.\" (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 1.223 2005/12/20 22:02:50 jmc Exp $
-.Dd September 25, 1999
+.\" $OpenBSD: ssh.1,v 1.282 2009/02/12 03:44:25 djm Exp $
+.Dd $Mdocdate$
.Dt SSH 1
.Os
.Sh NAME
.Nd OpenSSH SSH client (remote login program)
.Sh SYNOPSIS
.Nm ssh
-.Op Fl 1246AaCfgkMNnqsTtVvXxY
+.Op Fl 1246AaCfgKkMNnqsTtVvXxYy
.Op Fl b Ar bind_address
.Op Fl c Ar cipher_spec
.Oo Fl D\ \&
.Oc
.Op Fl S Ar ctl_path
.Bk -words
-.Op Fl w Ar tunnel : Ns Ar tunnel
+.Oo Fl w Ar local_tun Ns
+.Op : Ns Ar remote_tun Oc
.Oo Ar user Ns @ Oc Ns Ar hostname
.Op Ar command
.Ek
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
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 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.
-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
-.Dq cast128-cbc .
+cast128-cbc.
The default is:
.Bd -literal -offset indent
aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
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.
The recommended way to start X11 programs at a remote site is with
something like
.Ic ssh -f host xterm .
+.Pp
+If the
+.Cm ExitOnForwardFailure
+configuration option is set to
+.Dq yes ,
+then a client started with
+.Fl f
+will wait for all remote port forwards to be successfully established
+before placing itself in the background.
.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.
+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.
.Fl i
options (and multiple identities specified in
configuration files).
+.It Fl K
+Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
+credentials to the server.
.It Fl k
Disables forwarding (delegation) of GSSAPI credentials to the server.
.It Fl L Xo
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
.It ControlPath
.It DynamicForward
.It EscapeChar
+.It ExitOnForwardFailure
.It ForwardAgent
.It ForwardX11
.It ForwardX11Trusted
.It Protocol
.It ProxyCommand
.It PubkeyAuthentication
+.It RekeyLimit
.It RemoteForward
.It RhostsRSAAuthentication
.It RSAAuthentication
.It User
.It UserKnownHostsFile
.It VerifyHostKeyDNS
+.It VisualHostKey
.It XAuthLocation
.El
.It Fl p Ar port
per-host basis in the configuration file.
.It Fl q
Quiet mode.
-Causes all warning and diagnostic messages to be suppressed.
+Causes most warning and diagnostic messages to be suppressed.
.It Fl R Xo
.Sm off
.Oo Ar bind_address : Oc
.Pp
By default, the listening socket on the server will be bound to the loopback
interface only.
-This may be overriden by specifying a
+This may be overridden by specifying a
.Ar bind_address .
An empty
.Ar bind_address ,
.Cm GatewayPorts
option is enabled (see
.Xr sshd_config 5 ) .
+.Pp
+If the
+.Ar port
+argument is
+.Ql 0 ,
+the listen port will be dynamically allocated on the server and reported
+to the client at run time.
.It Fl S Ar ctl_path
Specifies the location of a control socket for connection sharing.
Refer to the description of
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.
+e.g. when implementing menu services.
Multiple
.Fl t
options force tty allocation, even if
.Fl v
options increase the verbosity.
The maximum is 3.
-.It Fl w Ar tunnel : Ns Ar tunnel
-Requests a
+.It Fl w Xo
+.Ar local_tun Ns Op : Ns Ar remote_tun
+.Xc
+Requests
+tunnel
+device forwarding with the specified
.Xr tun 4
-device on the client and server like the
+devices between the client
+.Pq Ar local_tun
+and the server
+.Pq Ar remote_tun .
+.Pp
+The devices may be specified by numerical ID or the keyword
+.Dq any ,
+which uses the next available tunnel device.
+If
+.Ar remote_tun
+is not specified, it defaults to
+.Dq any .
+See also the
.Cm Tunnel
-directive in
+and
+.Cm TunnelDevice
+directives in
.Xr ssh_config 5 .
+If the
+.Cm Tunnel
+directive is unset, it is set to the default tunnel mode, which is
+.Dq point-to-point .
.It Fl X
Enables X11 forwarding.
This can also be specified on a per-host basis in a configuration file.
Enables trusted X11 forwarding.
Trusted X11 forwardings are not subjected to the X11 SECURITY extension
controls.
+.It Fl y
+Send log information using the
+.Xr syslog 3
+system module.
+By default this information is sent to stderr.
.El
+.Pp
+.Nm
+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 .
+.Pp
+.Nm
+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.
but protocol 2 is preferred since
it provides additional mechanisms for confidentiality
(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
-and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
+and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
Protocol 1 lacks a strong mechanism for ensuring the
integrity of the connection.
.Pp
The methods available for authentication are:
+GSSAPI-based authentication,
host-based authentication,
public key authentication,
challenge-response authentication,
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.
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.
-The exit status of the remote program is returned as the exit status of
-.Nm ssh .
