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sshd (8)
  • sshd (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • >> sshd (8) ( Solaris man: Команды системного администрирования )
  • sshd (8) ( FreeBSD man: Команды системного администрирования )
  • sshd (8) ( Русские man: Команды системного администрирования )
  • sshd (8) ( Linux man: Команды системного администрирования )
  • 
    NAME
         sshd - OpenSSH SSH daemon
    
    SYNOPSIS
         sshd   [-deiqD46]   [-b   bits]   [-f    config_file]    [-g
         login_grace_time]  [-h  host_key_file] [-k key_gen_time] [-p
         port] [-u len] [-V client_protocol_id]
    
    DESCRIPTION
         sshd  (SSH  Daemon)  is  the  daemon  program  for   ssh(1).
         Together  these programs replace rlogin and rsh, and provide
         secure encrypted communications between two untrusted  hosts
         over  an  insecure network.  The programs are intended to be
         as easy to install and use as possible.
    
         sshd  is  the  daemon  that  listens  for  connections  from
         clients.   It  is normally started at boot from /etc/rc.  It
         forks a new daemon for each incoming connection.  The forked
         daemons  handle  key  exchange,  encryption, authentication,
         command execution, and data exchange.   This  implementation
         of  sshd  supports  both SSH protocol version 1 and 2 simul-
         taneously.  sshd works as follows.
    
      SSH protocol version 1
         Each host has a host-specific RSA key (normally  1024  bits)
         used  to  identify  the host.  Additionally, when the daemon
         starts, it generates a server RSA key (normally  768  bits).
         This  key  is normally regenerated every hour if it has been
         used, and is never stored on disk.
    
         Whenever a client connects the daemon responds with its pub-
         lic  host and server keys.  The client compares the RSA host
         key against its own database  to  verify  that  it  has  not
         changed.  The client then generates a 256 bit random number.
         It encrypts this random number using both the host  key  and
         the  server  key,  and  sends  the  encrypted  number to the
         server.  Both sides then use this random number as a session
         key  which  is used to encrypt all further communications in
         the session.  The rest of the session is encrypted  using  a
         conventional  cipher,  currently Blowfish or 3DES, with 3DES
         being used by default.  The client  selects  the  encryption
         algorithm to use from those offered by the server.
    
         Next, the server and the client enter an authentication dia-
         log.   The client tries to authenticate itself using .rhosts
         authentication, .rhosts  authentication  combined  with  RSA
         host  authentication, RSA challenge-response authentication,
         or password based authentication.
    
         Rhosts authentication is normally  disabled  because  it  is
         fundamentally  insecure,  but  can  be enabled in the server
         configuration file  if  desired.   System  security  is  not
         improved  unless rshd(8), rlogind(8), rexecd(8), and rexd(8)
         are disabled (thus completely disabling rlogin(1) and rsh(1)
         into the machine).
    
      SSH protocol version 2
         Version 2 works similarly:  Each host  has  a  host-specific
         DSA key used to identify the host.  However, when the daemon
         starts, it does not generate a server key.  Forward security
         is  provided  through  a Diffie-Hellman key agreement.  This
         key agreement results in a shared session key.
    
         The rest of the  session  is  encrypted  using  a  symmetric
         cipher,  currently  128  bit  AES,  Blowfish, 3DES, CAST128,
         Arcfour, 192 bit AES, or 256 bit AES.   The  client  selects
         the  encryption  algorithm  to use from those offered by the
         server.  Additionally, session integrity is provided through
         a  cryptographic  message  authentication code (hmac-sha1 or
         hmac-md5).
    
         Protocol version 2 provides a public key  based  user  (Pub-
         keyAuthentication)  or client host (HostbasedAuthentication)
         authentication method, conventional password  authentication
         and challenge response based methods.
    
      Command execution and data forwarding
         If the client successfully authenticates  itself,  a  dialog
         for  preparing  the  session  is  entered.  At this time the
         client may request things like allocating a pseudo-tty, for-
         warding  X11  connections, forwarding TCP/IP connections, or
         forwarding the  authentication  agent  connection  over  the
         secure channel.
    
         Finally, the client either requests a shell or execution  of
         a  command.   The  sides  then  enter session mode.  In this
         mode, either side may send data at any time, and  such  data
         is  forwarded  to/from  the  shell  or command on the server
         side, and the user terminal in the client side.
    
         When the user program terminates and all forwarded  X11  and
         other connections have been closed, the server sends command
         exit status to the client, and both sides exit.
    
         sshd can be configured using command-line options or a  con-
         figuration   file.   Command-line  options  override  values
         specified in the configuration file.
    
         sshd rereads its  configuration  file  when  it  receives  a
         hangup  signal, SIGHUP, by executing itself with the name it
         was started as, ie.  /usr/sbin/sshd.
    
         The options are as follows:
    
         -b bits
              Specifies the number of bits in the ephemeral  protocol
              version 1 server key (default 768).
    
