.\" -*- 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.
+.\"
+.\" 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.
.\"
-.\" $Id$
+.\" 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 1.140 2001/08/16 19:18:34 jakob Exp $
.Dd September 25, 1999
.Dt SSHD 8
.Os
.Sh NAME
.Nm sshd
-.Nd secure shell daemon
+.Nd OpenSSH SSH daemon
.Sh SYNOPSIS
.Nm sshd
-.Op Fl diqQ46
+.Op Fl deiqD46
.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
-(Secure Shell Daemon) is the daemon program for
+(SSH Daemon) is the daemon program for
.Xr ssh 1 .
Together these programs replace rlogin and rsh, and
provide secure encrypted communications between two untrusted hosts
.Pp
.Ss SSH protocol version 2
.Pp
-Version 2 works similar:
-Each host has a host-specific DSA key used to identify the host.
+Version 2 works similarly:
+Each host has a host-specific key (RSA or DSA) 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
-Blowfish, 3DES or CAST128 in CBC mode or Arcfour.
+.Pp
+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
(hmac-sha1 or hmac-md5).
.Pp
Protocol version 2 provides a public key based
-user authentication method (DSAAuthentication)
-and conventional password authentication.
+user (PubkeyAuthentication) or
+client host (HostbasedAuthentication) authentication method,
+conventional password authentication and challenge response based methods.
.Pp
.Ss Command execution and data forwarding
.Pp
.Pp
.Nm
rereads its configuration file when it receives a hangup signal,
-.Dv SIGHUP .
+.Dv SIGHUP ,
+by executing itself with the name it was started as, i.e.,
+.Pa /usr/sbin/sshd .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl b Ar bits
-Specifies the number of bits in the server key (default 768).
-.Pp
+Specifies the number of bits in the ephemeral protocol version 1
+server key (default 768).
.It Fl d
Debug mode.
The server sends verbose debug output to the system
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 increase the debugging level.
+Maximum is 3.
+.It Fl e
+When this option is specified,
+.Nm
+will send the output to the standard error instead of the system log.
.It Fl f Ar configuration_file
Specifies the name of the configuration file.
The default is
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 and host key algorithms.
.It Fl i
Specifies that
.Nm
from inetd may
be feasible.
.It Fl k Ar key_gen_time
-Specifies how often the server key is regenerated (default 3600
-seconds, or one hour).
+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
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 V Ar client_protocol_id
-SSH2 compatibility mode.
+.It Fl t
+Test mode.
+Only check the validity of the configuration file and sanity of the keys.
+This is useful for updating
+.Nm
+reliably as configuration options may change.
+.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
-assumes the client has sent the supplied version string
-and skips the
-Protocol Version Identification Exchange.
+will not detach and does not become a daemon.
+This allows easy monitoring of
+.Nm sshd .
.It Fl 4
Forces
.Nm
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.
.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.
+If the pattern takes the form USER@HOST then USER and HOST
+are separately checked, allowing you to restrict logins to particular
+users from particular hosts.
+.Pp
+.It Cm AuthorizedKeysFile
+Specifies the file that contains the public keys that can be used
+for user authentication.
+.Cm AuthorizedKeysFile
+may contain tokens of the form %T which are substituted during connection
+set-up. The following tokens are defined; %% is replaces by a literal '%',
+%h is replaced by the home directory of the user being authenticated and
+%u is replaced by the username of that user.
+After expansion,
+.Cm AuthorizedKeysFile
+is taken to be an absolute path or one relative to the user's home
+directory.
+The default is
+.Dq .ssh/authorized_keys
+.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 ChallengeResponseAuthentication
+Specifies whether challenge response authentication is allowed.
+All authentication styles from
+.Xr login.conf 5
+are supported.
+The default is
+.Dq yes .
.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 .
-.It Cm CheckMail
-Specifies whether
+.Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
+.It Cm ClientAliveInterval
+Sets a timeout interval in seconds after which if no data has been received
+from the client,
.Nm
-should check for new mail for interactive logins.
