.\" (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 1.117 2001/06/23 17:48:19 itojun Exp $
+.\" $OpenBSD: ssh.1,v 1.140 2001/10/30 20:29:09 markus Exp $
.Dd September 25, 1999
.Dt SSH 1
.Os
.Sh SYNOPSIS
.Nm ssh
.Op Fl l Ar login_name
-.Op Ar hostname | user@hostname
+.Ar hostname | user@hostname
.Op Ar command
.Pp
.Nm ssh
.Op Fl m Ar mac_spec
.Op Fl o Ar option
.Op Fl p Ar port
+.Op Fl F Ar configfile
.Oo Fl L Xo
.Sm off
.Ar port :
.Sm on
.Xc
.Oc
-.Op Ar hostname | user@hostname
+.Op Fl D Ar port
+.Ar hostname | user@hostname
.Op Ar command
.Sh DESCRIPTION
.Nm
different authentication methods are available.
Using the default values for
.Cm PreferredAuthentications ,
-the client will try to authenticate first using the public key method;
-if this method fails password authentication is attempted,
-and finally if this method fails keyboard-interactive authentication
-is attempted.
-If this method fails password authentication is
-tried.
+the client will try to authenticate first using the hostbased method;
+if this method fails public key authentication is attempted,
+and finally if this method fails keyboard-interactive and
+password authentication are tried.
.Pp
The public key method is similar to RSA authentication described
in the previous section and allows the RSA or DSA algorithm to be used:
.Pp
A single tilde character can be sent as
.Ic ~~
-(or by following the tilde by a character other than those described above).
+or by following the tilde by a character other than those described below.
The escape character must always follow a newline to be interpreted as
special.
The escape character can be changed in configuration files using the
List forwarded connections
.It Cm ~&
Background ssh at logout when waiting for forwarded connection / X11 sessions
-to terminate (protocol version 1 only)
+to terminate
.It Cm ~?
Display a list of escape characters
.It Cm ~R
.Pp
If the user is using an authentication agent, the connection to the agent
is automatically forwarded to the remote side unless disabled on
-command line or in a configuration file.
+the command line or in a configuration file.
.Pp
Forwarding of arbitrary TCP/IP connections over the secure channel can
-be specified either on command line or in a configuration file.
+be specified either on the command line or in a configuration file.
One possible application of TCP/IP forwarding is a secure connection to an
electronic purse; another is going through firewalls.
.Pp
.It Fl b Ar bind_address
Specify the interface to transmit from on machines with multiple
interfaces or aliased addresses.
-.It Fl c Ar blowfish|3des
+.It Fl c Ar blowfish|3des|des
Selects the cipher to use for encrypting the session.
.Ar 3des
is used by default.
It is believed to be secure.
.Ar 3des
(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
-It is presumably more secure than the
-.Ar des
-cipher which is no longer fully supported in
-.Nm ssh .
.Ar blowfish
is a fast block cipher, it appears very secure and is much faster than
.Ar 3des .
+.Ar des
+is only supported in the
+.Nm
+client for interoperability with legacy protocol 1 implementations
+that do not support the
+.Ar 3des
+cipher. Its use is strongly discouraged due to cryptographic
+weaknesses.
.It Fl c Ar cipher_spec
Additionally, for protocol version 2 a comma-separated list of ciphers can
be specified in order of preference.
.Fl i
options (and multiple identities specified in
configuration files).
+.It Fl I Ar smartcard_device
+Specifies which smartcard device to use. The argument is
+the device
+.Nm
+should use to communicate with a smartcard used for storing the user's
+private RSA key.
.It Fl k
Disables forwarding of Kerberos tickets and AFS tokens.
This may also be specified on a per-host basis in the configuration file.
option.)
.It Fl N
Do not execute a remote command.
-This is useful if you just want to forward ports
+This is useful for just forwarding ports
(protocol version 2 only).
.It Fl o Ar option
-Can be used to give options in the format used in the config file.
