- (tim) [config.guess config.sub] Update to '2005-05-27' version.

[openssh.git] / ssh.1

diff --git a/ssh.1 b/ssh.1
index e2cd5d343877ea31f767a3e7f7c2da22ec765f32..4cc1738c13a0fc4d58e455c16f630e287f42e5dc 100644 (file)
--- a/ssh.1
+++ b/ssh.1
@@ -34,7 +34,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
 .\" (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 1.181 2003/12/16 15:49:51 markus Exp $
+.\" $OpenBSD: ssh.1,v 1.208 2005/05/23 23:32:46 djm Exp $

 .Dd September 25, 1999
 .Dt SSH 1
 .Os
 .Dd September 25, 1999
 .Dt SSH 1
 .Os


@@ -43,39 +43,35 @@
 .Nd OpenSSH SSH client (remote login program)
 .Sh SYNOPSIS
 .Nm ssh
 .Nd OpenSSH SSH client (remote login program)
 .Sh SYNOPSIS
 .Nm ssh

-.Op Fl 1246AaCfgkNnqsTtVvXxY
+.Bk -words
+.Op Fl 1246AaCfgkMNnqsTtVvXxY

 .Op Fl b Ar bind_address
 .Op Fl c Ar cipher_spec
 .Op Fl D Ar port
 .Op Fl e Ar escape_char
 .Op Fl F Ar configfile
 .Op Fl i Ar identity_file
 .Op Fl b Ar bind_address
 .Op Fl c Ar cipher_spec
 .Op Fl D Ar port
 .Op Fl e Ar escape_char
 .Op Fl F Ar configfile
 .Op Fl i Ar identity_file

-.Bk -words
-.Oo Fl L Xo
+.Oo Fl L\ \&

 .Sm off
 .Sm off

-.Ar port :
-.Ar host :
-.Ar hostport
+.Oo Ar bind_address : Oc
+.Ar port : host : hostport

 .Sm on
 .Sm on

-.Xc

 .Oc
 .Oc

-.Ek

 .Op Fl l Ar login_name
 .Op Fl m Ar mac_spec
 .Op Fl l Ar login_name
 .Op Fl m Ar mac_spec

+.Op Fl O Ar ctl_cmd

 .Op Fl o Ar option
 .Op Fl o Ar option

-.Bk -words

 .Op Fl p Ar port
 .Op Fl p Ar port

-.Ek
-.Oo Fl R Xo
+.Oo Fl R\ \&

 .Sm off
 .Sm off

-.Ar port :
-.Ar host :
-.Ar hostport
+.Oo Ar bind_address : Oc
+.Ar port : host : hostport

 .Sm on
 .Sm on

-.Xc

 .Oc
 .Oc

+.Op Fl S Ar ctl_path

 .Oo Ar user Ns @ Oc Ns Ar hostname
 .Op Ar command
 .Oo Ar user Ns @ Oc Ns Ar hostname
 .Op Ar command

+.Ek

 .Sh DESCRIPTION
 .Nm
 (SSH client) is a program for logging into a remote machine and for
 .Sh DESCRIPTION
 .Nm
 (SSH client) is a program for logging into a remote machine and for


@@ -102,39 +98,29 @@ is specified,
 .Ar command
 is executed on the remote host instead of a login shell.
 .Ss SSH protocol version 1
 .Ar command
 is executed on the remote host instead of a login shell.
 .Ss SSH protocol version 1

-First, if the machine the user logs in from is listed in
+The first authentication method is the
+.Em rhosts
+or
+.Em hosts.equiv
+method combined with RSA-based host authentication.
+If the machine the user logs in from is listed in

 .Pa /etc/hosts.equiv
 or
 .Pa /etc/shosts.equiv
 on the remote machine, and the user names are
 .Pa /etc/hosts.equiv
 or
 .Pa /etc/shosts.equiv
 on the remote machine, and the user names are

-the same on both sides, the user is immediately permitted to log in.
-Second, if
-.Pa .rhosts
+the same on both sides, or if the files
+.Pa ~/.rhosts

 or
 or

-.Pa .shosts
-exists in the user's home directory on the
-remote machine and contains a line containing the name of the client
+.Pa ~/.shosts
+exist in the user's home directory on the
+remote machine and contain a line containing the name of the client

 machine and the name of the user on that machine, the user is
 machine and the name of the user on that machine, the user is

