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Diff for /src/usr.bin/ssh/sshd.8 between version 1.51 and 1.51.2.3

version 1.51, 2000/05/08 17:42:31 version 1.51.2.3, 2000/11/08 21:31:31
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 .\"  -*- nroff -*-  .\"  -*- nroff -*-
 .\"  .\"
 .\" sshd.8.in  
 .\"  
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>  .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\"  
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland  .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 .\"                    All rights reserved  .\"                    All rights reserved
 .\"  .\"
 .\" Created: Sat Apr 22 21:55:14 1995 ylo  .\" As far as I am concerned, the code I have written for this software
   .\" can be used freely for any purpose.  Any derived versions of this
   .\" software must be clearly marked as such, and if the derived work is
   .\" incompatible with the protocol description in the RFC file, it must be
   .\" called by a name other than "ssh" or "Secure Shell".
 .\"  .\"
 .\" $Id$  .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
   .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
   .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
 .\"  .\"
   .\" Redistribution and use in source and binary forms, with or without
   .\" modification, are permitted provided that the following conditions
   .\" are met:
   .\" 1. Redistributions of source code must retain the above copyright
   .\"    notice, this list of conditions and the following disclaimer.
   .\" 2. Redistributions in binary form must reproduce the above copyright
   .\"    notice, this list of conditions and the following disclaimer in the
   .\"    documentation and/or other materials provided with the distribution.
   .\"
   .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   .\"
   .\" $OpenBSD$
 .Dd September 25, 1999  .Dd September 25, 1999
 .Dt SSHD 8  .Dt SSHD 8
 .Os  .Os
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 .Op Fl h Ar host_key_file  .Op Fl h Ar host_key_file
 .Op Fl k Ar key_gen_time  .Op Fl k Ar key_gen_time
 .Op Fl p Ar port  .Op Fl p Ar port
   .Op Fl u Ar len
 .Op Fl V Ar client_protocol_id  .Op Fl V Ar client_protocol_id
 .Sh DESCRIPTION  .Sh DESCRIPTION
 .Nm  .Nm
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 .Pp  .Pp
 .Ss SSH protocol version 2  .Ss SSH protocol version 2
 .Pp  .Pp
 Version 2 works similar:  Version 2 works similarly:
 Each host has a host-specific DSA key used to identify the host.  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.  However, when the daemon starts, it does not generate a server key.
 Forward security is provided through a Diffie-Hellman key agreement.  Forward security is provided through a Diffie-Hellman key agreement.
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 log, and does not put itself in the background.  log, and does not put itself in the background.
 The server also will not fork and will only process one connection.  The server also will not fork and will only process one connection.
 This option is only intended for debugging for the server.  This option is only intended for debugging for the server.
   Multiple -d options increases the debugging level.
   Maximum is 3.
 .It Fl f Ar configuration_file  .It Fl f Ar configuration_file
 Specifies the name of the configuration file.  Specifies the name of the configuration file.
 The default is  The default is
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 Nothing is sent to the system log.  Nothing is sent to the system log.
 Normally the beginning,  Normally the beginning,
 authentication, and termination of each connection is logged.  authentication, and termination of each connection is logged.
   .It Fl u Ar len
   This option is used to specify the size of the field
   in the
   .Li utmp
   structure that holds the remote host name.
   If the resolved host name is longer than
   .Ar 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
   .Fl u0
   indicates that only dotted decimal addresses
   should be put into the
   .Pa utmp
   file.
 .It Fl Q  .It Fl Q
 Do not print an error message if RSA support is missing.  Do not print an error message if RSA support is missing.
 .It Fl V Ar client_protocol_id  .It Fl V Ar client_protocol_id
 SSH2 compatibility mode.  SSH-2 compatibility mode.
 When this option is specified  When this option is specified
 .Nm  .Nm
 assumes the client has sent the supplied version string  assumes the client has sent the supplied version string
 and skips the  and skips the
 Protocol Version Identification Exchange.  Protocol Version Identification Exchange.
   This option is not intended to be called directly.
 .It Fl 4  .It Fl 4
 Forces  Forces
 .Nm  .Nm
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 .Ql ?  .Ql ?
 can be used as  can be used as
 wildcards in the patterns.  wildcards in the patterns.
 Only group names are valid, a numerical group ID isn't recognized.  Only group names are valid; a numerical group ID isn't recognized.
 By default login is allowed regardless of the primary group.  By default login is allowed regardless of the primary group.
 .Pp  .Pp
   .It Cm AllowTcpForwarding
   Specifies whether TCP forwarding is permitted.
   The default is
   .Dq yes .
   Note that disabling TCP forwarding does not improve security unless
   users are also denied shell access, as they can always install their
   own forwarders.