-The default is
-.Dq no .
+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.
+.It Cm ClientAliveCountMax
+Sets the number of client alive messages (see above) which may be
+sent without
+.Nm
+receiving any messages back from the client. If this threshold is
+reached while client alive messages are being sent,
+.Nm
+will disconnect the client, terminating the session. It is important
+to note that the use of client alive messages is very different from
+.Cm Keepalive
+(below). The client alive messages are sent through the
+encrypted channel and therefore will not be spoofable. The TCP keepalive
+option enabled by
+.Cm Keepalive
+is spoofable. You want to use the client
+alive mechanism when you are basing something important on
+clients having an active connection to the server.
+.Pp
+The default value is 3. If you set
+.Cm ClientAliveInterval
+(above) to 15, and leave this value at the default, unresponsive ssh clients
+will be disconnected after approximately 45 seconds.
.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
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.
-The default is
-.Dq yes .
-Note that this option applies to protocol version 2 only.
.It Cm GatewayPorts
Specifies whether remote hosts are allowed to connect to ports
forwarded for the client.
.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 HostbasedAuthentication
+Specifies whether rhosts or /etc/hosts.equiv authentication together
+with successful public key client host authentication is allowed
+(hostbased authentication).
+This option is similar to
+.Cm RhostsRSAAuthentication
+and applies to protocol version 2 only.
+The default is
+.Dq no .
.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
and
.Pa .shosts
-files will not be used in authentication.
+files will not be used in
+.Cm RhostsAuthentication ,
+.Cm RhostsRSAAuthentication
+or
+.Cm HostbasedAuthentication .
+.Pp
.Pa /etc/hosts.equiv
and
.Pa /etc/shosts.equiv
should ignore the user's
.Pa $HOME/.ssh/known_hosts
during
-.Cm RhostsRSAAuthentication .
+.Cm RhostsRSAAuthentication
+or
+.Cm HostbasedAuthentication .
The default is
.Dq no .
.It Cm KeepAlive
.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
Default is
.Dq yes .
.It Cm KeyRegenerationInterval
-The server key is automatically regenerated after this many seconds
-(if it has been used).
+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.
If the value is 0, the key is never regenerated.
The default is 3600 (seconds).
.It Cm ListenAddress
-Specifies what local address
+Specifies the local addresses
.Nm
should listen on.
-The default is to listen to all local addresses.
-Multiple options of this type are permitted.
-Additionally, the
-.Cm Ports
-options must precede this option.
+The following forms may be used:
+.Pp
+.Bl -item -offset indent -compact
+.It
+.Cm ListenAddress
+.Sm off
+.Ar host No | Ar IPv4_addr No | Ar IPv6_addr
+.Sm on
+.It
+.Cm ListenAddress
+.Sm off
+.Ar host No | Ar IPv4_addr No : Ar port
+.Sm on
+.It
+.Cm ListenAddress
+.Sm off
+.Oo
+.Ar host No | Ar IPv6_addr Oc : Ar port
+.Sm on
+.El
+.Pp
+If
+.Ar port
+is not specified,
+.Nm
+will listen on the address and all prior
+.Cm Port
+options specified. The default is to listen on all local
+addresses. Multiple
+.Cm ListenAddress
+options are permitted. Additionally, any
+.Cm Port
+options must precede this option for non port qualified addresses.
.It Cm LoginGraceTime
The server disconnects after this time if the user has not
successfully logged in.
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
+.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
.It Cm MaxStartups
Specifies the maximum number of concurrent unauthenticated connections to the
.Nm
.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 PAMAuthenticationViaKbdInt
+Specifies whether PAM challenge response authentication is allowed. This
+allows the use of most PAM challenge response authentication modules, but
+it will allow password authentication regardless of whether
+.Cm PasswordAuthentication
+is disabled.
+The default is
+.Dq no .
.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.
.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 no .
.It Cm PermitRootLogin
-Specifies whether the root can log in using
+Specifies whether root can login using
.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.
