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Diff for /src/usr.bin/ssh/ssh.1 between version 1.107.2.5 and 1.108

version 1.107.2.5, 2002/06/02 22:56:11 version 1.108, 2001/04/30 11:18:52
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 .Sh SYNOPSIS  .Sh SYNOPSIS
 .Nm ssh  .Nm ssh
 .Op Fl l Ar login_name  .Op Fl l Ar login_name
 .Ar hostname | user@hostname  .Op Ar hostname | user@hostname
 .Op Ar command  .Op Ar command
 .Pp  .Pp
 .Nm ssh  .Nm ssh
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 .Op Fl m Ar mac_spec  .Op Fl m Ar mac_spec
 .Op Fl o Ar option  .Op Fl o Ar option
 .Op Fl p Ar port  .Op Fl p Ar port
 .Op Fl F Ar configfile  
 .Oo Fl L Xo  .Oo Fl L Xo
 .Sm off  .Sm off
 .Ar port :  .Ar port :
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 .Sm on  .Sm on
 .Xc  .Xc
 .Oc  .Oc
 .Op Fl D Ar port  .Op Ar hostname | user@hostname
 .Ar hostname | user@hostname  
 .Op Ar command  .Op Ar command
 .Sh DESCRIPTION  .Sh DESCRIPTION
 .Nm  .Nm
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 .Pp  .Pp
 .Ss SSH protocol version 2  .Ss SSH protocol version 2
 .Pp  .Pp
 When a user connects using protocol version 2  When a user connects using the protocol version 2
 similar authentication methods are available.  different authentication methods are available.
 Using the default values for  Using the default values for
 .Cm PreferredAuthentications ,  .Cm PreferredAuthentications ,
 the client will try to authenticate first using the hostbased method;  the client will try to authenticate first using the public key method;
 if this method fails public key authentication is attempted,  if this method fails password authentication is attempted,
 and finally if this method fails keyboard-interactive and  and finally if this method fails keyboard-interactive authentication
 password authentication are tried.  is attempted.
   If this method fails password authentication is
   tried.
 .Pp  .Pp
 The public key method is similar to RSA authentication described  The public key method is similar to RSA authentication described
 in the previous section and allows the RSA or DSA algorithm to be used:  in the previous section and allows the RSA or DSA algorithm to be used:
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 .Pa $HOME/.ssh/id_rsa ,  .Pa $HOME/.ssh/id_rsa ,
 to sign the session identifier and sends the result to the server.  to sign the session identifier and sends the result to the server.
 The server checks whether the matching public key is listed in  The server checks whether the matching public key is listed in
 .Pa $HOME/.ssh/authorized_keys  .Pa $HOME/.ssh/authorized_keys2
 and grants access if both the key is found and the signature is correct.  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  The session identifier is derived from a shared Diffie-Hellman value
 and is only known to the client and the server.  and is only known to the client and the server.
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 .Ss Escape Characters  .Ss Escape Characters
 .Pp  .Pp
 When a pseudo terminal has been requested, ssh supports a number of functions  When a pseudo terminal has been requested, ssh supports a number of functions
 through the use of an escape character.  through the use of an escape character.
 .Pp  .Pp
 A single tilde character can be sent as  A single tilde character can be sent as
 .Ic ~~  .Ic ~~
 or by following the tilde by a character other than those described below.  (or by following the tilde by a character other than those described above).
 The escape character must always follow a newline to be interpreted as  The escape character must always follow a newline to be interpreted as
 special.  special.
 The escape character can be changed in configuration files using the  The escape character can be changed in configuration files using the
 .Cm EscapeChar  .Cm EscapeChar
 configuration directive or on the command line by the  configuration directive or on the command line by the
 .Fl e  .Fl e
 option.  option.
 .Pp  .Pp
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 List forwarded connections  List forwarded connections
 .It Cm ~&  .It Cm ~&
 Background ssh at logout when waiting for forwarded connection / X11 sessions  Background ssh at logout when waiting for forwarded connection / X11 sessions
 to terminate  to terminate (protocol version 1 only)
 .It Cm ~?  .It Cm ~?
