.\" -*- nroff -*-
.\"
-.\" ssh.1.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: ssh.1,v 1.164 2002/08/29 16:02:54 stevesk Exp $
.Dd September 25, 1999
.Dt SSH 1
.Os
.Sh NAME
.Nm ssh
-.Nd OpenSSH secure shell client (remote login program)
+.Nd OpenSSH SSH client (remote login program)
.Sh SYNOPSIS
.Nm ssh
.Op Fl l Ar login_name
-.Op Ar hostname | user@hostname
+.Ar hostname | user@hostname
.Op Ar command
.Pp
.Nm ssh
-.Op Fl afgknqtvxCPX246
+.Op Fl afgknqstvxACNTX1246
+.Op Fl b Ar bind_address
.Op Fl c Ar cipher_spec
.Op Fl e Ar escape_char
.Op Fl i Ar identity_file
.Op Fl l Ar login_name
+.Op Fl m Ar mac_spec
.Op Fl o Ar option
.Op Fl p Ar port
+.Op Fl F Ar configfile
.Oo Fl L Xo
.Sm off
.Ar port :
.Sm on
.Xc
.Oc
-.Op Ar hostname | user@hostname
+.Op Fl D Ar port
+.Ar hostname | user@hostname
.Op Ar command
.Sh DESCRIPTION
.Nm
-(Secure Shell) is a program for logging into a remote machine and for
+(SSH client) is a program for logging into a remote machine and for
executing commands on a remote machine.
It is intended to replace
rlogin and rsh, and provide secure encrypted communications between
This form of authentication alone is normally not
allowed by the server because it is not secure.
.Pp
-The second (and primary) authentication method is the
+The second authentication method is the
.Pa rhosts
or
.Pa hosts.equiv
.Pa /etc/shosts.equiv ,
and if additionally the server can verify the client's
host key (see
-.Pa /etc/ssh_known_hosts
+.Pa /etc/ssh/ssh_known_hosts
and
.Pa $HOME/.ssh/known_hosts
in the
.Pp
.Ss SSH protocol version 2
.Pp
-When a user connects using the protocol version 2
-different authentication methods are available:
-At first, the client attempts to authenticate using the public key method.
-If this method fails password authentication is tried.
+When a user connects using protocol version 2
+similar authentication methods are available.
+Using the default values for
+.Cm PreferredAuthentications ,
+the client will try to authenticate first using the hostbased method;
+if this method fails public key authentication is attempted,
+and finally if this method fails keyboard-interactive and
+password authentication are tried.
.Pp
The public key method is similar to RSA authentication described
-in the previous section except that the DSA algorithm is used
-instead of the patented RSA algorithm.
-The client uses his private DSA key
+in the previous section and allows the RSA or DSA algorithm to be used:
+The client uses his private key,
.Pa $HOME/.ssh/id_dsa
+or
+.Pa $HOME/.ssh/id_rsa ,
to sign the session identifier and sends the result to the server.
The server checks whether the matching public key is listed in
-.Pa $HOME/.ssh/authorized_keys2
+.Pa $HOME/.ssh/authorized_keys
and grants access if both the key is found and the signature is correct.
The session identifier is derived from a shared Diffie-Hellman value
and is only known to the client and the server.
.Pp
If public key authentication fails or is not available a password
can be sent encrypted to the remote host for proving the user's identity.
-This protocol 2 implementation does not yet support Kerberos or
-S/Key authentication.
+.Pp
+Additionally,
+.Nm
+supports hostbased or challenge response authentication.
.Pp
Protocol 2 provides additional mechanisms for confidentiality
(the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
-and integrity (hmac-sha1, hmac-md5).
+and integrity (hmac-md5, hmac-sha1).
Note that protocol 1 lacks a strong mechanism for ensuring the
integrity of the connection.
.Pp
the remote command or shell will be automatically encrypted.
.Pp
If a pseudo-terminal has been allocated (normal login session), the
-user can disconnect with
-.Ic ~. ,
-and suspend
-.Nm
-with
-.Ic ~^Z .
-All forwarded connections can be listed with
-.Ic ~#
-and if
-the session blocks waiting for forwarded X11 or TCP/IP
-connections to terminate, it can be backgrounded with
-.Ic ~&
-(this should not be used while the user shell is active, as it can cause the
-shell to hang).
-All available escapes can be listed with
-.Ic ~? .
