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Diff for /src/usr.bin/ssh/ssh.1 between version 1.139.2.7 and 1.140

version 1.139.2.7, 2002/10/11 14:53:07 version 1.140, 2001/10/30 20:29:09
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 .Op Ar command  .Op Ar command
 .Pp  .Pp
 .Nm ssh  .Nm ssh
 .Op Fl afgknqstvxACNTX1246  .Op Fl afgknqstvxACNPTX1246
 .Op Fl b Ar bind_address  .Op Fl b Ar bind_address
 .Op Fl c Ar cipher_spec  .Op Fl c Ar cipher_spec
 .Op Fl e Ar escape_char  .Op Fl e Ar escape_char
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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 hostbased method;
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 to terminate  to terminate
 .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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 The real authentication cookie is never  The real authentication cookie is never
 sent to the server machine (and no cookies are sent in the plain).  sent to the server machine (and no cookies are sent in the plain).
 .Pp  .Pp
 If the  If the user is using an authentication agent, the connection to the agent
 .Cm ForwardAgent  is automatically forwarded to the remote side unless disabled on
 variable is set to  the command line or in a configuration file.
 .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  .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 the command line or in a configuration file.
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 otherwise be used to circumvent the encryption.  otherwise be used to circumvent the encryption.
 The  The
 .Cm StrictHostKeyChecking  .Cm StrictHostKeyChecking
 option can be used to prevent logins to machines whose  option (see below) can be used to prevent logins to machines whose
 host key is not known or has changed.  host key is not known or has changed.
 .Pp  .Pp
 The options are as follows:  The options are as follows:
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 .It Fl A  .It Fl A
 Enables forwarding of the authentication agent connection.  Enables forwarding of the authentication agent connection.
 This can also be specified on a per-host basis in a configuration file.  This can also be specified on a per-host basis in a configuration file.
 .Pp  
 Agent forwarding should be enabled with caution.  Users with the  
 ability to bypass file permissions on the remote host (for the agent's  
 Unix-domain socket) can access the local agent through the forwarded  
 connection.  An attacker cannot obtain key material from the agent,  
 however they can perform operations on the keys that enable them to  
 authenticate using the identities loaded into the agent.  
 .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.
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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
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 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
   Use a non-privileged port for outgoing connections.
   This can be used if a firewall does
   not permit connections from privileged ports.
   Note that this option turns off
   .Cm RhostsAuthentication
   and
   .Cm RhostsRSAAuthentication
   for older servers.
 .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 applications (eg. sftp). The
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 .It Fl X  .It Fl X
 Enables X11 forwarding.  Enables X11 forwarding.
 This can also be specified on a per-host basis in a configuration file.  This can also be specified on a per-host basis in a configuration file.
 .Pp  
 X11 forwarding should be enabled with caution.  Users with the ability  
 to bypass file permissions on the remote host (for the user's X  
 authorization database) can access the local X11 display through the  
 forwarded connection.  An attacker may then be able to perform  
 activities such as keystroke monitoring.  
 .It Fl C  .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and  Requests compression of all data (including stdin, stdout, stderr, and
 data for forwarded X11 and TCP/IP connections).  data for forwarded X11 and TCP/IP connections).
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 .Dq level  .Dq level
 can be controlled by the  can be controlled by the
 .Cm CompressionLevel  .Cm CompressionLevel
 option for protocol version 1.  option (see below).
 Compression is desirable on modem lines and other  Compression is desirable on modem lines and other
 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 Compression
 option.  option below.
 .It Fl F Ar configfile  .It Fl F Ar configfile
 Specifies an alternative per-user configuration file.  Specifies an alternative per-user configuration file.
 If a configuration file is given on the command line,  If a configuration file is given on the command line,
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 .El  .El
 .Sh CONFIGURATION FILES  .Sh CONFIGURATION FILES
 .Nm  .Nm
 may additionally obtain configuration data from  obtains configuration data from the following sources in
 a per-user configuration file and a system-wide configuration file.  the following order:
 The file format and configuration options are described in  command line options, user's configuration file
 .Xr ssh_config 5 .  .Pq Pa $HOME/.ssh/config ,
   and system-wide configuration file
   .Pq Pa /etc/ssh_config .
   For each parameter, the first obtained value
   will be used.
   The configuration files contain sections bracketed by
   .Dq Host
   specifications, and that section is only applied for hosts that
   match one of the patterns given in the specification.
   The matched host name is the one given on the command line.