 Display a list of escape characters  Display a list of escape characters
 .It Cm ~C  
 Open command line (only useful for adding port forwardings using the  
 .Fl L  
 and  
 .Fl R  
 options)  
 .It Cm ~R  .It Cm ~R
 Request rekeying of the connection (only useful for SSH protocol version 2  Request rekeying of the connection (only useful for SSH protocol version 2
 and if the peer supports it)  and if the peer supports it)
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 .Pp  .Pp
 .Ss X11 and TCP forwarding  .Ss X11 and TCP forwarding
 .Pp  .Pp
 If the  If the user is using X11 (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  .Ev DISPLAY
 environment variable is set), the connection to the X11 display is  environment variable is set), the connection to the X11 display is
 automatically forwarded to the remote side in such a way that any X11  automatically forwarded to the remote side in such a way that any X11
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 .Pp  .Pp
 If the user is using an authentication agent, the connection to the agent  If the user is using an authentication agent, the connection to the agent
 is automatically forwarded to the remote side unless disabled on  is automatically forwarded to the remote side unless disabled on
 the command line or in a configuration file.  command line or in a configuration file.
 .Pp  .Pp
 Forwarding of arbitrary TCP/IP connections over the secure channel can  Forwarding of arbitrary TCP/IP connections over the secure channel can
 be specified either on the command line or in a configuration file.  be specified either on command line or in a configuration file.
 One possible application of TCP/IP forwarding is a secure connection to an  One possible application of TCP/IP forwarding is a secure connection to an
 electronic purse; another is going through firewalls.  electronic purse; another is going through firewalls.
 .Pp  .Pp
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 .Nm  .Nm
 automatically maintains and checks a database containing  automatically maintains and checks a database containing
 identifications for all hosts it has ever been used with.  identifications for all hosts it has ever been used with.
 Host keys are stored in  RSA host keys are stored in
 .Pa $HOME/.ssh/known_hosts  .Pa $HOME/.ssh/known_hosts
   and
   host keys used in the protocol version 2 are stored in
   .Pa $HOME/.ssh/known_hosts2
 in the user's home directory.  in the user's home directory.
 Additionally, the file  Additionally, the files
 .Pa /etc/ssh_known_hosts  .Pa /etc/ssh_known_hosts
 is automatically checked for known hosts.  and
   .Pa /etc/ssh_known_hosts2
   are automatically checked for known hosts.
 Any new hosts are automatically added to the user's file.  Any new hosts are automatically added to the user's file.
 If a host's identification  If a host's identification
 ever changes,  ever changes,
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 .It Fl b Ar bind_address  .It Fl b Ar bind_address
 Specify the interface to transmit from on machines with multiple  Specify the interface to transmit from on machines with multiple
 interfaces or aliased addresses.  interfaces or aliased addresses.
 .It Fl c Ar blowfish|3des|des  .It Fl c Ar blowfish|3des
 Selects the cipher to use for encrypting the session.  Selects the cipher to use for encrypting the session.
 .Ar 3des  .Ar 3des
 is used by default.  is used by default.
 It is believed to be secure.  It is believed to be secure.
 .Ar 3des  .Ar 3des
 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.  (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  .Ar blowfish
 is a fast block cipher, it appears very secure and is much faster than  is a fast block cipher, it appears very secure and is much faster than
 .Ar 3des .  .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  .It Fl c Ar cipher_spec
 Additionally, for protocol version 2 a comma-separated list of ciphers can  Additionally, for protocol version 2 a comma-separated list of ciphers can
 be specified in order of preference.  be specified in order of preference.
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 .It Fl g  .It Fl g
 Allows remote hosts to connect to local forwarded ports.  Allows remote hosts to connect to local forwarded ports.
 .It Fl i Ar identity_file  .It Fl i Ar identity_file
 Selects a file from which the identity (private key) for  Selects the file from which the identity (private key) for
 RSA or DSA authentication is read.  RSA or DSA authentication is read.
 The default is  Default is
 .Pa $HOME/.ssh/identity  .Pa $HOME/.ssh/identity
 for protocol version 1, and  in the user's home directory.
