===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/ssh/sshd.8,v
retrieving revision 1.51
retrieving revision 1.51.2.4
diff -u -r1.51 -r1.51.2.4
--- src/usr.bin/ssh/sshd.8	2000/05/08 17:42:31	1.51
+++ src/usr.bin/ssh/sshd.8	2001/03/12 15:44:17	1.51.2.4
@@ -1,31 +1,56 @@
 .\"  -*- nroff -*-
 .\"
-.\" sshd.8.in
-.\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
-.\"
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 .\"                    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: sshd.8,v 1.51 2000/05/08 17:42:31 hugh Exp $
+.\" 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: sshd.8,v 1.51.2.4 2001/03/12 15:44:17 jason Exp $
 .Dd September 25, 1999
 .Dt SSHD 8
 .Os
 .Sh NAME
 .Nm sshd
-.Nd secure shell daemon
+.Nd OpenSSH secure shell daemon
 .Sh SYNOPSIS
 .Nm sshd
-.Op Fl diqQ46
+.Op Fl diqD46
 .Op Fl b Ar bits
 .Op Fl f Ar config_file
 .Op Fl g Ar login_grace_time
 .Op Fl h Ar host_key_file
 .Op Fl k Ar key_gen_time
 .Op Fl p Ar port
+.Op Fl u Ar len
 .Op Fl V Ar client_protocol_id
 .Sh DESCRIPTION
 .Nm
@@ -104,7 +129,7 @@
 .Pp
 .Ss SSH protocol version 2
 .Pp
-Version 2 works similar:
+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.
@@ -119,7 +144,7 @@
 (hmac-sha1 or hmac-md5).
 .Pp
 Protocol version 2 provides a public key based
-user authentication method (DSAAuthentication)
+user authentication method (PubkeyAuthentication)
 and conventional password authentication.
 .Pp
 .Ss Command execution and data forwarding
@@ -162,6 +187,8 @@
 log, and does not put itself in the background.
 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 increases the debugging level.
+Maximum is 3.
 .It Fl f Ar configuration_file
 Specifies the name of the configuration file.
 The default is
@@ -170,17 +197,19 @@
 refuses to start if there is no configuration file.
 .It Fl g Ar login_grace_time
 Gives the grace time for clients to authenticate themselves (default
-300 seconds).
+600 seconds).
 If the client fails to authenticate the user within
 this many seconds, the server disconnects and exits.
 A value of zero indicates no limit.
 .It Fl h Ar host_key_file
-Specifies the file from which the RSA host key is read (default
+Specifies the file from which the host key is read (default
 .Pa /etc/ssh_host_key ) .
 This option must be given if
 .Nm
 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.
 .It Fl i
 Specifies that
 .Nm
@@ -211,15 +240,36 @@
 Nothing is sent to the system log.
 Normally the beginning,
 authentication, and termination of each connection is logged.
-.It Fl Q
-Do not print an error message if RSA support is missing.
+.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 D
+When this option is specified
+.Nm
+will not detach and does not become a daemon.
+This allows easy monitoring of
+.Nm sshd .
 .It Fl V Ar client_protocol_id
-SSH2 compatibility mode.
+SSH-2 compatibility mode.
 When this option is specified
 .Nm
 assumes the client has sent the supplied version string
 and skips the
 Protocol Version Identification Exchange.
+This option is not intended to be called directly.
 .It Fl 4
 Forces
 .Nm
@@ -248,20 +298,28 @@
 Default is
 .Dq yes .
 .It Cm AllowGroups
-This keyword can be followed by a number of group names, separated
+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 matches one of the patterns.
+group or supplementary group list matches one of the patterns.
 .Ql \&*
 and
 .Ql ?
 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 primary group.
+Only group names are valid; a numerical group ID isn't recognized.
+By default login is allowed regardless of the group list.
 .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
-This keyword can be followed by a number of user names, separated
+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.
@@ -270,14 +328,21 @@
 .Ql ?
 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.
 .Pp
+.It Cm Banner
+In some jurisdictions, sending a warning message before authentication
+may be relevant for getting legal protection.
+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.
+.Pp
 .It Cm Ciphers
 Specifies the ciphers allowed for protocol version 2.
 Multiple ciphers must be comma-separated.
 The default is
-.Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
+.Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc .
 .It Cm CheckMail
 Specifies whether
 .Nm
@@ -287,15 +352,15 @@
 .It Cm DenyGroups
 This keyword can be followed by a number of group names, separated
 by spaces.
-Users whose primary group matches one of the patterns
-aren't allowed to log in.