-permitted to log in.
-This form of authentication alone is normally not
-allowed by the server because it is not secure.
-.Pp
-The second authentication method is the
-.Em rhosts
-or
-.Em hosts.equiv
-method combined with RSA-based host authentication.
-It means that if the login would be permitted by
-.Pa $HOME/.rhosts ,
-.Pa $HOME/.shosts ,
-.Pa /etc/hosts.equiv ,
-or
-.Pa /etc/shosts.equiv ,
-and if additionally the server can verify the client's
+considered for log in.
+Additionally, if the server can verify the client's

 host key (see
 .Pa /etc/ssh/ssh_known_hosts
 and
 host key (see
 .Pa /etc/ssh/ssh_known_hosts
 and

-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts

 in the
 .Sx FILES
 section), only then is login permitted.
 in the
 .Sx FILES
 section), only then is login permitted.


@@ -142,11 +128,11 @@ This authentication method closes security holes due to IP
 spoofing, DNS spoofing and routing spoofing.
 [Note to the administrator:
 .Pa /etc/hosts.equiv ,
 spoofing, DNS spoofing and routing spoofing.
 [Note to the administrator:
 .Pa /etc/hosts.equiv ,

-.Pa $HOME/.rhosts ,
+.Pa ~/.rhosts ,

 and the rlogin/rsh protocol in general, are inherently insecure and should be
 disabled if security is desired.]
 .Pp
 and the rlogin/rsh protocol in general, are inherently insecure and should be
 disabled if security is desired.]
 .Pp

-As a third authentication method,
+As a second authentication method,

 .Nm
 supports RSA based authentication.
 The scheme is based on public-key cryptography: there are cryptosystems
 .Nm
 supports RSA based authentication.
 The scheme is based on public-key cryptography: there are cryptosystems


@@ -158,7 +144,7 @@ key pair for authentication purposes.
 The server knows the public key, and only the user knows the private key.
 .Pp
 The file
 The server knows the public key, and only the user knows the private key.
 .Pp
 The file

-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys

 lists the public keys that are permitted for logging in.
 When the user logs in, the
 .Nm
 lists the public keys that are permitted for logging in.
 When the user logs in, the
 .Nm


@@ -179,24 +165,21 @@ implements the RSA authentication protocol automatically.
 The user creates his/her RSA key pair by running
 .Xr ssh-keygen 1 .
 This stores the private key in
 The user creates his/her RSA key pair by running
 .Xr ssh-keygen 1 .
 This stores the private key in

-.Pa $HOME/.ssh/identity
+.Pa ~/.ssh/identity

 and stores the public key in
 and stores the public key in

-.Pa $HOME/.ssh/identity.pub
+.Pa ~/.ssh/identity.pub

 in the user's home directory.
 The user should then copy the
 .Pa identity.pub
 to
 in the user's home directory.
 The user should then copy the
 .Pa identity.pub
 to

-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys

 in his/her home directory on the remote machine (the
 .Pa authorized_keys
 file corresponds to the conventional
 in his/her home directory on the remote machine (the
 .Pa authorized_keys
 file corresponds to the conventional

-.Pa $HOME/.rhosts
+.Pa ~/.rhosts

 file, and has one key
 per line, though the lines can be very long).
 After this, the user can log in without giving the password.
 file, and has one key
 per line, though the lines can be very long).
 After this, the user can log in without giving the password.

-RSA authentication is much more secure than
-.Em rhosts
-authentication.

 .Pp
 The most convenient way to use RSA authentication may be with an
 authentication agent.
 .Pp
 The most convenient way to use RSA authentication may be with an
 authentication agent.


@@ -223,12 +206,12 @@ password authentication are tried.
 The public key method is similar to RSA authentication described
 in the previous section and allows the RSA or DSA algorithm to be used:
 The client uses his private key,
 The public key method is similar to RSA authentication described
 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
+.Pa ~/.ssh/id_dsa

 or
 or

-.Pa $HOME/.ssh/id_rsa ,
+.Pa ~/.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
 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_keys
+.Pa ~/.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.
 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.


