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    Command:

    ssh

    
             [bind_address:]port] [-e escape_char] [-F configfile] [-I pkcs11]
             [-i identity_file] [-L  [bind_address:]port:host:hostport]
             [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port] [-R
             [bind_address:]port:host:hostport] [-S ctl_path] [-W host:port] [-w
             local_tun[:remote_tun]] [user@]hostname [command]
    
    
    

    DESCRIPTION

         ssh (SSH client) is a program for logging into a remote machine and for
         executing commands on a remote machine.  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 can also be forwarded over the secure channel.
    
         ssh connects and logs into the specified hostname (with optional user
         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).
    
         If command is specified, it is executed on the remote host instead of a
         login shell.
    
         The options are as follows:
    
         -1      Forces ssh to try protocol version 1 only.
    
         -2      Forces ssh to try protocol version 2 only.
    
         -4      Forces ssh to use IPv4 addresses only.
    
         -6      Forces ssh to use IPv6 addresses only.
    
         -A      Enables forwarding of the authentication agent connection.  This
                 can also be specified on a per-host basis in a configuration
                 file.
    
                 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.
    
         -a      Disables forwarding of the authentication agent connection.
    
         -b bind_address
                 Use bind_address on the local machine as the source address of
                 the connection.  Only useful on systems with more than one
                 address.
    
         -C      Requests compression of all data (including stdin, stdout,
                 stderr, and data for forwarded X11 and TCP connections).  The
                 block cipher; it appears very secure and is much faster than
                 3des.  des is only supported in the ssh client for interoperabil-
                 ity with legacy protocol 1 implementations that do not support
                 the 3des cipher.  Its use is strongly discouraged due to crypto-
                 graphic weaknesses.  The default is "3des".
    
                 For protocol version 2, cipher_spec is a comma-separated list of
                 ciphers listed in order of preference.  See the Ciphers keyword
                 for more information.
    
         -D [bind_address:]port
                 Specifies a local "dynamic" application-level port forwarding.
                 This works by allocating a socket to listen to port on the local
                 side, optionally bound to the specified bind_address.  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 and SOCKS5 protocols are supported, and ssh will act
                 as a SOCKS server.  Only root can forward privileged ports.
                 Dynamic port forwardings can also be specified in the configura-
                 tion file.
    
                 IPv6 addresses can be specified with an alternative syntax:
                 [bind_address/]port or by enclosing the address in square brack-
                 ets.  Only the superuser can forward privileged ports.  By
                 default, the local port is bound in accordance with the
                 GatewayPorts setting.  However, an explicit bind_address may be
                 used to bind the connection to a specific address.  The
                 bind_address of "localhost" indicates that the listening port be
                 bound for local use only, while an empty address or '*' indicates
                 that the port should be available from all interfaces.
    
         -e escape_char
                 Sets the escape character for sessions with a pty (default: '~').
                 The escape character is only recognized at the beginning of a
                 line.  The escape character followed by a dot ('.') closes the
                 connection; followed by control-Z suspends the connection; and
                 followed by itself sends the escape character once.  Setting the
                 character to "none" disables any escapes and makes the session
                 fully transparent.
    
         -F configfile
                 Specifies an alternative per-user configuration file.  If a con-
                 figuration file is given on the command line, the system-wide
                 configuration file (/etc/ssh/ssh_config) will be ignored.  The
                 default for the per-user configuration file is ~/.ssh/config.
    
         -f      Requests ssh to go to background just before command execution.
                 This is useful if ssh is going to ask for passwords or
                 passphrases, but the user wants it in the background.  This
                 implies -n.  The recommended way to start X11 programs at a
                 remote site is with something like ssh -f host xterm.
    
         -i identity_file
                 Selects a file from which the identity (private key) for public
                 key authentication is read.  The default is ~/.ssh/identity for
                 protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and
                 ~/.ssh/id_rsa for protocol version 2.  Identity files may also be
                 specified on a per-host basis in the configuration file.  It is
                 possible to have multiple -i options (and multiple identities
                 specified in configuration files).  ssh will also try to load
                 certificate information from the filename obtained by appending
                 -cert.pub to identity filenames.
    
         -K      Enables GSSAPI-based authentication and forwarding (delegation)
                 of GSSAPI credentials to the server.
    