+Can be used to give options in the format used in the configuration file.
This is useful for specifying options for which there is no separate
command-line flag.
-The option has the same format as a line in the configuration file.
.It Fl p Ar port
Port to connect to on the remote host.
This can be specified on a
per-host basis in the configuration file.
.It Fl P
Use a non-privileged port for outgoing connections.
-This can be used if your firewall does
+This can be used if a firewall does
not permit connections from privileged ports.
Note that this option turns off
.Cm RhostsAuthentication
slow connections, but will only slow down things on fast networks.
The default value can be set on a host-by-host basis in the
configuration files; see the
-.Cm Compress
+.Cm Compression
option below.
+.It Fl F Ar configfile
+Specifies an alternative per-user configuration file.
+If a configuration file is given on the command line,
+the system-wide configuration file
+.Pq Pa /etc/ssh_config
+will be ignored.
+The default for the per-user configuration file is
+.Pa $HOME/.ssh/config .
.It Fl L Ar port:host:hostport
Specifies that the given port on the local (client) host is to be
forwarded to the given host and port on the remote side.
logging in as root on the remote machine.
IPv6 addresses can be specified with an alternative syntax:
.Ar port/host/hostport
+.It Fl D Ar port
+Specifies a local
+.Dq dynamic
+application-level port forwarding.
+This works by allocating a socket to listen to
+.Ar port
+on the local side, and whenever a connection is made to this port, the
+connection is forwarded over the secure channel, and the application
+protocol is then used to determine where to connect to from the
+remote machine. Currently the SOCKS4 protocol is supported, and
+.Nm
+will act as a SOCKS4 server.
+Only root can forward privileged ports.
+Dynamic port forwardings can also be specified in the configuration file.
.It Fl 1
Forces
.Nm
.El
.Sh CONFIGURATION FILES
.Nm
-obtains configuration data from the following sources (in this order):
+obtains configuration data from the following sources in
+the following order:
command line options, user's configuration file
.Pq Pa $HOME/.ssh/config ,
and system-wide configuration file
.Pp
Otherwise a line is of the format
.Dq keyword arguments .
+Configuration options may be separated by whitespace or
+optional whitespace and exactly one
+.Ql = ;
+the latter format is useful to avoid the need to quote whitespace
+when specifying configuration options using the
+.Nm ssh ,
+.Nm scp
+and
+.Nm sftp
+.Fl o
+option.
+.Pp
The possible
-keywords and their meanings are as follows (note that the
-configuration files are case-sensitive):
+keywords and their meanings are as follows (note that
+keywords are case-insensitive and arguments are case-sensitive):
.Bl -tag -width Ds
.It Cm Host
Restricts the following declarations (up to the next
If set to
.Dq yes ,
passphrase/password querying will be disabled.
-This option is useful in scripts and other batch jobs where you have no
-user to supply the password.
+This option is useful in scripts and other batch jobs where no user
+is present to supply the password.
The argument must be
.Dq yes
or
Specifies the cipher to use for encrypting the session
in protocol version 1.
Currently,
-.Dq blowfish
+.Dq blowfish ,
+.Dq 3des ,
and
-.Dq 3des
+.Dq des
are supported.
+.Ar des
+is only supported in the
+.Nm
+client for interoperability with legacy protocol 1 implementations
+that do not support the
+.Ar 3des
+cipher. Its use is strongly discouraged due to cryptographic
+weaknesses.
The default is
.Dq 3des .
.It Cm Ciphers
``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
aes192-cbc,aes256-cbc''
.Ed
+.It Cm ClearAllForwardings
+Specifies that all local, remote and dynamic port forwardings
+specified in the configuration files or on the command line be
+cleared. This option is primarily useful when used from the
+.Nm
+command line to clear port forwardings set in
+configuration files, and is automatically set by
+.Xr scp 1
+and
+.Xr sftp 1 .