@@ -241,8 +224,8 @@ Additionally,
 supports hostbased or challenge response authentication.
 .Pp
 Protocol 2 provides additional mechanisms for confidentiality
 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-md5, hmac-sha1).
+(the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
+and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).

 Note that protocol 1 lacks a strong mechanism for ensuring the
 integrity of the connection.
 .Ss Login session and remote execution
 Note that protocol 1 lacks a strong mechanism for ensuring the
 integrity of the connection.
 .Ss Login session and remote execution


@@ -302,11 +285,18 @@ Display a list of escape characters.
 Send a BREAK to the remote system
 (only useful for SSH protocol version 2 and if the peer supports it).
 .It Cm ~C
 Send a BREAK to the remote system
 (only useful for SSH protocol version 2 and if the peer supports it).
 .It Cm ~C

-Open command line (only useful for adding port forwardings using the
+Open command line.
+Currently this allows the addition of port forwardings using the

 .Fl L
 and
 .Fl R
 .Fl L
 and
 .Fl R

-options).
+options (see below).
+It also allows the cancellation of existing remote port-forwardings
+using
+.Fl KR Ar hostport .
+Basic help is available, using the
+.Fl h
+option.

 .It Cm ~R
 Request rekeying of the connection
 (only useful for SSH protocol version 2 and if the peer supports it).
 .It Cm ~R
 Request rekeying of the connection
 (only useful for SSH protocol version 2 and if the peer supports it).


@@ -375,7 +365,7 @@ electronic purse; another is going through firewalls.
 automatically maintains and checks a database containing
 identifications for all hosts it has ever been used with.
 Host keys are stored in
 automatically maintains and checks a database containing
 identifications for all hosts it has ever been used with.
 Host keys are stored in

-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts

 in the user's home directory.
 Additionally, the file
 .Pa /etc/ssh/ssh_known_hosts
 in the user's home directory.
 Additionally, the file
 .Pa /etc/ssh/ssh_known_hosts


@@ -392,6 +382,15 @@ The
 option can be used to prevent logins to machines whose
 host key is not known or has changed.
 .Pp
 option can be used to prevent logins to machines whose
 host key is not known or has changed.
 .Pp

+.Nm
+can be configured to verify host identification using fingerprint resource
+records (SSHFP) published in DNS.
+The
+.Cm VerifyHostKeyDNS
+option can be used to control how DNS lookups are performed.
+SSHFP resource records can be generated using
+.Xr ssh-keygen 1 .
+.Pp

 The options are as follows:
 .Bl -tag -width Ds
 .It Fl 1
 The options are as follows:
 .Bl -tag -width Ds
 .It Fl 1


@@ -424,7 +423,7 @@ authenticate using the identities loaded into the agent.
 .It Fl a
 Disables forwarding of the authentication agent connection.
 .It Fl b Ar bind_address
 .It Fl a
 Disables forwarding of the authentication agent connection.
 .It Fl b Ar bind_address

-Specify the interface to transmit from on machines with multiple
+Specify the interface address to transmit from on machines with multiple

 interfaces or aliased addresses.
 .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and
 interfaces or aliased addresses.
 .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and


@@ -442,13 +441,18 @@ The default value can be set on a host-by-host basis in the
 configuration files; see the
 .Cm Compression
 option.
 configuration files; see the
 .Cm Compression
 option.

-.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.
+.It Fl c Ar cipher_spec
+Selects the cipher specification for encrypting the session.
+.Pp
+Protocol version 1 allows specification of a single cipher.
+The suported values are
+.Dq 3des ,
+.Dq blowfish
+and
+.Dq des .

 .Ar 3des
 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
 .Ar 3des
 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.

+It is believed to be secure.

 .Ar blowfish
 is a fast block cipher; it appears very secure and is much faster than
 .Ar 3des .
 .Ar blowfish
 is a fast block cipher; it appears very secure and is much faster than
 .Ar 3des .