+.Pp
+If this option is set to
+.Dq no
+root is not allowed to login.
.It Cm PidFile
Specifies the file that contains the process identifier of the
.Nm
listens on.
The default is 22.
Multiple options of this type are permitted.
+See also
+.Cm ListenAddress .
+.It Cm PrintLastLog
+Specifies whether
+.Nm
+should print the date and time when the user last logged in.
+The default is
+.Dq yes .
.It Cm PrintMotd
Specifies whether
.Nm
.Dq 2 .
Multiple versions must be comma-separated.
The default is
-.Dq 1 .
-.It Cm RandomSeed
-Obsolete.
-Random number generation uses other techniques.
+.Dq 2,1 .
+.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.
+.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.
to normal rhosts or /etc/hosts.equiv authentication.
The default is
.Dq no .
+This option applies to protocol version 1 only.
.It Cm RhostsRSAAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together
with successful RSA host authentication is allowed.
The default is
.Dq no .
+This option applies to protocol version 1 only.
.It Cm RSAAuthentication
Specifies whether pure RSA authentication is allowed.
The default is
.Dq yes .
-Note that this option applies to protocol version 1 only.
+This option applies to protocol version 1 only.
.It Cm ServerKeyBits
-Defines the number of bits in the server key.
+Defines the number of bits in the ephemeral protocol version 1 server key.
The minimum value is 512, and the default is 768.
-.It Cm SkeyAuthentication
-Specifies whether
-.Xr skey 1
-authentication is allowed.
-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
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
Specifies whether
.Xr login 1
is used for interactive login sessions.
-Note that
-.Xr login 1
-is not never for remote command execution.
The default is
.Dq no .
+Note that
+.Xr login 1
+is never used for remote command execution.
+Note also, that if this is enabled,
+.Cm X11Forwarding
+will be disabled because
+.Xr login 1
+does not know how to handle
+.Xr xauth 1
+cookies.
.It Cm X11DisplayOffset
Specifies the first display number available for
.Nm sshd Ns 's
.Dq no .
Note that disabling X11 forwarding does not improve security in any
way, as users can always install their own forwarders.
+X11 forwarding is automatically disabled if
+.Cm UseLogin
+is enabled.
.It Cm XAuthLocation
Specifies the location of the
.Xr xauth 1
The default is
.Pa /usr/X11R6/bin/xauth .
.El
+.Ss Time Formats
+.Pp
+.Nm
+command-line arguments and configuration file options that specify time
+may be expressed using a sequence of the form:
+.Sm off
+.Ar time Oo Ar qualifier Oc ,
+.Sm on
+where
+.Ar time
+is a positive integer value and
+.Ar qualifier
+is one of the following:
+.Pp
+.Bl -tag -width Ds -compact -offset indent
+.It Cm <none>
+seconds
+.It Cm s | Cm S
+seconds
+.It Cm m | Cm M
+minutes
+.It Cm h | Cm H
+hours
+.It Cm d | Cm D
+days
+.It Cm w | Cm W
+weeks
+.El
+.Pp
+Each member of the sequence is added together to calculate
+the total time value.
+.Pp
+Time format examples:
+.Pp
+.Bl -tag -width Ds -compact -offset indent
+.It 600
+600 seconds (10 minutes)
+.It 10m
+10 minutes
+.It 1h30m
+1 hour 30 minutes (90 minutes)
+.El
.Sh LOGIN PROCESS
When a user successfully logs in,
.Nm
Runs user's shell or command.
.El
.Sh AUTHORIZED_KEYS FILE FORMAT
-The
.Pa $HOME/.ssh/authorized_keys
-file lists the RSA keys that are
-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.
+is the default file that lists the public keys that are
+permitted for RSA authentication in protocol version 1
+and for public key authentication (PubkeyAuthentication)
+in protocol version 2.
+.Cm AuthorizedKeysFile
+may be used to specify an alternative file.
