SSH(1)                     OpenBSD Reference Manual                     SSH(1)

NAME
     ssh - OpenSSH secure shell client (remote login program)



SYNOPSIS
     ssh [-l login_name] [hostname | user@hostname] [command]

     ssh [-afgknqtvxCPX] [-c blowfish | 3des] [-e escape_char] [-i
         identity_file] [-l login_name] [-o option] [-p port] [-L
         host:port:hostport] [-R host:port:hostport] [hostname |
         user@hostname] [command]

DESCRIPTION
     ssh (Secure Shell) 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 untrust-
     ed hosts over an insecure network.  X11 connections and arbitrary TCP/IP
     ports can also be forwarded over the secure channel.

     ssh connects and logs into the specified hostname. The user must prove
     his/her identity to the remote machine using one of several methods.

     First, if the machine the user logs in from is listed in /etc/hosts.equiv
     or /etc/shosts.equiv on the remote machine, and the user names are the
     same on both sides, the user is immediately permitted to log in.  Second,
     if .rhosts or .shosts exists in the user's home directory on the remote
     machine and contains a line containing the name of the client machine and
     the name of the user on that machine, the user is permitted to log in.
     This form of authentication alone is normally not allowed by the server
     because it is not secure.

     The second (and primary) authentication method is the rhosts or
     hosts.equiv method combined with RSA-based host authentication.  It means
     that if the login would be permitted by .rhosts, .shosts,
     /etc/hosts.equiv, or /etc/shosts.equiv, and if additionally the server
     can verify the client's host key (see /etc/ssh_known_hosts in the FILES
     section), only then login is permitted.  This authentication method clos-
     es 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 insecure and should be disabled if
     security is desired.]

     As a third authentication method, ssh supports RSA based authentication.
     The scheme is based on public-key cryptography: there are cryptosystems
     where encryption and decryption are done using separate keys, and it is
     not possible to derive the decryption key from the encryption key.  RSA
     is one such system.  The idea is that each user creates a public/private
     key pair for authentication purposes.  The server knows the public key,
     and only the user knows the private key.  The file
     $HOME/.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 server
     checks if this key is permitted, and if so, sends the user (actually the
     ssh program running on behalf of the user) a challenge, a random number,
     encrypted by the user's public key.  The challenge can only be decrypted
     using the proper private key.  The user's client then decrypts the chal-
     lenge using the private key, proving that he/she knows the private key
     but without disclosing it to the server.

     ssh implements the RSA authentication protocol automatically.  The user
     creates his/her RSA key pair by running ssh-keygen(1).  This stores the
     private key in .ssh/identity and the public key in .ssh/identity.pub in
     the user's home directory.  The user should then copy the identity.pub 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.  RSA authentication is
     much more secure than rhosts authentication.

     The most convenient way to use RSA authentication may be with an authen-
     tication agent.  See ssh-agent(1) for more information.

     If other authentication methods fail, ssh prompts the user for a pass-
     word.  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.

     When the user's identity has been accepted by the server, the server ei-
     ther 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
     can disconnect with ~., and suspend ssh with ~^Z. All forwarded connec-
     tions can be listed with ~# and if the session blocks waiting for for-
     warded X11 or TCP/IP connections to terminate, it can be backgrounded
     with ~& (this should not be used while the user shell is active, as it
     can cause the shell to hang).  All available escapes can be listed with
     ~?.

     A single tilde character can be sent as ~~ (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 special.  The escape charac-
     ter can be changed in configuration files or on the command line.

     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 in on the remote machine
     exists and all X11 and TCP/IP connections have been closed.  The exit
     status of the remote program is returned as the exit status of ssh.

     If the user is using X11 (the DISPLAY environment variable is set), the
     connection to the X11 display is automatically forwarded to the remote
     side in such a way that any X11 programs started from the shell (or com-
     mand) 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.
     For this purpose, it will generate a random authorization cookie, store
     it in Xauthority on the server, and verify that any forwarded connections
     carry this cookie and replace it by the real cookie when the connection
     is opened.  The real authentication cookie is never sent to the server
     machine (and no cookies are sent in the plain).

     If the user is using an authentication agent, the connection to the agent
     is automatically forwarded to the remote side unless disabled on command
     line or in a configuration file.