@@ -460,12 +464,33 @@ that do not support the
 .Ar 3des
 cipher.
 Its use is strongly discouraged due to cryptographic weaknesses.
 .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.
-See
-.Cm Ciphers
-for more information.
+The default is
+.Dq 3des .
+.Pp
+For protocol version 2
+.Ar cipher_spec
+is a comma-separated list of ciphers
+listed in order of preference.
+The supported ciphers are
+.Dq 3des-cbc ,
+.Dq aes128-cbc ,
+.Dq aes192-cbc ,
+.Dq aes256-cbc ,
+.Dq aes128-ctr ,
+.Dq aes192-ctr ,
+.Dq aes256-ctr ,
+.Dq arcfour128 ,
+.Dq arcfour256 ,
+.Dq arcfour ,
+.Dq blowfish-cbc ,
+and
+.Dq cast128-cbc .
+The default is
+.Bd -literal
+  ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
+    arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
+    aes192-ctr,aes256-ctr''
+.Ed

 .It Fl D Ar port
 Specifies a local
 .Dq dynamic
 .It Fl D Ar port
 Specifies a local
 .Dq dynamic


@@ -500,7 +525,7 @@ the system-wide configuration file
 .Pq Pa /etc/ssh/ssh_config
 will be ignored.
 The default for the per-user configuration file is
 .Pq Pa /etc/ssh/ssh_config
 will be ignored.
 The default for the per-user configuration file is

-.Pa $HOME/.ssh/config .
+.Pa ~/.ssh/config .

 .It Fl f
 Requests
 .Nm
 .It Fl f
 Requests
 .Nm


@@ -526,11 +551,11 @@ private RSA key.
 Selects a file from which the identity (private key) for
 RSA or DSA authentication is read.
 The 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
+.Pa ~/.ssh/identity

 for protocol version 1, and
 for protocol version 1, and

-.Pa $HOME/.ssh/id_rsa
+.Pa ~/.ssh/id_rsa

 and
 and

-.Pa $HOME/.ssh/id_dsa
+.Pa ~/.ssh/id_dsa

 for protocol version 2.
 Identity files may also be specified on
 a per-host basis in the configuration file.
 for protocol version 2.
 Identity files may also be specified on
 a per-host basis in the configuration file.


@@ -542,6 +567,7 @@ configuration files).
 Disables forwarding (delegation) of GSSAPI credentials to the server.
 .It Fl L Xo
 .Sm off
 Disables forwarding (delegation) of GSSAPI credentials to the server.
 .It Fl L Xo
 .Sm off

+.Oo Ar bind_address : Oc

 .Ar port : host : hostport
 .Sm on
 .Xc
 .Ar port : host : hostport
 .Sm on
 .Xc


@@ -549,7 +575,9 @@ Specifies that the given port on the local (client) host is to be
 forwarded to the given host and port on the remote side.
 This works by allocating a socket to listen to
 .Ar port
 forwarded to the given host and port on the remote side.
 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
+on the local side, optionally bound to the specified
+.Ar bind_address .
+Whenever a connection is made to this port, the

 connection is forwarded over the secure channel, and a connection is
 made to
 .Ar host
 connection is forwarded over the secure channel, and a connection is
 made to
 .Ar host


@@ -557,17 +585,44 @@ port
 .Ar hostport
 from the remote machine.
 Port forwardings can also be specified in the configuration file.
 .Ar hostport
 from the remote machine.
 Port forwardings can also be specified in the configuration file.

-Only root can forward privileged ports.

 IPv6 addresses can be specified with an alternative syntax:
 .Sm off
 .Xo
 IPv6 addresses can be specified with an alternative syntax:
 .Sm off
 .Xo

+.Op Ar bind_address No /

 .Ar port No / Ar host No /
 .Ar port No / Ar host No /

-.Ar hostport .
+.Ar hostport

 .Xc
 .Sm on
 .Xc
 .Sm on

+or by enclosing the address in square brackets.
+Only the superuser can forward privileged ports.
+By default, the local port is bound in accordance with the
+.Cm GatewayPorts
+setting.
+However, an explicit
+.Ar bind_address
+may be used to bind the connection to a specific address.
+The
+.Ar bind_address
+of
+.Dq localhost
+indicates that the listening port be bound for local use only, while an
+empty address or
+.Sq *
+indicates that the port should be available from all interfaces.

 .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 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
+Places the
+.Nm
+client into
+.Dq master
+mode for connection sharing.
+Refer to the description of
+.Cm ControlMaster
+in
+.Xr ssh_config 5
+for details.