    
         -d   Debug mode.  The server sends verbose debug  output  to
              the  system  log,  and does not put itself in the back-
              ground.  The server also will not fork  and  will  only
              process  one  connection.  This option is only intended
              for debugging for  the  server.   Multiple  -d  options
              increase the debugging level.  Maximum is 3.
    
         -e   When this option is specified, sshd will send the  out-
              put to the standard error instead of the system log.
    
         -f configuration_file
              Specifies the name  of  the  configuration  file.   The
              default  is  /usr/local/sparcv9/etc/sshd_config.   sshd
              refuses to start if there is no configuration file.
    
         -g login_grace_time
              Gives the grace time for clients to authenticate  them-
              selves  (default  600 seconds).  If the client fails to
              authenticate the user within  this  many  seconds,  the
              server  disconnects  and  exits.  A value of zero indi-
              cates no limit.
    
         -h host_key_file
              Specifies the file from which  the  host  key  is  read
              (default  /usr/local/sparcv9/etc/ssh_host_key ) .  This
              option must be given if sshd is not run as root (as the
              normal host file is normally not readable by anyone but
              root).  It is possible to have multiple host key  files
              for  the different protocol versions and host key algo-
              rithms.
    
         -i   Specifies that sshd is being run from inetd.   sshd  is
              normally  not  run  from inetd because it needs to gen-
              erate the server key  before  it  can  respond  to  the
              client,  and  this  may  take tens of seconds.  Clients
              would have to wait too long if the key was  regenerated
              every  time.  However, with small key sizes (e.g., 512)
              using sshd from inetd may be feasible.
    
         -k key_gen_time
              Specifies how often the ephemeral  protocol  version  1
              server key is regenerated (default 3600 seconds, or one
              hour).  The motivation for regenerating the key  fairly
              often is that the key is not stored anywhere, and after
              about an hour, it becomes impossible to recover the key
              for  decrypting  intercepted communications even if the
              machine is cracked into or physically seized.  A  value
              of  zero  indicates  that  the key will never be regen-
              erated.
    
         -p port
              Specifies the port on which the server listens for con-
              nections (default 22).
    
         -q   Quiet mode.  Nothing is sent to the system  log.   Nor-
              mally the beginning, authentication, and termination of
              each connection is logged.
    
         -u len
              This option is used to specify the size of the field in
              the utmp structure that holds the remote host name.  If
              the resolved host name is longer than len , the  dotted
              decimal  value will be used instead.  This allows hosts
              with very long host names that overflow this  field  to
              still be uniquely identified.  Specifying -u0 indicates
              that only dotted decimal addresses should be  put  into
              the utmp file.
    
         -D   When this option is specified sshd will not detach  and
              does  not become a daemon.  This allows easy monitoring
              of sshd.
    
         -4   Forces sshd to use IPv4 addresses only.
    
         -6   Forces sshd to use IPv6 addresses only.
    
    CONFIGURATION FILE
         sshd       reads       configuration        data        from
         /usr/local/sparcv9/etc/sshd_config  (or  the  file specified
         with -f on the command line).  The  file  contains  keyword-
         value  pairs,  one  per  line.   Lines starting with `#' and
         empty lines are interpreted as comments.
    
         The following keywords are possible.
    
         AFSTokenPassing
              Specifies whether an AFS token may be forwarded to  the
              server.  Default is ``yes''.
    
         AllowGroups
              This keyword can be followed by a list of group  names,
              separated  by  spaces.   If specified, login is allowed
              only for users whose  primary  group  or  supplementary
              group  list  matches  one of the patterns.  `*' and `?'
              can be used as wildcards in the patterns.   Only  group
              names are valid; a numerical group ID isn't recognized.
              By default login is allowed  regardless  of  the  group
              list.
    
         AllowTcpForwarding
              Specifies whether TCP  forwarding  is  permitted.   The
              default is ``yes''.  Note that disabling TCP forwarding
              does not improve security unless users are also  denied
              shell access, as they can always install their own for-
              warders.
    
    
         AllowUsers
              This keyword can be followed by a list of  user  names,
              separated  by  spaces.   If specified, login is allowed
              only for users names that match one  of  the  patterns.
              `*'  and `?'  can be used as wildcards in the patterns.
              Only user names are valid; a numerical  user  ID  isn't
              recognized.   By default login is allowed regardless of
              the user name.
    
    
         Banner
              In some jurisdictions, sending a warning message before
              authentication  may  be relevant for getting legal pro-
              tection.  The contents of the specified file  are  sent
              to  the  remote  user before authentication is allowed.
              This option is only available for protocol version 2.
    
    
         ChallengeResponseAuthentication
              Specifies whether challenge response authentication  is
              allowed.   Currently  there is only support for skey(1)
              authentication.  The default is ``yes''.
    