   .Pp
 .It Cm AllowUsers  .It Cm AllowUsers
 This keyword can be followed by a number of user names, separated  This keyword can be followed by a number of user names, separated
 by spaces.  by spaces.
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 .Ql ?  .Ql ?
 can be used as  can be used as
 wildcards in the patterns.  wildcards in the patterns.
 Only user names are valid, a numerical user ID isn't recognized.  Only user names are valid; a numerical user ID isn't recognized.
 By default login is allowed regardless of the user name.  By default login is allowed regardless of the user name.
 .Pp  .Pp
 .It Cm Ciphers  .It Cm Ciphers
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 .Ql ?  .Ql ?
 can be used as  can be used as
 wildcards in the patterns.  wildcards in the patterns.
 Only group names are valid, a numerical group ID isn't recognized.  Only group names are valid; a numerical group ID isn't recognized.
 By default login is allowed regardless of the primary group.  By default login is allowed regardless of the primary group.
 .Pp  .Pp
 .It Cm DenyUsers  .It Cm DenyUsers
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 and  and
 .Ql ?  .Ql ?
 can be used as wildcards in the patterns.  can be used as wildcards in the patterns.
 Only user names are valid, a numerical user ID isn't recognized.  Only user names are valid; a numerical user ID isn't recognized.
 By default login is allowed regardless of the user name.  By default login is allowed regardless of the user name.
 .It Cm DSAAuthentication  .It Cm DSAAuthentication
 Specifies whether DSA authentication is allowed.  Specifies whether DSA authentication is allowed.
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 .Dq no .  .Dq no .
 The default is  The default is
 .Dq no .  .Dq no .
 .It Cm HostDsaKey  .It Cm HostDSAKey
 Specifies the file containing the private DSA host key (default  Specifies the file containing the private DSA host key (default
 .Pa /etc/ssh_host_dsa_key )  .Pa /etc/ssh_host_dsa_key )
 used by SSH protocol 2.0.  used by SSH protocol 2.0.
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 .Cm PasswordAuthentication  .Cm PasswordAuthentication
 is yes, the password provided by the user will be validated through  is yes, the password provided by the user will be validated through
 the Kerberos KDC.  the Kerberos KDC.
   To use this option, the server needs a
   Kerberos servtab which allows the verification of the KDC's identity.
 Default is  Default is
 .Dq yes .  .Dq yes .
 .It Cm KerberosOrLocalPasswd  .It Cm KerberosOrLocalPasswd
 If set then if password authentication through Kerberos fails then  If set then if password authentication through Kerberos fails then
 the password will be validated via any additional local mechanism  the password will be validated via any additional local mechanism
 such as  such as
 .Pa /etc/passwd  .Pa /etc/passwd .
 or SecurID.  
 Default is  Default is
 .Dq yes .  .Dq yes .
 .It Cm KerberosTgtPassing  .It Cm KerberosTgtPassing
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 The default is INFO.  The default is INFO.
 Logging with level DEBUG violates the privacy of users  Logging with level DEBUG violates the privacy of users
 and is not recommended.  and is not recommended.
   .It Cm MaxStartups
   Specifies the maximum number of concurrent unauthenticated connections to the
   .Nm
   daemon.
   Additional connections will be dropped until authentication succeeds or the
   .Cm LoginGraceTime
   expires for a connection.
   The default is 10.
   .Pp
   Alternatively, random early drop can be enabled by specifying
   the three colon separated values
   .Dq start:rate:full
   (e.g., "10:30:60").
   .Nm
   will refuse connection attempts with a probabillity of
   .Dq rate/100
   (30%)
   if there are currently
   .Dq start
   (10)
   unauthenticated connections.
   The probabillity increases linearly and all connection attempts
   are refused if the number of unauthenticated connections reaches
   .Dq full
   (60).
 .It Cm PasswordAuthentication  .It Cm PasswordAuthentication
 Specifies whether password authentication is allowed.  Specifies whether password authentication is allowed.
 The default is  The default is
 .Dq yes .  .Dq yes .
 Note that this option applies to both protocol version 1 and 2.  Note that this option applies to both protocol versions 1 and 2.
 .It Cm PermitEmptyPasswords  .It Cm PermitEmptyPasswords
 When password authentication is allowed, it specifies whether the  When password authentication is allowed, it specifies whether the
 server allows login to accounts with empty password strings.  server allows login to accounts with empty password strings.
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 directory or files world-writable.  directory or files world-writable.
 The default is  The default is
 .Dq yes .  .Dq yes .
   .It Cm 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
   .Xr sftp-server 8
   implements the
   .Dq sftp
   file transfer subsystem.
   By default no subsystems are defined.
   Note that this option applies to protocol version 2 only.