 .It Fl m Ar mac_spec
 Additionally, for protocol version 2 a comma-separated list of MAC
 (message authentication code) algorithms can
 .It Fl m Ar mac_spec
 Additionally, for protocol version 2 a comma-separated list of MAC
 (message authentication code) algorithms can


@@ -599,6 +654,18 @@ program will be put in the background.
 needs to ask for a password or passphrase; see also the
 .Fl f
 option.)
 needs to ask for a password or passphrase; see also the
 .Fl f
 option.)

+.It Fl O Ar ctl_cmd
+Control an active connection multiplexing master process.
+When the
+.Fl O
+option is specified, the
+.Ar ctl_cmd
+argument is interpreted and passed to the master process.
+Valid commands are:
+.Dq check
+(check that the master process is running) and
+.Dq exit
+(request the master to exit).

 .It Fl o Ar option
 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
 .It Fl o Ar option
 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


@@ -618,7 +685,9 @@ For full details of the options listed below, and their possible values, see
 .It Compression
 .It CompressionLevel
 .It ConnectionAttempts
 .It Compression
 .It CompressionLevel
 .It ConnectionAttempts

-.It ConnectionTimeout
+.It ConnectTimeout
+.It ControlMaster
+.It ControlPath

 .It DynamicForward
 .It EscapeChar
 .It ForwardAgent
 .It DynamicForward
 .It EscapeChar
 .It ForwardAgent


@@ -628,12 +697,15 @@ For full details of the options listed below, and their possible values, see
 .It GlobalKnownHostsFile
 .It GSSAPIAuthentication
 .It GSSAPIDelegateCredentials
 .It GlobalKnownHostsFile
 .It GSSAPIAuthentication
 .It GSSAPIDelegateCredentials

+.It HashKnownHosts

 .It Host
 .It HostbasedAuthentication
 .It HostKeyAlgorithms
 .It HostKeyAlias
 .It HostName
 .It IdentityFile
 .It Host
 .It HostbasedAuthentication
 .It HostKeyAlgorithms
 .It HostKeyAlias
 .It HostName
 .It IdentityFile

+.It IdentitiesOnly
+.It KbdInteractiveDevices

 .It LocalForward
 .It LogLevel
 .It MACs
 .It LocalForward
 .It LogLevel
 .It MACs


@@ -648,6 +720,7 @@ For full details of the options listed below, and their possible values, see
 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication
 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication

+.It SendEnv

 .It ServerAliveInterval
 .It ServerAliveCountMax
 .It SmartcardDevice
 .It ServerAliveInterval
 .It ServerAliveCountMax
 .It SmartcardDevice


@@ -668,6 +741,7 @@ Quiet mode.
 Causes all warning and diagnostic messages to be suppressed.
 .It Fl R Xo
 .Sm off
 Causes all warning and diagnostic messages to be suppressed.
 .It Fl R Xo
 .Sm off

+.Oo Ar bind_address : Oc

 .Ar port : host : hostport
 .Sm on
 .Xc
 .Ar port : host : hostport
 .Sm on
 .Xc


@@ -682,16 +756,44 @@ made to
 port
 .Ar hostport
 from the local machine.
 port
 .Ar hostport
 from the local machine.

+.Pp

 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.
 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:
+IPv6 addresses can be specified by enclosing the address in square braces or
+using an alternative syntax:

 .Sm off
 .Xo
 .Sm off
 .Xo

-.Ar port No / Ar host No /
-.Ar hostport .
-.Xc
+.Op Ar bind_address No /
+.Ar host No / Ar port No /
+.Ar hostport
+.Xc .

 .Sm on
 .Sm on

+.Pp
+By default, the listening socket on the server will be bound to the loopback
+interface only.
+This may be overriden by specifying a
+.Ar bind_address .
+An empty
+.Ar bind_address ,
+or the address
+.Ql * ,
+indicates that the remote socket should listen on all interfaces.
+Specifying a remote
+.Ar bind_address
+will only succeed if the server's
+.Cm GatewayPorts
+option is enabled (see
+.Xr sshd_config 5 ) .
+.It Fl S Ar ctl_path
+Specifies the location of a control socket for connection sharing.
+Refer to the description of
+.Cm ControlPath
+and
+.Cm ControlMaster
+in
+.Xr ssh_config 5
+for details.