         Ciphers
              Specifies the ciphers allowed for protocol  version  2.
              Multiple  ciphers must be comma-separated.  The default
              is          ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-
              cbc,arcfour.''
    
         CheckMail
              Specifies whether sshd should check for  new  mail  for
              interactive logins.  The default is ``no''.
    
         ClientAliveInterval
              Sets a timeout interval in seconds after  which  if  no
              data  has been received from the client, sshd will send
              a message through the encrypted channel  to  request  a
              response from the client.  The default is 0, indicating
              that these messages will not be  sent  to  the  client.
              This option applies to protocol version 2 only.
    
         ClientAliveCountMax
              Sets the number of client alive  messages  (see  above)
              which  may  be sent without sshd receiving any messages
              back from the client.  If  this  threshold  is  reached
              while  client  alive messages are being sent, sshd will
              disconnect the client, terminating the session.  It  is
              important to note that the use of client alive messages
              is very different from Keepalive  (below).  The  client
              alive  messages  are sent through the encrypted channel
              and therefore will not be spoofable. The TCP  keepalive
              option  enabled  by Keepalive is spoofable. You want to
              use the client alive  mechanism  when  you  are  basing
              something important on clients having an active connec-
              tion to the server.
    
              The default value is 3. If you set  ClientAliveInterval
              (above)  to  15,  and  leave this value at the default,
              unresponsive ssh clients  will  be  disconnected  after
              approximately 45 seconds.
    
         DenyGroups
              This keyword can be  followed  by  a  number  of  group
              names,  separated by spaces.  Users whose primary group
              or supplementary group list matches one of the patterns
              aren't  allowed to log in.  `*' and `?'  can be used as
              wildcards in the patterns.  Only group names are valid;
              a  numerical  group  ID  isn't  recognized.  By default
              login is allowed regardless of the group list.
    
    
         DenyUsers
              This keyword can be followed by a number of user names,
              separated  by  spaces.   Login  is  disallowed for user
              names that match one of the patterns.  `*' and `?'  can
              be  used as wildcards in the patterns.  Only user names
              are valid; a numerical user ID  isn't  recognized.   By
              default login is allowed regardless of the user name.
    
         GatewayPorts
              Specifies whether remote hosts are allowed  to  connect
              to  ports  forwarded for the client.  The argument must
              be ``yes'' or ``no''.  The default is ``no''.
    
         HostbasedAuthentication
              Specifies whether rhosts or /etc/hosts.equiv  authenti-
              cation  together with successful public key client host
              authentication is allowed  (hostbased  authentication).
              This  option  is similar to RhostsRSAAuthentication and
              applies to protocol version 2  only.   The  default  is
              ``no''.
    
         HostKey
              Specifies the file containing  the  private  host  keys
              (default  /usr/local/sparcv9/etc/ssh_host_key ) used by
              SSH protocol versions 1 and 2.   Note  that  sshd  will
              refuse  to  use a file if it is group/world-accessible.
              It  is  possible  to  have  multiple  host  key  files.
              ``rsa1''  keys  are  used  for version 1 and ``dsa'' or
              ``rsa'' are used for version 2 of the SSH protocol.
    
         IgnoreRhosts
              Specifies that .rhosts and .shosts files  will  not  be
              used  in RhostsAuthentication , RhostsRSAAuthentication
              or HostbasedAuthentication .
    
              /etc/hosts.equiv                                    and
              /usr/local/sparcv9/etc/shosts.equiv   are  still  used.
              The default is ``yes''.
    
         IgnoreUserKnownHosts
              Specifies  whether  sshd  should  ignore   the   user's
              $HOME/.ssh/known_hosts  during  RhostsRSAAuthentication
              or HostbasedAuthentication .  The default is ``no''.
    
         KeepAlive
              Specifies whether the system should send keepalive mes-
              sages  to  the  other side.  If they are sent, death of
              the connection or crash of one of the machines will  be
              properly noticed.  However, this means that connections
              will die if the route is  down  temporarily,  and  some
              people  find  it  annoying.   On  the  other  hand,  if
              keepalives are not sent, sessions may hang indefinitely
              on  the  server,  leaving ``ghost'' users and consuming
              server resources.
    
              The default is ``yes'' (to send  keepalives),  and  the
              server  will  notice  if  the  network goes down or the
              client host reboots.  This  avoids  infinitely  hanging
              sessions.
    
              To disable keepalives,  the  value  should  be  set  to
              ``no''  in both the server and the client configuration
              files.
    
         KerberosAuthentication
              Specifies whether Kerberos authentication  is  allowed.
              This  can  be  in  the form of a Kerberos ticket, or if
              PasswordAuthentication is yes, the password provided by
              the  user  will  be validated through the Kerberos KDC.
              To use this option, the server needs a Kerberos servtab
              which  allows  the  verification of the KDC's identity.
              Default is ``yes''.
    