 .It Cm SyslogFacility  .It Cm SyslogFacility
 Gives the facility code that is used when logging messages from  Gives the facility code that is used when logging messages from
 .Nm sshd .  .Nm sshd .
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 .It Cm UseLogin  .It Cm UseLogin
 Specifies whether  Specifies whether
 .Xr login 1  .Xr login 1
 is used.  is used for interactive login sessions.
   Note that
   .Xr login 1
   is never used for remote command execution.
 The default is  The default is
 .Dq no .  .Dq no .
 .It Cm X11DisplayOffset  .It Cm X11DisplayOffset
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 .Dq no .  .Dq no .
 Note that disabling X11 forwarding does not improve security in any  Note that disabling X11 forwarding does not improve security in any
 way, as users can always install their own forwarders.  way, as users can always install their own forwarders.
   .It Cm XAuthLocation
   Specifies the location of the
   .Xr xauth 1
   program.
   The default is
   .Pa /usr/X11R6/bin/xauth .
 .El  .El
 .Sh LOGIN PROCESS  .Sh LOGIN PROCESS
 When a user successfully logs in,  When a user successfully logs in,
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 .Pa identity.pub  .Pa identity.pub
 file and edit it.  file and edit it.
 .Pp  .Pp
 The options (if present) consists of comma-separated option  The options (if present) consist of comma-separated option
 specifications.  specifications.
 No spaces are permitted, except within double quotes.  No spaces are permitted, except within double quotes.
 The following option specifications are supported:  The following option specifications are supported:
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 files contain host public keys for all known hosts.  files contain host public keys for all known hosts.
 The global file should  The global file should
 be prepared by the administrator (optional), and the per-user file is  be prepared by the administrator (optional), and the per-user file is
 maintained automatically: whenever the user connects an unknown host  maintained automatically: whenever the user connects from an unknown host
 its key is added to the per-user file.  its key is added to the per-user file.
 .Pp  .Pp
 Each line in these files contains the following fields: hostnames,  Each line in these files contains the following fields: hostnames,
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 listening for connections (if there are several daemons running  listening for connections (if there are several daemons running
 concurrently for different ports, this contains the pid of the one  concurrently for different ports, this contains the pid of the one
 started last).  started last).
 The contents of this file are not sensitive; it can be world-readable.  The content of this file is not sensitive; it can be world-readable.
 .It Pa $HOME/.ssh/authorized_keys  .It Pa $HOME/.ssh/authorized_keys
 Lists the RSA keys that can be used to log into the user's account.  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  This file must be readable by root (which may on some machines imply
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 authentication to check the public key of the host.  authentication to check the public key of the host.
 The key must be listed in one of these files to be accepted.  The key must be listed in one of these files to be accepted.
 The client uses the same files  The client uses the same files
 to verify that the remote host is the one we intended to connect.  to verify that the remote host is the one it intended to connect.
 These files should be writable only by root/the owner.  These files should be writable only by root/the owner.
 .Pa /etc/ssh_known_hosts  .Pa /etc/ssh_known_hosts
 should be world-readable, and  should be world-readable, and
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 .Pa .rhosts .  .Pa .rhosts .
 However, this file is  However, this file is
 not used by rlogin and rshd, so using this permits access using SSH only.  not used by rlogin and rshd, so using this permits access using SSH only.
 .Pa /etc/hosts.equiv  .It Pa /etc/hosts.equiv
 This file is used during  This file is used during
 .Pa .rhosts  .Pa .rhosts
 authentication.  authentication.
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 This can be used to specify  This can be used to specify
 machine-specific login-time initializations globally.  machine-specific login-time initializations globally.
 This file should be writable only by root, and should be world-readable.  This file should be writable only by root, and should be world-readable.
   .El
 .Sh AUTHOR  .Sh AUTHOR
 OpenSSH  OpenSSH
 is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,  is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
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 .Xr skey 1 .  .Xr skey 1 .
 .El  .El
 .Pp  .Pp
 The libraries described in  
 .Xr ssl 8  
 are required for proper operation.  
 .Pp  
 OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,  OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
 Niels Provos, Theo de Raadt, and Dug Song.  Niels Provos, Theo de Raadt, and Dug Song.
 .Pp  .Pp
 The support for SSH protocol 2 was written by Markus Friedl.  The support for SSH protocol 2 was written by Markus Friedl.
 .Sh SEE ALSO  .Sh SEE ALSO
 .Xr scp 1 ,  .Xr scp 1 ,
   .Xr sftp-server 8 ,
 .Xr ssh 1 ,  .Xr ssh 1 ,
 .Xr ssh-add 1 ,  .Xr ssh-add 1 ,
 .Xr ssh-agent 1 ,  .Xr ssh-agent 1 ,
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