-.Pp
-A single tilde character can be sent as
-.Ic ~~
-(or by following the tilde by a character other than those described above).
-The escape character must always follow a newline to be interpreted as
-special.
-The escape character can be changed in configuration files
-or on the command line.
+user may use the escape characters noted below.
.Pp
If no pseudo tty has been allocated, the
session is transparent and can be used to reliably transfer binary
.Dq none
will also make the session transparent even if a tty is used.
.Pp
-The session terminates when the command or shell in on the remote
-machine exists and all X11 and TCP/IP connections have been closed.
+The session terminates when the command or shell on the remote
+machine exits and all X11 and TCP/IP connections have been closed.
The exit status of the remote program is returned as the exit status
of
.Nm ssh .
.Pp
+.Ss Escape Characters
+.Pp
+When a pseudo terminal has been requested, ssh supports a number of functions
+through the use of an escape character.
+.Pp
+A single tilde character can be sent as
+.Ic ~~
+or by following the tilde by a character other than those described below.
+The escape character must always follow a newline to be interpreted as
+special.
+The escape character can be changed in configuration files using the
+.Cm EscapeChar
+configuration directive or on the command line by the
+.Fl e
+option.
+.Pp
+The supported escapes (assuming the default
+.Ql ~ )
+are:
+.Bl -tag -width Ds
+.It Cm ~.
+Disconnect
+.It Cm ~^Z
+Background ssh
+.It Cm ~#
+List forwarded connections
+.It Cm ~&
+Background ssh at logout when waiting for forwarded connection / X11 sessions
+to terminate
+.It Cm ~?
+Display a list of escape characters
+.It Cm ~C
+Open command line (only useful for adding port forwardings using the
+.Fl L
+and
+.Fl R
+options)
+.It Cm ~R
+Request rekeying of the connection (only useful for SSH protocol version 2
+and if the peer supports it)
+.El
+.Pp
.Ss X11 and TCP forwarding
.Pp
-If the user is using X11 (the
+If the
+.Cm ForwardX11
+variable is set to
+.Dq yes
+(or, see the description of the
+.Fl X
+and
+.Fl x
+options described later)
+and the user is using X11 (the
.Ev DISPLAY
environment variable is set), the connection to the X11 display is
automatically forwarded to the remote side in such a way that any X11
The real authentication cookie is never
sent to the server machine (and no cookies are sent in the plain).
.Pp
-If the user is using an authentication agent, the connection to the agent
-is automatically forwarded to the remote side unless disabled on
-command line or in a configuration file.
+If the
+.Cm ForwardAgent
+variable is set to
+.Dq yes
+(or, see the description of the
+.Fl A
+and
+.Fl a
+options described later) and
+the user is using an authentication agent, the connection to the agent
+is automatically forwarded to the remote side.
.Pp
Forwarding of arbitrary TCP/IP connections over the secure channel can
-be specified either on command line or in a configuration file.
+be specified either on the command line or in a configuration file.
One possible application of TCP/IP forwarding is a secure connection to an
-electronic purse; another is going trough firewalls.
+electronic purse; another is going through firewalls.
.Pp
.Ss Server authentication
.Pp
.Nm
automatically maintains and checks a database containing
identifications for all hosts it has ever been used with.
-RSA host keys are stored in
+Host keys are stored in
.Pa $HOME/.ssh/known_hosts
-and
-DSA host keys are stored in
-.Pa $HOME/.ssh/known_hosts2
in the user's home directory.
-Additionally, the files
-.Pa /etc/ssh_known_hosts
-and
-.Pa /etc/ssh_known_hosts2
-are automatically checked for known hosts.
+Additionally, the file
+.Pa /etc/ssh/ssh_known_hosts
+is automatically checked for known hosts.
Any new hosts are automatically added to the user's file.
If a host's identification
ever changes,
otherwise be used to circumvent the encryption.
The
.Cm StrictHostKeyChecking
-option (see below) can be used to prevent logins to machines whose
+option can be used to prevent logins to machines whose
host key is not known or has changed.
-.Sh OPTIONS
+.Pp
+The options are as follows:
.Bl -tag -width Ds
.It Fl a
Disables forwarding of the authentication agent connection.
-This may also be specified on a per-host basis in the configuration file.
-.It Fl c Ar blowfish|3des
+.It Fl A
+Enables forwarding of the authentication agent connection.
