.\" (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 1.290 2010/01/11 01:39:46 dtucker 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\ \&
.Sm on
.Oc
.Op Fl S Ar ctl_path
-.Bk -words
-.Op Fl w Ar tunnel : Ns Ar tunnel
+.Op Fl W Ar host : Ns Ar port
+.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
.Sh DESCRIPTION
.Nm
(SSH client) is a program for logging into a remote machine and for
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
.Pp
Agent forwarding should be enabled with caution.
Users with the ability to bypass file permissions on the remote host
-(for the agent's Unix-domain socket)
-can access the local agent through the forwarded connection.
+(for the agent's
+.Ux Ns -domain
+socket) can access the local agent through the forwarded connection.
An attacker cannot obtain key material from the agent,
however they can perform operations on the keys that enable them to
authenticate using the identities loaded into the agent.
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 ,
-and
-.Dq cast128-cbc .
-The default is:
-.Bd -literal -offset indent
-aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
-arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
-aes192-ctr,aes256-ctr
-.Ed
+See the
+.Cm Ciphers
+keyword for more information.
.It Fl D Xo
.Sm off
.Oo Ar bind_address : Oc
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 Ar host : Ns Ar port
+Requests that standard input and output on the client be forwarded to
+.Ar host
+on
+.Ar port
+over the secure channel.
+Implies
+.Fl N ,
+.Fl T ,
+.Cm ExitOnForwardFailure
+and
+.Cm ClearAllForwardings
+and works with Protocol version 2 only.
+.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
-.Sh AUTHENTICATION
-The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
-Protocol 2 is the default, with
+.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
-falling back to protocol 1 if it detects protocol 2 is unsupported.
-These settings may be altered using the
+exits with the exit status of the remote command or with 255
+if an error occurred.
+.Sh AUTHENTICATION
+The OpenSSH SSH client supports SSH protocols 1 and 2.
+The default is to use protocol 2 only,
+though this can be changed via the
.Cm Protocol
option in
-.Xr ssh_config 5 ,
-or enforced using the
+.Xr ssh_config 5
+or the
.Fl 1
and
.Fl 2
options (see above).
Both protocols support similar authentication methods,
-but protocol 2 is preferred since
+but protocol 2 is the default 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