===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/ssh/ssh.1,v
retrieving revision 1.209.2.3
retrieving revision 1.210
diff -u -r1.209.2.3 -r1.210
--- src/usr.bin/ssh/ssh.1	2006/11/08 00:44:05	1.209.2.3
+++ src/usr.bin/ssh/ssh.1	2005/09/19 11:37:34	1.210
@@ -34,7 +34,7 @@
 .\" (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 1.209.2.3 2006/11/08 00:44:05 brad Exp $
+.\" $OpenBSD: ssh.1,v 1.210 2005/09/19 11:37:34 djm Exp $
 .Dd September 25, 1999
 .Dt SSH 1
 .Os
@@ -43,6 +43,7 @@
 .Nd OpenSSH SSH client (remote login program)
 .Sh SYNOPSIS
 .Nm ssh
+.Bk -words
 .Op Fl 1246AaCfgkMNnqsTtVvXxY
 .Op Fl b Ar bind_address
 .Op Fl c Ar cipher_spec
@@ -54,18 +55,14 @@
 .Oc
 .Op Fl e Ar escape_char
 .Op Fl F Ar configfile
-.Bk -words
 .Op Fl i Ar identity_file
-.Ek
 .Oo Fl L\ \&
 .Sm off
 .Oo Ar bind_address : Oc
 .Ar port : host : hostport
 .Sm on
 .Oc
-.Bk -words
 .Op Fl l Ar login_name
-.Ek
 .Op Fl m Ar mac_spec
 .Op Fl O Ar ctl_cmd
 .Op Fl o Ar option
@@ -77,9 +74,6 @@
 .Sm on
 .Oc
 .Op Fl S Ar ctl_path
-.Bk -words
-.Oo Fl w Ar local_tun Ns
-.Op : Ns Ar remote_tun Oc
 .Oo Ar user Ns @ Oc Ns Ar hostname
 .Op Ar command
 .Ek
@@ -90,7 +84,7 @@
 It is intended to replace rlogin and rsh,
 and provide secure encrypted communications between
 two untrusted hosts over an insecure network.
-X11 connections and arbitrary TCP ports
+X11 connections and arbitrary TCP/IP ports
 can also be forwarded over the secure channel.
 .Pp
 .Nm
@@ -101,13 +95,307 @@
 name).
 The user must prove
 his/her identity to the remote machine using one of several methods
-depending on the protocol version used (see below).
+depending on the protocol version used.
 .Pp
 If
 .Ar command
 is specified,
-it is executed on the remote host instead of a login shell.
+.Ar command
+is executed on the remote host instead of a login shell.
+.Ss SSH protocol version 1
+The first authentication method is the
+.Em rhosts
+or
+.Em hosts.equiv
+method combined with RSA-based host authentication.
+If the machine the user logs in from is listed in
+.Pa /etc/hosts.equiv
+or
+.Pa /etc/shosts.equiv
+on the remote machine, and the user names are
+the same on both sides, or if the files
+.Pa ~/.rhosts
+or
+.Pa ~/.shosts
+exist in the user's home directory on the
+remote machine and contain a line containing the name of the client
+machine and the name of the user on that machine, the user is
+considered for log in.
+Additionally, if the server can verify the client's
+host key (see
+.Pa /etc/ssh/ssh_known_hosts
+and
+.Pa ~/.ssh/known_hosts
+in the
+.Sx FILES
+section), only then is login permitted.
+This authentication method closes security holes due to IP
+spoofing, DNS spoofing and routing spoofing.
+[Note to the administrator:
+.Pa /etc/hosts.equiv ,
+.Pa ~/.rhosts ,
+and the rlogin/rsh protocol in general, are inherently insecure and should be
+disabled if security is desired.]
 .Pp
+As a second authentication method,
+.Nm
+supports RSA based authentication.
+The scheme is based on public-key cryptography: there are cryptosystems
+where encryption and decryption are done using separate keys, and it
+is not possible to derive the decryption key from the encryption key.
+RSA is one such system.
+The idea is that each user creates a public/private
+key pair for authentication purposes.
+The server knows the public key, and only the user knows the private key.
+.Pp
+The file
+.Pa ~/.ssh/authorized_keys
+lists the public keys that are permitted for logging in.
+When the user logs in, the
+.Nm
+program tells the server which key pair it would like to use for
+authentication.
+The server checks if this key is permitted, and if so,
+sends the user (actually the
+.Nm
+program running on behalf of the user) a challenge, a random number,
+encrypted by the user's public key.
+The challenge can only be decrypted using the proper private key.
+The user's client then decrypts the challenge using the private key,
+proving that he/she knows the private key
+but without disclosing it to the server.
+.Pp
+.Nm
+implements the RSA authentication protocol automatically.
+The user creates his/her RSA key pair by running
+.Xr ssh-keygen 1 .
+This stores the private key in
+.Pa ~/.ssh/identity
+and stores the public key in
+.Pa ~/.ssh/identity.pub
+in the user's home directory.
+The user should then copy the
+.Pa identity.pub
+to
+.Pa ~/.ssh/authorized_keys
+in his/her home directory on the remote machine (the
+.Pa authorized_keys
+file corresponds to the conventional
+.Pa ~/.rhosts
+file, and has one key
+per line, though the lines can be very long).
+After this, the user can log in without giving the password.
+.Pp
+The most convenient way to use RSA authentication may be with an
+authentication agent.
