- (tim) [configure.ac] Add AC_REVISION. Add sys/time.h to lastlog.h test

[openssh.git] / ssh.1

diff --git a/ssh.1 b/ssh.1
index caa78f4afbab8917e7e77454c7418684398f36c9..f4c677628ce291aafb648d7bd23f9e6b59c171b4 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 1.224 2005/12/20 22:09:41 jmc Exp $
+.\" $OpenBSD: ssh.1,v 1.253 2006/01/30 13:37:49 jmc Exp $

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


@@ -89,7 +89,7 @@ executing commands on a remote machine.
 It is intended to replace rlogin and rsh,
 and provide secure encrypted communications between
 two untrusted hosts over an insecure network.
 It is intended to replace rlogin and rsh,
 and provide secure encrypted communications between
 two untrusted hosts over an insecure network.

-X11 connections and arbitrary TCP/IP ports
+X11 connections and arbitrary TCP ports

 can also be forwarded over the secure channel.
 .Pp
 .Nm
 can also be forwarded over the secure channel.
 .Pp
 .Nm


@@ -146,7 +146,7 @@ of the connection.
 Only useful on systems with more than one address.
 .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and
 Only useful on systems with more than one address.
 .It Fl C
 Requests compression of all data (including stdin, stdout, stderr, and

-data for forwarded X11 and TCP/IP connections).
+data for forwarded X11 and TCP connections).

 The compression algorithm is the same used by
 .Xr gzip 1 ,
 and the
 The compression algorithm is the same used by
 .Xr gzip 1 ,
 and the


@@ -186,24 +186,24 @@ Its use is strongly discouraged due to cryptographic weaknesses.
 The default is
 .Dq 3des .
 .Pp
 The default is
 .Dq 3des .
 .Pp

-For protocol version 2
+For protocol version 2,

 .Ar cipher_spec
 is a comma-separated list of ciphers
 listed in order of preference.
 .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 ,
+The supported ciphers are:
+3des-cbc,
+aes128-cbc,
+aes192-cbc,
+aes256-cbc,
+aes128-ctr,
+aes192-ctr,
+aes256-ctr,
+arcfour128,
+arcfour256,
+arcfour,
+blowfish-cbc,

 and
 and

-.Dq cast128-cbc .
+cast128-cbc.

 The default is:
 .Bd -literal -offset indent
 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
 The default is:
 .Bd -literal -offset indent
 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,


@@ -256,7 +256,7 @@ 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.
 empty address or
 .Sq *
 indicates that the port should be available from all interfaces.

-.It Fl e Ar ch | ^ch | none
+.It Fl e Ar escape_char

 Sets the escape character for sessions with a pty (default:
 .Ql ~ ) .
 The escape character is only recognized at the beginning of a line.
 Sets the escape character for sessions with a pty (default:
 .Ql ~ ) .
 The escape character is only recognized at the beginning of a line.


@@ -292,11 +292,12 @@ something like
 .It Fl g
 Allows remote hosts to connect to local forwarded ports.
 .It Fl I Ar smartcard_device
 .It Fl g
 Allows remote hosts to connect to local forwarded ports.
 .It Fl I Ar smartcard_device

-Specifies which smartcard device to use.
-The argument is the device
+Specify the device

 .Nm
 should use to communicate with a smartcard used for storing the user's
 private RSA key.
 .Nm
 should use to communicate with a smartcard used for storing the user's
 private RSA key.

+This option is only available if support for smartcard devices
+is compiled in (default is no support).

 .It Fl i Ar identity_file
 Selects a file from which the identity (private key) for
 RSA or DSA authentication is read.
 .It Fl i Ar identity_file
 Selects a file from which the identity (private key) for
 RSA or DSA authentication is read.


@@ -368,6 +369,13 @@ Places the
 client into
 .Dq master
 mode for connection sharing.
 client into
 .Dq master
 mode for connection sharing.

+Multiple
+.Fl M
+options places
+.Nm
+into
+.Dq master
+mode with confirmation required before slave connections are accepted.