     Forwarding of arbitrary TCP/IP connections over the secure channel can be
     specified either on command line or in a configuration file.  One possi-
     ble application of TCP/IP forwarding is a secure connection to an elec-
     tronic purse; another is going trough firewalls.

     ssh automatically maintains and checks a database containing RSA-based
     identifications for all hosts it has ever been used with.  The database
     is stored in .ssh/known_hosts in the user's home directory.  Additional-
     ly, the file /etc/ssh_known_hosts is automatically checked for known
     hosts.  Any new hosts are automatically added to the user's file.  If a
     host's identification ever changes, ssh warns about this and disables
     password authentication to prevent a trojan horse from getting the user's
     password.  Another purpose of this mechanism is to prevent man-in-the-
     middle attacks which could otherwise be used to circumvent the encryp-
     tion.  The StrictHostKeyChecking option (see below) can be used to pre-
     vent logins to machines whose host key is not known or has changed.

OPTIONS
     -a      Disables forwarding of the authentication agent connection. This
             may also be specified on a per-host basis in the configuration
             file.

     -c blowfish|3des
             Selects the cipher to use for encrypting the session.  3des is
             used by default.  It is believed to be secure.  3des (triple-des)
             is an encrypt-decrypt-encrypt triple with three different keys.
             It is presumably more secure than the des cipher which is no
             longer supported in ssh.  blowfish is a fast block cipher, it ap-
             pears very secure and is much faster than 3des.

     -e ch|^ch|none
             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      Requests ssh to go to background after authentication.  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 recom-
             mended way to start X11 programs at a remote site is with some-
             thing like ssh -f host xterm.

     -i identity_file
             Selects the file from which the identity (private key) for RSA
             authentication is read.  Default is .ssh/identity in the user's
             home directory.  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 config-
             uration files).

     -g      Allows remote hosts to connect to local forwarded ports.

     -k      Disables forwarding of Kerberos tickets and AFS tokens. This may
             also be specified on a per-host basis in the configuration file.

     -l login_name
             Specifies the user to log in as on the remote machine.  This may
             also be specified on a per-host basis in the configuration file.

     -n      Redirects stdin from /dev/null (actually, prevents reading from
             stdin).  This must be used when ssh is run in the background.  A
             common trick is to use this to run X11 programs in a remote ma-
             chine.  For example, ssh -n shadows.cs.hut.fi emacs & will start
             an emacs on shadows.cs.hut.fi, and the X11 connection will be au-
             tomatically forwarded over an encrypted channel.  The ssh program
             will be put in the background.  (This does not work if ssh needs
             to ask for a password or passphrase; see also the -f option.)

     -o option
             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 command-line flag.  The option has the same format as
             a line in the configuration file.

     -p port
             Port to connect to on the remote host.  This can be specified on
             a per-host basis in the configuration file.

     -P      Use a non-privileged port for outgoing connections.  This can be
             used if your firewall does not permit connections from privileged
             ports.  Note that this option turns of RhostsAuthentication and
             RhostsRSAAuthentication.

     -q      Quiet mode.  Causes all warning and diagnostic messages to be
             suppressed.  Only fatal errors are displayed.

     -t      Force pseudo-tty allocation.  This can be used to execute ar-
             bitary screen-based programs on a remote machine, which can be
             very useful e.g. when implementing menu services.

     -v      Verbose mode.  Causes ssh to print debugging messages about its
             progress.  This is helpful in debugging connection, authentica-
             tion, and configuration problems.  The verbose mode is also used
             to display skey(1) challenges, if the user entered "s/key" as
             password.

     -x      Disables X11 forwarding.  This can also be specified on a per-
             host basis in a configuration file.

     -X      Enables X11 forwarding.

     -C      Requests compression of all data (including stdin, stdout,
             stderr, and data for forwarded X11 and TCP/IP connections).  The
             compression algorithm is the same used by gzip, and the ``level''
             can be controlled by the CompressionLevel option (see below).
             Compression is desirable on modem lines and other slow connec-
             tions, but will only slow down things on fast networks.  The de-
             fault value can be set on a host-by-host basis in the configura-
             tion files; see the Compress option below.

     -L 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,
             and whenever a connection is made to this port, the connection is
             forwarded over the secure channel, and a connection is made to
             host:hostport from the remote machine.  Port forwardings can also
             be specified in the configuration file.  Only root can forward
             privileged ports.

     -R 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: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.

CONFIGURATION FILES
     ssh obtains configuration data from the following sources (in this or-
     der): command line options, user's configuration file
     ($HOME/.ssh/config), and system-wide configuration file
     (/etc/ssh_config). For each parameter, the first obtained value will be
     used.  The configuration files contain sections bracketed by "Host" spec-
     ifications, 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.

     Since the first obtained value for each parameter is used, more host-spe-
     cific declarations should be given near the beginning of the file, and
     general defaults at the end.