+.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
+.Pa identity.pub ,
+.Pa id_dsa.pub
+or the
+.Pa id_rsa.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:
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.
authentication.
.It Cm no-pty
Prevents tty allocation (a request to allocate a pty will fail).
+.It Cm permitopen="host:port"
+Limit local
+.Li ``ssh -L''
+port forwarding such that it may only connect to the specified host and
+port. Multiple
+.Cm permitopen
+options may be applied separated by commas. No pattern matching is
+performed on the specified hostnames, they must be literal domains or
+addresses.
.El
.Ss Examples
1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
.Pp
command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
+.Pp
+permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
.Sh SSH_KNOWN_HOSTS FILE FORMAT
The
.Pa /etc/ssh_known_hosts ,
-.Pa /etc/ssh_known_hosts2 ,
-.Pa $HOME/.ssh/known_hosts ,
and
-.Pa $HOME/.ssh/known_hosts2
+.Pa $HOME/.ssh/known_hosts
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,
.Pa /etc/ssh_host_key.pub
and adding the host names at the front.
.Ss Examples
-closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
+.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
.Sh FILES
.Bl -tag -width Ds
.It Pa /etc/sshd_config
.Nm sshd .
This file should be writable by root only, but it is recommended
(though not necessary) that it be world-readable.
-.It Pa /etc/ssh_host_key
-Contains the private part of the host key.
-This file should only be owned by root, readable only by root, and not
+.It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
+These three files contain the private parts of the host keys.
+These files should only be owned by root, readable only by root, and not
accessible to others.
Note that
.Nm
does not start if this file is group/world-accessible.
-.It Pa /etc/ssh_host_key.pub
-Contains the public part of the host key.
-This file should be world-readable but writable only by
+.It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
+These three files contain the public parts of the host keys.
+These files should be world-readable but writable only by
root.
-Its contents should match the private part.
-This file is not
-really used for anything; it is only provided for the convenience of
-the user so its contents can be copied to known hosts files.
-These two files are created using
+Their contents should match the respective private parts.
+These files are not
+really used for anything; they are provided for the convenience of
+the user so their contents can be copied to known hosts files.
+These files are created using
.Xr ssh-keygen 1 .
+.It Pa /etc/moduli
+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
-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
-.Pa identity.pub
-files into this file, as described in
-.Xr ssh-keygen 1 .
-.It Pa $HOME/.ssh/authorized_keys2
-Lists the DSA keys that can be used to log into the user's account.
+Lists the public keys (RSA or DSA) that can be used to log into the user's account.
This file must be readable by root (which may on some machines imply
it being world-readable if the user's home directory resides on an NFS
volume).
It is recommended that it not be accessible by others.
The format of this file is described above.
Users will place the contents of their
+.Pa identity.pub ,
.Pa id_dsa.pub
+and/or
+.Pa id_rsa.pub
files into this file, as described in
.Xr ssh-keygen 1 .
.It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
These files are consulted when using rhosts with RSA host
-authentication to check the public key of the host.
+authentication or 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 the remote host is the one we intended to connect.
+to verify that it is connecting to the correct remote host.
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.
accessible; AFS is a particular example of such an environment.
.Pp
This file will probably contain some initialization code followed by
-something similar to: "if read proto cookie; then echo add $DISPLAY
-$proto $cookie | xauth -q -; fi".
+something similar to:
+.Bd -literal
+ if read proto cookie; then
+ echo add $DISPLAY $proto $cookie | xauth -q -
+ fi
+.Ed
.Pp
If this file does not exist,
.Pa /etc/sshrc
machine-specific login-time initializations globally.
This file should be writable only by root, and should be world-readable.
.El
-.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)
-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
-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 ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1 ,
-.Xr rlogin 1 ,
-.Xr rsh 1
+.Xr login.conf 5 ,
+.Xr moduli 5 ,
+.Xr sftp-server 8
+.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-09.txt
+.%D July 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-01.txt
+.%D April 2001
+.%O work in progress material
+.Re
andersk / openssh.git / blobdiff