+The argument must be
+.Dq yes
+or
+.Dq no .
+The default is
+.Dq no .
.It Cm Compression
Specifies whether to use compression.
The argument must be
back to rsh or exiting.
The argument must be an integer.
This may be useful in scripts if the connection sometimes fails.
-The default is 4.
+The default is 1.
+.It Cm DynamicForward
+Specifies that a TCP/IP port on the local machine be forwarded
+over the secure channel, and the application
+protocol is then used to determine where to connect to from the
+remote machine. The argument must be a port number.
+Currently the SOCKS4 protocol is supported, and
+.Nm
+will act as a SOCKS4 server.
+Multiple forwardings may be specified, and
+additional forwardings can be given on the command line. Only
+the superuser can forward privileged ports.
.It Cm EscapeChar
Sets the escape character (default:
.Ql ~ ) .
.It Cm GatewayPorts
Specifies whether remote hosts are allowed to connect to local
forwarded ports.
+By default,
+.Nm
+binds local port forwardings to the loopback addresss. This
+prevents other remote hosts from connecting to forwarded ports.
+.Cm GatewayPorts
+can be used to specify that
+.Nm
+should bind local port forwardings to the wildcard address,
+thus allowing remote hosts to connect to forwarded ports.
The argument must be
.Dq yes
or
real host name when looking up or saving the host key
in the host key database files.
This option is useful for tunneling ssh connections
-or if you have multiple servers running on a single host.
+or for multiple servers running on a single host.
.It Cm HostName
Specifies the real host name to log into.
This can be used to specify nicknames or abbreviations for hosts.
.Dq no .
.It Cm LocalForward
Specifies that a TCP/IP port on the local machine be forwarded over
-the secure channel to given host:port from the remote machine.
+the secure channel to the specified host and port from the remote machine.
The first argument must be a port number, and the second must be
-host:port.
+.Ar host:port .
+IPv6 addresses can be specified with an alternative syntax:
+.Ar host/port .
Multiple forwardings may be specified, and additional
forwardings can be given on the command line.
Only the superuser can forward privileged ports.
Multiple algorithms must be comma-separated.
The default is
.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
+.It Cm NoHostAuthenticationForLocalhost
+This option can be used if the home directory is shared across machines.
+In this case localhost will refer to a different machine on each of
+the machines and the user will get many warnings about changed host keys.
+However, this option disables host authentication for localhost.
+The argument to this keyword must be
+.Dq yes
+or
+.Dq no .
+The default is to check the host key for localhost.
.It Cm NumberOfPasswordPrompts
Specifies the number of password prompts before giving up.
The argument to this keyword must be an integer.
over another method (e.g.
.Cm password )
The default for this option is:
-.Dq publickey,hostbased,password,keyboard-interactive
+.Dq hostbased,publickey,keyboard-interactive,password
.It Cm Protocol
Specifies the protocol versions
.Nm
This option applies to protocol version 2 only.
.It Cm RemoteForward
Specifies that a TCP/IP port on the remote machine be forwarded over
-the secure channel to given host:port from the local machine.
+the secure channel to the specified host and port from the local machine.
The first argument must be a port number, and the second must be
-host:port.
+.Ar host:port .
+IPv6 addresses can be specified with an alternative syntax:
+.Ar host/port .
Multiple forwardings may be specified, and additional
forwardings can be given on the command line.
Only the superuser can forward privileged ports.
Note that this option applies to protocol version 1 only.
.It Cm ChallengeResponseAuthentication
Specifies whether to use challenge response authentication.
-Currently there is only support for
-.Xr skey 1
-authentication.
The argument to this keyword must be
.Dq yes
or
.Dq no .
The default is
-.Dq no .
+.Dq yes .
+.It Cm SmartcardDevice
+Specifies which smartcard device to use. The argument to this keyword is
+the device
+.Nm
+should use to communicate with a smartcard used for storing the user's
+private RSA key. By default, no device is specified and smartcard support
+is not activated.