 .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
 .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


@@ -732,10 +834,23 @@ Users with the ability to bypass file permissions on the remote host
 (for the user's X authorization database)
 can access the local X11 display through the forwarded connection.
 An attacker may then be able to perform activities such as keystroke monitoring.
 (for the user's X authorization database)
 can access the local X11 display through the forwarded connection.
 An attacker may then be able to perform activities such as keystroke monitoring.

+.Pp
+For this reason, X11 forwarding is subjected to X11 SECURITY extension
+restrictions by default.
+Please refer to the
+.Nm
+.Fl Y
+option and the
+.Cm ForwardX11Trusted
+directive in
+.Xr ssh_config 5
+for more information.

 .It Fl x
 Disables X11 forwarding.
 .It Fl Y
 Enables trusted X11 forwarding.
 .It Fl x
 Disables X11 forwarding.
 .It Fl Y
 Enables trusted X11 forwarding.

+Trusted X11 forwardings are not subjected to the X11 SECURITY extension
+controls.

 .El
 .Sh CONFIGURATION FILES
 .Nm
 .El
 .Sh CONFIGURATION FILES
 .Nm


@@ -795,7 +910,7 @@ and open an X11 window to read the passphrase.
 This is particularly useful when calling
 .Nm
 from a
 This is particularly useful when calling
 .Nm
 from a

-.Pa .Xsession
+.Pa .xsession

 or related script.
 (Note that on some machines it
 may be necessary to redirect the input from
 or related script.
 (Note that on some machines it
 may be necessary to redirect the input from


@@ -829,7 +944,7 @@ Set to the name of the user logging in.
 Additionally,
 .Nm
 reads
 Additionally,
 .Nm
 reads

-.Pa $HOME/.ssh/environment ,
+.Pa ~/.ssh/environment ,

 and adds lines of the format
 .Dq VARNAME=value
 to the environment if the file exists and if users are allowed to
 and adds lines of the format
 .Dq VARNAME=value
 to the environment if the file exists and if users are allowed to


@@ -840,13 +955,13 @@ option in
 .Xr sshd_config 5 .
 .Sh FILES
 .Bl -tag -width Ds
 .Xr sshd_config 5 .
 .Sh FILES
 .Bl -tag -width Ds

-.It Pa $HOME/.ssh/known_hosts
+.It Pa ~/.ssh/known_hosts

 Records host keys for all hosts the user has logged into that are not
 in
 .Pa /etc/ssh/ssh_known_hosts .
 See
 .Xr sshd 8 .
 Records host keys for all hosts the user has logged into that are not
 in
 .Pa /etc/ssh/ssh_known_hosts .
 See
 .Xr sshd 8 .

-.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
+.It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.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
 Contains the authentication identity of the user.
 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
 These files


@@ -858,21 +973,21 @@ ignores a private key file if it is accessible by others.
 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 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, $HOME/.ssh/id_rsa.pub
+.It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub

 Contains the public key for authentication (public part of the
 identity file in human-readable form).
 The contents of the
 Contains the public key for authentication (public part of the
 identity file in human-readable form).
 The contents of the

-.Pa $HOME/.ssh/identity.pub
+.Pa ~/.ssh/identity.pub

 file should be added to the file
 file should be added to the file

-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys

 on all machines
 where the user wishes to log in using protocol version 1 RSA authentication.
 The contents of the
 on all machines
 where the user wishes to log in using protocol version 1 RSA authentication.
 The contents of the

-.Pa $HOME/.ssh/id_dsa.pub
+.Pa ~/.ssh/id_dsa.pub

 and
 and

-.Pa $HOME/.ssh/id_rsa.pub
+.Pa ~/.ssh/id_rsa.pub

 file should be added to
 file should be added to

-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys

 on all machines
 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
 These files are not
 on all machines
 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
 These files are not


@@ -880,11 +995,13 @@ sensitive and can (but need not) be readable by anyone.
 These files are
 never used automatically and are not necessary; they are only provided for
 the convenience of the user.
 These files are
 never used automatically and are not necessary; they are only provided for
 the convenience of the user.