         -k      Disables forwarding (delegation) of GSSAPI credentials to the
                 server.
    
         -L [bind_address:]port:host:hostport
                 Specifies that the given port on the local (client) host is to be
                 forwarded to the given host and port on the remote side.  This
                 works by allocating a socket to listen to port on the local side,
                 optionally bound to the specified bind_address.  Whenever a con-
                 nection is made to this port, the connection is forwarded over
                 the secure channel, and a connection is made to host port
                 hostport from the remote machine.  Port forwardings can also be
                 specified in the configuration file.  IPv6 addresses can be spec-
                 ified with an alternative syntax:
                 [bind_address/]port/host/hostport or by enclosing the address in
                 square brackets.  Only the superuser can forward privileged
                 ports.  By default, the local port is bound in accordance with
                 the GatewayPorts setting.  However, an explicit bind_address may
                 be used to bind the connection to a specific address.  The
                 bind_address of "localhost" indicates that the listening port be
                 bound for local use only, while an empty address or '*' indicates
                 that the port should be available from all interfaces.
    
         -l login_name
                 Specifies the user to log in as on the remote machine.  This also
                 may be specified on a per-host basis in the configuration file.
    
         -M      Places the ssh client into "master" mode for connection sharing.
                 Multiple -M options places ssh into "master" mode with confirma-
                 tion required before slave connections are accepted.  Refer to
                 the description of ControlMaster in ssh_config(5) for details.
    
         -m mac_spec
                 Additionally, for protocol version 2 a comma-separated list of
                 MAC (message authentication code) algorithms can be specified in
                 order of preference.  See the MACs keyword for more information.
    
         -N      Do not execute a remote command.  This is useful for just for-
                 warding ports (protocol version 2 only).
                 and passed to the master process.  Valid commands are: "check"
                 (check that the master process is running) and "exit" (request
                 the master to exit).
    
         -o option
                 Can be used to give options in the format used in the configura-
                 tion file.  This is useful for specifying options for which there
                 is no separate command-line flag.  For full details of the
                 options listed below, and their possible values, see
                 ssh_config(5).
    
                       AddressFamily
                       BatchMode
                       BindAddress
                       ChallengeResponseAuthentication
                       CheckHostIP
                       Cipher
                       Ciphers
                       ClearAllForwardings
                       Compression
                       CompressionLevel
                       ConnectionAttempts
                       ConnectTimeout
                       ControlMaster
                       ControlPath
                       ControlPersist
                       DynamicForward
                       EscapeChar
                       ExitOnForwardFailure
                       ForwardAgent
                       ForwardX11
                       ForwardX11Trusted
                       GatewayPorts
                       GlobalKnownHostsFile
                       GSSAPIAuthentication
                       GSSAPIKeyExchange
                       GSSAPIClientIdentity
                       GSSAPIDelegateCredentials
                       GSSAPIRenewalForcesRekey
                       GSSAPITrustDns
                       HashKnownHosts
                       Host
                       HostbasedAuthentication
                       HostKeyAlgorithms
                       HostKeyAlias
                       HostName
                       IdentityFile
                       IdentitiesOnly
                       KbdInteractiveAuthentication
                       KbdInteractiveDevices
                       KexAlgorithms
                       LocalCommand
                       RemoteForward
                       RhostsRSAAuthentication
                       RSAAuthentication
                       SendEnv
                       ServerAliveInterval
                       ServerAliveCountMax
                       StrictHostKeyChecking
                       TCPKeepAlive
                       Tunnel
                       TunnelDevice
                       UsePrivilegedPort
                       User
                       UserKnownHostsFile
                       VerifyHostKeyDNS
                       VisualHostKey
                       XAuthLocation
    
         -p port
                 Port to connect to on the remote host.  This can be specified on
                 a per-host basis in the configuration file.
    
         -q      Quiet mode.  Causes most warning and diagnostic messages to be
                 suppressed.
    
         -R [bind_address:]port:host:hostport
                 Specifies that the given port on the remote (server) host is to
                 be forwarded to the given host and port on the local side.  This
                 works by allocating a socket to listen to port on the remote
                 side, and whenever a connection is made to this port, the connec-
                 tion is forwarded over the secure channel, and a connection is
                 made to host port hostport from the local machine.
    