 Refer to the description of
 .Cm ControlMaster
 in
 Refer to the description of
 .Cm ControlMaster
 in


@@ -469,6 +477,7 @@ For full details of the options listed below, and their possible values, see
 .It Protocol
 .It ProxyCommand
 .It PubkeyAuthentication
 .It Protocol
 .It ProxyCommand
 .It PubkeyAuthentication

+.It RekeyLimit

 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication
 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication


@@ -582,7 +591,18 @@ The maximum is 3.
 .It Fl w Ar tunnel : Ns Ar tunnel
 Requests a
 .Xr tun 4
 .It Fl w Ar tunnel : Ns Ar tunnel
 Requests a
 .Xr tun 4

-device on the client and server like the
+device on the client
+(first
+.Ar tunnel
+arg)
+and server
+(second
+.Ar tunnel
+arg).
+The devices may be specified by numerical ID or the keyword
+.Dq any ,
+which uses the next available tunnel device.
+See also the

 .Cm Tunnel
 directive in
 .Xr ssh_config 5 .
 .Cm Tunnel
 directive in
 .Xr ssh_config 5 .


@@ -624,7 +644,7 @@ The file format and configuration options are described in
 exits with the exit status of the remote command or with 255
 if an error occurred.
 .Sh AUTHENTICATION
 exits with the exit status of the remote command or with 255
 if an error occurred.
 .Sh AUTHENTICATION

-The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
+The OpenSSH SSH client supports SSH protocols 1 and 2.

 Protocol 2 is the default, with
 .Nm
 falling back to protocol 1 if it detects protocol 2 is unsupported.
 Protocol 2 is the default, with
 .Nm
 falling back to protocol 1 if it detects protocol 2 is unsupported.


@@ -769,7 +789,27 @@ prompts the user for a password.
 The password is sent to the remote
 host for checking; however, since all communications are encrypted,
 the password cannot be seen by someone listening on the network.
 The password is sent to the remote
 host for checking; however, since all communications are encrypted,
 the password cannot be seen by someone listening on the network.

-.Sh LOGIN SESSION AND REMOTE EXECUTION
+.Pp
+.Nm
+automatically maintains and checks a database containing
+identification for all hosts it has ever been used with.
+Host keys are stored in
+.Pa ~/.ssh/known_hosts
+in the user's home directory.
+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,
+.Nm
+warns about this and disables password authentication to prevent
+server spoofing or man-in-the-middle attacks,
+which could otherwise be used to circumvent the encryption.
+The
+.Cm StrictHostKeyChecking
+option can be used to control logins to machines whose
+host key is not known or has changed.
+.Pp

 When the user's identity has been accepted by the server, the server
 either executes the given command, or logs into the machine and gives
 the user a normal shell on the remote machine.
 When the user's identity has been accepted by the server, the server
 either executes the given command, or logs into the machine and gives
 the user a normal shell on the remote machine.


@@ -786,7 +826,7 @@ On most systems, setting the escape character to
 will also make the session transparent even if a tty is used.
 .Pp
 The session terminates when the command or shell on the remote
 will also make the session transparent even if a tty is used.
 .Pp
 The session terminates when the command or shell on the remote

-machine exits and all X11 and TCP/IP connections have been closed.
+machine exits and all X11 and TCP connections have been closed.

 .Sh ESCAPE CHARACTERS
 When a pseudo-terminal has been requested,
 .Nm
 .Sh ESCAPE CHARACTERS
 When a pseudo-terminal has been requested,
 .Nm


@@ -811,7 +851,7 @@ are:
 Disconnect.
 .It Cm ~^Z
 Background
 Disconnect.
 .It Cm ~^Z
 Background

-.Nm ssh .
+.Nm .

 .It Cm ~#
 List forwarded connections.
 .It Cm ~&
 .It Cm ~#
 List forwarded connections.
 .It Cm ~&


@@ -829,7 +869,7 @@ Currently this allows the addition of port forwardings using the
 .Fl L
 and
 .Fl R
 .Fl L
 and
 .Fl R

-options (see below).
+options (see above).

 It also allows the cancellation of existing remote port-forwardings
 using
 .Fl KR Ar hostport .
 It also allows the cancellation of existing remote port-forwardings
 using
 .Fl KR Ar hostport .


