specify user name. This option is deprecated in favor of the
user@hostname syntax.
-A authlist
specify an ordered space-separated list of authentication proto‐
cols to try. The full set of authentication protocols is rsa
(RSA using factotum(4) to moderate key usage), password (use a
password gathered from factotum), and tis (challenge-response).
The default list is all three in that order.
-c cipherlist
specify an ordered space-separated list of allowed ciphers to
use when encrypting the channel. The full set of ciphers is des
(standard DES), 3des (a somewhat doubtful variation on triple
DES), blowfish (Bruce Schneier's Blowfish), rc4 (RC4), and none
(no encryption). The default cipher list is blowfish rc4 3des.
The control-\ character is a local escape, as in con(1). It prompts
with >>>. Legitimate responses to the prompt are
q Exit.
. Return from the escape.
!cmd Run the command with the network connection as its standard in‐
put and standard output. Standard error will go to the screen.
r Toggle printing of carriage returns.
If no command is specified, a login session is started on the remote
host. Otherwise, the command is executed with its arguments.
Ssh establishes a connection with an ssh daemon on the remote host.
The daemon sends to ssh its RSA public host key and session key. Using
these, ssh sends a session key which, presumably, only the daemon can
decipher. After this, both sides start encrypting their data with this
session key.
When the daemon's host key has been received, ssh looks it up in
$home/lib/keyring and in /sys/lib/ssh/keyring. If the key is found
there, and it matches the received key, ssh is satisfied. If not, ssh
reports this and offers to add the key to $home/lib/keyring.
Over the encrypted channel, ssh attempts to convince the daemon to ac‐
cept the call using the listed authentication protocols (see the -A op‐
tion above).
The preferred way to authenticate is a netkey-style challenge/response
or via a SecurID token. Ssh users on other systems than Plan 9 should
enable TIS_Authentication.
When the connection is authenticated, the given command line, (by de‐
fault, a login shell) is executed on the remote host.
The SSH protocol allows clients to make outgoing TCP calls via the
server. Sshnet establishes an SSH connection and, rather than execute
a remote command, presents the remote server's TCP stack as a network
stack (see the discussion of TCP in ip(3)) mounted at mtpt (default
/net), optionally posting a 9P service descriptor for the new file sys‐
tem as /srv/service. The -A and -c arguments are as in ssh.
Scp uses ssh to copy files from one host to another. A remote file is
identified by a host name, a colon and a file name (no spaces). Scp
can copy files from remote hosts and to remote hosts.
Sshserve is the server that services ssh calls from remote hosts. The
-A and -c options set valid authentication methods and ciphers as in
ssh, except that there is no rsa authentication method. Unlike in ssh,
the list is not ordered: the server presents a set and the client makes
the choice. The default sets are tis and blowfish rc4 3des. By de‐
fault, users start with the namespace defined in /lib/namespace. Users
in group noworld in /adm/users start with the namespace defined in
/lib/namespace.noworld. Sshserve does not provide the TCP forwarding
functionality used by sshnet, because many Unix clients present this
capability in an insecure manner.
Sshserve requires that factotum(4) hold the host key, identified by
having attributes proto=rsa service=sshserve. To generate a host key:
auth/rsagen -t 'service=sshserve' >/mnt/factotum/ctl
To extract the public part of the host key in the form used by SSH key
rings:
grep 'service=sshserve' /mnt/factotum/ctl | auth/rsa2ssh
FILES
/sys/lib/ssh/keyring
System key ring file containing public keys for remote ssh
clients and servers.
/usr/user/lib/keyring
Personal key ring file containing public keys for remote ssh
clients and servers.
SOURCE
/sys/src/cmd/ssh
SEE ALSO
/lib/rfc/rfc425[0-6]
factotum(4), authsrv(6), rsa(8)
BUGS
Only version 1 of the SSH protocol is implemented.
SSH(1)