.\" -*- 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".
+.\"
+.\" 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.
.\"
-.\" $Id$
+.\" 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 1.73 2000/11/22 15:38:30 provos Exp $
.Dd September 25, 1999
.Dt SSHD 8
.Os
.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
.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.
(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
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
Nothing is sent to the system log.
Normally the beginning,
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
Do not print an error message if RSA support is missing.
.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
.Ql ?
can be used as
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.
.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
by spaces.
.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 Ciphers
.Ql ?
can be used as
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.
.Pp
.It Cm DenyUsers
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.
.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.
+if this file 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
.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
The default is INFO.
Logging with level DEBUG violates the privacy of users
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
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.
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.
+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
is used for interactive login sessions.
Note that
.Xr login 1
-is not never for remote command execution.
+is never used for remote command execution.
The default is
.Dq no .
.It Cm X11DisplayOffset
.Pa identity.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:
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,
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
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
.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.
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
+.El
+.Sh AUTHORS
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.
This version of OpenSSH
.Bl -bullet
.It
-has all components of a restrictive nature (i.e., patents)
+has all components of a restrictive nature (i.e., patents, see
+.Xr crypto 3 )
directly removed from the source code; any licensed or patented components
are chosen from
external libraries.
The support for SSH protocol 2 was written by Markus Friedl.
.Sh SEE ALSO
.Xr scp 1 ,
+.Xr sftp-server 8 ,
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1 ,
+.Xr crypto 3 ,
.Xr rlogin 1 ,
.Xr rsh 1
andersk / openssh.git / blobdiff