   .Pp
   Since the first obtained value for each parameter is used, more
   host-specific declarations should be given near the beginning of the
   file, and general defaults at the end.
   .Pp
   The configuration file has the following format:
   .Pp
   Empty lines and lines starting with
   .Ql #
   are comments.
   .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
   keywords are case-insensitive and arguments are case-sensitive):
   .Bl -tag -width Ds
   .It Cm Host
   Restricts the following declarations (up to the next
   .Cm Host
   keyword) to be only for those hosts that match one of the patterns
   given after the keyword.
   .Ql \&*
   and
   .Ql ?
   can be used as wildcards in the
   patterns.
   A single
   .Ql \&*
   as a pattern can be used to provide global
   defaults for all hosts.
   The host is the
   .Ar hostname
   argument given on the command line (i.e., the name is not converted to
   a canonicalized host name before matching).
   .It Cm AFSTokenPassing
   Specifies whether to pass AFS tokens to remote host.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   This option applies to protocol version 1 only.
   .It Cm BatchMode
   If set to
   .Dq yes ,
   passphrase/password querying will be disabled.
   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
   .Dq no .
   The default is
   .Dq no .
   .It Cm BindAddress
   Specify the interface to transmit from on machines with multiple
   interfaces or aliased addresses.
   Note that this option does not work if
   .Cm UsePrivilegedPort
   is set to
   .Dq yes .
   .It Cm CheckHostIP
   If this flag is set to
   .Dq yes ,
   ssh will additionally check the host IP address in the
   .Pa known_hosts
   file.
   This allows ssh to detect if a host key changed due to DNS spoofing.
   If the option is set to
   .Dq no ,
   the check will not be executed.
   The default is
   .Dq yes .
   .It Cm Cipher
   Specifies the cipher to use for encrypting the session
   in protocol version 1.
   Currently,
   .Dq blowfish ,
   .Dq 3des ,
   and
   .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
   Specifies the ciphers allowed for protocol version 2
   in order of preference.
   Multiple ciphers must be comma-separated.
   The default is
   .Pp
   .Bd -literal
     ``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
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   .It Cm CompressionLevel
   Specifies the compression level to use if compression is enabled.
   The argument must be an integer from 1 (fast) to 9 (slow, best).
   The default level is 6, which is good for most applications.
   The meaning of the values is the same as in
   .Xr gzip 1 .
   Note that this option applies to protocol version 1 only.
   .It Cm ConnectionAttempts
   Specifies the number of tries (one per second) to make before falling
   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 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 ~ ) .
   The escape character can also
   be set on the command line.
   The argument should be a single character,
   .Ql ^
   followed by a letter, or
   .Dq none
   to disable the escape
   character entirely (making the connection transparent for binary
   data).
   .It Cm FallBackToRsh
   Specifies that if connecting via
   .Nm
   fails due to a connection refused error (there is no
   .Xr sshd 8
   listening on the remote host),
   .Xr rsh 1
   should automatically be used instead (after a suitable warning about
   the session being unencrypted).
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   .It Cm ForwardAgent
   Specifies whether the connection to the authentication agent (if any)
   will be forwarded to the remote machine.
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   .It Cm ForwardX11
   Specifies whether X11 connections will be automatically redirected
   over the secure channel and
   .Ev DISPLAY
   set.
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   .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
   .Dq no .
   The default is
   .Dq no .
   .It Cm GlobalKnownHostsFile
   Specifies a file to use for the global
   host key database instead of
   .Pa /etc/ssh_known_hosts .
   .It Cm HostbasedAuthentication
   Specifies whether to try rhosts based authentication with public key
   authentication.
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   This option applies to protocol version 2 only and
   is similar to
   .Cm RhostsRSAAuthentication .
   .It Cm HostKeyAlgorithms
   Specifies the protocol version 2 host key algorithms
   that the client wants to use in order of preference.
   The default for this option is:
   .Dq ssh-rsa,ssh-dss
   .It Cm HostKeyAlias
   Specifies an alias that should be used instead of the
   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 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.
   Default is the name given on the command line.
   Numeric IP addresses are also permitted (both on the command line and in
   .Cm HostName
   specifications).
   .It Cm IdentityFile
   Specifies the file from which the user's RSA or DSA authentication identity
   is read (default
   .Pa $HOME/.ssh/identity
   in the user's home directory).
   Additionally, any identities represented by the authentication agent
   will be used for authentication.
   The file name may use the tilde
   syntax to refer to a user's home directory.
   It is possible to have
   multiple identity files specified in configuration files; all these
   identities will be tried in sequence.