                 Port forwardings can also be specified in the configuration file.
                 Privileged ports can be forwarded only when logging in as root on
                 the remote machine.  IPv6 addresses can be specified by enclosing
                 the address in square braces or using an alternative syntax:
                 [bind_address/]host/port/hostport.
    
                 By default, the listening socket on the server will be bound to
                 the loopback interface only.  This may be overridden by specify-
                 ing a bind_address.  An empty bind_address, or the address '*',
                 indicates that the remote socket should listen on all interfaces.
                 Specifying a remote bind_address will only succeed if the
                 server's GatewayPorts option is enabled (see sshd_config(5)).
    
                 If the port argument is '0', the listen port will be dynamically
                 allocated on the server and reported to the client at run time.
    
         -S ctl_path
                 Specifies the location of a control socket for connection shar-
                 ing.  Refer to the description of ControlPath and ControlMaster
                 in ssh_config(5) for details.
    
         -V      Display the version number and exit.
    
         -v      Verbose mode.  Causes ssh to print debugging messages about its
                 progress.  This is helpful in debugging connection, authentica-
                 tion, and configuration problems.  Multiple -v options increase
                 the verbosity.  The maximum is 3.
    
         -W host:port
                 Requests that standard input and output on the client be for-
                 warded to host on port over the secure channel.  Implies -N, -T,
                 ExitOnForwardFailure and ClearAllForwardings and works with Pro-
                 tocol version 2 only.
    
         -w local_tun[:remote_tun]
                 Requests tunnel device forwarding with the specified tun(4)
                 devices between the client (local_tun) and the server
                 (remote_tun).
    
                 The devices may be specified by numerical ID or the keyword
                 "any", which uses the next available tunnel device.  If
                 remote_tun is not specified, it defaults to "any".  See also the
                 Tunnel and TunnelDevice directives in ssh_config(5).  If the
                 Tunnel directive is unset, it is set to the default tunnel mode,
                 which is "point-to-point".
    
         -X      Enables X11 forwarding.  This can also be specified on a per-host
                 basis in a configuration file.
    
                 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.
    
                 For this reason, X11 forwarding is subjected to X11 SECURITY
                 extension restrictions by default.  Please refer to the ssh -Y
                 option and the ForwardX11Trusted directive in ssh_config(5) for
                 more information.
    
         -x      Disables X11 forwarding.
    
         -Y      Enables trusted X11 forwarding.  Trusted X11 forwardings are not
                 subjected to the X11 SECURITY extension controls.
    
         -y      Send log information using the syslog(3) system module.  By
                 default this information is sent to stderr.
    
         ssh may additionally obtain configuration data from a per-user configura-
         tion file and a system-wide configuration file.  The file format and con-
         figuration options are described in ssh_config(5).
    
         ssh exits with the exit status of the remote command or with 255 if an
         The methods available for authentication are: GSSAPI-based authentica-
         tion, 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:
         PreferredAuthentications.
    
         Host-based authentication works as follows: If the machine the user logs
         in from is listed in /etc/hosts.equiv or /etc/ssh/shosts.equiv on the
         remote machine, and the user names are the same on both sides, or if the
         files ~/.rhosts or ~/.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 must be able to verify the client's
         host key (see the description of /etc/ssh/ssh_known_hosts and
         ~/.ssh/known_hosts, below) for login to be permitted.  This authentica-
         tion method closes security holes due to IP spoofing, DNS spoofing, and
         routing spoofing.  [Note to the administrator: /etc/hosts.equiv,
         ~/.rhosts, and the rlogin/rsh protocol in general, are inherently inse-
         cure and should be disabled if security is desired.]
    
         Public key authentication works as follows: The scheme is based on pub-
         lic-key cryptography, using cryptosystems where encryption and decryption
         are done using separate keys, and it is unfeasible to derive the decryp-
         tion 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.  ssh implements
         public key authentication protocol automatically, using one of the DSA,
         ECDSA or RSA algorithms.  Protocol 1 is restricted to using only RSA
         keys, but protocol 2 may use any.  The HISTORY section of ssl(8) contains
         a brief discussion of the two algorithms.
    
         The file ~/.ssh/authorized_keys lists the public keys that are permitted
         for logging in.  When the user logs in, the ssh 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.
    