 .Pa $HOME/.ssh/id_rsa  
 and  
 .Pa $HOME/.ssh/id_dsa  
 for protocol version 2.  
 Identity files may also be specified on  Identity files may also be specified on
 a per-host basis in the configuration file.  a per-host basis in the configuration file.
 It is possible to have multiple  It is possible to have multiple
 .Fl i  .Fl i
 options (and multiple identities specified in  options (and multiple identities specified in
 configuration files).  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  .It Fl k
 Disables forwarding of Kerberos tickets and AFS tokens.  Disables forwarding of Kerberos tickets and AFS tokens.
 This may also be specified on a per-host basis in the configuration file.  This may also be specified on a per-host basis in the configuration file.
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 option.)  option.)
 .It Fl N  .It Fl N
 Do not execute a remote command.  Do not execute a remote command.
 This is useful for just forwarding ports  This is useful if you just want to forward ports
 (protocol version 2 only).  (protocol version 2 only).
 .It Fl o Ar option  .It Fl o Ar option
 Can be used to give options in the format used in the configuration file.  Can be used to give options in the format used in the config file.
 This is useful for specifying options for which there is no separate  This is useful for specifying options for which there is no separate
 command-line flag.  command-line flag.
   The option has the same format as a line in the configuration file.
 .It Fl p Ar port  .It Fl p Ar port
 Port to connect to on the remote host.  Port to connect to on the remote host.
 This can be specified on a  This can be specified on a
 per-host basis in the configuration file.  per-host basis in the configuration file.
 .It Fl P  .It Fl P
 Use a non-privileged port for outgoing connections.  Use a non-privileged port for outgoing connections.
 This can be used if a firewall does  This can be used if your firewall does
 not permit connections from privileged ports.  not permit connections from privileged ports.
 Note that this option turns off  Note that this option turns off
 .Cm RhostsAuthentication  .Cm RhostsAuthentication
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 .It Fl q  .It Fl q
 Quiet mode.  Quiet mode.
 Causes all warning and diagnostic messages to be suppressed.  Causes all warning and diagnostic messages to be suppressed.
   Only fatal errors are displayed.
 .It Fl s  .It Fl s
 May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use  May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use
 of SSH as a secure transport for other applications (eg. sftp). The  of SSH as a secure transport for other application (eg. sftp). The
 subsystem is specified as the remote command.  subsystem is specified as the remote command.
 .It Fl t  .It Fl t
 Force pseudo-tty allocation.  Force pseudo-tty allocation.
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 slow connections, but will only slow down things on fast networks.  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  The default value can be set on a host-by-host basis in the
 configuration files; see the  configuration files; see the
 .Cm Compression  .Cm Compress
 option below.  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  .It Fl L Ar port:host:hostport
 Specifies that the given port on the local (client) host is to be  Specifies that the given port on the local (client) host is to be
 forwarded to the given host and port on the remote side.  forwarded to the given host and port on the remote side.
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 logging in as root on the remote machine.  logging in as root on the remote machine.
 IPv6 addresses can be specified with an alternative syntax:  IPv6 addresses can be specified with an alternative syntax:
 .Ar port/host/hostport  .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  .It Fl 1
 Forces  Forces
 .Nm  .Nm
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 .El  .El
 .Sh CONFIGURATION FILES  .Sh CONFIGURATION FILES
 .Nm  .Nm
 obtains configuration data from the following sources in  obtains configuration data from the following sources (in this order):
 the following order:  
 command line options, user's configuration file  command line options, user's configuration file
 .Pq Pa $HOME/.ssh/config ,  .Pq Pa $HOME/.ssh/config ,
 and system-wide configuration file  and system-wide configuration file
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 .Pp  .Pp
 Otherwise a line is of the format  Otherwise a line is of the format
 .Dq keyword arguments .  .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  The possible
 keywords and their meanings are as follows (note that  keywords and their meanings are as follows (note that the
 keywords are case-insensitive and arguments are case-sensitive):  configuration files are case-sensitive):
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Cm Host  .It Cm Host
 Restricts the following declarations (up to the next  Restricts the following declarations (up to the next
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 If set to  If set to
 .Dq yes ,  .Dq yes ,
 passphrase/password querying will be disabled.  passphrase/password querying will be disabled.