+See
+.Xr ssh-agent 1
+for more information.
+.Pp
+If other authentication methods fail,
+.Nm
+prompts the user for a password.
+The password is sent to the remote
+host for checking; however, since all communications are encrypted,
+the password cannot be seen by someone listening on the network.
+.Ss SSH protocol version 2
+When a user connects using protocol version 2,
+similar authentication methods are available.
+Using the default values for
+.Cm PreferredAuthentications ,
+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:
+The client uses his private key,
+.Pa ~/.ssh/id_dsa
+or
+.Pa ~/.ssh/id_rsa ,
+to sign the session identifier and sends the result to the server.
+The server checks whether the matching public key is listed in
+.Pa ~/.ssh/authorized_keys
+and grants access if both the key is found and the signature is correct.
+The session identifier is derived from a shared Diffie-Hellman value
+and is only known to the client and the server.
+.Pp
+If public key authentication fails or is not available, a password
+can be sent encrypted to the remote host to prove the user's identity.
+.Pp
+Additionally,
+.Nm
+supports hostbased or challenge response authentication.
+.Pp
+Protocol 2 provides additional mechanisms for confidentiality
+(the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
+and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
+Note that protocol 1 lacks a strong mechanism for ensuring the
+integrity of the connection.
+.Ss Login session and remote execution
+When the user's identity has been accepted by the server, the server
+either executes the given command, or logs into the machine and gives
+the user a normal shell on the remote machine.
+All communication with
+the remote command or shell will be automatically encrypted.
+.Pp
+If a pseudo-terminal has been allocated (normal login session), the
+user may use the escape characters noted below.
+.Pp
+If no pseudo-tty has been allocated,
+the session is transparent and can be used to reliably transfer binary data.
+On most systems, setting the escape character to
+.Dq none
+will also make the session transparent even if a tty is used.
+.Pp
+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
+.Nm ssh .
+.Ss Escape Characters
+When a pseudo-terminal has been requested,
+.Nm
+supports a number of functions through the use of an escape character.
+.Pp
+A single tilde character can be sent as
+.Ic ~~
+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
+.Cm EscapeChar
+configuration directive or on the command line by the
+.Fl e
+option.
+.Pp
+The supported escapes (assuming the default
+.Ql ~ )
+are:
+.Bl -tag -width Ds
+.It Cm ~.
+Disconnect.
+.It Cm ~^Z
+Background
+.Nm ssh .
+.It Cm ~#
+List forwarded connections.
+.It Cm ~&
+Background
+.Nm
+at logout when waiting for forwarded connection / X11 sessions to terminate.
+.It Cm ~?
+Display a list of escape characters.
+.It Cm ~B
+Send a BREAK to the remote system
+(only useful for SSH protocol version 2 and if the peer supports it).
+.It Cm ~C
+Open command line.
+Currently this allows the addition of port forwardings using the
+.Fl L
+and
+.Fl R
+options (see below).
+It also allows the cancellation of existing remote port-forwardings
+using
+.Fl KR Ar hostport .
+Basic help is available, using the
+.Fl h
+option.
+.It Cm ~R
+Request rekeying of the connection
+(only useful for SSH protocol version 2 and if the peer supports it).
+.El
+.Ss X11 and TCP forwarding
+If the
+.Cm ForwardX11
+variable is set to
+.Dq yes
+(or see the description of the
+.Fl X
+and
+.Fl x
+options described later)
+and the user is using X11 (the
+.Ev DISPLAY
+environment variable is set), the connection to the X11 display is
+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
+.Ev DISPLAY .
+Forwarding of X11 connections can be
+configured on the command line or in configuration files.
+.Pp
+The
+.Ev DISPLAY
+value set by
+.Nm
+will point to the server machine, but with a display number greater than zero.
+This is normal, and happens because
+.Nm
+creates a
+.Dq proxy
+X server on the server machine for forwarding the
+connections over the encrypted channel.
+.Pp
+.Nm
+will also automatically set up Xauthority data on the server machine.
+For this purpose, it will generate a random authorization cookie,
+store it in Xauthority on the server, and verify that any forwarded
+connections carry this cookie and replace it by 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).
+.Pp
+If the
+.Cm ForwardAgent
+variable is set to
+.Dq yes
+(or see the description of the
+.Fl A
+and
+.Fl a
+options described later) and
+the user is using an authentication agent, the connection to the agent
+is automatically forwarded to the remote side.
+.Pp
+Forwarding of arbitrary TCP/IP connections over the secure channel can
+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.
+.Ss Server authentication
+.Nm
+automatically maintains and checks a database containing
+identifications for all hosts it has ever been used with.
+Host keys are stored in
+.Pa ~/.ssh/known_hosts
+in the user's home directory.
+Additionally, the file
+.Pa /etc/ssh/ssh_known_hosts
+is automatically checked for known hosts.
+Any new hosts are automatically added to the user's file.
+If a host's identification ever changes,
+.Nm
+warns about this and disables password authentication to prevent a
+trojan horse from getting the user's password.
+Another purpose of this mechanism is to prevent man-in-the-middle attacks
+which could otherwise be used to circumvent the encryption.
+The
+.Cm StrictHostKeyChecking
+option can be used to prevent logins to machines whose
+host key is not known or has changed.
+.Pp
+.Nm
+can be configured to verify host identification using fingerprint resource
+records (SSHFP) published in DNS.