@@ -845,16 +885,74 @@ option.
 Request rekeying of the connection
 (only useful for SSH protocol version 2 and if the peer supports it).
 .El
 Request rekeying of the connection
 (only useful for SSH protocol version 2 and if the peer supports it).
 .El

-.Sh X11 AND TCP FORWARDING
+.Sh TCP FORWARDING
+Forwarding of arbitrary TCP connections over the secure channel can
+be specified either on the command line or in a configuration file.
+One possible application of TCP forwarding is a secure connection to a
+mail server; another is going through firewalls.
+.Pp
+In the example below, we look at encrypting communication between
+an IRC client and server, even though the IRC server does not directly
+support encrypted communications.
+This works as follows:
+the user connects to the remote host using
+.Nm ,
+specifying a port to be used to forward connections
+to the remote server.
+After that it is possible to start the service which is to be encrypted
+on the client machine,
+connecting to the same local port,
+and
+.Nm
+will encrypt and forward the connection.
+.Pp
+The following example tunnels an IRC session from client machine
+.Dq 127.0.0.1
+(localhost)
+to remote server
+.Dq server.example.com :
+.Bd -literal -offset 4n
+$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
+$ irc -c '#users' -p 1234 pinky 127.0.0.1
+.Ed
+.Pp
+This tunnels a connection to IRC server
+.Dq server.example.com ,
+joining channel
+.Dq #users ,
+nickname
+.Dq pinky ,
+using port 1234.
+It doesn't matter which port is used,
+as long as it's greater than 1023
+(remember, only root can open sockets on privileged ports)
+and doesn't conflict with any ports already in use.
+The connection is forwarded to port 6667 on the remote server,
+since that's the standard port for IRC services.
+.Pp
+The
+.Fl f
+option backgrounds
+.Nm
+and the remote command
+.Dq sleep 10
+is specified to allow an amount of time
+(10 seconds, in the example)
+to start the service which is to be tunnelled.
+If no connections are made within the time specified,
+.Nm
+will exit.
+.Sh X11 FORWARDING

 If the
 .Cm ForwardX11
 variable is set to
 .Dq yes
 (or see the description of the
 If the
 .Cm ForwardX11
 variable is set to
 .Dq yes
 (or see the description of the

-.Fl X
+.Fl X ,
+.Fl x ,

 and
 and

-.Fl x
-options described later)
+.Fl Y
+options above)

 and the user is using X11 (the
 .Ev DISPLAY
 environment variable is set), the connection to the X11 display is
 and the user is using X11 (the
 .Ev DISPLAY
 environment variable is set), the connection to the X11 display is


@@ -896,48 +994,113 @@ variable is set to
 .Fl A
 and
 .Fl a
 .Fl A
 and
 .Fl a

-options described later) and
+options above) and

 the user is using an authentication agent, the connection to the agent
 is automatically forwarded to the remote side.
 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 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 through firewalls.
-.Sh SERVER AUTHENTICATION
-.Nm
-automatically maintains and checks a database containing
-identifications for all hosts it has ever been used with.
-Host keys are stored in
-.Pa ~/.ssh/known_hosts
-in the user's home directory.
-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,
-.Nm
-warns about this and disables password authentication to prevent a
-trojan horse from getting the user's password.
-Another purpose of this mechanism is to prevent man-in-the-middle attacks
-which could otherwise be used to circumvent the encryption.
-The
+.Sh VERIFYING HOST KEYS
+When connecting to a server for the first time,
+a fingerprint of the server's public key is presented to the user
+(unless the option

 .Cm StrictHostKeyChecking
 .Cm StrictHostKeyChecking

-option can be used to prevent logins to machines whose
-host key is not known or has changed.
+has been disabled).
+Fingerprints can be determined using
+.Xr ssh-keygen 1 :
+.Pp
+.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
+.Pp
+If the fingerprint is already known,
+it can be matched and verified,
+and the key can be accepted.
+If the fingerprint is unknown,
+an alternative method of verification is available:
+SSH fingerprints verified by DNS.
+An additional resource record (RR),
+SSHFP,
+is added to a zonefile
+and the connecting client is able to match the fingerprint
+with that of the key presented.
+.Pp
+In this example, we are connecting a client to a server,
+.Dq host.example.com .
+The SSHFP resource records should first be added to the zonefile for
+host.example.com:
+.Bd -literal -offset indent
+$ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
+$ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
+.Ed
+.Pp
+The output lines will have to be added to the zonefile.
+To check that the zone is answering fingerprint queries:

 .Pp
 .Pp

+.Dl $ dig -t SSHFP host.example.com
+.Pp
+Finally the client connects:
+.Bd -literal -offset indent
+$ ssh -o "VerifyHostKeyDNS ask" host.example.com
+[...]
+Matching host key fingerprint found in DNS.
+Are you sure you want to continue connecting (yes/no)?
+.Ed
+.Pp
+See the
+.Cm VerifyHostKeyDNS
+option in
+.Xr ssh_config 5
+for more information.
+.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS

 .Nm
 .Nm

-can be configured to verify host identification using fingerprint resource
-records (SSHFP) published in DNS.
+contains support for Virtual Private Network (VPN) tunnelling
+using the
+.Xr tun 4
+network pseudo-device,
+allowing two networks to be joined securely.

 The
 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 .
+.Xr sshd_config 5
+configuration option
+.Cm PermitTunnel
+controls whether the server supports this,
+and at what level (layer 2 or 3 traffic).
+.Pp
+The following example would connect client network 10.0.50.0/24
+with remote network 10.0.99.0/24, provided that the SSH server
+running on the gateway to the remote network,
+at 192.168.1.15, allows it:
+.Bd -literal -offset indent
+# ssh -f -w 0:1 192.168.1.15 true
+# ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
+.Ed
+.Pp
+Client access may be more finely tuned via the
+.Pa /root/.ssh/authorized_keys
+file (see below) and the
+.Cm PermitRootLogin
+server option.
+The following entry would permit connections on the first
+.Xr tun 4
+device from user
+.Dq jane
+and on the second device from user
+.Dq john ,
+if
+.Cm PermitRootLogin
+is set to
+.Dq forced-commands-only :
+.Bd -literal -offset 2n
+tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
+tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
+.Ed
+.Pp
+Since a SSH-based setup entails a fair amount of overhead,
+it may be more suited to temporary setups,
+such as for wireless VPNs.
+More permanent VPNs are better provided by tools such as
+.Xr ipsecctl 8
+and
+.Xr isakmpd 8 .

 .Sh ENVIRONMENT
 .Nm
 will normally set the following environment variables:
 .Sh ENVIRONMENT
 .Nm
 will normally set the following environment variables:

-.Bl -tag -width LOGNAME
+.Bl -tag -width "SSH_ORIGINAL_COMMAND"

 .It Ev DISPLAY
 The
 .Ev DISPLAY
 .It Ev DISPLAY
 The
 .Ev DISPLAY


@@ -945,9 +1108,12 @@ variable indicates the location of the X11 server.
 It is automatically set by
 .Nm
 to point to a value of the form
 It is automatically set by
 .Nm
 to point to a value of the form

-.Dq hostname:n
-where hostname indicates
-the host where the shell runs, and n is an integer \*(Ge 1.
+.Dq hostname:n ,
+where
+.Dq hostname
+indicates the host where the shell runs, and
+.Sq n
+is an integer \*(Ge 1.

 .Nm
 uses this special value to forward X11 connections over the secure
 channel.
 .Nm
 uses this special value to forward X11 connections over the secure
 channel.


@@ -968,7 +1134,7 @@ Set to the path of the user's mailbox.
 Set to the default
 .Ev PATH ,
 as specified when compiling
 Set to the default
 .Ev PATH ,
 as specified when compiling

-.Nm ssh .
+.Nm .

 .It Ev SSH_ASKPASS
 If
 .Nm
 .It Ev SSH_ASKPASS
 If
 .Nm


@@ -993,15 +1159,16 @@ may be necessary to redirect the input from
 .Pa /dev/null
 to make this work.)
 .It Ev SSH_AUTH_SOCK
 .Pa /dev/null
 to make this work.)
 .It Ev SSH_AUTH_SOCK

-Identifies the path of a unix-domain socket used to communicate with the
-agent.
+Identifies the path of a
+.Ux Ns -domain
+socket used to communicate with the agent.

 .It Ev SSH_CONNECTION
 Identifies the client and server ends of the connection.
 The variable contains
 .It Ev SSH_CONNECTION
 Identifies the client and server ends of the connection.
 The variable contains

-four space-separated values: client ip-address, client port number,
-server ip-address and server port number.
+four space-separated values: client IP address, client port number,
+server IP address, and server port number.