+Users whose primary group or supplementary group list matches
+one of the patterns aren't allowed to log in.
 .Ql \&*
 and
 .Ql ?
 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 primary group.
+Only group names are valid; a numerical group ID isn't recognized.
+By default login is allowed regardless of the group list.
 .Pp
 .It Cm DenyUsers
 This keyword can be followed by a number of user names, separated
@@ -305,10 +370,10 @@
 and
 .Ql ?
 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.
-.It Cm DSAAuthentication
-Specifies whether DSA authentication is allowed.
+.It Cm PubkeyAuthentication
+Specifies whether public key authentication is allowed.
 The default is
 .Dq yes .
 Note that this option applies to protocol version 2 only.
@@ -321,20 +386,20 @@
 .Dq no .
 The default is
 .Dq no .
-.It Cm HostDsaKey
-Specifies the file containing the private DSA host key (default
-.Pa /etc/ssh_host_dsa_key )
-used by SSH protocol 2.0.
-Note that
-.Nm
-disables protocol 2.0 if this file is group/world-accessible.
 .It Cm HostKey
-Specifies the file containing the private RSA host key (default
+Specifies the file containing the private host keys (default
 .Pa /etc/ssh_host_key )
-used by SSH protocols 1.3 and 1.5.
+used by SSH protocol versions 1 and 2.
 Note that
 .Nm
-disables protocols 1.3 and 1.5 if this file is group/world-accessible.
+will refuse to use a file if it is group/world-accessible.
+It is possible to have multiple host key files.
+.Dq rsa1
+keys are used for version 1 and
+.Dq dsa
+or
+.Dq rsa
+are used for version 2 of the SSH protocol.
 .It Cm IgnoreRhosts
 Specifies that
 .Pa .rhosts
@@ -384,14 +449,15 @@
 .Cm 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
 .Dq yes .
 .It Cm KerberosOrLocalPasswd
 If set then if password authentication through Kerberos fails then
 the password will be validated via any additional local mechanism
 such as
-.Pa /etc/passwd
-or SecurID.
+.Pa /etc/passwd .
 Default is
 .Dq yes .
 .It Cm KerberosTgtPassing
@@ -435,11 +501,47 @@
 The default is INFO.
 Logging with level DEBUG violates the privacy of users
 and is not recommended.
+.It Cm MACs
+Specifies the available MAC (message 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
+.Pp
+.Bd -literal
+  ``hmac-sha1,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com,
+    hmac-sha1-96,hmac-md5-96''
+.Ed
+.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 probability of
+.Dq rate/100
+(30%)
+if there are currently
+.Dq start
+(10)
+unauthenticated connections.
+The probability increases linearly and all connection attempts
+are refused if the number of unauthenticated connections reaches
+.Dq full
+(60).
 .It Cm PasswordAuthentication
 Specifies whether password authentication is allowed.
 The default is
 .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
 When password authentication is allowed, it specifies whether the
 server allows login to accounts with empty password strings.
@@ -450,21 +552,26 @@
 .Xr ssh 1 .
 The argument must be
 .Dq yes ,
-.Dq without-password
+.Dq without-password ,
+.Dq forced-commands-only
 or
 .Dq no .
 The default is
 .Dq yes .
-If this options is set to
+.Pp
+If this option is set to
 .Dq without-password
-only password authentication is disabled for root.
+password authentication is disabled for root.
 .Pp
-Root login with RSA authentication when the
+If this option is set to
+.Dq forced-commands-only
+root login with public key authentication will be allowed,
+but only if the
 .Ar command
-option has been
-specified will be allowed regardless of the value of this setting
+option has been specified
 (which may be useful for taking remote backups even if root login is
-normally not allowed).
+normally not allowed). All other authentication methods are disabled
+for root.
 .It Cm PidFile
 Specifies the file that contains the process identifier of the
 .Nm
@@ -502,6 +609,14 @@
 .It Cm RandomSeed
 Obsolete.
 Random number generation uses other techniques.
+.It Cm ReverseMappingCheck
+Specifies whether
+.Nm
+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
+.Dq no .
 .It Cm RhostsAuthentication
 Specifies whether authentication using rhosts or /etc/hosts.equiv
 files is sufficient.
@@ -525,15 +640,15 @@
 .It Cm ServerKeyBits
 Defines the number of bits in the server key.
 The minimum value is 512, and the default is 768.
-.It Cm SkeyAuthentication
+.It Cm ChallengeResponseAuthentication
 Specifies whether
-.Xr skey 1
+challenge reponse
 authentication is allowed.