 This option is useful in scripts and other batch jobs where no user  This option is useful in scripts and other batch jobs where you have no
 is present to supply the password.  user to supply the password.
 The argument must be  The argument must be
 .Dq yes  .Dq yes
 or  or
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 Specifies the cipher to use for encrypting the session  Specifies the cipher to use for encrypting the session
 in protocol version 1.  in protocol version 1.
 Currently,  Currently,
 .Dq blowfish ,  .Dq blowfish
 .Dq 3des ,  
 and  and
 .Dq des  .Dq 3des
 are supported.  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  The default is
 .Dq 3des .  .Dq 3des .
 .It Cm Ciphers  .It Cm Ciphers
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   ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,    ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
     aes192-cbc,aes256-cbc''      aes192-cbc,aes256-cbc''
 .Ed  .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  .It Cm Compression
 Specifies whether to use compression.  Specifies whether to use compression.
 The argument must be  The argument must be
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 back to rsh or exiting.  back to rsh or exiting.
 The argument must be an integer.  The argument must be an integer.
 This may be useful in scripts if the connection sometimes fails.  This may be useful in scripts if the connection sometimes fails.
 The default is 1.  The default is 4.
 .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  .It Cm EscapeChar
 Sets the escape character (default:  Sets the escape character (default:
 .Ql ~ ) .  .Ql ~ ) .
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 .It Cm GatewayPorts  .It Cm GatewayPorts
 Specifies whether remote hosts are allowed to connect to local  Specifies whether remote hosts are allowed to connect to local
 forwarded ports.  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  The argument must be
 .Dq yes  .Dq yes
 or  or
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 The default is  The default is
 .Dq no .  .Dq no .
 .It Cm GlobalKnownHostsFile  .It Cm GlobalKnownHostsFile
 Specifies a file to use for the global  Specifies a file to use for the protocol version 1 global
 host key database instead of  host key database instead of
 .Pa /etc/ssh_known_hosts .  .Pa /etc/ssh_known_hosts .
   .It Cm GlobalKnownHostsFile2
   Specifies a file to use for the protocol version 2 global
   host key database instead of
   .Pa /etc/ssh_known_hosts2 .
 .It Cm HostbasedAuthentication  .It Cm HostbasedAuthentication
 Specifies whether to try rhosts based authentication with public key  Specifies whether to try rhosts based authentication with public key
 authentication.  authentication.
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 or  or
 .Dq no .  .Dq no .
 The default is  The default is
 .Dq no .  .Dq yes .
 This option applies to protocol version 2 only and  This option applies to protocol version 2 only and
 is similar to  is similar to
 .Cm RhostsRSAAuthentication .  .Cm RhostsRSAAuthentication .
 .It Cm HostKeyAlgorithms  .It Cm HostKeyAlgorithms
 Specifies the protocol version 2 host key algorithms  Specfies the protocol version 2 host key algorithms
 that the client wants to use in order of preference.  that the client wants to use in order of preference.
 The default for this option is:  The default for this option is:
 .Dq ssh-rsa,ssh-dss .  .Dq ssh-rsa,ssh-dss
 .It Cm HostKeyAlias  .It Cm HostKeyAlias
 Specifies an alias that should be used instead of the  Specifies an alias that should be used instead of the
 real host name when looking up or saving the host key  real host name when looking up or saving the host key
 in the host key database files.  in the host key database files.
 This option is useful for tunneling ssh connections  This option is useful for tunneling ssh connections
 or for multiple servers running on a single host.  or if you have multiple servers running on a single host.
 .It Cm HostName  .It Cm HostName
 Specifies the real host name to log into.  Specifies the real host name to log into.
 This can be used to specify nicknames or abbreviations for hosts.  This can be used to specify nicknames or abbreviations for hosts.
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 .Cm HostName  .Cm HostName
 specifications).  specifications).