 .It Ev SSH_ORIGINAL_COMMAND
 .It Ev SSH_ORIGINAL_COMMAND

-The variable contains the original command line if a forced command
+This 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
 is executed.
 It can be used to extract the original arguments.
 .It Ev SSH_TTY


@@ -1023,217 +1190,150 @@ reads
 .Pa ~/.ssh/environment ,
 and adds lines of the format
 .Dq VARNAME=value
 .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
+to the environment if the file exists and users are allowed to

 change their environment.
 For more information, see the
 .Cm PermitUserEnvironment
 option in
 .Xr sshd_config 5 .
 .Sh FILES
 change their environment.
 For more information, see the
 .Cm PermitUserEnvironment
 option in
 .Xr sshd_config 5 .
 .Sh FILES

-.Bl -tag -width Ds
-.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 .
-.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.
+.Bl -tag -width Ds -compact
+.It ~/.rhosts
+This file is used for host-based authentication (see above).
+On some machines this file may need to be
+world-readable if the user's home directory is on an NFS partition,
+because
+.Xr sshd 8
+reads it as root.
+Additionally, this file must be owned by the user,
+and must not have write permissions for anyone else.
+The recommended
+permission for most machines is read/write for the user, and not
+accessible by others.
+.Pp
+.It ~/.shosts
+This file is used in exactly the same way as
+.Pa .rhosts ,
+but allows host-based authentication without permitting login with
+rlogin/rsh.
+.Pp
+.It ~/.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
+manual page.
+This file is not highly sensitive, but the recommended
+permissions are read/write for the user, and not accessible by others.
+.Pp
+.It ~/.ssh/config
+This is the per-user configuration file.
+The file format and configuration options are described in
+.Xr ssh_config 5 .
+Because of the potential for abuse, this file must have strict permissions:
+read/write for the user, and not accessible by others.
+.Pp
+.It ~/.ssh/environment
+Contains additional definitions for environment variables; see
+.Sx ENVIRONMENT ,
+above.
+.Pp
+.It ~/.ssh/identity
+.It ~/.ssh/id_dsa
+.It ~/.ssh/id_rsa
+Contains the private key for authentication.

 These files
 contain sensitive data and should be readable by the user but not
 accessible by others (read/write/execute).
 These files
 contain sensitive data and should be readable by the user but not
 accessible by others (read/write/execute).

-Note that

 .Nm
 .Nm

-ignores a private key file if it is accessible by others.
+will simply ignore a private key file if it is accessible by others.

 It is possible to specify a passphrase when
 It is possible to specify a passphrase when

-generating the key; the passphrase will be used to encrypt the
+generating the key which will be used to encrypt the

 sensitive part of this file using 3DES.
 sensitive part of this file using 3DES.

-.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
-.Pa ~/.ssh/identity.pub
-file should be added to the file
-.Pa ~/.ssh/authorized_keys
-on all machines
-where the user wishes to log in using protocol version 1 RSA authentication.
-The contents of the
-.Pa ~/.ssh/id_dsa.pub
-and
-.Pa ~/.ssh/id_rsa.pub
-file should be added to
-.Pa ~/.ssh/authorized_keys
-on all machines
-where the user wishes to log in using protocol version 2 DSA/RSA authentication.
+.Pp
+.It ~/.ssh/identity.pub
+.It ~/.ssh/id_dsa.pub
+.It ~/.ssh/id_rsa.pub
+Contains the public key for authentication.

 These files are not
 sensitive and can (but need not) be readable by anyone.
 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 are only provided for
-the convenience of the user.
-.It Pa ~/.ssh/config
-This is the per-user configuration file.
-The file format and configuration options are described in
-.Xr ssh_config 5 .
-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
-manual page.
-In the simplest form the format is the same as the
-.Pa .pub
-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/ssh_known_hosts
-Systemwide list of known host keys.
-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, public key and optional comment field.
-When different names are used
-for the same machine, all such names should be listed, separated by
-commas.
-The format is described in the
-.Xr sshd 8
-manual page.