   .It Cm KeepAlive
   Specifies whether the system should send keepalive messages to the
   other side.
   If they are sent, death of the connection or crash of one
   of the machines will be properly noticed.
   However, this means that
   connections will die if the route is down temporarily, and some people
   find it annoying.
   .Pp
   The default is
   .Dq yes
   (to send keepalives), and the client will notice
   if the network goes down or the remote host dies.
   This is important in scripts, and many users want it too.
   .Pp
   To disable keepalives, the value should be set to
   .Dq no
   in both the server and the client configuration files.
   .It Cm KerberosAuthentication
   Specifies whether Kerberos authentication will be used.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   .It Cm KerberosTgtPassing
   Specifies whether a Kerberos TGT will be forwarded to the server.
   This will only work if the Kerberos server is actually an AFS kaserver.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   .It Cm LocalForward
   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 first argument must be a port number, and the second must be
   .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.
   .It Cm LogLevel
   Gives the verbosity level that is used when logging messages from
   .Nm ssh .
   The possible values are:
   QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
   The default is INFO.
   .It Cm MACs
   Specifies the MAC (message authentication code) algorithms
   in order of preference.
   The MAC algorithm is used in protocol version 2
   for data integrity protection.
   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.
   Default is 3.
   .It Cm PasswordAuthentication
   Specifies whether to use password authentication.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq yes .
   .It Cm Port
   Specifies the port number to connect on the remote host.
   Default is 22.
   .It Cm PreferredAuthentications
   Specifies the order in which the client should try protocol 2
   authentication methods. This allows a client to prefer one method (e.g.
   .Cm keyboard-interactive )
   over another method (e.g.
   .Cm password )
   The default for this option is:
   .Dq hostbased,publickey,keyboard-interactive,password
   .It Cm Protocol
   Specifies the protocol versions
   .Nm
   should support in order of preference.
   The possible values are
   .Dq 1
   and
   .Dq 2 .
   Multiple versions must be comma-separated.
   The default is
   .Dq 2,1 .
   This means that
   .Nm
   tries version 2 and falls back to version 1
   if version 2 is not available.
   .It Cm ProxyCommand
   Specifies the command to use to connect to the server.
   The command
   string extends to the end of the line, and is executed with
   .Pa /bin/sh .
   In the command string,
   .Ql %h
   will be substituted by the host name to
   connect and
   .Ql %p
   by the port.
   The command can be basically anything,
   and should read from its standard input and write to its standard output.
   It should eventually connect an
   .Xr sshd 8
   server running on some machine, or execute
   .Ic sshd -i
   somewhere.
   Host key management will be done using the
   HostName of the host being connected (defaulting to the name typed by
   the user).
   Note that
   .Cm CheckHostIP
   is not available for connects with a proxy command.
   .Pp
   .It Cm PubkeyAuthentication
   Specifies whether to try public key authentication.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq yes .
   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 the specified host and port from the local machine.
   The first argument must be a port number, and the second must be
   .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.
   .It Cm RhostsAuthentication
   Specifies whether to try rhosts based authentication.
   Note that this
   declaration only affects the client side and has no effect whatsoever
   on security.
   Disabling rhosts authentication may reduce
   authentication time on slow connections when rhosts authentication is
   not used.
   Most servers do not permit RhostsAuthentication because it
   is not secure (see
   .Cm RhostsRSAAuthentication ) .
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq yes .
   This option applies to protocol version 1 only.
   .It Cm RhostsRSAAuthentication
   Specifies whether to try rhosts based authentication with RSA host
   authentication.
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq yes .
   This option applies to protocol version 1 only.
   .It Cm RSAAuthentication
   Specifies whether to try RSA authentication.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   RSA authentication will only be
   attempted if the identity file exists, or an authentication agent is
   running.
   The default is
   .Dq yes .
   Note that this option applies to protocol version 1 only.
   .It Cm ChallengeResponseAuthentication
   Specifies whether to use challenge response authentication.
   The argument to this keyword must be
   .Dq yes
   or
   .Dq no .
   The default is
   .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 ,
   .Nm
   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, can be annoying when the
   .Pa /etc/ssh_known_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 ,
   .Nm
   will automatically add new host keys to the
   user known hosts files.
   If this flag is set to
   .Dq ask ,
   new host keys
   will be added to the user known host files only after the user
   has confirmed that is what they really want to do, and
   .Nm
   will refuse to connect to hosts whose host key has changed.