         KerberosOrLocalPasswd
              If set then if password authentication through Kerberos
              fails then the password will be validated via any addi-
              tional local mechanism such as /etc/passwd.  Default is
              ``yes''.
    
         KerberosTgtPassing
              Specifies whether a Kerberos TGT may  be  forwarded  to
              the server.  Default is ``no'', as this only works when
              the Kerberos KDC is actually an AFS kaserver.
    
         KerberosTicketCleanup
              Specifies whether to automatically destroy  the  user's
              ticket cache file on logout.  Default is ``yes''.
    
         KeyRegenerationInterval
              In protocol version 1,  the  ephemeral  server  key  is
              automatically  regenerated  after this many seconds (if
              it has been used).  The purpose of regeneration  is  to
              prevent  decrypting captured sessions by later breaking
              into the machine and stealing the  keys.   The  key  is
              never  stored  anywhere.  If the value is 0, the key is
              never regenerated.  The default is 3600 (seconds).
    
         ListenAddress
              Specifies the local addresses sshd  should  listen  on.
              The following forms may be used:
    
    
         ListenAddress
              host|IPv4_addr|IPv6_addr
    
         ListenAddress
              host|IPv4_addr:port
    
         ListenAddress
              [host|IPv6_addr]:port
    
         If port is not specified, sshd will listen  on  the  address
         and  all  prior  Port  options  specified. The default is to
         listen  on  all  local  addresses.   Multiple  ListenAddress
         options  are  permitted. Additionally, any Port options must
         precede this option for non port  qualified  addresses.   It
         LoginGraceTime The server disconnects after this time if the
         user has not successfully logged in.  If  the  value  is  0,
         there  is  no time limit.  The default is 600 (seconds).  It
         LogLevel Gives the verbosity level that is used when logging
         messages from sshd.  The possible values are:  QUIET, FATAL,
         ERROR, INFO, VERBOSE and DEBUG.  The default is INFO.   Log-
         ging  with  level DEBUG violates the privacy of users and is
         not recommended.  It MACs Specifies the available MAC  (mes-
         sage  authentication code) algorithms.  The MAC algorithm is
         used in protocol version 2 for  data  integrity  protection.
         Multiple algorithms must be comma-separated.  The default is
    
    
         Bd -literal
           ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-
         ripemd160@openssh.com,
             hmac-sha1-96,hmac-md5-96'' Ed It  MaxStartups  Specifies
         the maximum number of concurrent unauthenticated connections
         to the sshd daemon.  Additional connections will be  dropped
         until  authentication succeeds or the LoginGraceTime expires
         for a connection.  The default is 10.
    
         Alternatively, random early drop can be enabled by  specify-
         ing  the  three  colon  separated values ``start:rate:full''
         (e.g., "10:30:60").  sshd will  refuse  connection  attempts
         with  a  probability  of  ``rate/100''  (30%)  if  there are
         currently ``start'' (10) unauthenticated  connections.   The
         probability  increases  linearly and all connection attempts
         are refused if the  number  of  unauthenticated  connections
         reaches ``full'' (60).  It PAMAuthenticationViaKbdInt Speci-
         fies  whether  PAM  challenge  response  authentication   is
         allowed.  This allows the use of most PAM challenge response
         authentication modules, but it will allow password authenti-
         cation  regardless of whether PasswordAuthentication is dis-
         abled.  The default is  ``no''.   It  PasswordAuthentication
         Specifies  whether  password authentication is allowed.  The
         default is ``yes''.  It PermitEmptyPasswords  When  password
         authentication  is  allowed, it specifies whether the server
         allows login to accounts with empty password  strings.   The
         default  is  ``no''.   It  PermitRootLogin Specifies whether
         root can login using ssh(1).  The argument must be  ``yes'',
         ``without-password'',  ``forced-commands-only''  or  ``no''.
         The default is ``yes''.
    
         If this  option  is  set  to  ``without-password''  password
         authentication is disabled for root.
    
         If this option is set to ``forced-commands-only'' root login
         with  public key authentication will be allowed, but only if
         the command option has been specified (which may  be  useful
         for taking remote backups even if root login is normally not
         allowed). All other authentication methods are disabled  for
         root.
    