+This can also be specified on a per-host basis in a configuration file.
+.It Fl b Ar bind_address
+Specify the interface to transmit from on machines with multiple
+interfaces or aliased addresses.
+.It Fl c Ar blowfish|3des|des
Selects the cipher to use for encrypting the session.
.Ar 3des
is used by default.
It is believed to be secure.
.Ar 3des
(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
-It is presumably more secure than the
-.Ar des
-cipher which is no longer supported in
-.Nm ssh .
.Ar blowfish
is a fast block cipher, it appears very secure and is much faster than
.Ar 3des .
-.It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc"
+.Ar des
+is only supported in the
+.Nm
+client for interoperability with legacy protocol 1 implementations
+that do not support the
+.Ar 3des
+cipher. Its use is strongly discouraged due to cryptographic
+weaknesses.
+.It Fl c Ar cipher_spec
Additionally, for protocol version 2 a comma-separated list of ciphers can
-be specified in order of preference. Protocol version 2 supports
-3DES, Blowfish and CAST128 in CBC mode and Arcfour.
+be specified in order of preference.
+See
+.Cm Ciphers
+for more information.
.It Fl e Ar ch|^ch|none
Sets the escape character for sessions with a pty (default:
.Ql ~ ) .
.It Fl g
Allows remote hosts to connect to local forwarded ports.
.It Fl i Ar identity_file
-Selects the file from which the identity (private key) for
-RSA authentication is read.
-Default is
+Selects a file from which the identity (private key) for
+RSA or DSA authentication is read.
+The default is
.Pa $HOME/.ssh/identity
-in the user's home directory.
+for protocol version 1, and
+.Pa $HOME/.ssh/id_rsa
+and
+.Pa $HOME/.ssh/id_dsa
+for protocol version 2.
Identity files may also be specified on
a per-host basis in the configuration file.
It is possible to have multiple
.Fl i
options (and multiple identities specified in
configuration files).
+.It Fl I Ar smartcard_device
+Specifies which smartcard device to use. The argument is
+the device
+.Nm
+should use to communicate with a smartcard used for storing the user's
+private RSA key.
.It Fl k
Disables forwarding of Kerberos tickets and AFS tokens.
This may also be specified on a per-host basis in the configuration file.
.It Fl l Ar login_name
Specifies the user to log in as on the remote machine.
This also may be specified on a per-host basis in the configuration file.
+.It Fl m Ar mac_spec
+Additionally, for protocol version 2 a comma-separated list of MAC
+(message authentication code) algorithms can
+be specified in order of preference.
+See the
+.Cm MACs
+keyword for more information.
.It Fl n
Redirects stdin from
.Pa /dev/null
needs to ask for a password or passphrase; see also the
.Fl f
option.)
+.It Fl N
+Do not execute a remote command.
+This is useful for just forwarding ports
+(protocol version 2 only).
.It Fl o Ar option
-Can be used to give options in the format used in the config file.
+Can be used to give options in the format used in the configuration file.
This is useful for specifying options for which there is no separate
command-line flag.
-The option has the same format as a line in the configuration file.
.It Fl p Ar port
Port to connect to on the remote host.
This can be specified on a
per-host basis in the configuration file.
-.It Fl P
-Use a non-privileged port for outgoing connections.
-This can be used if your firewall does
-not permit connections from privileged ports.
-Note that this option turns off
-.Cm RhostsAuthentication
-and
-.Cm RhostsRSAAuthentication .
.It Fl q
Quiet mode.
Causes all warning and diagnostic messages to be suppressed.
-Only fatal errors are displayed.
+.It Fl s
+May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use
+of SSH as a secure transport for other applications (eg. sftp). The
+subsystem is specified as the remote command.
.It Fl t
Force pseudo-tty allocation.
This can be used to execute arbitrary
screen-based programs on a remote machine, which can be very useful,
e.g., when implementing menu services.
+Multiple
+.Fl t
+options force tty allocation, even if
+.Nm
+has no local tty.
+.It Fl T
+Disable pseudo-tty allocation.
.It Fl v
Verbose mode.
Causes
to print debugging messages about its progress.
This is helpful in
debugging connection, authentication, and configuration problems.
-The verbose mode is also used to display
-.Xr skey 1
-challenges, if the user entered "s/key" as password.
+Multiple
+.Fl v
+options increases the verbosity.