 .It Cm IdentityFile  .It Cm IdentityFile
 Specifies a file from which the user's RSA or DSA authentication identity  Specifies the file from which the user's RSA or DSA authentication identity
 is read. The default is  is read (default
 .Pa $HOME/.ssh/identity  .Pa $HOME/.ssh/identity
 for protocol version 1, and  in the user's home directory).
 .Pa $HOME/.ssh/id_rsa  
 and  
 .Pa $HOME/.ssh/id_dsa  
 for protocol version 2.  
 Additionally, any identities represented by the authentication agent  Additionally, any identities represented by the authentication agent
 will be used for authentication.  will be used for authentication.
 The file name may use the tilde  The file name may use the tilde
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 multiple identity files specified in configuration files; all these  multiple identity files specified in configuration files; all these
 identities will be tried in sequence.  identities will be tried in sequence.
 .It Cm KeepAlive  .It Cm KeepAlive
 Specifies whether the system should send TCP keepalive messages to the  Specifies whether the system should send keepalive messages to the
 other side.  other side.
 If they are sent, death of the connection or crash of one  If they are sent, death of the connection or crash of one
 of the machines will be properly noticed.  of the machines will be properly noticed.
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 This is important in scripts, and many users want it too.  This is important in scripts, and many users want it too.
 .Pp  .Pp
 To disable keepalives, the value should be set to  To disable keepalives, the value should be set to
 .Dq no .  .Dq no
   in both the server and the client configuration files.
 .It Cm KerberosAuthentication  .It Cm KerberosAuthentication
 Specifies whether Kerberos authentication will be used.  Specifies whether Kerberos authentication will be used.
 The argument to this keyword must be  The argument to this keyword must be
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 .Dq no .  .Dq no .
 .It Cm LocalForward  .It Cm LocalForward
 Specifies that a TCP/IP port on the local machine be forwarded over  Specifies that a TCP/IP port on the local machine be forwarded over
 the secure channel to the specified host and port from the remote machine.  the secure channel to given host:port from the remote machine.
 The first argument must be a port number, and the second must be  The first argument must be a port number, and the second must be
 .Ar host:port .  host:port.
 IPv6 addresses can be specified with an alternative syntax:  
 .Ar host/port .  
 Multiple forwardings may be specified, and additional  Multiple forwardings may be specified, and additional
 forwardings can be given on the command line.  forwardings can be given on the command line.
 Only the superuser can forward privileged ports.  Only the superuser can forward privileged ports.
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 Gives the verbosity level that is used when logging messages from  Gives the verbosity level that is used when logging messages from
 .Nm ssh .  .Nm ssh .
 The possible values are:  The possible values are:
 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.  QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
 The default is INFO.  DEBUG and DEBUG1 are equivalent.  DEBUG2  The default is INFO.
 and DEBUG3 each specify higher levels of verbose output.  
 .It Cm MACs  .It Cm MACs
 Specifies the MAC (message authentication code) algorithms  Specifies the MAC (message authentication code) algorithms
 in order of preference.  in order of preference.
 The MAC algorithm is used in protocol version 2  The MAC algorithm is used in protocol version 2
 for data integrity protection.  for data integrity protection.
 Multiple algorithms must be comma-separated.  Multiple algorithms must be comma-separated.
 The default is  The default is
 .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .  .Pp
 .It Cm NoHostAuthenticationForLocalhost  .Bd -literal
 This option can be used if the home directory is shared across machines.    ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
 In this case localhost will refer to a different machine on each of      hmac-sha1-96,hmac-md5-96''
 the machines and the user will get many warnings about changed host keys.  .Ed
 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  .It Cm NumberOfPasswordPrompts
 Specifies the number of password prompts before giving up.  Specifies the number of password prompts before giving up.
 The argument to this keyword must be an integer.  The argument to this keyword must be an integer.
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 Specifies the port number to connect on the remote host.  Specifies the port number to connect on the remote host.
 Default is 22.  Default is 22.
 .It Cm PreferredAuthentications  .It Cm PreferredAuthentications
 Specifies the order in which the client should try protocol 2  Specifies the order in which the client should try protocol 2
 authentication methods. This allows a client to prefer one method (e.g.  authentication methods. This allows a client to prefer one method (e.g.