         The user creates his/her key pair by running ssh-keygen(1).  This stores
         the private key in ~/.ssh/identity (protocol 1), ~/.ssh/id_dsa (protocol
         2 DSA), ~/.ssh/id_ecdsa (protocol 2 ECDSA), or ~/.ssh/id_rsa (protocol 2
         RSA) and stores the public key in ~/.ssh/identity.pub (protocol 1),
         ~/.ssh/id_dsa.pub (protocol 2 DSA), ~/.ssh/id_ecdsa.pub (protocol 2
         ECDSA), or ~/.ssh/id_rsa.pub (protocol 2 RSA) in the user's home direc-
         tory.  The user should then copy the public key to ~/.ssh/authorized_keys
         in his/her home directory on the remote machine.  The authorized_keys
         file corresponds to the conventional ~/.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.
    
         A variation on public key authentication is available in the form of cer-
         tificate authentication: instead of a set of public/private keys, signed
    
         Finally, if other authentication methods fail, ssh 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.
    
         ssh automatically maintains and checks a database containing identifica-
         tion for all hosts it has ever been used with.  Host keys are stored in
         ~/.ssh/known_hosts in the user's home directory.  Additionally, the file
         /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 iden-
         tification ever changes, ssh 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
         StrictHostKeyChecking option can be used to control logins to machines
         whose host key is not known or has changed.
    
         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.
    
         If a pseudo-terminal has been allocated (normal login session), the user
         may use the escape characters noted below.
    
         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 "none" will also make the session transparent even if
         a tty is used.
    
         The session terminates when the command or shell on the remote machine
         exits and all X11 and TCP connections have been closed.
    
    
    

    ESCAPE CHARACTERS

         When a pseudo-terminal has been requested, ssh supports a number of func-
         tions through the use of an escape character.
    
         A single tilde character can be sent as ~~ 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 charac-
         ter can be changed in configuration files using the EscapeChar configura-
         tion directive or on the command line by the -e option.
    
         The supported escapes (assuming the default '~') are:
    
         ~.      Disconnect.
    
         ~^Z     Background ssh.
    
         ~#      List forwarded connections.
    
         ~&      Background ssh at logout when waiting for forwarded connection /
         ~R      Request rekeying of the connection (only useful for SSH protocol
                 version 2 and if the peer supports it).
    
    
    

    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.
    
         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 ssh, specifying a port to be used to forward con-
         nections 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 ssh will encrypt and forward the connection.
    
         The following example tunnels an IRC session from client machine
         "127.0.0.1" (localhost) to remote server "server.example.com":
    
             $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
             $ irc -c '#users' -p 1234 pinky 127.0.0.1
    
         This tunnels a connection to IRC server "server.example.com", joining
         channel "#users", nickname "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.
    
         The -f option backgrounds ssh and the remote command "sleep 10" is speci-
         fied 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, ssh will exit.
    
    
    

    X11 FORWARDING

         If the ForwardX11 variable is set to "yes" (or see the description of the
         -X, -x, and -Y options above) and the user is using X11 (the DISPLAY
         environment variable is set), the connection to the X11 display is auto-
         matically forwarded to the remote side in such a way that any X11 pro-
         grams 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 DISPLAY.  Forwarding of
         X11 connections can be configured on the command line or in configuration
         files.
    
         The DISPLAY value set by ssh will point to the server machine, but with a
         display number greater than zero.  This is normal, and happens because
         ssh creates a "proxy" X server on the server machine for forwarding the
         connections over the encrypted channel.
    
         ssh will also automatically set up Xauthority data on the server machine.
         StrictHostKeyChecking has been disabled).  Fingerprints can be determined
         using ssh-keygen(1):
    
               $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
    
         If the fingerprint is already known, it can be matched and the key can be
         accepted or rejected.  Because of the difficulty of comparing host keys
         just by looking at hex strings, there is also support to compare host
         keys visually, using random art.  By setting the VisualHostKey option to
         "yes", a small ASCII graphic gets displayed on every login to a server,
         no matter if the session itself is interactive or not.  By learning the
         pattern a known server produces, a user can easily find out that the host
         key has changed when a completely different pattern is displayed.
         Because these patterns are not unambiguous however, a pattern that looks
         similar to the pattern remembered only gives a good probability that the
         host key is the same, not guaranteed proof.
    