+Maximum is 3.
.It Fl x
Disables X11 forwarding.
-This can also be specified on a per-host basis in a configuration file.
.It Fl X
Enables X11 forwarding.
+This can also be specified on a per-host basis in a configuration file.
.It Fl C
Requests compression of all data (including stdin, stdout, stderr, and
data for forwarded X11 and TCP/IP connections).
.Dq level
can be controlled by the
.Cm CompressionLevel
-option (see below).
+option.
Compression is desirable on modem lines and other
slow connections, but will only slow down things on fast networks.
The default value can be set on a host-by-host basis in the
configuration files; see the
-.Cm Compress
-option below.
+.Cm Compression
+option.
+.It Fl F Ar configfile
+Specifies an alternative per-user configuration file.
+If a configuration file is given on the command line,
+the system-wide configuration file
+.Pq Pa /etc/ssh/ssh_config
+will be ignored.
+The default for the per-user configuration file is
+.Pa $HOME/.ssh/config .
.It Fl L Ar port:host:hostport
Specifies that the given port on the local (client) host is to be
forwarded to the given host and port on the remote side.
Port forwardings can also be specified in the configuration file.
Privileged ports can be forwarded only when
logging in as root on the remote machine.
+IPv6 addresses can be specified with an alternative syntax:
+.Ar port/host/hostport
+.It Fl D Ar port
+Specifies a local
+.Dq dynamic
+application-level port forwarding.
+This works by allocating a socket to listen to
+.Ar port
+on the local side, and whenever a connection is made to this port, the
+connection is forwarded over the secure channel, and the application
+protocol is then used to determine where to connect to from the
+remote machine. Currently the SOCKS4 protocol is supported, and
+.Nm
+will act as a SOCKS4 server.
+Only root can forward privileged ports.
+Dynamic port forwardings can also be specified in the configuration file.
+.It Fl 1
+Forces
+.Nm
+to try protocol version 1 only.
.It Fl 2
Forces
.Nm
.El
.Sh CONFIGURATION FILES
.Nm
-obtains configuration data from the following sources (in this order):
-command line options, user's configuration file
-.Pq Pa $HOME/.ssh/config ,
-and system-wide configuration file
-.Pq Pa /etc/ssh_config .
-For each parameter, the first obtained value
-will be used.
-The configuration files contain sections bracketed by
-.Dq Host
-specifications, and that section is only applied for hosts that
-match one of the patterns given in the specification.
-The matched host name is the one given on the command line.
-.Pp
-Since the first obtained value for each parameter is used, more
-host-specific declarations should be given near the beginning of the
-file, and general defaults at the end.
-.Pp
-The configuration file has the following format:
-.Pp
-Empty lines and lines starting with
-.Ql #
-are comments.
-.Pp
-Otherwise a line is of the format
-.Dq keyword arguments .
-The possible
-keywords and their meanings are as follows (note that the
-configuration files are case-sensitive):
-.Bl -tag -width Ds
-.It Cm Host
-Restricts the following declarations (up to the next
-.Cm Host
-keyword) to be only for those hosts that match one of the patterns
-given after the keyword.
-.Ql \&*
-and
-.Ql ?
-can be used as wildcards in the
-patterns.
-A single
-.Ql \&*
-as a pattern can be used to provide global
-defaults for all hosts.
-The host is the
-.Ar hostname
-argument given on the command line (i.e., the name is not converted to
-a canonicalized host name before matching).
-.It Cm AFSTokenPassing
-Specifies whether to pass AFS tokens to remote host.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-.It Cm BatchMode
-If set to
-.Dq yes ,
-passphrase/password querying will be disabled.
-This option is useful in scripts and other batch jobs where you have no
-user to supply the password.
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm CheckHostIP
-If this flag is set to
-.Dq yes ,
-ssh will additionally check the host ip address in the
-.Pa known_hosts
-file.
-This allows ssh to detect if a host key changed due to DNS spoofing.
-If the option is set to
-.Dq no ,
-the check will not be executed.
-.It Cm Cipher
-Specifies the cipher to use for encrypting the session.
-Currently,
-.Dq blowfish ,
-and
-.Dq 3des
-are supported.
-The default is
-.Dq 3des .
-.It Cm Ciphers
-Specifies the ciphers allowed for protocol version 2
-in order of preference.
-Multiple ciphers must be comma-separated.