     The configuration file has the following format:

     Empty lines and lines starting with `#' are comments.

     Otherwise a line is of the format ``keyword arguments''. The possible
     keywords and their meanings are as follows (note that the configuration
     files are case-sensitive):

     Host    Restricts the following declarations (up to the next Host key-
             word) to be only for those hosts that match one of the patterns
             given after the keyword.  `*' and `?' can be used as wildcards in
             the patterns.  A single `*' as a pattern can be used to provide
             global defaults for all hosts.  The host is the hostname argument
             given on the command line (i.e., the name is not converted to a
             canonicalized host name before matching).

     AFSTokenPassing
             Specifies whether to pass AFS tokens to remote host. The argument
             to this keyword must be ``yes'' or ``no''.

     BatchMode
             If set to ``yes'', passphrase/password querying will be disabled.
             This option is useful in scripts and other batch jobs where you
             have no user to supply the password.  The argument must be
             ``yes'' or ``no''.

     Cipher  Specifies the cipher to use for encrypting the session.  Current-
             ly, ``blowfish'', and ``3des'' are supported.  The default is
             ``3des''.

     Compression
             Specifies whether to use compression.  The argument must be
             ``yes'' or ``no''.

     CompressionLevel
             Specifies the compression level to use if compression is enable.
             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 GNU GZIP.

     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.

     EscapeChar
             Sets the escape character (default: `~'). The escape character
             can also be set on the command line.  The argument should be a
             single character, `^' followed by a letter, or ``none'' to dis-
             able the escape character entirely (making the connection trans-


             parent for binary data).

     FallBackToRsh
             Specifies that if connecting via ssh fails due to a connection
             refused error (there is no sshd(8) listening on the remote host),
             rsh(1) should automatically be used instead (after a suitable
             warning about the session being unencrypted).  The argument must
             be ``yes'' or ``no''.

     ForwardAgent
             Specifies whether the connection to the authentication agent (if
             any) will be forwarded to the remote machine.  The argument must
             be ``yes'' or ``no''.

     ForwardX11
             Specifies whether X11 connections will be automatically redirect-
             ed over the secure channel and DISPLAY set.  The argument must be
             ``yes'' or ``no''.

     GatewayPorts
             Specifies whether remote hosts are allowed to connect to local
             forwarded ports.  The argument must be ``yes'' or ``no''. The de-
             fault is ``no''.

     GlobalKnownHostsFile
             Specifies a file to use instead of /etc/ssh_known_hosts.

     HostName
             Specifies the real host name to log into.  This can be used to
             specify nicnames or abbreviations for hosts.  Default is the name
             given on the command line.  Numeric IP addresses are also permit-
             ted (both on the command line and in HostName specifications).

     IdentityFile
             Specifies the file from which the user's RSA authentication iden-
             tity is read (default .ssh/identity in the user's home directo-
             ry).  Additionally, any identities represented by the authentica-
             tion 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 configura-
             tion files; all these identities will be tried in sequence.

     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 tem-
             porarily, and some people find it annoying.

             The default is ``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.

             To disable keepalives, the value should be set to ``no'' in both
             the server and the client configuration files.

     KerberosAuthentication
             Specifies whether Kerberos authentication will be used. The argu-
             ment to this keyword must be ``yes'' or ``no''.

     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 ``yes'' or ``no''.

     LocalForward
             Specifies that a TCP/IP port on the local machine be forwarded
             over the secure channel to given host:port from the remote ma-
             chine.  The first argument must be a port number, and the second
             must be host:port.  Multiple forwardings may be specified, and
             additional forwardings can be given on the command line.  Only
             the root can forward privileged ports.

     PasswordAuthentication
             Specifies whether to use password authentication.  The argument
             to this keyword must be ``yes'' or ``no''.

     NumberOfPasswordPrompts
             Specifies the number of password prompts before giving up. The
             argument to this keyword must be an integer. Default is 3.

     Port    Specifies the port number to connect on the remote host.  Default
             is 22.

     ProxyCommand
             Specifies the command to use to connect to the server.  The com-
             mand string extends to the end of the line, and is executed with
             /bin/sh.  In the command string, %h will be substituted by the
             host name to connect and %p by the port.  The command can be ba-
             sically anything, and should read from its stdin and write to its
             stdout.  It should eventually connect an sshd(8) server running
             on some machine, or execute sshd -i somewhere.  Host key manage-
             ment will be done using the HostName of the host being connected
             (defaulting to the name typed by the user).