         To get a listing of the fingerprints along with their random art for all
         known hosts, the following command line can be used:
    
               $ ssh-keygen -lv -f ~/.ssh/known_hosts
    
         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.
    
         In this example, we are connecting a client to a server,
         "host.example.com".  The SSHFP resource records should first be added to
         the zonefile for host.example.com:
    
               $ ssh-keygen -r host.example.com.
    
         The output lines will have to be added to the zonefile.  To check that
         the zone is answering fingerprint queries:
    
               $ dig -t SSHFP host.example.com
    
         Finally the client connects:
    
               $ ssh -o "VerifyHostKeyDNS ask" host.example.com
               [...]
               Matching host key fingerprint found in DNS.
               Are you sure you want to continue connecting (yes/no)?
    
         See the VerifyHostKeyDNS option in ssh_config(5) for more information.
    
    
    

    SSH-BASED VIRTUAL PRIVATE NETWORKS

         ssh contains support for Virtual Private Network (VPN) tunnelling using
         the tun(4) network pseudo-device, allowing two networks to be joined
         securely.  The sshd_config(5) configuration option PermitTunnel controls
         whether the server supports this, and at what level (layer 2 or 3 traf-
    
               # 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
    
         Client access may be more finely tuned via the /root/.ssh/authorized_keys
         file (see below) and the PermitRootLogin server option.  The following
         entry would permit connections on tun(4) device 1 from user "jane" and on
         tun device 2 from user "john", if PermitRootLogin is set to
         "forced-commands-only":
    
           tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
           tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
    
         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 perma-
         nent VPNs are better provided by tools such as ipsecctl(8) and
         isakmpd(8).
    
    
    

    ENVIRONMENT

         ssh will normally set the following environment variables:
    
         DISPLAY               The DISPLAY variable indicates the location of the
                               X11 server.  It is automatically set by ssh to
                               point to a value of the form "hostname:n", where
                               "hostname" indicates the host where the shell runs,
                               and 'n' is an integer >= 1.  ssh uses this special
                               value to forward X11 connections over the secure
                               channel.  The user should normally not set DISPLAY
                               explicitly, as that will render the X11 connection
                               insecure (and will require the user to manually
                               copy any required authorization cookies).
    
         HOME                  Set to the path of the user's home directory.
    
         LOGNAME               Synonym for USER; set for compatibility with sys-
                               tems that use this variable.
    
         MAIL                  Set to the path of the user's mailbox.
    
         PATH                  Set to the default PATH, as specified when compil-
                               ing ssh.
    
         SSH_ASKPASS           If ssh needs a passphrase, it will read the
                               passphrase from the current terminal if it was run
                               from a terminal.  If ssh does not have a terminal
                               associated with it but DISPLAY and SSH_ASKPASS are
                               set, it will execute the program specified by
                               SSH_ASKPASS and open an X11 window to read the
                               passphrase.  This is particularly useful when call-
                               ing ssh from a .xsession or related script.  (Note
                               that on some machines it may be necessary to redi-
                               rect the input from /dev/null to make this work.)
                               device) associated with the current shell or com-
                               mand.  If the current session has no tty, this
                               variable is not set.
    
         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 on to new connec-
                               tions).
    
         USER                  Set to the name of the user logging in.
    
         Additionally, ssh reads ~/.ssh/environment, and adds lines of the format
         "VARNAME=value" to the environment if the file exists and users are
         allowed to change their environment.  For more information, see the
         PermitUserEnvironment option in sshd_config(5).
    
    
    

    ENVIRONMENT

         SSH_USE_STRONG_RNG
                 The reseeding of the OpenSSL random generator is usually done
                 from /dev/urandom.  If the SSH_USE_STRONG_RNG environment vari-
                 able is set to value other than 0 the OpenSSL random generator is
                 reseeded from /dev/random.  The number of bytes read is defined
                 by the SSH_USE_STRONG_RNG value.  Minimum is 14 bytes.  This set-
                 ting is not recommended on the computers without the hardware
                 random generator because insufficient entropy causes the connec-
                 tion to be blocked until enough entropy is available.
    
    
    

    FILES

         ~/.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 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.
    