-The default is
-.Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
-.It Cm Compression
-Specifies whether to use compression.
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm CompressionLevel
-Specifies the compression level to use if compression is enable.
-The argument must be an integer from 1 (fast) to 9 (slow, best).
-The default level is 6, which is good for most applications.
-The meaning of the values is the same as in
-.Xr gzip 1 .
-.It Cm ConnectionAttempts
-Specifies the number of tries (one per second) to make before falling
-back to rsh or exiting.
-The argument must be an integer.
-This may be useful in scripts if the connection sometimes fails.
-.It Cm DSAAuthentication
-Specifies whether to try DSA authentication.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-DSA authentication will only be
-attempted if a DSA identity file exists.
-Note that this option applies to protocol version 2 only.
-.It Cm EscapeChar
-Sets the escape character (default:
-.Ql ~ ) .
-The escape character can also
-be set on the command line.
-The argument should be a single character,
-.Ql ^
-followed by a letter, or
-.Dq none
-to disable the escape
-character entirely (making the connection transparent for binary
-data).
-.It Cm FallBackToRsh
-Specifies that if connecting via
-.Nm
-fails due to a connection refused error (there is no
-.Xr sshd 8
-listening on the remote host),
-.Xr rsh 1
-should automatically be used instead (after a suitable warning about
-the session being unencrypted).
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm ForwardAgent
-Specifies whether the connection to the authentication agent (if any)
-will be forwarded to the remote machine.
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm ForwardX11
-Specifies whether X11 connections will be automatically redirected
-over the secure channel and
-.Ev DISPLAY
-set.
-The argument must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq no .
-.It Cm GatewayPorts
-Specifies whether remote hosts are allowed to connect to local
-forwarded ports.
-The argument must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq no .
-.It Cm GlobalKnownHostsFile
-Specifies a file to use instead of
-.Pa /etc/ssh_known_hosts .
-.It Cm HostName
-Specifies the real host name to log into.
-This can be used to specify nicknames or abbreviations for hosts.
-Default is the name given on the command line.
-Numeric IP addresses are also permitted (both on the command line and in
-.Cm HostName
-specifications).
-.It Cm IdentityFile
-Specifies the file from which the user's RSA authentication identity
-is read (default
-.Pa $HOME/.ssh/identity
-in the user's home directory).
-Additionally, any identities represented by the authentication agent
-will be used for authentication.
-The file name may use the tilde
-syntax to refer to a user's home directory.
-It is possible to have
-multiple identity files specified in configuration files; all these
-identities will be tried in sequence.
-.It Cm IdentityFile2
-Specifies the file from which the user's DSA authentication identity
-is read (default
-.Pa $HOME/.ssh/id_dsa
-in the user's home directory).
-The file name may use the tilde
-syntax to refer to a user's home directory.
-It is possible to have
-multiple identity files specified in configuration files; all these
-identities will be tried in sequence.
-.It Cm KeepAlive
-Specifies whether the system should send keepalive messages 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.
-.Pp
-The default is
-.Dq yes
-(to send keepalives), and the client will notice
-if the network goes down or the remote host dies.
-This is important in scripts, and many users want it too.
-.Pp
-To disable keepalives, the value should be set to
-.Dq no
-in both the server and the client configuration files.
-.It Cm KerberosAuthentication
-Specifies whether Kerberos authentication will be used.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-.It Cm KerberosTgtPassing
-Specifies whether a Kerberos TGT will be forwarded to the server.
-This will only work if the Kerberos server is actually an AFS kaserver.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-.It Cm LocalForward
-Specifies that a TCP/IP port on the local machine be forwarded over
-the secure channel to given host:port from the remote machine.
-The first argument must be a port number, and the second must be
-host:port.
-Multiple forwardings may be specified, and additional
-forwardings can be given on the command line.
-Only the superuser can forward privileged ports.
-.It Cm LogLevel
-Gives the verbosity level that is used when logging messages from
-.Nm ssh .
-The possible values are:
-QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
-The default is INFO.
-.It Cm NumberOfPasswordPrompts
-Specifies the number of password prompts before giving up.
-The argument to this keyword must be an integer.
-Default is 3.
-.It Cm PasswordAuthentication
-Specifies whether to use password authentication.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-Note that this option applies to both protocol version 1 and 2.
-.It Cm Port
-Specifies the port number to connect on the remote host.