     RemoteForward
             Specifies that a TCP/IP port on the remote machine be forwarded
             over the secure channel to given host:port from the local ma-
             chine.  The first argument must be a port number, and the second
             must be host:port.  Multiple forwardings may be specified, and
             additional forwardings can be given on the command line.  Only
             the root can forward privileged ports.

     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 re-
             duce authentication time on slow connections when rhosts authen-
             tication is not used.  Most servers do not permit RhostsAuthenti-
             cation because it is not secure (see RhostsRSAAuthentication).
             The argument to this keyword must be ``yes'' or ``no''.

     RhostsRSAAuthentication
             Specifies whether to try rhosts based authentication with RSA
             host authentication.  This is the primary authentication method
             for most sites.  The argument must be ``yes'' or ``no''.

     RSAAuthentication
             Specifies whether to try RSA authentication.  The argument to
             this keyword must be ``yes'' or ``no''. RSA authentication will
             only be attempted if the identity file exists, or an authentica-
             tion agent is running.

     CheckHostIP
             If this flag is set to ``yes'', ssh will additionally check the
             host ip address in the known_hosts file. This allows ssh to de-
             tect if a host key changed due to DNS spoofing.  If the option is
             set to ``no'', the check will not be executed.

     StrictHostKeyChecking
             If this flag is set to ``yes'', ssh ssh will never automatically
             add host keys to the $HOME/.ssh/known_hosts file, and refuses to
             connect 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 /etc/ssh_known_hosts
             files installed and frequently connect new hosts.  Basically this
             option forces the user to manually add any new hosts.  Normally
             this option is disabled, and new hosts will automatically be
             added to the known host files.  The host keys of known hosts will
             be verified automatically in either case.  The argument must be
             ``yes'' or ``no''.

     User    Specifies the user to log in as.  This can be useful if you have
             a different user name in different machines.  This saves the
             trouble of having to remember to give the user name on the com-
             mand line.

     UserKnownHostsFile
             Specifies a file to use instead of $HOME/.ssh/known_hosts.

     UsePrivilegedPort
             Specifies whether to use a privileged port for outgoing connec-
             tions.  The argument must be ``yes'' or ``no''. The default is
             ``yes''. Note that setting this option to ``no'' turns of
             RhostsAuthentication and RhostsRSAAuthentication.

     UseRsh  Specifies that rlogin/rsh should be used for this host.  It is
             possible that the host does not at all support the ssh protocol.
             This causes ssh to immediately exec rsh(1).  All other options
             (except HostName) are ignored if this has been specified.  The
             argument must be ``yes'' or ``no''.

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 systems that use
             this variable.

     MAIL    Set to point the user's mailbox.

     PATH    Set to the default PATH, as specified when compiling ssh.

     SSH_AUTH_SOCK
             indicates the path of a unix-domain socket used to communicate
             with the agent.

     SSH_CLIENT
             Identifies the client end of the connection.  The variable con-
             tains three space-separated values: client ip-address, client
             port number, and server port number.

     SSH_TTY
             This is set to the name of the tty (path to the device) associat-
             ed with the current shell or command.  If the current session has

             no tty, this variable is not set.

     TZ      The timezone variable is set to indicate the present timezone if
             it was set when the daemon was started (e.i., the daemon passes
             the value on to new connections).

     USER    Set to the name of the user logging in.

     Additionally, ssh reads $HOME/.ssh/environment, and adds lines of the
     format ``VARNAME=value'' to the environment.

FILES
     $HOME/.ssh/known_hosts  Records host keys for all hosts the user has
                             logged into (that are not in
                             /etc/ssh_known_hosts). See sshd(8).

     $HOME/.ssh/random_seed  Used for seeding the random number generator.
                             This file contains sensitive data and should
                             read/write for the user and not accessible for
                             others.  This file is created the first time the
                             program is run and updated automatically.  The
                             user should never need to read or modify this
                             file.

     $HOME/.ssh/identity     Contains the RSA authentication identity of the
                             user.  This file contains sensitive data and
                             should be readable by the user but not accessible
                             by others (read/write/execute).  Note that ssh
                             ignores this file if it is accessible by others.
                             It is possible to specify a passphrase when gen-
                             erating the key; the passphrase will be used to
                             encrypt the sensitive part of this file using
                             3DES.

     $HOME/.ssh/identity.pub
                             Contains the public key for authentication (pub-
                             lic part of the identity file in human-readable
                             form).  The contents of this file should be added
                             to $HOME/.ssh/authorized_keys on all machines
                             where you wish to log in using RSA authentica-
                             tion.  This file is not sensitive and can (but
                             need not) be readable by anyone.  This file is
                             never used automatically and is not necessary; it
                             is only provided for the convenience of the user.