 .Cm keyboard-interactive )  .Cm keyboard-interactive )
 over another method (e.g.  over another method (e.g.
 .Cm password )  .Cm password )
 The default for this option is:  The default for this option is:
 .Dq hostbased,publickey,keyboard-interactive,password .  .Dq publickey, password, keyboard-interactive
 .It Cm Protocol  .It Cm Protocol
 Specifies the protocol versions  Specifies the protocol versions
 .Nm  .Nm
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 This option applies to protocol version 2 only.  This option applies to protocol version 2 only.
 .It Cm RemoteForward  .It Cm RemoteForward
 Specifies that a TCP/IP port on the remote machine be forwarded over  Specifies that a TCP/IP port on the remote machine be forwarded over
 the secure channel to the specified host and port from the local machine.  the secure channel to given host:port from the local machine.
 The first argument must be a port number, and the second must be  The first argument must be a port number, and the second must be
 .Ar host:port .  host:port.
 IPv6 addresses can be specified with an alternative syntax:  
 .Ar host/port .  
 Multiple forwardings may be specified, and additional  Multiple forwardings may be specified, and additional
 forwardings can be given on the command line.  forwardings can be given on the command line.
 Only the superuser can forward privileged ports.  Only the superuser can forward privileged ports.
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 authentication time on slow connections when rhosts authentication is  authentication time on slow connections when rhosts authentication is
 not used.  not used.
 Most servers do not permit RhostsAuthentication because it  Most servers do not permit RhostsAuthentication because it
 is not secure (see  is not secure (see
 .Cm RhostsRSAAuthentication ) .  .Cm RhostsRSAAuthentication ).
 The argument to this keyword must be  The argument to this keyword must be
 .Dq yes  .Dq yes
 or  or
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 Note that this option applies to protocol version 1 only.  Note that this option applies to protocol version 1 only.
 .It Cm ChallengeResponseAuthentication  .It Cm ChallengeResponseAuthentication
 Specifies whether to use challenge response authentication.  Specifies whether to use challenge response authentication.
   Currently there is only support for
   .Xr skey 1
   authentication.
 The argument to this keyword must be  The argument to this keyword must be
 .Dq yes  .Dq yes
 or  or
 .Dq no .  .Dq no .
 The default is  The default is
 .Dq yes .  .Dq no .
 .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  .It Cm StrictHostKeyChecking
 If this flag is set to  If this flag is set to
 .Dq yes ,  .Dq yes ,
 .Nm  .Nm
 will never automatically add host keys to the  will never automatically add host keys to the
 .Pa $HOME/.ssh/known_hosts  .Pa $HOME/.ssh/known_hosts
 file, and refuses to connect to hosts whose host key has changed.  and
 This provides maximum protection against trojan horse attacks,  .Pa $HOME/.ssh/known_hosts2
 however, can be annoying when the  files, 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
 .Pa /etc/ssh_known_hosts  .Pa /etc/ssh_known_hosts
 file is poorly maintained, or connections to new hosts are  and
 frequently made.  .Pa /etc/ssh_known_hosts2
   files installed and frequently
   connect to new hosts.
 This option forces the user to manually  This option forces the user to manually
 add all new hosts.  add all new hosts.
 If this flag is set to  If this flag is set to
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 .Dq no .  .Dq no .
 The default is  The default is
 .Dq no .  .Dq no .
 Note that this option must be set to  Note that you need to set this option to
 .Dq yes  .Dq yes
 if  if you want to use
 .Cm RhostsAuthentication  .Cm RhostsAuthentication
 and  and
 .Cm RhostsRSAAuthentication  .Cm RhostsRSAAuthentication
 authentications are needed with older servers.  with older servers.
 .It Cm User  .It Cm User
 Specifies the user to log in as.  Specifies the user to log in as.
 This can be useful when a different user name is used on different machines.  This can be useful if you have a different user name on different machines.
 This saves the trouble of  This saves the trouble of
 having to remember to give the user name on the command line.  having to remember to give the user name on the command line.