-Default is 22.
-.It Cm Protocol
-Specifies the protocol versions
-.Nm
-should support in order of preference.
-The possible values are
-.Dq 1
-and
-.Dq 2 .
-Multiple versions must be comma-separated.
-The default is
-.Dq 1,2 .
-This means that
-.Nm
-tries version 1 and falls back to version 2
-if version 1 is not available.
-.It Cm ProxyCommand
-Specifies the command to use to connect to the server.
-The command
-string extends to the end of the line, and is executed with
-.Pa /bin/sh .
-In the command string,
-.Ql %h
-will be substituted by the host name to
-connect and
-.Ql %p
-by the port.
-The command can be basically anything,
-and should read from its standard input and write to its standard output.
-It should eventually connect an
-.Xr sshd 8
-server running on some machine, or execute
-.Ic sshd -i
-somewhere.
-Host key management will be done using the
-HostName of the host being connected (defaulting to the name typed by
-the user).
-Note that
-.Cm CheckHostIP
-is not available for connects with a proxy command.
-.Pp
-.It Cm RemoteForward
-Specifies that a TCP/IP port on the remote machine be forwarded over
-the secure channel to given host:port from the local machine.
-The first argument must be a port number, and the second must be
-host:port.
-Multiple forwardings may be specified, and additional
-forwardings can be given on the command line.
-Only the superuser can forward privileged ports.
-.It Cm RhostsAuthentication
-Specifies whether to try rhosts based authentication.
-Note that this
-declaration only affects the client side and has no effect whatsoever
-on security.
-Disabling rhosts authentication may reduce
-authentication time on slow connections when rhosts authentication is
-not used.
-Most servers do not permit RhostsAuthentication because it
-is not secure (see RhostsRSAAuthentication).
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-.It Cm RhostsRSAAuthentication
-Specifies whether to try rhosts based authentication with RSA host
-authentication.
-This is the primary authentication method for most sites.
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm RSAAuthentication
-Specifies whether to try RSA authentication.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-RSA authentication will only be
-attempted if the identity file exists, or an authentication agent is
-running.
-Note that this option applies to protocol version 1 only.
-.It Cm SkeyAuthentication
-Specifies whether to use
-.Xr skey 1
-authentication.
-The argument to this keyword must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq no .
-.It Cm StrictHostKeyChecking
-If this flag is set to
-.Dq yes ,
-.Nm
-ssh will never automatically add host keys to the
-.Pa $HOME/.ssh/known_hosts
-and
-.Pa $HOME/.ssh/known_hosts2
-files, and refuses to connect hosts whose host key has changed.
-This provides maximum protection against trojan horse attacks.
-However, it can be somewhat annoying if you don't have good
-.Pa /etc/ssh_known_hosts
-and
-.Pa /etc/ssh_known_hosts2
-files installed and frequently
-connect new hosts.
-Basically this option forces the user to manually
-add any new hosts.
-Normally this option is disabled, and new hosts
-will automatically be added to the known host files.
-The host keys of
-known hosts will be verified automatically in either case.
-The argument must be
-.Dq yes
-or
-.Dq no .
-.It Cm UsePrivilegedPort
-Specifies whether to use a privileged port for outgoing connections.
-The argument must be
-.Dq yes
-or
-.Dq no .
-The default is
-.Dq yes .
-Note that setting this option to
-.Dq no
-turns off
-.Cm RhostsAuthentication
-and
-.Cm RhostsRSAAuthentication .
-.It Cm User
-Specifies the user to log in as.
-This can be useful if you have a different user name on different machines.
-This saves the trouble of
-having to remember to give the user name on the command line.
-.It Cm UserKnownHostsFile
-Specifies a file to use instead of
-.Pa $HOME/.ssh/known_hosts .
-.It Cm UseRsh
-Specifies that rlogin/rsh should be used for this host.
-It is possible that the host does not at all support the
-.Nm
-protocol.
-This causes
-.Nm
-to immediately execute
-.Xr rsh 1 .
-All other options (except
-.Cm HostName )
-are ignored if this has been specified.
-The argument must be
-.Dq yes
-or
-.Dq no .
+may additionally obtain configuration data from
+a per-user configuration file and a system-wide configuration file.
+The file format and configuration options are described in
+.Xr ssh_config 5 .