 .Pp
 .Pp

-The canonical system name (as returned by name servers) is used by
+.It ~/.ssh/known_hosts
+Contains a list of host keys for all hosts the user has logged into
+that are not already in the systemwide list of known host keys.
+See

 .Xr sshd 8
 .Xr sshd 8

-to verify the client host when logging in; other names are needed because
+for further details of the format of this file.
+.Pp
+.It ~/.ssh/rc
+Commands in this file are executed by

 .Nm
 .Nm

-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.
+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.
+.Pp
+.It /etc/hosts.equiv
+This file is for host-based authentication (see above).
+It should only be writable by root.
+.Pp
+.It /etc/shosts.equiv
+This file is used in exactly the same way as
+.Pa hosts.equiv ,
+but allows host-based authentication without permitting login with
+rlogin/rsh.
+.Pp

 .It Pa /etc/ssh/ssh_config
 Systemwide configuration file.
 The file format and configuration options are described in
 .Xr ssh_config 5 .
 .It Pa /etc/ssh/ssh_config
 Systemwide configuration file.
 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
+.Pp
+.It /etc/ssh/ssh_host_key
+.It /etc/ssh/ssh_host_dsa_key
+.It /etc/ssh/ssh_host_rsa_key

 These three files contain the private parts of the host keys
 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,
+and are used for host-based authentication.
+If protocol version 1 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
 .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
+to access the host keys,
+eliminating the requirement that

 .Nm
 .Nm

-be setuid root when that authentication method is used.
+be setuid root when host-based authentication is used.

 By default
 .Nm
 is not setuid root.
 By default
 .Nm
 is not setuid root.

-.It Pa ~/.rhosts
-This file is used in
-.Cm RhostsRSAAuthentication
-and
-.Cm HostbasedAuthentication
-authentication to list the
-host/user pairs that are permitted to log in.
-(Note that this file is
-also used by rlogin and rsh, which makes using this file insecure.)
-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.
-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
-reads it as root.
-Additionally, this file must be owned by the user,
-and must not have write permissions for anyone else.
-The recommended
-permission for most machines is read/write for the user, and not
-accessible by others.

 .Pp
 .Pp

-Note that
-.Xr sshd 8
-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
-.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
-.Pa ~/.ssh/known_hosts .
-.It Pa ~/.shosts
-This file is used exactly the same way as
-.Pa .rhosts .
-The purpose for
-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
-.Cm RhostsRSAAuthentication
-and
-.Cm HostbasedAuthentication
-authentication.
-It contains
-canonical hosts names, one per line (the full format is described in the
-.Xr sshd 8
-manual page).
-If the client host is found in this file, login is
-automatically permitted provided client and server user names are the
-same.
-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
-.Pa /etc/hosts.equiv .
-This file may be useful to permit logins using
-.Nm
-but not using rsh/rlogin.
-.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.
-See the
+.It /etc/ssh/ssh_known_hosts
+Systemwide list of known host keys.
+This file should be prepared by the
+system administrator to contain the public host keys of all machines in the
+organization.
+It should be world-readable.
+See

 .Xr sshd 8
 .Xr sshd 8

-manual page for more information.
-.It Pa ~/.ssh/rc
+for further details of the format of this file.
+.Pp
+.It /etc/ssh/sshrc

 Commands in this file are executed by
 .Nm
 Commands in this file are executed by
 .Nm

-when the user logs in just before the user's shell (or command) is
-started.
+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 ~/.ssh/environment
-Contains additional definitions for environment variables, see section
-.Sx ENVIRONMENT
-above.

 .El
 .Sh SEE ALSO
 .El
 .Sh SEE ALSO

-.Xr gzip 1 ,
-.Xr rsh 1 ,

 .Xr scp 1 ,
 .Xr sftp 1 ,
 .Xr ssh-add 1 ,
 .Xr ssh-agent 1 ,
 .Xr ssh-keygen 1 ,
 .Xr scp 1 ,
 .Xr sftp 1 ,
 .Xr ssh-add 1 ,
 .Xr ssh-agent 1 ,
 .Xr ssh-keygen 1 ,

-.Xr telnet 1 ,
+.Xr ssh-keyscan 1 ,
+.Xr tun 4 ,

 .Xr hosts.equiv 5 ,
 .Xr ssh_config 5 ,
 .Xr ssh-keysign 8 ,
 .Xr hosts.equiv 5 ,
 .Xr ssh_config 5 ,
 .Xr ssh-keysign 8 ,