         If this option is set to  ``no''  root  is  not  allowed  to
         login.  It PidFile Specifies the file that contains the pro-
         cess  identifier  of  the  sshd  daemon.   The  default   is
         /var/run/sshd.pid.   It  Port Specifies the port number that
         sshd listens on.  The default is 22.   Multiple  options  of
         this  type  are  permitted.   See  also  ListenAddress .  It
         PrintLastLog Specifies whether sshd should  print  the  date
         and  time  when  the  user  last  logged in.  The default is
         ``yes''.  It PrintMotd Specifies whether sshd  should  print
         /etc/motd  when a user logs in interactively.  (On some sys-
         tems it is also  printed  by  the  shell,  /etc/profile,  or
         equivalent.)  The default is ``yes''.  It Protocol Specifies
         the protocol versions sshd  should  support.   The  possible
         values  are  ``1''  and  ``2''.   Multiple  versions must be
         comma-separated.  The default is ``2,1''.  It  PubkeyAuthen-
         tication  Specifies  whether  public  key  authentication is
         allowed.  The default is ``yes''.   Note  that  this  option
         applies  to protocol version 2 only.  It ReverseMappingCheck
         Specifies whether sshd should try to verify the remote  host
         name and check that the resolved host name for the remote IP
         address maps back to the very same IP address.  The  default
         is   ``no''.    It  RhostsAuthentication  Specifies  whether
         authentication using rhosts  or  /etc/hosts.equiv  files  is
         sufficient.   Normally,  this method should not be permitted
         because it is insecure.  RhostsRSAAuthentication  should  be
         used instead, because it performs RSA-based host authentica-
         tion  in  addition  to  normal  rhosts  or  /etc/hosts.equiv
         authentication.  The default is ``no''.  This option applies
         to protocol  version  1  only.   It  RhostsRSAAuthentication
         Specifies  whether rhosts or /etc/hosts.equiv authentication
         together with successful RSA host authentication is allowed.
         The default is ``no''.  This option applies to protocol ver-
         sion 1 only.  It RSAAuthentication  Specifies  whether  pure
         RSA  authentication  is  allowed.   The  default is ``yes''.
         This option applies to protocol version  1  only.   It  Ser-
         verKeyBits  Defines the number of bits in the ephemeral pro-
         tocol version 1 server key.  The minimum value is  512,  and
         the  default  is 768.  It StrictModes Specifies whether sshd
         should check file modes and ownership of  the  user's  files
         and home directory before accepting login.  This is normally
         desirable because novices sometimes accidentally leave their
         directory  or files world-writable.  The default is ``yes''.
         It Subsystem Configures an external  subsystem  (e.g.,  file
         transfer  daemon).  Arguments should be a subsystem name and
         a command to execute upon subsystem  request.   The  command
         sftp-server(8) implements the ``sftp'' file transfer subsys-
         tem.  By default no subsystems are defined.  Note that  this
         option  applies to protocol version 2 only.  It SyslogFacil-
         ity Gives the facility code that is used when  logging  mes-
         sages  from  sshd.   The  possible values are: DAEMON, USER,
         AUTH,  LOCAL0,  LOCAL1,  LOCAL2,  LOCAL3,  LOCAL4,   LOCAL5,
         LOCAL6, LOCAL7.  The default is AUTH.  It UseLogin Specifies
         whether login(1) is used  for  interactive  login  sessions.
         Note  that  login(1) is never used for remote command execu-
         tion.  The default is ``no''.  It X11DisplayOffset Specifies
         the  first  display number available for sshd's X11 forward-
         ing.  This prevents sshd  from  interfering  with  real  X11
         servers.   The  default  is  10.  It X11Forwarding Specifies
         whether X11 forwarding is permitted.  The default is ``no''.
         Note that disabling X11 forwarding does not improve security
         in any way, as users can always install their  own  forward-
         ers.    It  XAuthLocation  Specifies  the  location  of  the
         xauth(1) program.  The default is /usr/openwin/bin/xauth.
    
    LOGIN PROCESS
         When a user successfully logs in, sshd does the following:
    
         1.   If the login is on a  tty,  and  no  command  has  been
              specified, prints last login time and /etc/motd (unless
              prevented   in   the   configuration   file    or    by
              $HOME/.hushlogin ; see the FILES section).
    
         2.   If the login is on a tty, records login time.
    
         3.   Checks /etc/nologin ; if it exists, prints contents and
              quits (unless root).
    
         4.   Changes to run with normal user privileges.
    
         5.   Sets up basic environment.
    
         6.   Reads $HOME/.ssh/environment if it exists.
    
         7.   Changes to user's home directory.
    
         8.   If   $HOME/.ssh/rc   exists,   runs   it;    else    if
              /usr/local/sparcv9/etc/sshrc exists, runs it; otherwise
              runs xauth.  The ``rc'' files are given the X11 authen-
              tication protocol and cookie in standard input.
    
         9.   Runs user's shell or command.
    
    AUTHORIZED_KEYS FILE FORMAT
         The $HOME/.ssh/authorized_keys file lists the RSA keys  that
         are  permitted  for RSA authentication in protocol version 1
         Similarly, the $HOME/.ssh/authorized_keys2  file  lists  the
         DSA and RSA keys that are permitted for public key authenti-
         cation (PubkeyAuthentication) in protocol version 2.
    