.Sh ENVIRONMENT
.Nm
will normally set the following environment variables:
.Nm
uses this special value to forward X11 connections over the secure
channel.
-The user should normally not set DISPLAY explicitly, as that
+The user should normally not set
+.Ev DISPLAY
+explicitly, as that
will render the X11 connection insecure (and will require the user to
manually copy any required authorization cookies).
.It Ev HOME
.Ev USER ;
set for compatibility with systems that use this variable.
.It Ev MAIL
-Set to point the user's mailbox.
+Set to the path of the user's mailbox.
.It Ev PATH
Set to the default
.Ev PATH ,
as specified when compiling
.Nm ssh .
+.It Ev SSH_ASKPASS
+If
+.Nm
+needs a passphrase, it will read the passphrase from the current
+terminal if it was run from a terminal.
+If
+.Nm
+does not have a terminal associated with it but
+.Ev DISPLAY
+and
+.Ev SSH_ASKPASS
+are set, it will execute the program specified by
+.Ev SSH_ASKPASS
+and open an X11 window to read the passphrase.
+This is particularly useful when calling
+.Nm
+from a
+.Pa .Xsession
+or related script.
+(Note that on some machines it
+may be necessary to redirect the input from
+.Pa /dev/null
+to make this work.)
.It Ev SSH_AUTH_SOCK
-indicates the path of a unix-domain socket used to communicate with the
+Identifies the path of a unix-domain socket used to communicate with the
agent.
.It Ev SSH_CLIENT
Identifies the client end of the connection.
The variable contains
three space-separated values: client ip-address, client port number,
and server port number.
+.It Ev SSH_ORIGINAL_COMMAND
+The variable contains the original command line if a forced command
+is executed.
+It can be used to extract the original arguments.
.It Ev SSH_TTY
This is set to the name of the tty (path to the device) associated
with the current shell or command.
this variable is not set.
.It Ev TZ
The timezone variable is set to indicate the present timezone if it
-was set when the daemon was started (e.i., the daemon passes the value
+was set when the daemon was started (i.e., the daemon passes the value
on to new connections).
.It Ev USER
Set to the name of the user logging in.
.Pa $HOME/.ssh/environment ,
and adds lines of the format
.Dq VARNAME=value
-to the environment.
+to the environment if the file exists and if users are allowed to
+change their environment.
+See the
+.Cm PermitUserEnvironment
+option in
+.Xr sshd_config 5 .
.Sh FILES
.Bl -tag -width Ds
.It Pa $HOME/.ssh/known_hosts
-Records host keys for all hosts the user has logged into (that are not
+Records host keys for all hosts the user has logged into that are not
in
-.Pa /etc/ssh_known_hosts ) .
+.Pa /etc/ssh/ssh_known_hosts .
See
.Xr sshd 8 .
-.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
-Contains the RSA and the DSA authentication identity of the user.
+.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
+Contains the authentication identity of the user.
+They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
These files
contain sensitive data and should be readable by the user but not
accessible by others (read/write/execute).
It is possible to specify a passphrase when
generating the key; the passphrase will be used to encrypt the
sensitive part of this file using 3DES.
-.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
+.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
Contains the public key for authentication (public part of the
identity file in human-readable form).
The contents of the
file should be added to
.Pa $HOME/.ssh/authorized_keys
on all machines
-where you wish to log in using RSA authentication.
+where the user wishes to log in using protocol version 1 RSA authentication.
The contents of the
.Pa $HOME/.ssh/id_dsa.pub
+and
+.Pa $HOME/.ssh/id_rsa.pub
file should be added to
-.Pa $HOME/.ssh/authorized_keys2
+.Pa $HOME/.ssh/authorized_keys
on all machines
-where you wish to log in using DSA authentication.
+where the user wishes to log in using protocol version 2 DSA/RSA authentication.
These files are not
sensitive and can (but need not) be readable by anyone.
These files are
-never used automatically and are not necessary; they is only provided for
+never used automatically and are not necessary; they are only provided for
the convenience of the user.
.It Pa $HOME/.ssh/config
This is the per-user configuration file.
-The format of this file is described above.
-This file is used by the
-.Nm
-client.
-This file does not usually contain any sensitive information,
-but the recommended permissions are read/write for the user, and not
-accessible by others.
+The file format and configuration options are described in
+.Xr ssh_config 5 .
.It Pa $HOME/.ssh/authorized_keys
-Lists the RSA keys that can be used for logging in as this user.