 .It Cm UserKnownHostsFile  .It Cm UserKnownHostsFile
 Specifies a file to use for the user  Specifies a file to use for the protocol version 1 user
 host key database instead of  host key database instead of
 .Pa $HOME/.ssh/known_hosts .  .Pa $HOME/.ssh/known_hosts .
   .It Cm UserKnownHostsFile2
   Specifies a file to use for the protocol version 2 user
   host key database instead of
   .Pa $HOME/.ssh/known_hosts2 .
 .It Cm UseRsh  .It Cm UseRsh
 Specifies that rlogin/rsh should be used for this host.  Specifies that rlogin/rsh should be used for this host.
 It is possible that the host does not at all support the  It is possible that the host does not at all support the
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 .Ev USER ;  .Ev USER ;
 set for compatibility with systems that use this variable.  set for compatibility with systems that use this variable.
 .It Ev MAIL  .It Ev MAIL
 Set to the path of the user's mailbox.  Set to point the user's mailbox.
 .It Ev PATH  .It Ev PATH
 Set to the default  Set to the default
 .Ev PATH ,  .Ev PATH ,
 as specified when compiling  as specified when compiling
 .Nm ssh .  .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  .It Ev SSH_AUTH_SOCK
 Identifies the path of a unix-domain socket used to communicate with the  indicates the path of a unix-domain socket used to communicate with the
 agent.  agent.
 .It Ev SSH_CLIENT  .It Ev SSH_CLIENT
 Identifies the client end of the connection.  Identifies the client end of the connection.
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 to the environment.  to the environment.
 .Sh FILES  .Sh FILES
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Pa $HOME/.ssh/known_hosts  .It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2
 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  in
 .Pa /etc/ssh_known_hosts .  .Pa /etc/ssh_known_hosts
   for protocol version 1 or
   .Pa /etc/ssh_known_hosts2
   for protocol version 2).
 See  See
 .Xr sshd 8 .  .Xr sshd 8 .
 .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa  .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
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 file should be added to  file should be added to
 .Pa $HOME/.ssh/authorized_keys  .Pa $HOME/.ssh/authorized_keys
 on all machines  on all machines
 where the user wishes to log in using protocol version 1 RSA authentication.  where you wish to log in using protocol version 1 RSA authentication.
 The contents of the  The contents of the
 .Pa $HOME/.ssh/id_dsa.pub  .Pa $HOME/.ssh/id_dsa.pub
 and  and
 .Pa $HOME/.ssh/id_rsa.pub  .Pa $HOME/.ssh/id_rsa.pub
 file should be added to  file should be added to
 .Pa $HOME/.ssh/authorized_keys  .Pa $HOME/.ssh/authorized_keys2
 on all machines  on all machines
 where the user wishes to log in using protocol version 2 DSA/RSA authentication.  where you wish to log in using protocol version 2 DSA/RSA authentication.
 These files are not  These files are not
 sensitive and can (but need not) be readable by anyone.  sensitive and can (but need not) be readable by anyone.
 These files are  These files are
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 but the recommended permissions are read/write for the user, and not  but the recommended permissions are read/write for the user, and not
 accessible by others.  accessible by others.
 .It Pa $HOME/.ssh/authorized_keys  .It Pa $HOME/.ssh/authorized_keys
 Lists the public keys (RSA/DSA) that can be used for logging in as this user.  Lists the RSA keys that can be used for logging in as this user.
 The format of this file is described in the  The format of this file is described in the
 .Xr sshd 8  .Xr sshd 8
 manual page.  manual page.
 In the simplest form the format is the same as the .pub  In the simplest form the format is the same as the .pub
 identity files.  identity files (that is, each line contains the number of bits in
   modulus, public exponent, modulus, and comment fields, separated by
   spaces).
 This file is not highly sensitive, but the recommended  This file is not highly sensitive, but the recommended
 permissions are read/write for the user, and not accessible by others.  permissions are read/write for the user, and not accessible by others.
 .It Pa /etc/ssh_known_hosts  .It Pa $HOME/.ssh/authorized_keys2
   Lists the public keys (RSA/DSA) that can be used for logging in as this user.