-.It Pa $HOME/.ssh/config
+.It Pa ~/.ssh/config

 This is the per-user configuration file.
 The file format and configuration options are described in
 .Xr ssh_config 5 .
 This is the per-user configuration file.
 The file format and configuration options are described in
 .Xr ssh_config 5 .

-.It Pa $HOME/.ssh/authorized_keys
+Because of the potential for abuse, this file must have strict permissions:
+read/write for the user, and not accessible by others.
+.It Pa ~/.ssh/authorized_keys

 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
 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


@@ -944,9 +1061,11 @@ be setuid root when that authentication method is used.
 By default
 .Nm
 is not setuid root.
 By default
 .Nm
 is not setuid root.

-.It Pa $HOME/.rhosts
+.It Pa ~/.rhosts

 This file is used in
 This file is used in

-.Em rhosts
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication

 authentication to list the
 host/user pairs that are permitted to log in.
 (Note that this file is
 authentication to list the
 host/user pairs that are permitted to log in.
 (Note that this file is


@@ -965,33 +1084,35 @@ The recommended
 permission for most machines is read/write for the user, and not
 accessible by others.
 .Pp
 permission for most machines is read/write for the user, and not
 accessible by others.
 .Pp

-Note that by default
+Note that

 .Xr sshd 8
 .Xr sshd 8

-will be installed so that it requires successful RSA host
-authentication before permitting
-.Em rhosts
-authentication.
+allows authentication only in combination with client host key
+authentication before permitting log 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
 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 .
+.Pa ~/.ssh/known_hosts .

 The easiest way to do this is to
 connect back to the client from the server machine using ssh; this
 will automatically add the host key to
 The easiest way to do this is to
 connect back to the client from the server machine using ssh; this
 will automatically add the host key to

-.Pa $HOME/.ssh/known_hosts .
-.It Pa $HOME/.shosts
+.Pa ~/.ssh/known_hosts .
+.It Pa ~/.shosts

 This file is used exactly the same way as
 .Pa .rhosts .
 The purpose for
 This file is used exactly the same way as
 .Pa .rhosts .
 The purpose for

-having this file is to be able to use rhosts authentication with
-.Nm
-without permitting login with
+having this file is to be able to use
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication
+authentication without permitting login with

 .Xr rlogin
 or
 .Xr rsh 1 .
 .It Pa /etc/hosts.equiv
 This file is used during
 .Xr rlogin
 or
 .Xr rsh 1 .
 .It Pa /etc/hosts.equiv
 This file is used during

-.Em rhosts
+.Cm RhostsRSAAuthentication
+and
+.Cm HostbasedAuthentication

 authentication.
 It contains
 canonical hosts names, one per line (the full format is described in the
 authentication.
 It contains
 canonical hosts names, one per line (the full format is described in the


@@ -1000,8 +1121,7 @@ manual page).
 If the client host is found in this file, login is
 automatically permitted provided client and server user names are the
 same.
 If the client host is found in this file, login is
 automatically permitted provided client and server user names are the
 same.

-Additionally, successful RSA host authentication is normally
-required.
+Additionally, successful client host key authentication is required.

 This file should only be writable by root.
 .It Pa /etc/shosts.equiv
 This file is processed exactly as
 This file should only be writable by root.
 .It Pa /etc/shosts.equiv
 This file is processed exactly as


@@ -1016,7 +1136,7 @@ when the user logs in just before the user's shell (or command) is started.
 See the
 .Xr sshd 8
 manual page for more information.
 See the
 .Xr sshd 8
 manual page for more information.

-.It Pa $HOME/.ssh/rc
+.It Pa ~/.ssh/rc

 Commands in this file are executed by
 .Nm
 when the user logs in just before the user's shell (or command) is
 Commands in this file are executed by
 .Nm
 when the user logs in just before the user's shell (or command) is


@@ -1024,7 +1144,7 @@ started.
 See the
 .Xr sshd 8
 manual page for more information.
 See the
 .Xr sshd 8
 manual page for more information.

-.It Pa $HOME/.ssh/environment
+.It Pa ~/.ssh/environment

 Contains additional definitions for environment variables, see section
 .Sx ENVIRONMENT
 above.
 Contains additional definitions for environment variables, see section
 .Sx ENVIRONMENT
 above.