+Lists the public keys (RSA/DSA) that can be used for logging in as this user.
The format of this file is described in the
.Xr sshd 8
manual page.
In the simplest form the format is the same as the .pub
-identity files (that is, each line contains the number of bits in
-modulus, public exponent, modulus, and comment fields, separated by
-spaces).
-This file is not highly sensitive, but the recommended
-permissions are read/write for the user, and not accessible by others.
-.It Pa $HOME/.ssh/authorized_keys2
-Lists the DSA keys that can be used for logging in as this user.
+identity files.
This file is not highly sensitive, but the recommended
permissions are read/write for the user, and not accessible by others.
-.It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
+.It Pa /etc/ssh/ssh_known_hosts
Systemwide list of known host keys.
-.Pa /etc/ssh_known_hosts
-contains RSA and
-.Pa /etc/ssh_known_hosts2
-contains DSA keys.
-These files should be prepared by the
+This file should be prepared by the
system administrator to contain the public host keys of all machines in the
organization.
This file should be world-readable.
This file contains
public keys, one per line, in the following format (fields separated
-by spaces): system name, number of bits in modulus, public exponent,
-modulus, and optional comment field.
+by spaces): system name, public key and optional comment field.
When different names are used
for the same machine, all such names should be listed, separated by
commas.
does not convert the user-supplied name to a canonical name before
checking the key, because someone with access to the name servers
would then be able to fool host authentication.
-.It Pa /etc/ssh_config
+.It Pa /etc/ssh/ssh_config
Systemwide configuration file.
-This file provides defaults for those
-values that are not specified in the user's configuration file, and
-for those users who do not have a configuration file.
-This file must be world-readable.
+The file format and configuration options are described in
+.Xr ssh_config 5 .
+.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
+These three files contain the private parts of the host keys
+and are used for
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication .
+If the protocol version 1
+.Cm RhostsRSAAuthentication
+method is used,
+.Nm
+must be setuid root, since the host key is readable only by root.
+For protocol version 2,
+.Nm
+uses
+.Xr ssh-keysign 8
+to access the host keys for
+.Cm HostbasedAuthentication .
+This eliminates the requirement that
+.Nm
+be setuid root when that authentication method is used.
+By default
+.Nm
+is not setuid root.
.It Pa $HOME/.rhosts
This file is used in
.Pa \&.rhosts
Each line of the file contains a host name (in the canonical form
returned by name servers), and then a user name on that host,
separated by a space.
-One some machines this file may need to be
+On some machines this file may need to be
world-readable if the user's home directory is on a NFS partition,
because
.Xr sshd 8
.Xr sshd 8
will be installed so that it requires successful RSA host
authentication before permitting \s+2.\s0rhosts authentication.
-If your server machine does not have the client's host key in
-.Pa /etc/ssh_known_hosts ,
-you can store it in
+If the server machine does not have the client's host key in
+.Pa /etc/ssh/ssh_known_hosts ,
+it can be stored in
.Pa $HOME/.ssh/known_hosts .
The easiest way to do this is to
connect back to the client from the server machine using ssh; this
having this file is to be able to use rhosts authentication with
.Nm
without permitting login with
-.Xr rlogin 1
+.Nm rlogin
or
.Xr rsh 1 .
.It Pa /etc/hosts.equiv
This file may be useful to permit logins using
.Nm
but not using rsh/rlogin.
-.It Pa /etc/sshrc
+.It Pa /etc/ssh/sshrc
Commands in this file are executed by
.Nm
when the user logs in just before the user's shell (or command) is started.
Contains additional definitions for environment variables, see section
.Sx ENVIRONMENT
above.
-.It Pa libcrypto.so.X.1
-A version of this library which includes support for the RSA algorithm
-is required for proper operation.
-.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 DIAGNOSTICS
+.Nm
+exits with the exit status of the remote command or with 255
+if an error occurred.
+.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 rlogin 1 ,
.Xr rsh 1 ,
.Xr scp 1 ,
+.Xr sftp 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1 ,
.Xr telnet 1 ,
-.Xr sshd 8 ,
+.Xr ssh_config 5 ,
+.Xr ssh-keysign 8 ,
+.Xr sshd 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-12.txt
+.%D January 2002
+.%O work in progress material
+.Re
andersk / openssh.git / blobdiff