+Currently there is only support for
+.Xr skey 1
+authentication.
 The default is
 .Dq yes .
-Note that s/key authentication is enabled only if
-.Cm PasswordAuthentication
-is allowed, too.
 .It Cm StrictModes
 Specifies whether
 .Nm
@@ -543,6 +658,17 @@
 directory or files world-writable.
 The default is
 .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
 Gives the facility code that is used when logging messages from
 .Nm sshd .
@@ -552,7 +678,10 @@
 .It Cm UseLogin
 Specifies whether
 .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
 .Dq no .
 .It Cm X11DisplayOffset
@@ -569,6 +698,12 @@
 .Dq no .
 Note that disabling X11 forwarding does not improve security in any
 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
 .Sh LOGIN PROCESS
 When a user successfully logs in,
@@ -622,29 +757,40 @@
 permitted for RSA authentication in SSH protocols 1.3 and 1.5
 Similarly, the
 .Pa $HOME/.ssh/authorized_keys2
-file lists the DSA keys that are
-permitted for DSA authentication in SSH protocol 2.0.
+file lists the DSA and RSA keys that are
+permitted for public key authentication (PubkeyAuthentication)
+in SSH protocol 2.0.
+.Pp
 Each line of the file contains one
 key (empty lines and lines starting with a
 .Ql #
 are ignored as
 comments).
-Each line consists of the following fields, separated by
+Each RSA public key consists of the following fields, separated by
 spaces: options, bits, exponent, modulus, comment.
-The options field
-is optional; its presence is determined by whether the line starts
+Each protocol version 2 public key consists of:
+options, keytype, 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; the
+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
+.Dq ssh-dss
+or
+.Dq ssh-rsa .
 .Pp
 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
 .Pa identity.pub
+or the
+.Pa id_dsa.pub
 file and edit it.
 .Pp
-The options (if present) consists of comma-separated option
+The options (if present) consist of comma-separated option
 specifications.
 No spaces are permitted, except within double quotes.
 The following option specifications are supported:
@@ -675,6 +821,9 @@
 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
+.Cm no-pty .
 A quote may be included in the command by quoting it with a backslash.
 This option might be useful
 to restrict certain RSA keys to perform just a specific operation.
@@ -718,7 +867,7 @@
 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 an unknown host
+maintained automatically: whenever the user connects from an unknown host
 its key is added to the per-user file.
 .Pp
 Each line in these files contains the following fields: hostnames,
@@ -787,13 +936,15 @@
 the user so its contents can be copied to known hosts files.
 These two files are created using
 .Xr ssh-keygen 1 .
+.It Pa /etc/primes
+Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
 .It Pa /var/run/sshd.pid
 Contains the process ID of the
 .Nm
 listening for connections (if there are several daemons running
 concurrently for different ports, this contains the pid of the one
 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
 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
@@ -821,7 +972,7 @@
 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 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.
 .Pa /etc/ssh_known_hosts
 should be world-readable, and
@@ -860,7 +1011,7 @@
 .Pa .rhosts .
 However, this file is
 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
 .Pa .rhosts
 authentication.
@@ -940,48 +1091,23 @@
 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.
-.Sh AUTHOR
-OpenSSH
-is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
-but with bugs removed and newer features re-added.
-Rapidly after the
-1.2.12 release, newer versions of the original ssh bore successively
-more restrictive licenses, and thus demand for a free version was born.
-.Pp
-This version of OpenSSH
-.Bl -bullet
-.It
-has all components of a restrictive nature (i.e., patents, see
-.Xr ssl 8 )
-directly removed from the source code; any licensed or patented components
-are chosen from
-external libraries.
-.It
-has been updated to support SSH protocol 1.5 and 2, making it compatible with
-all other SSH clients and servers.
-.It
-contains added support for
-.Xr kerberos 8
-authentication and ticket passing.
-.It
-supports one-time password authentication with
-.Xr skey 1 .
 .El
-.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,
-Niels Provos, Theo de Raadt, and Dug Song.
-.Pp
-The support for SSH protocol 2 was written by Markus Friedl.
+.Sh 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 versions 1.5 and 2.0.
 .Sh SEE ALSO
 .Xr scp 1 ,
+.Xr sftp 1 ,
+.Xr sftp-server 8 ,
 .Xr ssh 1 ,
 .Xr ssh-add 1 ,
 .Xr ssh-agent 1 ,
 .Xr ssh-keygen 1 ,
-.Xr ssl 8 ,
 .Xr rlogin 1 ,
 .Xr rsh 1