+The
+.Cm VerifyHostKeyDNS
+option can be used to control how DNS lookups are performed.
+SSHFP resource records can be generated using
+.Xr ssh-keygen 1 .
+.Pp
 The options are as follows:
 .Bl -tag -width Ds
 .It Fl 1
@@ -147,7 +435,7 @@
 Only useful on systems with more than one address.
 .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and
-data for forwarded X11 and TCP connections).
+data for forwarded X11 and TCP/IP connections).
 The compression algorithm is the same used by
 .Xr gzip 1 ,
 and the
@@ -165,9 +453,9 @@
 Selects the cipher specification for encrypting the session.
 .Pp
 Protocol version 1 allows specification of a single cipher.
-The supported values are
+The suported values are
 .Dq 3des ,
-.Dq blowfish ,
+.Dq blowfish
 and
 .Dq des .
 .Ar 3des
@@ -187,29 +475,29 @@
 The default is
 .Dq 3des .
 .Pp
-For protocol version 2,
+For protocol version 2
 .Ar cipher_spec
 is a comma-separated list of ciphers
 listed in order of preference.
-The supported ciphers are:
-3des-cbc,
-aes128-cbc,
-aes192-cbc,
-aes256-cbc,
-aes128-ctr,
-aes192-ctr,
-aes256-ctr,
-arcfour128,
-arcfour256,
-arcfour,
-blowfish-cbc,
+The supported ciphers are
+.Dq 3des-cbc ,
+.Dq aes128-cbc ,
+.Dq aes192-cbc ,
+.Dq aes256-cbc ,
+.Dq aes128-ctr ,
+.Dq aes192-ctr ,
+.Dq aes256-ctr ,
+.Dq arcfour128 ,
+.Dq arcfour256 ,
+.Dq arcfour ,
+.Dq blowfish-cbc ,
 and
-cast128-cbc.
-The default is:
-.Bd -literal -offset indent
-aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
-arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
-aes192-ctr,aes256-ctr
+.Dq cast128-cbc .
+The default is
+.Bd -literal
+  ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
+    arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
+    aes192-ctr,aes256-ctr''
 .Ed
 .It Fl D Xo
 .Sm off
@@ -257,7 +545,7 @@
 empty address or
 .Sq *
 indicates that the port should be available from all interfaces.
-.It Fl e Ar escape_char
+.It Fl e Ar ch | ^ch | none
 Sets the escape character for sessions with a pty (default:
 .Ql ~ ) .
 The escape character is only recognized at the beginning of a line.
@@ -293,12 +581,11 @@
 .It Fl g
 Allows remote hosts to connect to local forwarded ports.
 .It Fl I Ar smartcard_device
-Specify the 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.
-This option is only available if support for smartcard devices
-is compiled in (default is no support).
 .It Fl i Ar identity_file
 Selects a file from which the identity (private key) for
 RSA or DSA authentication is read.
@@ -370,13 +657,6 @@
 client into
 .Dq master
 mode for connection sharing.
-Multiple
-.Fl M
-options places
-.Nm
-into
-.Dq master
-mode with confirmation required before slave connections are accepted.
 Refer to the description of
 .Cm ControlMaster
 in
@@ -449,7 +729,6 @@
 .It ControlPath
 .It DynamicForward
 .It EscapeChar
-.It ExitOnForwardFailure
 .It ForwardAgent
 .It ForwardX11
 .It ForwardX11Trusted
@@ -466,20 +745,17 @@
 .It IdentityFile
 .It IdentitiesOnly
 .It KbdInteractiveDevices
-.It LocalCommand
 .It LocalForward
 .It LogLevel
 .It MACs
 .It NoHostAuthenticationForLocalhost
 .It NumberOfPasswordPrompts
 .It PasswordAuthentication
-.It PermitLocalCommand
 .It Port
 .It PreferredAuthentications
 .It Protocol
 .It ProxyCommand
 .It PubkeyAuthentication
-.It RekeyLimit
 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication
@@ -489,8 +765,6 @@
 .It SmartcardDevice
 .It StrictHostKeyChecking
 .It TCPKeepAlive
-.It Tunnel
-.It TunnelDevice
 .It UsePrivilegedPort
 .It User
 .It UserKnownHostsFile
@@ -571,7 +845,7 @@
 Force pseudo-tty allocation.
 This can be used to execute arbitrary
 screen-based programs on a remote machine, which can be very useful,
-e.g. when implementing menu services.
+e.g., when implementing menu services.
 Multiple
 .Fl t
 options force tty allocation, even if
@@ -590,35 +864,6 @@
 .Fl v
 options increase the verbosity.
 The maximum is 3.
-.It Fl w Xo
-.Ar local_tun Ns Op : Ns Ar remote_tun
-.Xc
-Requests
-tunnel
-device forwarding with the specified
-.Xr tun 4
-devices between the client
-.Pq Ar local_tun
-and the server
-.Pq Ar remote_tun .
-.Pp
-The devices may be specified by numerical ID or the keyword
-.Dq any ,
-which uses the next available tunnel device.
-If
-.Ar remote_tun
-is not specified, it defaults to
-.Dq any .
-See also the
-.Cm Tunnel
-and
-.Cm TunnelDevice
-directives in
-.Xr ssh_config 5 .
-If the
-.Cm Tunnel
-directive is unset, it is set to the default tunnel mode, which is
-.Dq point-to-point .
