.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: ssh.1,v 1.265 2006/10/28 18:08:10 otto Exp $
-.Dd September 25, 1999
+.\" $OpenBSD: ssh.1,v 1.282 2009/02/12 03:44:25 djm Exp $
+.Dd $Mdocdate: February 12 2009 $
.Dt SSH 1
.Os
.Sh NAME
.Nd OpenSSH SSH client (remote login program)
.Sh SYNOPSIS
.Nm ssh
-.Op Fl 1246AaCfgkMNnqsTtVvXxY
+.Op Fl 1246AaCfgKkMNnqsTtVvXxYy
.Op Fl b Ar bind_address
.Op Fl c Ar cipher_spec
.Oo Fl D\ \&
The recommended way to start X11 programs at a remote site is with
something like
.Ic ssh -f host xterm .
+.Pp
+If the
+.Cm ExitOnForwardFailure
+configuration option is set to
+.Dq yes ,
+then a client started with
+.Fl f
+will wait for all remote port forwards to be successfully established
+before placing itself in the background.
.It Fl g
Allows remote hosts to connect to local forwarded ports.
.It Fl I Ar smartcard_device
.Fl i
options (and multiple identities specified in
configuration files).
+.It Fl K
+Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
+credentials to the server.
.It Fl k
Disables forwarding (delegation) of GSSAPI credentials to the server.
.It Fl L Xo
.It User
.It UserKnownHostsFile
.It VerifyHostKeyDNS
+.It VisualHostKey
.It XAuthLocation
.El
.It Fl p Ar port
per-host basis in the configuration file.
.It Fl q
Quiet mode.
-Causes all warning and diagnostic messages to be suppressed.
+Causes most warning and diagnostic messages to be suppressed.
.It Fl R Xo
.Sm off
.Oo Ar bind_address : Oc
.Pp
By default, the listening socket on the server will be bound to the loopback
interface only.
-This may be overriden by specifying a
+This may be overridden by specifying a
.Ar bind_address .
An empty
.Ar bind_address ,
.Cm GatewayPorts
option is enabled (see
.Xr sshd_config 5 ) .
+.Pp
+If the
+.Ar port
+argument is
+.Ql 0 ,
+the listen port will be dynamically allocated on the server and reported
+to the client at run time.
.It Fl S Ar ctl_path
Specifies the location of a control socket for connection sharing.
Refer to the description of
Enables trusted X11 forwarding.
Trusted X11 forwardings are not subjected to the X11 SECURITY extension
controls.
+.It Fl y
+Send log information using the
+.Xr syslog 3
+system module.
+By default this information is sent to stderr.
.El
.Pp
.Nm
but protocol 2 is preferred since
it provides additional mechanisms for confidentiality
(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
-and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
+and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
Protocol 1 lacks a strong mechanism for ensuring the
integrity of the connection.
.Pp
.It Cm ~C
Open command line.
Currently this allows the addition of port forwardings using the
-.Fl L
-and
+.Fl L ,
.Fl R
+and
+.Fl D
options (see above).
It also allows the cancellation of existing remote port-forwardings
using
.Pp
.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
.Pp
-If the fingerprint is already known,
-it can be matched and verified,
-and the key can be accepted.
+If the fingerprint is already known, it can be matched
+and the key can be accepted or rejected.
+Because of the difficulty of comparing host keys
+just by looking at hex strings,
+there is also support to compare host keys visually,
+using
+.Em random art .
+By setting the
+.Cm VisualHostKey
+option to
+.Dq yes ,
+a small ASCII graphic gets displayed on every login to a server, no matter
+if the session itself is interactive or not.
+By learning the pattern a known server produces, a user can easily
+find out that the host key has changed when a completely different pattern
+is displayed.
+Because these patterns are not unambiguous however, a pattern that looks
+similar to the pattern remembered only gives a good probability that the
+host key is the same, not guaranteed proof.
+.Pp
+To get a listing of the fingerprints along with their random art for
+all known hosts, the following command line can be used:
+.Pp
+.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
+.Pp
If the fingerprint is unknown,
an alternative method of verification is available:
SSH fingerprints verified by DNS.
but allows host-based authentication without permitting login with
rlogin/rsh.
.Pp
+.It ~/.ssh/
+This directory is the default location for all user-specific configuration
+and authentication information.
+There is no general requirement to keep the entire contents of this directory
+secret, but the recommended permissions are read/write/execute for the user,
+and not accessible by others.
+.Pp
.It ~/.ssh/authorized_keys
Lists the public keys (RSA/DSA) that can be used for logging in as this user.
The format of this file is described in the
.%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
.%D 2006
.Re
+.Rs
+.%R RFC 4716
+.%T "The Secure Shell (SSH) Public Key File Format"
+.%D 2006
+.Re
+.Rs
+.%T "Hash Visualization: a New Technique to improve Real-World Security"
+.%A A. Perrig
+.%A D. Song
+.%D 1999
+.%O "International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)"
+.Re
.Sh AUTHORS
OpenSSH is a derivative of the original and free
ssh 1.2.12 release by Tatu Ylonen.
andersk / gssapi-openssh.git / blobdiff