   The host keys of
   known hosts will be verified automatically in all cases.
   The argument must be
   .Dq yes ,
   .Dq no
   or
   .Dq ask .
   The default is
   .Dq ask .
   .It Cm UsePrivilegedPort
   Specifies whether to use a privileged port for outgoing connections.
   The argument must be
   .Dq yes
   or
   .Dq no .
   The default is
   .Dq no .
   Note that this option must be set to
   .Dq yes
   if
   .Cm RhostsAuthentication
   and
   .Cm RhostsRSAAuthentication
   authentications are needed with older servers.
   .It Cm User
   Specifies the user to log in as.
   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
   Specifies a file to use for the user
   host key database instead of
   .Pa $HOME/.ssh/known_hosts .
   .It Cm UseRsh
   Specifies that rlogin/rsh should be used for this host.
   It is possible that the host does not at all support the
   .Nm
   protocol.
   This causes
   .Nm
   to immediately execute
   .Xr rsh 1 .
   All other options (except
   .Cm HostName )
   are ignored if this has been specified.
   The argument must be
   .Dq yes
   or
   .Dq no .
   .It Cm XAuthLocation
   Specifies the location of the
   .Xr xauth 1
   program.
   The default is
   .Pa /usr/X11R6/bin/xauth .
   .El
 .Sh ENVIRONMENT  .Sh ENVIRONMENT
 .Nm  .Nm
 will normally set the following environment variables:  will normally set the following environment variables:
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 .It Ev SSH_AUTH_SOCK  .It Ev SSH_AUTH_SOCK
 Identifies 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.  agent.
 .It Ev SSH_CONNECTION  .It Ev SSH_CLIENT
 Identifies the client and server ends of the connection.  Identifies the client end of the connection.
 The variable contains  The variable contains
 four space-separated values: client ip-address, client port number,  three space-separated values: client ip-address, client port number,
 server ip-address and server port number.  and server port number.
 .It Ev SSH_ORIGINAL_COMMAND  .It Ev SSH_ORIGINAL_COMMAND
 The variable contains the original command line if a forced command  The variable contains the original command line if a forced command
 is executed.  is executed.
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 .Pa $HOME/.ssh/environment ,  .Pa $HOME/.ssh/environment ,
 and adds lines of the format  and adds lines of the format
 .Dq VARNAME=value  .Dq VARNAME=value
 to the environment if the file exists and if users are allowed to  to the environment.
 change their environment.  
 See the  
 .Cm PermitUserEnvironment  
 option in  
 .Xr sshd_config 5 .  
 .Sh FILES  .Sh FILES
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Pa $HOME/.ssh/known_hosts  .It Pa $HOME/.ssh/known_hosts
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 the convenience of the user.  the convenience of the user.
 .It Pa $HOME/.ssh/config  .It Pa $HOME/.ssh/config
 This is the per-user configuration file.  This is the per-user configuration file.
 The file format and configuration options are described in  The format of this file is described above.
 .Xr ssh_config 5 .  This file is used by the
   .Nm
   client.
   This file does not usually contain any sensitive information,
   but the recommended permissions are read/write for the user, and not
   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 public keys (RSA/DSA) 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
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 would then be able to fool host authentication.  would then be able to fool host authentication.
 .It Pa /etc/ssh_config  .It Pa /etc/ssh_config
 Systemwide configuration file.  Systemwide configuration file.
 The file format and configuration options are described in  This file provides defaults for those
 .Xr ssh_config 5 .  values that are not specified in the user's configuration file, and
 .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key  for those users who do not have a configuration file.
 These three files contain the private parts of the host keys  This file must be world-readable.
 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 for  
 .Cm HostbasedAuthentication .  
 This eliminates the requirement that  
 .Nm  
 be setuid root when that authentication method is used.  
 By default  
 .Nm  
 is not setuid root.  
 .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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 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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 .Xr ssh-agent 1 ,  .Xr ssh-agent 1 ,
 .Xr ssh-keygen 1 ,  .Xr ssh-keygen 1 ,
 .Xr telnet 1 ,  .Xr telnet 1 ,
 .Xr ssh_config 5 ,  
 .Xr ssh-keysign 8 ,  
 .Xr sshd 8  .Xr sshd 8
 .Rs  .Rs
 .%A T. Ylonen  .%A T. Ylonen
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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-09.txt
 .%D January 2002  .%D July 2001
 .%O work in progress material  .%O work in progress material
 .Re  .Re
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Removed from v.1.139.2.7  
changed lines
  Added in v.1.140