   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_known_hosts, /etc/ssh_known_hosts2
 Systemwide list of known host keys.  Systemwide list of known host keys.
 This file should be prepared by the  .Pa /etc/ssh_known_hosts
   contains RSA and
   .Pa /etc/ssh_known_hosts2
   contains RSA or DSA keys for protocol version 2.
   These files should be prepared by the
 system administrator to contain the public host keys of all machines in the  system administrator to contain the public host keys of all machines in the
 organization.  organization.
 This file should be world-readable.  This file should be world-readable.
 This file contains  This file contains
 public keys, one per line, in the following format (fields separated  public keys, one per line, in the following format (fields separated
 by spaces): system name, public key and optional comment field.  by spaces): system name, number of bits in modulus, public exponent,
   modulus, and optional comment field.
 When different names are used  When different names are used
 for the same machine, all such names should be listed, separated by  for the same machine, all such names should be listed, separated by
 commas.  commas.
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 values that are not specified in the user's configuration file, and  values that are not specified in the user's configuration file, and
 for those users who do not have a configuration file.  for those users who do not have a configuration file.
 This file must be world-readable.  This file must be world-readable.
 .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key  
 These three files contain the private parts of the host keys  
 and are used for  
 .Cm RhostsRSAAuthentication  
 and  
 .Cm HostbasedAuthentication .  
 Since they are readable only by root  
 .Nm  
 must be setuid root if these authentication methods are desired.  
 .It Pa $HOME/.rhosts  .It Pa $HOME/.rhosts
 This file is used in  This file is used in
 .Pa \&.rhosts  .Pa \&.rhosts
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 .Xr sshd 8  .Xr sshd 8
 will be installed so that it requires successful RSA host  will be installed so that it requires successful RSA host
 authentication before permitting \s+2.\s0rhosts authentication.  authentication before permitting \s+2.\s0rhosts authentication.
 If the server machine does not have the client's host key in  If your server machine does not have the client's host key in
 .Pa /etc/ssh_known_hosts ,  .Pa /etc/ssh_known_hosts ,
 it can be stored in  you can store it in
 .Pa $HOME/.ssh/known_hosts .  .Pa $HOME/.ssh/known_hosts .
 The easiest way to do this is to  The easiest way to do this is to
 connect back to the client from the server machine using ssh; this  connect back to the client from the server machine using ssh; this
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 having this file is to be able to use rhosts authentication with  having this file is to be able to use rhosts authentication with
 .Nm  .Nm
 without permitting login with  without permitting login with
 .Nm rlogin  .Xr rlogin 1
 or  or
 .Xr rsh 1 .  .Xr rsh 1 .
 .It Pa /etc/hosts.equiv  .It Pa /etc/hosts.equiv
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 .Sx ENVIRONMENT  .Sx ENVIRONMENT
 above.  above.
 .El  .El
 .Sh DIAGNOSTICS  
 .Nm  
 exits with the exit status of the remote command or with 255  
 if an error occurred.  
 .Sh AUTHORS  .Sh AUTHORS
 OpenSSH is a derivative of the original and free  OpenSSH is a derivative of the original and free
 ssh 1.2.12 release by Tatu Ylonen.  ssh 1.2.12 release by Tatu Ylonen.
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 Markus Friedl contributed the support for SSH  Markus Friedl contributed the support for SSH
 protocol versions 1.5 and 2.0.  protocol versions 1.5 and 2.0.
 .Sh SEE ALSO  .Sh SEE ALSO
   .Xr rlogin 1 ,
 .Xr rsh 1 ,  .Xr rsh 1 ,
 .Xr scp 1 ,  .Xr scp 1 ,
 .Xr sftp 1 ,  .Xr sftp 1 ,
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 .%A T. Rinne  .%A T. Rinne
 .%A S. Lehtinen  .%A S. Lehtinen
 .%T "SSH Protocol Architecture"  .%T "SSH Protocol Architecture"
 .%N draft-ietf-secsh-architecture-12.txt  .%N draft-ietf-secsh-architecture-07.txt
 .%D January 2002  .%D January 2001
 .%O work in progress material  .%O work in progress material
 .Re  .Re

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