 .It Fl X
 Enables X11 forwarding.
 This can also be specified on a per-host basis in a configuration file.
@@ -646,486 +891,16 @@
 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
 controls.
 .El
-.Pp
+.Sh CONFIGURATION FILES
 .Nm
 may additionally obtain configuration data from
 a per-user configuration file and a system-wide configuration file.
 The file format and configuration options are described in
 .Xr ssh_config 5 .
-.Pp
-.Nm
-exits with the exit status of the remote command or with 255
-if an error occurred.
-.Sh AUTHENTICATION
-The OpenSSH SSH client supports SSH protocols 1 and 2.
-Protocol 2 is the default, with
-.Nm
-falling back to protocol 1 if it detects protocol 2 is unsupported.
-These settings may be altered using the
-.Cm Protocol
-option in
-.Xr ssh_config 5 ,
-or enforced using the
-.Fl 1
-and
-.Fl 2
-options (see above).
-Both protocols support similar authentication methods,
-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).
-Protocol 1 lacks a strong mechanism for ensuring the
-integrity of the connection.
-.Pp
-The methods available for authentication are:
-GSSAPI-based authentication,
-host-based authentication,
-public key authentication,
-challenge-response authentication,
-and password authentication.
-Authentication methods are tried in the order specified above,
-though protocol 2 has a configuration option to change the default order:
-.Cm PreferredAuthentications .
-.Pp
-Host-based authentication works as follows:
-If the machine the user logs in from is listed in
-.Pa /etc/hosts.equiv
-or
-.Pa /etc/shosts.equiv
-on the remote machine, and the user names are
-the same on both sides, or if the files
-.Pa ~/.rhosts
-or
-.Pa ~/.shosts
-exist in the user's home directory on the
-remote machine and contain a line containing the name of the client
-machine and the name of the user on that machine, the user is
-considered for login.
-Additionally, the server
-.Em must
-be able to verify the client's
-host key (see the description of
-.Pa /etc/ssh/ssh_known_hosts
-and
-.Pa ~/.ssh/known_hosts ,
-below)
-for login to be permitted.
-This authentication method closes security holes due to IP
-spoofing, DNS spoofing, and routing spoofing.
-[Note to the administrator:
-.Pa /etc/hosts.equiv ,
-.Pa ~/.rhosts ,
-and the rlogin/rsh protocol in general, are inherently insecure and should be
-disabled if security is desired.]
-.Pp
-Public key authentication works as follows:
-The scheme is based on public-key cryptography,
-using cryptosystems
-where encryption and decryption are done using separate keys,
-and it is unfeasible to derive the decryption key from the encryption key.
-The idea is that each user creates a public/private
-key pair for authentication purposes.
-The server knows the public key, and only the user knows the private key.
-.Nm
-implements public key authentication protocol automatically,
-using either the RSA or DSA algorithms.
-Protocol 1 is restricted to using only RSA keys,
-but protocol 2 may use either.
-The
-.Sx HISTORY
-section of
-.Xr ssl 8
-contains a brief discussion of the two algorithms.
-.Pp
-The file
-.Pa ~/.ssh/authorized_keys
-lists the public keys that are permitted for logging in.
-When the user logs in, the
-.Nm
-program tells the server which key pair it would like to use for
-authentication.
-The client proves that it has access to the private key
-and the server checks that the corresponding public key
-is authorized to accept the account.
-.Pp
-The user creates his/her key pair by running
-.Xr ssh-keygen 1 .
-This stores the private key in
-.Pa ~/.ssh/identity
-(protocol 1),
-.Pa ~/.ssh/id_dsa
-(protocol 2 DSA),
-or
-.Pa ~/.ssh/id_rsa
-(protocol 2 RSA)
-and stores the public key in
-.Pa ~/.ssh/identity.pub
-(protocol 1),
-.Pa ~/.ssh/id_dsa.pub
-(protocol 2 DSA),
-or
-.Pa ~/.ssh/id_rsa.pub
-(protocol 2 RSA)
-in the user's home directory.
-The user should then copy the public key
-to
-.Pa ~/.ssh/authorized_keys
-in his/her home directory on the remote machine.
-The
-.Pa authorized_keys
-file corresponds to the conventional
-.Pa ~/.rhosts
-file, and has one key
-per line, though the lines can be very long.
-After this, the user can log in without giving the password.
-.Pp
-The most convenient way to use public key authentication may be with an
-authentication agent.
-See
-.Xr ssh-agent 1
-for more information.
-.Pp
-Challenge-response authentication works as follows:
-The server sends an arbitrary
-.Qq challenge
-text, and prompts for a response.
-Protocol 2 allows multiple challenges and responses;
-protocol 1 is restricted to just one challenge/response.
-Examples of challenge-response authentication include
-BSD Authentication (see
-.Xr login.conf 5 )
-and PAM (some non-OpenBSD systems).
-.Pp
-Finally, if other authentication methods fail,
-.Nm
-prompts the user for a password.
-The password is sent to the remote
-host for checking; however, since all communications are encrypted,
-the password cannot be seen by someone listening on the network.
-.Pp
-.Nm
-automatically maintains and checks a database containing
-identification for all hosts it has ever been used with.
-Host keys are stored in
-.Pa ~/.ssh/known_hosts
-in the user's home directory.
-Additionally, the file
-.Pa /etc/ssh/ssh_known_hosts
-is automatically checked for known hosts.