         ~/.shosts
                 This file is used in exactly the same way as .rhosts, but allows
                 host-based authentication without permitting login with
                 rlogin/rsh.
    
         ~/.ssh/
                 This directory is the default location for all user-specific con-
                 figuration and authentication information.  There is no general
                 requirement to keep the entire contents of this directory secret,
                 but the recommended permissions are read/write/execute for the
                 user, and not accessible by others.
    
         ~/.ssh/authorized_keys
                 Lists the public keys (RSA/ECDSA/DSA) that can be used for log-
                 ging in as this user.  The format of this file is described in
    
         ~/.ssh/identity
         ~/.ssh/id_dsa
         ~/.ssh/id_ecdsa
         ~/.ssh/id_rsa
                 Contains the private key for authentication.  These files contain
                 sensitive data and should be readable by the user but not acces-
                 sible by others (read/write/execute).  ssh will simply ignore 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 sensitive part of this file using 3DES.
    
         ~/.ssh/identity.pub
         ~/.ssh/id_dsa.pub
         ~/.ssh/id_ecdsa.pub
         ~/.ssh/id_rsa.pub
                 Contains the public key for authentication.  These files are not
                 sensitive and can (but need not) be readable by anyone.
    
         ~/.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 sshd(8) for further details of the format of this
                 file.
    
         ~/.ssh/rc
                 Commands in this file are executed by ssh when the user logs in,
                 just before the user's shell (or command) is started.  See the
                 sshd(8) manual page for more information.
    
         /etc/hosts.equiv
                 This file is for host-based authentication (see above).  It
                 should only be writable by root.
    
         /etc/ssh/shosts.equiv
                 This file is used in exactly the same way as hosts.equiv, but
                 allows host-based authentication without permitting login with
                 rlogin/rsh.
    
         /etc/ssh/ssh_config
                 Systemwide configuration file.  The file format and configuration
                 options are described in ssh_config(5).
    
         /etc/ssh/ssh_host_key
         /etc/ssh/ssh_host_dsa_key
         /etc/ssh/ssh_host_ecdsa_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, ssh must be setuid root, since the host key is readable
                 only by root.  For protocol version 2, ssh uses ssh-keysign(8) to
                 access the host keys, eliminating the requirement that ssh be
                 setuid root when host-based authentication is used.  By default
    
         IPv6 address can be used everywhere where IPv4 address. In all entries
         must be the IPv6 address enclosed in square brackets. Note: The square
         brackets are metacharacters for the shell and must be escaped in shell.
    
    
    

    SEE ALSO

         scp(1), sftp(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), ssh-keyscan(1),
         tun(4), hosts.equiv(5), ssh_config(5), ssh-keysign(8), sshd(8)
    
         The Secure Shell (SSH) Protocol Assigned Numbers, RFC 4250, 2006.
    
         The Secure Shell (SSH) Protocol Architecture, RFC 4251, 2006.
    
         The Secure Shell (SSH) Authentication Protocol, RFC 4252, 2006.
    
         The Secure Shell (SSH) Transport Layer Protocol, RFC 4253, 2006.
    
         The Secure Shell (SSH) Connection Protocol, RFC 4254, 2006.
    
         Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints, RFC
         4255, 2006.
    
         Generic Message Exchange Authentication for the Secure Shell Protocol
         (SSH), RFC 4256, 2006.
    
         The Secure Shell (SSH) Session Channel Break Extension, RFC 4335, 2006.
    
         The Secure Shell (SSH) Transport Layer Encryption Modes, RFC 4344, 2006.
    
         Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer
         Protocol, RFC 4345, 2006.
    
         Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer
         Protocol, RFC 4419, 2006.
    
         The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
    
         Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer,
         RFC 5656, 2009.
    
         A. Perrig and D. Song, Hash Visualization: a New Technique to improve
         Real-World Security, 1999, International Workshop on Cryptographic
         Techniques and E-Commerce (CrypTEC '99).
    
    
    

    AUTHORS

         OpenSSH is a derivative of the original and free ssh 1.2.12 release by
         Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
         de Raadt and Dug Song removed many bugs, re-added newer features and cre-
         ated OpenSSH.  Markus Friedl contributed the support for SSH protocol
         versions 1.5 and 2.0.
    
    
    

    BSD September 25, 2017 BSD

    
    
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