.It Cm StrictHostKeyChecking
If this flag is set to
.Dq yes ,
will never automatically add host keys to the
.Pa $HOME/.ssh/known_hosts
file, and refuses to connect to hosts whose host key has changed.
-This provides maximum protection against trojan horse attacks.
-However, it can be somewhat annoying if you don't have good
+This provides maximum protection against trojan horse attacks,
+however, can be annoying when the
.Pa /etc/ssh_known_hosts
-files installed and frequently
-connect to new hosts.
+file is poorly maintained, or connections to new hosts are
+frequently made.
This option forces the user to manually
add all new hosts.
If this flag is set to
.Dq no .
The default is
.Dq no .
-Note that you need to set this option to
+Note that this option must be set to
.Dq yes
-if you want to use
+if
.Cm RhostsAuthentication
and
.Cm RhostsRSAAuthentication
-with older servers.
+authentications are needed with older servers.
.It Cm User
Specifies the user to log in as.
-This can be useful if you have a different user name on different machines.
+This can be useful when a different user name is used on different machines.
This saves the trouble of
having to remember to give the user name on the command line.
.It Cm UserKnownHostsFile
.Ev USER ;
set for compatibility with systems that use this variable.
.It Ev MAIL
-Set to point the user's mailbox.
+Set to the path of the user's mailbox.
.It Ev PATH
Set to the default
.Ev PATH ,
as specified when compiling
.Nm ssh .
+.It Ev SSH_ASKPASS
+If
+.Nm
+needs a passphrase, it will read the passphrase from the current
+terminal if it was run from a terminal.
+If
+.Nm
+does not have a terminal associated with it but
+.Ev DISPLAY
+and
+.Ev SSH_ASKPASS
+are set, it will execute the program specified by
+.Ev SSH_ASKPASS
+and open an X11 window to read the passphrase.
+This is particularly useful when calling
+.Nm
+from a
+.Pa .Xsession
+or related script.
+(Note that on some machines it
+may be necessary to redirect the input from
+.Pa /dev/null
+to make this work.)
.It Ev SSH_AUTH_SOCK
-indicates the path of a unix-domain socket used to communicate with the
+Identifies the path of a unix-domain socket used to communicate with the
agent.
.It Ev SSH_CLIENT
Identifies the client end of the connection.
.Sh FILES
.Bl -tag -width Ds
.It Pa $HOME/.ssh/known_hosts
-Records host keys for all hosts the user has logged into (that are not
+Records host keys for all hosts the user has logged into that are not
in
.Pa /etc/ssh_known_hosts .
See
file should be added to
.Pa $HOME/.ssh/authorized_keys
on all machines
-where you wish to log in using protocol version 1 RSA authentication.
+where the user wishes to log in using protocol version 1 RSA authentication.
The contents of the
.Pa $HOME/.ssh/id_dsa.pub
and
file should be added to
.Pa $HOME/.ssh/authorized_keys
on all machines
-where you wish to log in using protocol version 2 DSA/RSA authentication.
+where the user wishes to log in using protocol version 2 DSA/RSA authentication.
These files are not
sensitive and can (but need not) be readable by anyone.
These files are
.Xr sshd 8
will be installed so that it requires successful RSA host
authentication before permitting \s+2.\s0rhosts authentication.
-If your server machine does not have the client's host key in
+If the server machine does not have the client's host key in
.Pa /etc/ssh_known_hosts ,
-you can store it in
+it can be stored in
.Pa $HOME/.ssh/known_hosts .
The easiest way to do this is to
connect back to the client from the server machine using ssh; this
.%A T. Rinne
.%A S. Lehtinen
.%T "SSH Protocol Architecture"
-.%N draft-ietf-secsh-architecture-07.txt
-.%D January 2001
+.%N draft-ietf-secsh-architecture-09.txt
+.%D July 2001
.%O work in progress material
.Re
andersk / openssh.git / blobdiff