-Any new hosts are automatically added to the user's file.
-If a host's identification ever changes,
-.Nm
-warns about this and disables password authentication to prevent
-server spoofing or man-in-the-middle attacks,
-which could otherwise be used to circumvent the encryption.
-The
-.Cm StrictHostKeyChecking
-option can be used to control logins to machines whose
-host key is not known or has changed.
-.Pp
-When the user's identity has been accepted by the server, the server
-either executes the given command, or logs into the machine and gives
-the user a normal shell on the remote machine.
-All communication with
-the remote command or shell will be automatically encrypted.
-.Pp
-If a pseudo-terminal has been allocated (normal login session), the
-user may use the escape characters noted below.
-.Pp
-If no pseudo-tty has been allocated,
-the session is transparent and can be used to reliably transfer binary data.
-On most systems, setting the escape character to
-.Dq none
-will also make the session transparent even if a tty is used.
-.Pp
-The session terminates when the command or shell on the remote
-machine exits and all X11 and TCP connections have been closed.
-.Sh ESCAPE CHARACTERS
-When a pseudo-terminal has been requested,
-.Nm
-supports a number of functions through the use of an escape character.
-.Pp
-A single tilde character can be sent as
-.Ic ~~
-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
-.Cm EscapeChar
-configuration directive or on the command line by the
-.Fl e
-option.
-.Pp
-The supported escapes (assuming the default
-.Ql ~ )
-are:
-.Bl -tag -width Ds
-.It Cm ~.
-Disconnect.
-.It Cm ~^Z
-Background
-.Nm .
-.It Cm ~#
-List forwarded connections.
-.It Cm ~&
-Background
-.Nm
-at logout when waiting for forwarded connection / X11 sessions to terminate.
-.It Cm ~?
-Display a list of escape characters.
-.It Cm ~B
-Send a BREAK to the remote system
-(only useful for SSH protocol version 2 and if the peer supports it).
-.It Cm ~C
-Open command line.
-Currently this allows the addition of port forwardings using the
-.Fl L
-and
-.Fl R
-options (see above).
-It also allows the cancellation of existing remote port-forwardings
-using
-.Sm off
-.Fl KR Oo Ar bind_address : Oc Ar port .
-.Sm on
-.Ic !\& Ns Ar command
-allows the user to execute a local command if the
-.Ic PermitLocalCommand
-option is enabled in
-.Xr ssh_config 5 .
-Basic help is available, using the
-.Fl h
-option.
-.It Cm ~R
-Request rekeying of the connection
-(only useful for SSH protocol version 2 and if the peer supports it).
-.El
-.Sh TCP FORWARDING
-Forwarding of arbitrary TCP connections over the secure channel can
-be specified either on the command line or in a configuration file.
-One possible application of TCP forwarding is a secure connection to a
-mail server; another is going through firewalls.
-.Pp
-In the example below, we look at encrypting communication between
-an IRC client and server, even though the IRC server does not directly
-support encrypted communications.
-This works as follows:
-the user connects to the remote host using
-.Nm ,
-specifying a port to be used to forward connections
-to the remote server.
-After that it is possible to start the service which is to be encrypted
-on the client machine,
-connecting to the same local port,
-and
-.Nm
-will encrypt and forward the connection.
-.Pp
-The following example tunnels an IRC session from client machine
-.Dq 127.0.0.1
-(localhost)
-to remote server
-.Dq server.example.com :
-.Bd -literal -offset 4n
-$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
-$ irc -c '#users' -p 1234 pinky 127.0.0.1
-.Ed
-.Pp
-This tunnels a connection to IRC server
-.Dq server.example.com ,
-joining channel
-.Dq #users ,
-nickname
-.Dq pinky ,
-using port 1234.
-It doesn't matter which port is used,
-as long as it's greater than 1023
-(remember, only root can open sockets on privileged ports)
-and doesn't conflict with any ports already in use.
-The connection is forwarded to port 6667 on the remote server,
-since that's the standard port for IRC services.
-.Pp
-The
-.Fl f
-option backgrounds
-.Nm
-and the remote command
-.Dq sleep 10
-is specified to allow an amount of time
-(10 seconds, in the example)
-to start the service which is to be tunnelled.
-If no connections are made within the time specified,
-.Nm
-will exit.
-.Sh X11 FORWARDING
-If the
-.Cm ForwardX11
-variable is set to
-.Dq yes
-(or see the description of the
-.Fl X ,
-.Fl x ,
-and
-.Fl Y
-options above)
-and the user is using X11 (the
-.Ev DISPLAY
-environment variable is set), the connection to the X11 display is
-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
-.Ev DISPLAY .
-Forwarding of X11 connections can be
-configured on the command line or in configuration files.
-.Pp
-The
-.Ev DISPLAY
-value set by
-.Nm
-will point to the server machine, but with a display number greater than zero.
-This is normal, and happens because
-.Nm
-creates a
-.Dq proxy
-X server on the server machine for forwarding the
-connections over the encrypted channel.
-.Pp
-.Nm
-will also automatically set up Xauthority data on the server machine.
-For this purpose, it will generate a random authorization cookie,
-store it in Xauthority on the server, and verify that any forwarded
-connections carry this cookie and replace it by 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).