     $HOME/.ssh/config       This is the per-user configuration file.  The
                             format of this file is described above.  This
                             file is used by the ssh 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.

     $HOME/.ssh/authorized_keys
                             Lists the RSA keys that can be used for logging
                             in as this user.  The format of this file is de-
                             scribed in the sshd(8) manual page.  In the sim-
                             plest form the format is the same as the .pub
                             identity files (that is, each line contains the
                             number of bits in modulus, public exponent, modu-
                             lus, and comment fields, separated by spaces).
                             This file is not highly sensitive, but the recom-
                             mended permissions are read/write for the user,
                             and not accessible by others.

     /etc/ssh_known_hosts    Systemwide list of known host keys.  This file
                             should be prepared by the system administrator to
                             contain the public host keys of all machines in
                             the organization.  This file should be world-
                             readable.  This file contains public keys, one
                             per line, in the following format (fields sepa-
                             rated by spaces): system name, number of bits in
                             modulus, public exponent, modulus, and optional
                             comment field.  When different names are used for
                             the same machine, all such names should be list-
                             ed, separated by commas.  The format is described
                             on the sshd(8) manual page.

                             The canonical system name (as returned by name
                             servers) is used by sshd(8) to verify the client
                             host when logging in; other names are needed be-
                             cause ssh does not convert the user-supplied name
                             to a canonical name before checking the key, be-
                             cause someone with access to the name servers
                             would then be able to fool host authentication.

     /etc/ssh_config         Systemwide configuration file.  This file pro-
                             vides defaults for those values that are not
                             specified in the user's configuration file, and
                             for those users who do not have a configuration
                             file.  This file must be world-readable.

     $HOME/.rhosts           This file is used in .rhosts authentication to
                             list the host/user pairs that are permitted to
                             log in.  (Note that this file is also used by
                             rlogin and rsh, which makes using this file inse-
                             cure.)  Each line of the file contains a host
                             name (in the canonical form returned by name
                             servers), and then a user name on that host, sep-
                             arated by a space.  One some machines this file
                             may need to be world-readable if the user's home
                             directory is on a 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.

                             Note that by default sshd(8) will be installed so
                             that it requires successful RSA host authentica-
                             tion before permitting .rhosts authentication.
                             If your server machine does not have the client's
                             host key in /etc/ssh_known_hosts, you can store
                             it in $HOME/.ssh/known_hosts. The easiest way to
                             do this is to connect back to the client from the
                             server machine using ssh; this will automatically
                             add the host key inxi $HOME/.ssh/known_hosts.

     $HOME/.shosts           This file is used exactly the same way as
                             .rhosts. The purpose for having this file is to
                             be able to use rhosts authentication with ssh
                             without permitting login with rlogin(1) or
                             rsh(1).

     /etc/hosts.equiv        This file is used during .rhosts authentication.
                             It contains canonical hosts names, one per line
                             (the full format is described on the sshd(8) man-
                             ual page).  If the client host is found in this
                             file, login is automatically permitted provided
                             client and server user names are the same.  Addi-
                             tionally, successful RSA host authentication is
                             normally required.  This file should only be

                             writable by root.

     /etc/shosts.equiv       This file is processed exactly as
                             /etc/hosts.equiv. This file may be useful to per-
                             mit logins using ssh but not using rsh/rlogin.

     /etc/sshrc              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.

     $HOME/.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.

     libcrypto.so.X.1        A version of this library which includes support
                             for the RSA algorithm is required for proper op-
                             eration.

AUTHOR
     Tatu Ylonen <ylo@cs.hut.fi>

     Issues can be found from the SSH WWW home page:

           http://www.cs.hut.fi/ssh

     OpenSSH is a derivative of the original (free) ssh 1.2.12 release, but
     with bugs removed and newer features re-added.   Rapidly after the 1.2.12
     release, newer versions bore successively more restrictive licenses.
     This version of OpenSSH

     -   has all components of a restrictive nature (ie. patents, see ssl(8))
         directly removed from the source code; any licensed or patented com-
         ponents are chosen from external libraries.

     -   has been updated to support ssh protocol 1.5.

     -   contains added support for kerberos(8) authentication and ticket
         passing.

     -   supports one-time password authentication with skey(1).

     The libraries described in ssl(8) are required for proper operation.

SEE ALSO
     rlogin(1),  rsh(1),  scp(1),  ssh-add(1),  ssh-agent(1),  ssh-keygen(1),
     telnet(1),  sshd(8),  ssl(8)

OpenBSD 2.6                   September 25, 1999                            11