         Each line of the file contains  one  key  (empty  lines  and
         lines  starting  with  a `#' are ignored as comments).  Each
         RSA public key consists of the following  fields,  separated
         by  spaces: options, bits, exponent, modulus, comment.  Each
         protocol version 2 public key consists  of:   options,  key-
         type,  base64  encoded key, comment.  The options fields are
         optional; its presence is determined  by  whether  the  line
         starts  with  a number or not (the option field never starts
         with a number).  The bits,  exponent,  modulus  and  comment
         fields  give the RSA key for protocol version 1; the comment
         field is not used for anything (but may  be  convenient  for
         the  user  to identify the key).  For protocol version 2 the
         keytype is ``ssh-dss'' or ``ssh-rsa''.
    
         Note that lines in this file  are  usually  several  hundred
         bytes  long  (because  of  the size of the RSA key modulus).
         You  don't  want  to  type  them  in;  instead,   copy   the
         identity.pub, id_dsa.pub or the id_rsa.pub file and edit it.
    
         The options (if present) consist of  comma-separated  option
         specifications.  No spaces are permitted, except within dou-
         ble quotes.  The following option  specifications  are  sup-
         ported:
    
         from="pattern-list"
              Specifies that in addition to RSA  authentication,  the
              canonical  name  of  the remote host must be present in
              the comma-separated  list  of  patterns  (`*'  and  `?'
              serve  as  wildcards).   The list may also contain pat-
              terns negated by prefixing  them  with  `!'  ;  if  the
              canonical  host name matches a negated pattern, the key
              is not accepted.  The purpose  of  this  option  is  to
              optionally  increase  security:  RSA  authentication by
              itself does not trust the network or  name  servers  or
              anything  (but  the  key); however, if somebody somehow
              steals the key, the key permits an intruder to  log  in
              from  anywhere  in  the  world.  This additional option
              makes using a stolen key more difficult  (name  servers
              and/or routers would have to be compromised in addition
              to just the key).
    
         command="command"
              Specifies that the command is  executed  whenever  this
              key  is  used for authentication.  The command supplied
              by the user (if any) is ignored.  The command is run on
              a pty if the connection requests a pty; otherwise it is
              run without a tty.  Note that if you want a 8-bit clean
              channel,  you  must not request a pty or should specify
              no-pty .  A quote may be included  in  the  command  by
              quoting it with a backslash.  This option might be use-
              ful to restrict certain RSA  keys  to  perform  just  a
              specific  operation.   An  example  might be a key that
              permits remote backups but nothing else.  Note that the
              client  may specify TCP/IP and/or X11 forwarding unless
              they are explicitly prohibited.
    
         environment="NAME=value"
              Specifies that  the  string  is  to  be  added  to  the
              environment  when  logging in using this key.  Environ-
              ment variables set  this  way  override  other  default
              environment  values.  Multiple options of this type are
              permitted.
    
         no-port-forwarding
              Forbids TCP/IP forwarding when this  key  is  used  for
              authentication.   Any  port  forward  requests  by  the
              client will return an error.  This might be used, e.g.,
              in connection with the command option.
    
         no-X11-forwarding
              Forbids X11  forwarding  when  this  key  is  used  for
              authentication.  Any X11 forward requests by the client
              will return an error.
    
         no-agent-forwarding
              Forbids authentication agent forwarding when  this  key
              is used for authentication.
    
         no-pty
              Prevents tty allocation (a request to  allocate  a  pty
              will fail).
    
         permitopen="host:port"
              Limit local ``ssh -L'' port forwarding such that it may
              only  connect  to the specified host and port. Multiple
              permitopen options may be applied separated by  commas.
              No pattern matching is performed on the specified host-
              names, they must be literal domains or addresses.
    
      Examples
         1024 33 12121...312314325 ylo@foo.bar
    
         from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23...2334
         ylo@niksula
    
         command="dump   /home",no-pty,no-port-forwarding   1024   33
         23...2323 backup.hut.fi
    
         permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024  33
         23...2323
    
    SSH_KNOWN_HOSTS FILE FORMAT
         The                  /usr/local/sparcv9/etc/ssh_known_hosts,
         /usr/local/sparcv9/etc/ssh_known_hosts2,
         $HOME/.ssh/known_hosts,  and  $HOME/.ssh/known_hosts2  files
         contain  host  public  keys for all known hosts.  The global
         file should be prepared by the administrator (optional), and
         the  per-user file is maintained automatically: whenever the
         user connects from an unknown host its key is added  to  the
         per-user file.
    
         Each line in these  files  contains  the  following  fields:
         hostnames, bits, exponent, modulus, comment.  The fields are
         separated by spaces.
    
         Hostnames is a comma-separated list of patterns ('*' and '?'
         act  as  wildcards); each pattern in turn is matched against
         the canonical host name (when authenticating  a  client)  or
         against   the  user-supplied  name  (when  authenticating  a
         server).  A pattern may also be preceded by `!'  to indicate
         negation:  if the host name matches a negated pattern, it is
         not accepted (by that line) even if it matched another  pat-
         tern on the line.
    