-.Pp
-If the
-.Cm ForwardAgent
-variable is set to
-.Dq yes
-(or see the description of the
-.Fl A
-and
-.Fl a
-options above) and
-the user is using an authentication agent, the connection to the agent
-is automatically forwarded to the remote side.
-.Sh VERIFYING HOST KEYS
-When connecting to a server for the first time,
-a fingerprint of the server's public key is presented to the user
-(unless the option
-.Cm StrictHostKeyChecking
-has been disabled).
-Fingerprints can be determined using
-.Xr ssh-keygen 1 :
-.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 unknown,
-an alternative method of verification is available:
-SSH fingerprints verified by DNS.
-An additional resource record (RR),
-SSHFP,
-is added to a zonefile
-and the connecting client is able to match the fingerprint
-with that of the key presented.
-.Pp
-In this example, we are connecting a client to a server,
-.Dq host.example.com .
-The SSHFP resource records should first be added to the zonefile for
-host.example.com:
-.Bd -literal -offset indent
-$ ssh-keygen -r host.example.com.
-.Ed
-.Pp
-The output lines will have to be added to the zonefile.
-To check that the zone is answering fingerprint queries:
-.Pp
-.Dl $ dig -t SSHFP host.example.com
-.Pp
-Finally the client connects:
-.Bd -literal -offset indent
-$ ssh -o "VerifyHostKeyDNS ask" host.example.com
-[...]
-Matching host key fingerprint found in DNS.
-Are you sure you want to continue connecting (yes/no)?
-.Ed
-.Pp
-See the
-.Cm VerifyHostKeyDNS
-option in
-.Xr ssh_config 5
-for more information.
-.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
-.Nm
-contains support for Virtual Private Network (VPN) tunnelling
-using the
-.Xr tun 4
-network pseudo-device,
-allowing two networks to be joined securely.
-The
-.Xr sshd_config 5
-configuration option
-.Cm PermitTunnel
-controls whether the server supports this,
-and at what level (layer 2 or 3 traffic).
-.Pp
-The following example would connect client network 10.0.50.0/24
-with remote network 10.0.99.0/24 using a point-to-point connection
-from 10.1.1.1 to 10.1.1.2,
-provided that the SSH server running on the gateway to the remote network,
-at 192.168.1.15, allows it.
-.Pp
-On the client:
-.Bd -literal -offset indent
-# ssh -f -w 0:1 192.168.1.15 true
-# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
-# route add 10.0.99.0/24 10.1.1.2
-.Ed
-.Pp
-On the server:
-.Bd -literal -offset indent
-# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
-# route add 10.0.50.0/24 10.1.1.1
-.Ed
-.Pp
-Client access may be more finely tuned via the
-.Pa /root/.ssh/authorized_keys
-file (see below) and the
-.Cm PermitRootLogin
-server option.
-The following entry would permit connections on
-.Xr tun 4
-device 1 from user
-.Dq jane
-and on tun device 2 from user
-.Dq john ,
-if
-.Cm PermitRootLogin
-is set to
-.Dq forced-commands-only :
-.Bd -literal -offset 2n
-tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
-tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
-.Ed
-.Pp
-Since an SSH-based setup entails a fair amount of overhead,
-it may be more suited to temporary setups,
-such as for wireless VPNs.
-More permanent VPNs are better provided by tools such as
-.Xr ipsecctl 8
-and
-.Xr isakmpd 8 .
 .Sh ENVIRONMENT
 .Nm
 will normally set the following environment variables:
-.Bl -tag -width "SSH_ORIGINAL_COMMAND"
+.Bl -tag -width LOGNAME
 .It Ev DISPLAY
 The
 .Ev DISPLAY
@@ -1133,12 +908,9 @@
 It is automatically set by
 .Nm
 to point to a value of the form
-.Dq hostname:n ,
-where
-.Dq hostname
-indicates the host where the shell runs, and
-.Sq n
-is an integer \*(Ge 1.
+.Dq hostname:n
+where hostname indicates
+the host where the shell runs, and n is an integer \*(Ge 1.
 .Nm
 uses this special value to forward X11 connections over the secure
 channel.
@@ -1159,7 +931,7 @@
 Set to the default
 .Ev PATH ,
 as specified when compiling
-.Nm .
+.Nm ssh .
 .It Ev SSH_ASKPASS
 If
 .Nm
@@ -1184,16 +956,15 @@
 .Pa /dev/null
 to make this work.)
 .It Ev SSH_AUTH_SOCK
-Identifies the path of a
-.Ux Ns -domain
-socket used to communicate with the agent.
+Identifies the path of a unix-domain socket used to communicate with the
+agent.
 .It Ev SSH_CONNECTION
 Identifies the client and server ends of the connection.
 The variable contains
-four space-separated values: client IP address, client port number,
-server IP address, and server port number.
+four space-separated values: client ip-address, client port number,
+server ip-address and server port number.
 .It Ev SSH_ORIGINAL_COMMAND
-This variable contains the original command line if a forced command
+The variable contains the original command line if a forced command
 is executed.
 It can be used to extract the original arguments.
 .It Ev SSH_TTY
@@ -1202,8 +973,8 @@
 If the current session has no tty,
 this variable is not set.
 .It Ev TZ
-This variable is set to indicate the present time zone if it
-was set when the daemon was started (i.e. the daemon passes the value
+The timezone variable is set to indicate the present timezone if it
+was set when the daemon was started (i.e., the daemon passes the value
 on to new connections).