-.Pp
-.Nm
-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 .
+machine exits and all X11 and TCP connections have been closed.
.Sh ESCAPE CHARACTERS
When a pseudo-terminal has been requested,
.Nm
Disconnect.
.It Cm ~^Z
Background
-.Nm ssh .
+.Nm .
.It Cm ~#
List forwarded connections.
.It Cm ~&
.It Cm ~C
Open command line.
Currently this allows the addition of port forwardings using the
-.Fl L
-and
+.Fl L ,
.Fl R
-options (see below).
+and
+.Fl D
+options (see above).
It also allows the cancellation of existing remote port-forwardings
using
-.Fl KR Ar hostport .
+.Sm off
+.Fl KR Oo Ar bind_address : Oc Ar port .
+.Sm on
.Ic !\& Ns Ar command
allows the user to execute a local command if the
.Ic PermitLocalCommand
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
-.Fl X
+.Fl X ,
+.Fl x ,
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
.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.
-.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
-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 the key can be accepted or rejected.
+Because of the difficulty of comparing host keys
+just by looking at hex strings,
+there is also support to compare host keys visually,
+using
+.Em random art .
+By setting the
+.Cm VisualHostKey
+option to
+.Dq yes ,
+a small ASCII graphic gets displayed on every login to a server, no matter
+if the session itself is interactive or not.
+By learning the pattern a known server produces, a user can easily
+find out that the host key has changed when a completely different pattern
+is displayed.
+Because these patterns are not unambiguous however, a pattern that looks
+similar to the pattern remembered only gives a good probability that the
+host key is the same, not guaranteed proof.
+.Pp
+To get a listing of the fingerprints along with their random art for
+all known hosts, the following command line can be used:
+.Pp
+.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
+.Pp
+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 -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
+.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
-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
-.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 using a point-to-point connection
+from 10.1.1.1 to 10.1.1.2,
+provided that the SSH server running on the gateway to the remote network,
+at 192.168.1.15, allows it.
+.Pp
+On the client:
+.Bd -literal -offset indent
+# ssh -f -w 0:1 192.168.1.15 true
+# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
+# route add 10.0.99.0/24 10.1.1.2
+.Ed
+.Pp
+On the server:
+.Bd -literal -offset indent
+# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
+# route add 10.0.50.0/24 10.1.1.1
+.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
+.Xr tun 4
+device 1 from user
+.Dq jane
+and on tun device 2 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 tun2" ssh-rsa ... john
+.Ed
+.Pp
+Since an 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:
-.Bl -tag -width LOGNAME
+.Bl -tag -width "SSH_ORIGINAL_COMMAND"
.It Ev DISPLAY
The
.Ev DISPLAY
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.
Set to the default
.Ev PATH ,
as specified when compiling
-.Nm ssh .
+.Nm .
.It Ev SSH_ASKPASS
If
.Nm
.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
-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
-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
this variable is not set.
.It Ev TZ
This variable is set to indicate the present time zone if it
-was set when the daemon was started (i.e., 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 ~/.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
-.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/
+This directory is the default location for all user-specific configuration
+and authentication information.
+There is no general requirement to keep the entire contents of this directory
+secret, but the recommended permissions are read/write/execute for the user,
+and not accessible by others.
+.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).
-Note that
.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
-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.
-.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
-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
-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
-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
-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_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
-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
-to access the host keys for
-.Cm HostbasedAuthentication .
-This eliminates the requirement that
+to access the host keys,
+eliminating the requirement that
.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.
-.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
-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
-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
-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.
-.It Pa ~/.ssh/environment
-Contains additional definitions for environment variables, see section
-.Sx ENVIRONMENT
-above.
.El
-.Sh DIAGNOSTICS
-.Nm
-exits with the exit status of the remote command or with 255
-if an error occurred.
.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 telnet 1 ,
+.Xr ssh-keyscan 1 ,
+.Xr tun 4 ,
.Xr hosts.equiv 5 ,
.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
+.%R RFC 4250
+.%T "The Secure Shell (SSH) Protocol Assigned Numbers"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4251
+.%T "The Secure Shell (SSH) Protocol Architecture"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4252
+.%T "The Secure Shell (SSH) Authentication Protocol"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4253
+.%T "The Secure Shell (SSH) Transport Layer Protocol"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4254
+.%T "The Secure Shell (SSH) Connection Protocol"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4255
+.%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4256
+.%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4335
+.%T "The Secure Shell (SSH) Session Channel Break Extension"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4344
+.%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4345
+.%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4419
+.%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
+.%D 2006
+.Re
+.Rs
+.%R RFC 4716
+.%T "The Secure Shell (SSH) Public Key File Format"
+.%D 2006
+.Re
+.Rs
+.%T "Hash Visualization: a New Technique to improve Real-World Security"
+.%A A. Perrig
+.%A D. Song
+.%D 1999
+.%O "International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)"
.Re
.Sh AUTHORS
OpenSSH is a derivative of the original and free
andersk / openssh.git / blobdiff