         Bits, exponent, and modulus are taken directly from the  RSA
         host    key;    they    can    be   obtained,   e.g.,   from
         /usr/local/sparcv9/etc/ssh_host_key.pub.  The optional  com-
         ment  field  continues  to  the  end of the line, and is not
         used.
    
         Lines starting with `#' and empty lines are ignored as  com-
         ments.
    
         When  performing  host  authentication,  authentication   is
         accepted  if  any  matching  line has the proper key.  It is
         thus permissible (but not recommended) to have several lines
         or  different host keys for the same names.  This will inev-
         itably happen when short forms of host names from  different
         domains  are put in the file.  It is possible that the files
         contain conflicting information; authentication is  accepted
         if valid information can be found from either file.
    
         Note that the lines in these files are typically hundreds of
         characters  long,  and  you definitely don't want to type in
         the host keys by hand.  Rather, generate them by a script or
         by taking /usr/local/sparcv9/etc/ssh_host_key.pub and adding
         the host names at the front.
    
      Examples
         Bd -literal  closenet,...,130.233.208.41  1024  37  159...93
         closenet.hut.fi     cvs.openbsd.org,199.185.137.3    ssh-rsa
         AAAA1234.....= Ed
    
    FILES
         /usr/local/sparcv9/etc/sshd_config
              Contains configuration data for sshd.  This file should
              be writable by root only, but it is recommended (though
              not necessary) that it be world-readable.
    
    /usr/local/sparcv9/etc/ssh_host_dsa_key,
    /usr/local/sparcv9/etc/ssh_host_rsa_key
         /usr/local/sparcv9/etc/ssh_host_key,
              These three files contain the private parts of the host
              keys.   These files should only be owned by root, read-
              able only by root, and not accessible to others.   Note
              that  sshd  does not start if this file is group/world-
              accessible.
    
    /usr/local/sparcv9/etc/ssh_host_dsa_key.pub,
    /usr/local/sparcv9/etc/ssh_host_rsa_key.pub
         /usr/local/sparcv9/etc/ssh_host_key.pub,
              These three files contain the public parts of the  host
              keys.    These   files  should  be  world-readable  but
              writable only by root.  Their contents should match the
              respective  private  parts.  These files are not really
              used for anything; they are provided for  the  conveni-
              ence  of  the  user  so their contents can be copied to
              known hosts files.  These files are created using  ssh-
              keygen(1).
    
         /usr/local/sparcv9/etc/primes
              Contains Diffie-Hellman groups used  for  the  "Diffie-
              Hellman Group Exchange".
    
         /var/run/sshd.pid
              Contains the process ID of the sshd listening for  con-
              nections  (if  there  are  several daemons running con-
              currently for different ports, this contains the pid of
              the one started last).  The content of this file is not
              sensitive; it can be world-readable.
    
         $HOME/.ssh/authorized_keys
              Lists the RSA keys that can be used  to  log  into  the
              user's  account.   This  file  must be readable by root
              (which may on  some  machines  imply  it  being  world-
              readable if the user's home directory resides on an NFS
              volume).  It is recommended that it not  be  accessible
              by others.  The format of this file is described above.
              Users will place the  contents  of  their  identity.pub
              files into this file, as described in ssh-keygen(1).
    
         $HOME/.ssh/authorized_keys2
              Lists the public keys (RSA or DSA) that can be used  to
              log  into  the user's account.  This file must be read-
              able by root (which may on some machines imply it being
              world-readable  if the user's home directory resides on
              an NFS volume).  It  is  recommended  that  it  not  be
              accessible  by  others.   The  format  of  this file is
              described above.  Users  will  place  the  contents  of
              their  id_dsa.pub  and/or  id_rsa.pub  files  into this
              file, as described in ssh-keygen(1).
    
         /usr/local/sparcv9/etc/ssh_known_hosts and $HOME/.ssh/known_hosts
              These  files  are  consulted when using rhosts with RSA
              host authentication to check  the  public  key  of  the
              host.   The key must be listed in one of these files to
              be accepted.  The client uses the same files to  verify
              that  it  is  connecting  to  the  correct remote host.
              These files should be writable only by root/the  owner.
              /usr/local/sparcv9/etc/ssh_known_hosts     should    be
              world-readable, and $HOME/.ssh/known_hosts can but need
              not be world-readable.
    
    $HOME/.ssh/known_hosts2
         /usr/local/sparcv9/etc/ssh_known_hosts2                       and
              These files are consulted when using protocol version 2
              hostbased authentication to check the public key of the
              host.   The key must be listed in one of these files to
              be accepted.  The client uses the same files to  verify
              that  it  is  connecting  to  the  correct remote host.
              These files should be writable only by root/the  owner.
              /usr/local/sparcv9/etc/ssh_known_hosts2    should    be
              world-readable,  and  $HOME/.ssh/known_hosts2  can  but
              need not be world-readable.
    