 .It Ev USER
 Set to the name of the user logging in.
@@ -1215,208 +986,235 @@
 .Pa ~/.ssh/environment ,
 and adds lines of the format
 .Dq VARNAME=value
-to the environment if the file exists and users are allowed to
+to the environment if the file exists and if users are allowed to
 change their environment.
 For more information, see the
 .Cm PermitUserEnvironment
 option in
 .Xr sshd_config 5 .
 .Sh FILES
-.Bl -tag -width Ds -compact
-.It ~/.rhosts
-This file is used for host-based authentication (see above).
-On some machines this file may need to be
-world-readable if the user's home directory is on an NFS partition,
-because
-.Xr sshd 8
-reads it as root.
-Additionally, this file must be owned by the user,
-and must not have write permissions for anyone else.
-The recommended
-permission for most machines is read/write for the user, and not
-accessible by others.
-.Pp
-.It ~/.shosts
-This file is used in exactly the same way as
-.Pa .rhosts ,
-but allows host-based authentication without permitting login with
-rlogin/rsh.
-.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
-.Xr sshd 8
-manual page.
-This file is not highly sensitive, but the recommended
-permissions are read/write for the user, and not accessible by others.
-.Pp
-.It ~/.ssh/config
-This is the per-user configuration file.
-The file format and configuration options are described in
-.Xr ssh_config 5 .
-Because of the potential for abuse, this file must have strict permissions:
-read/write for the user, and not accessible by others.
-.Pp
-.It ~/.ssh/environment
-Contains additional definitions for environment variables; see
-.Sx ENVIRONMENT ,
-above.
-.Pp
-.It ~/.ssh/identity
-.It ~/.ssh/id_dsa
-.It ~/.ssh/id_rsa
-Contains the private key for authentication.
+.Bl -tag -width Ds
+.It Pa ~/.ssh/known_hosts
+Records host keys for all hosts the user has logged into that are not
+in
+.Pa /etc/ssh/ssh_known_hosts .
+See
+.Xr sshd 8 .
+.It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
+Contains the authentication identity of the user.
+They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
 These files
 contain sensitive data and should be readable by the user but not
 accessible by others (read/write/execute).
+Note that
 .Nm
-will simply ignore a private key file if it is accessible by others.
+ignores a private key file if it is accessible by others.
 It is possible to specify a passphrase when
-generating the key which will be used to encrypt the
+generating the key; the passphrase will be used to encrypt the
 sensitive part of this file using 3DES.
-.Pp
-.It ~/.ssh/identity.pub
-.It ~/.ssh/id_dsa.pub
-.It ~/.ssh/id_rsa.pub
-Contains the public key for authentication.
+.It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
+Contains the public key for authentication (public part of the
+identity file in human-readable form).
+The contents of the
+.Pa ~/.ssh/identity.pub
+file should be added to the file
+.Pa ~/.ssh/authorized_keys
+on all machines
+where the user wishes to log in using protocol version 1 RSA authentication.
+The contents of the
+.Pa ~/.ssh/id_dsa.pub
+and
+.Pa ~/.ssh/id_rsa.pub
+file should be added to
+.Pa ~/.ssh/authorized_keys
+on all machines
+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.
-.Pp
-.It ~/.ssh/known_hosts
-Contains a list of host keys for all hosts the user has logged into
-that are not already in the systemwide list of known host keys.
-See
+These files are
+never used automatically and are not necessary; they are only provided for
+the convenience of the user.
+.It Pa ~/.ssh/config
+This is the per-user configuration file.
+The file format and configuration options are described in
+.Xr ssh_config 5 .
+Because of the potential for abuse, this file must have strict permissions:
+read/write for the user, and not accessible by others.
+.It Pa ~/.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
 .Xr sshd 8
-for further details of the format of this file.
-.Pp
-.It ~/.ssh/rc
-Commands in this file are executed by
-.Nm
-when the user logs in, just before the user's shell (or command) is
-started.
-See the
+manual page.
+In the simplest form the format is the same as the
+.Pa .pub
+identity files.
+This file is not highly sensitive, but the recommended
+permissions are read/write for the user, and not accessible by others.
+.It Pa /etc/ssh/ssh_known_hosts
+Systemwide list of known host keys.
+This file should be prepared by the
+system administrator to contain the public host keys of all machines in the
+organization.
+This file should be world-readable.
+This file contains
+public keys, one per line, in the following format (fields separated
+by spaces): system name, public key and optional comment field.
+When different names are used
+for the same machine, all such names should be listed, separated by
+commas.
+The format is described in the
 .Xr sshd 8
-manual page for more information.
+manual page.
 .Pp
-.It /etc/hosts.equiv
-This file is for host-based authentication (see above).
-It should only be writable by root.
-.Pp
-.It /etc/shosts.equiv
-This file is used in exactly the same way as
-.Pa hosts.equiv ,
-but allows host-based authentication without permitting login with
-rlogin/rsh.
-.Pp
+The canonical system name (as returned by name servers) is used by
+.Xr sshd 8
+to verify the client host when logging in; other names are needed because
+.Nm
+does not convert the user-supplied name to a canonical name before
+checking the key, because someone with access to the name servers
+would then be able to fool host authentication.
 .It Pa /etc/ssh/ssh_config
 Systemwide configuration file.
 The file format and configuration options are described in
 .Xr ssh_config 5 .
