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SSH(1) FreeBSD General Commands Manual SSH(1)

Содержание

[править] NAME

    ssh — OpenSSH SSH client (remote login program)

[править] SYNOPSIS

    ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]
        [-D [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]

[править] 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
            compression algorithm is the same used by gzip(1), and the
            “level” can be controlled by the CompressionLevel option for pro‐
            tocol version 1.  Compression is desirable on modem lines and
            other 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 configuration files; see the Compression option.
    -c cipher_spec
            Selects the cipher specification for encrypting the session.
            Protocol version 1 allows specification of a single cipher.  The
            supported values are “3des”, “blowfish”, and “des”.  3des
            (triple-des) is an encrypt-decrypt-encrypt triple with three dif‐
            ferent keys.  It is believed to be secure.  blowfish is a fast
            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
            in ssh_config(5) 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 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.
    -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.
            If the ExitOnForwardFailure configuration option is set to “yes”,
            then a client started with -f will wait for all remote port for‐
            wards to be successfully established before placing itself in the
            background.
    -g      Allows remote hosts to connect to local forwarded ports.
    -I pkcs11
            Specify the PKCS#11 shared library ssh should use to communicate
            with a PKCS#11 token providing the user's private RSA key.
    -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 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.  How‐
            ever, 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).
    -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 on a remote
            machine.  For example, ssh -n shadows.cs.hut.fi emacs & will
            start an emacs on shadows.cs.hut.fi, and the X11 connection will
            be automatically 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 ctl_cmd
            Control an active connection multiplexing master process.  When
            the -O option is specified, the ctl_cmd argument is interpreted
            and passed to the master process.  Valid commands are: “check”
            (check that the master process is running), “forward” (request
            forwardings without command execution) 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
                  DynamicForward
                  EscapeChar
                  ExitOnForwardFailure
                  ForwardAgent
                  ForwardX11
                  ForwardX11Trusted
                  GatewayPorts
                  GlobalKnownHostsFile
                  GSSAPIAuthentication
                  GSSAPIDelegateCredentials
                  HashKnownHosts
                  Host
                  HostbasedAuthentication
                  HostKeyAlgorithms
                  HostKeyAlias
                  HostName
                  IdentityFile
                  IdentitiesOnly
                  IPQoS
                  KbdInteractiveDevices
                  KexAlgorithms
                  LocalCommand
                  LocalForward
                  LogLevel
                  MACs
                  NoHostAuthenticationForLocalhost
                  NumberOfPasswordPrompts
                  PasswordAuthentication
                  PermitLocalCommand
                  PKCS11Provider
                  Port
                  PreferredAuthentications
                  Protocol
                  ProxyCommand
                  PubkeyAuthentication
                  RekeyLimit
                  RemoteForward
                  RhostsRSAAuthentication
                  RSAAuthentication
                  SendEnv
                  ServerAliveInterval
                  ServerAliveCountMax
                  StrictHostKeyChecking
                  TCPKeepAlive
                  Tunnel
                  TunnelDevice
                  UsePrivilegedPort
                  User
                  UserKnownHostsFile
                  VerifyHostKeyDNS
                  VersionAddendum
                  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.
            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.
            When used together with -O forward the allocated port will be
            printed to the standard output.
    -S ctl_path
            Specifies the location of a control socket for connection shar‐
            ing, or the string “none” to disable connection sharing.  Refer
            to the description of ControlPath and ControlMaster in
            ssh_config(5) for details.
    -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 of SSH as a secure transport for other appli‐
            cations (eg. sftp(1)).  The subsystem is specified as the remote
            command.
    -T      Disable pseudo-tty allocation.
    -t      Force pseudo-tty allocation.  This can be used to execute arbi‐
            trary screen-based programs on a remote machine, which can be
            very useful, e.g. when implementing menu services.  Multiple -t
            options force tty allocation, even if ssh has no local tty.
    -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).