         /etc/nologin
              If this file exists, sshd refuses to let anyone  except
              root log in.  The contents of the file are displayed to
              anyone trying to log in, and non-root  connections  are
              refused.  The file should be world-readable.
    
         /etc/hosts.allow, /etc/hosts.deny
              If compiled with LIBWRAP support,  tcp-wrappers  access
              controls   may   be   defined   here  as  described  in
              hosts_access(5).
    
         $HOME/.rhosts
              This file contains host-username pairs, separated by  a
              space, one per line.  The given user on the correspond-
              ing host is permitted to log in without password.   The
              same  file  is used by rlogind and rshd.  The file must
              be writable only by the user; it is recommended that it
              not be accessible by others.
    
              If is also possible  to  use  netgroups  in  the  file.
              Either host or user name may be of the form +@groupname
              to specify all hosts or all users in the group.
    
         $HOME/.shosts
              For ssh, this file is exactly the same as for  .rhosts.
              However,  this  file is not used by rlogin and rshd, so
              using this permits access using SSH only.
    
         /etc/hosts.equiv
              This file is used during  .rhosts  authentication.   In
              the  simplest  form, this file contains host names, one
              per line.  Users on those hosts are permitted to log in
              without  a  password,  provided they have the same user
              name on both machines.  The host name may also be  fol-
              lowed  by  a user name; such users are permitted to log
              in as any user on this machine  (except  root).   Addi-
              tionally, the syntax ``+@group'' can be used to specify
              netgroups.  Negated entries start with `-'.
    
              If the client host/user is successfully matched in this
              file,  login  is  automatically  permitted provided the
              client  and   server   user   names   are   the   same.
              Additionally,  successful  RSA  host  authentication is
              normally required.  This file must be writable only  by
              root; it is recommended that it be world-readable.
    
              Warning: It is almost never a good  idea  to  use  user
              names in hosts.equiv.  Beware that it really means that
              the named user(s) can log in as anybody, which includes
              bin,  daemon, adm, and other accounts that own critical
              binaries and directories.  Using a  user  name  practi-
              cally  grants the user root access.  The only valid use
              for user names that I  can  think  of  is  in  negative
              entries.
    
              Note that this warning also applies to rsh/rlogin.
    
         /usr/local/sparcv9/etc/shosts.equiv
              This is processed exactly  as  /etc/hosts.equiv.   How-
              ever, this file may be useful in environments that want
              to run both rsh/rlogin and ssh.
    
         $HOME/.ssh/environment
              This file is read into the environment at login (if  it
              exists).   It  can  only  contain  empty lines, comment
              lines (that start with `#' ) , and assignment lines  of
              the  form name=value.  The file should be writable only
              by the user; it need not be readable by anyone else.
    
         $HOME/.ssh/rc
              If this file exists, it is run with /bin/sh after read-
              ing  the  environment  files  but  before  starting the
              user's shell or command.  If X11 spoofing  is  in  use,
              this  will  receive the "proto cookie" pair in standard
              input (and DISPLAY in  environment).   This  must  call
              xauth(1) in that case.
    
              The primary purpose of this file is to run any initial-
              ization  routines which may be needed before the user's
              home directory becomes accessible; AFS is a  particular
              example of such an environment.
    
              This file will  probably  contain  some  initialization
              code  followed  by  something  similar to:  Bd -literal
                   if read  proto  cookie;  then            echo  add
              $DISPLAY $proto $cookie | xauth -q -      fi Ed
    
              If      this      file      does       not       exist,
              /usr/local/sparcv9/etc/sshrc  is  run, and if that does
              not exist either, xauth is used to store the cookie.
    
              This file should be writable only by the user, and need
              not be readable by anyone else.
    
         /usr/local/sparcv9/etc/sshrc
              Like  $HOME/.ssh/rc.   This  can  be  used  to  specify
              machine-specific  login-time  initializations globally.
              This file should be writable only by root,  and  should
              be world-readable.
    
    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 created OpenSSH.
         Markus Friedl contributed the support for SSH protocol  ver-
         sions 1.5 and 2.0.
    
    SEE ALSO
         scp(1), sftp(1), sftp-server(8),  ssh(1),  ssh-add(1),  ssh-
         agent(1),  ssh-keygen(1),  rlogin(1), rsh(1) Rs %A T. Ylonen
         %A T. Kivinen %A M. Saarinen %A T. Rinne %A S.  Lehtinen  %T
         "SSH    Protocol    Architecture"    %N    draft-ietf-secsh-
         architecture-07.txt %D January  2001  %O  work  in  progress
         material Re Rs %A M. Friedl %A N. Provos %A W. A. Simpson %T
         "Diffie-Hellman Group Exchange for the SSH  Transport  Layer
         Protocol"  %N  draft-ietf-secsh-dh-group-exchange-00.txt  %D
         January 2001 %O work in progress material Re
    
    
    
    


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