-.Pp
-.It /etc/ssh/ssh_host_key
-.It /etc/ssh/ssh_host_dsa_key
-.It /etc/ssh/ssh_host_rsa_key
+.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
 These three files contain the private parts of the host keys
-and are used for host-based authentication.
-If protocol version 1 is used,
+and are used for
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication .
+If the protocol version 1
+.Cm RhostsRSAAuthentication
+method is used,
 .Nm
 must be setuid root, since the host key is readable only by root.
 For protocol version 2,
 .Nm
 uses
 .Xr ssh-keysign 8
-to access the host keys,
-eliminating the requirement that
+to access the host keys for
+.Cm HostbasedAuthentication .
+This eliminates the requirement that
 .Nm
-be setuid root when host-based authentication is used.
+be setuid root when that authentication method is used.
 By default
 .Nm
 is not setuid root.
-.Pp
-.It /etc/ssh/ssh_known_hosts
-Systemwide list of known host keys.
-This file should be prepared by the
-system administrator to contain the public host keys of all machines in the
-organization.
-It should be world-readable.
-See
+.It Pa ~/.rhosts
+This file is used in
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication
+authentication to list the
+host/user pairs that are permitted to log in.
+(Note that this file is
+also used by rlogin and rsh, which makes using this file insecure.)
+Each line of the file contains a host name (in the canonical form
+returned by name servers), and then a user name on that host,
+separated by a space.
+On some machines this file may need to be
+world-readable if the user's home directory is on a NFS partition,
+because
 .Xr sshd 8
-for further details of the format of this file.
+reads it as root.
+Additionally, this file must be owned by the user,
+and must not have write permissions for anyone else.
+The recommended
+permission for most machines is read/write for the user, and not
+accessible by others.
 .Pp
-.It /etc/ssh/sshrc
+Note that
+.Xr sshd 8
+allows authentication only in combination with client host key
+authentication before permitting log in.
+If the server machine does not have the client's host key in
+.Pa /etc/ssh/ssh_known_hosts ,
+it can be stored in
+.Pa ~/.ssh/known_hosts .
+The easiest way to do this is to
+connect back to the client from the server machine using ssh; this
+will automatically add the host key to
+.Pa ~/.ssh/known_hosts .
+.It Pa ~/.shosts
+This file is used exactly the same way as
+.Pa .rhosts .
+The purpose for
+having this file is to be able to use
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication
+authentication without permitting login with
+.Xr rlogin
+or
+.Xr rsh 1 .
+.It Pa /etc/hosts.equiv
+This file is used during
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication
+authentication.
+It contains
+canonical hosts names, one per line (the full format is described in the
+.Xr sshd 8
+manual page).
+If the client host is found in this file, login is
+automatically permitted provided client and server user names are the
+same.
+Additionally, successful client host key authentication is required.
+This file should only be writable by root.
+.It Pa /etc/shosts.equiv
+This file is processed exactly as
+.Pa /etc/hosts.equiv .
+This file may be useful to permit logins using
+.Nm
+but not using rsh/rlogin.
+.It Pa /etc/ssh/sshrc
 Commands in this file are executed by
 .Nm
-when the user logs in, just before the user's shell (or command) is started.
+when the user logs in just before the user's shell (or command) is started.
 See the
 .Xr sshd 8
 manual page for more information.
+.It Pa ~/.ssh/rc
+Commands in this file are executed by
+.Nm
+when the user logs in just before the user's shell (or command) is
+started.
+See the
+.Xr sshd 8
+manual page for more information.
+.It Pa ~/.ssh/environment
+Contains additional definitions for environment variables, see section
+.Sx ENVIRONMENT
+above.
 .El
+.Sh DIAGNOSTICS
+.Nm
+exits with the exit status of the remote command or with 255
+if an error occurred.
 .Sh SEE ALSO
+.Xr gzip 1 ,
+.Xr rsh 1 ,
 .Xr scp 1 ,
 .Xr sftp 1 ,
 .Xr ssh-add 1 ,
 .Xr ssh-agent 1 ,
 .Xr ssh-keygen 1 ,
-.Xr ssh-keyscan 1 ,
-.Xr tun 4 ,
+.Xr telnet 1 ,
 .Xr hosts.equiv 5 ,
 .Xr ssh_config 5 ,
 .Xr ssh-keysign 8 ,
 .Xr sshd 8
 .Rs
-.%R RFC 4250
-.%T "The Secure Shell (SSH) Protocol Assigned Numbers"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4251
-.%T "The Secure Shell (SSH) Protocol Architecture"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4252
-.%T "The Secure Shell (SSH) Authentication Protocol"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4253
-.%T "The Secure Shell (SSH) Transport Layer Protocol"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4254
-.%T "The Secure Shell (SSH) Connection Protocol"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4255
-.%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4256
-.%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4335
-.%T "The Secure Shell (SSH) Session Channel Break Extension"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4344
-.%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4345
-.%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
-.%D 2006
-.Re
-.Rs
-.%R RFC 4419
-.%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
-.%D 2006
+.%A T. Ylonen
+.%A T. Kivinen
+.%A M. Saarinen
+.%A T. Rinne
+.%A S. Lehtinen
+.%T "SSH Protocol Architecture"
+.%N draft-ietf-secsh-architecture-12.txt
+.%D January 2002
+.%O work in progress material
 .Re
 .Sh AUTHORS
 OpenSSH is a derivative of the original and free