[править] AUTHENTICATION

    The OpenSSH SSH client supports SSH protocols 1 and 2.  The default is to
    use protocol 2 only, though this can be changed via the Protocol option
    in ssh_config(5) or the -1 and -2 options (see above).  Both protocols
    support similar authentication methods, but protocol 2 is the default
    since it provides additional mechanisms for confidentiality (the traffic
    is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) and
    integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).  Protocol 1
    lacks a strong mechanism for ensuring the integrity of the connection.
    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/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 authentication 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 insecure 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 DSA and RSA 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
    certificates are used.  This has the advantage that a single trusted cer‐
    tification authority can be used in place of many public/private keys.
    See the CERTIFICATES section of ssh-keygen(1) for more information.
    The most convenient way to use public key or certificate authentication
    may be with an authentication agent.  See ssh-agent(1) for more informa‐
    tion.
    Challenge-response authentication works as follows: The server sends an
    arbitrary "challenge" text, and prompts for a response.  Protocol 2
    allows multiple challenges and responses; protocol 1 is restricted to
    just one challenge/response.  Examples of challenge-response authentica‐
    tion include BSD Authentication (see login.conf(5)) and PAM (some non-
    OpenBSD systems).
    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.

[править] 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 /
            X11 sessions to terminate.
    ~?      Display a list of escape characters.
    ~B      Send a BREAK to the remote system (only useful for SSH protocol
            version 2 and if the peer supports it).
    ~C      Open command line.  Currently this allows the addition of port
            forwardings using the -L, -R and -D options (see above).  It also
            allows the cancellation of existing remote port-forwardings using
            -KR[bind_address:]port.  !command allows the user to execute a
            local command if the PermitLocalCommand option is enabled in
            ssh_config(5).  Basic help is available, using the -h option.
    ~R      Request rekeying of the connection (only useful for SSH protocol
            version 2 and if the peer supports it).

[править] 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.

[править] 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.
    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 ForwardAgent variable is set to “yes” (or see the description of
    the -A and -a options above) and the user is using an authentication
    agent, the connection to the agent is automatically forwarded to the
    remote side.

[править] VERIFYING HOST KEYS

    When connecting to a server for the first time, a fingerprint of the
    server's public key is presented to the user (unless the option
    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.

[править] 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‐
    fic).
    The following example would connect client network 10.0.50.0/24 with
    remote network 10.0.99.0/24 using a point-to-point connection from
    10.1.1.1 to 10.1.1.2, provided that the SSH server running on the gateway
    to the remote network, at 192.168.1.15, allows it.
    On the client:
          # ssh -f -w 0:1 192.168.1.15 true
          # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
          # route add 10.0.99.0/24 10.1.1.2
    On the server:
          # 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).

[править] 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.)
    SSH_AUTH_SOCK         Identifies the path of a UNIX-domain socket used to
                          communicate with the agent.
    SSH_CONNECTION        Identifies the client and server ends of the con‐
                          nection.  The variable contains four space-sepa‐
                          rated values: client IP address, client port num‐
                          ber, server IP address, and server port number.
    SSH_ORIGINAL_COMMAND  This variable contains the original command line if
                          a forced command is executed.  It can be used to
                          extract the original arguments.
    SSH_TTY               This is set to the name of the tty (path to the
                          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).

[править] 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 (DSA/ECDSA/RSA) that can be used for log‐
            ging in as this user.  The format of this file is described in
            the sshd(8) manual page.  This file is not highly sensitive, but
            the recommended permissions are read/write for the user, and not
            accessible by others.
    ~/.ssh/config
            This is the per-user configuration file.  The file format and
            configuration options are described in ssh_config(5).  Because of
            the potential for abuse, this file must have strict permissions:
            read/write for the user, and not accessible by others.
    ~/.ssh/environment
            Contains additional definitions for environment variables; see
            ENVIRONMENT, above.
    ~/.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/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
            ssh is not setuid root.
    /etc/ssh/ssh_known_hosts
            Systemwide list of known host keys.  This file should be prepared
            by the system administrator to contain the public host keys of
            all machines in the organization.  It should be world-readable.
            See sshd(8) for further details of the format of this file.
    /etc/ssh/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.

[править] EXIT STATUS

    ssh exits with the exit status of the remote command or with 255 if an
    error occurred.

[править] 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).

[править] 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.

FreeBSD 9.0 November 18, 2010 FreeBSD 9.0

Источник — «http://871460.xgu.ru/wiki/man/orig/ssh»