src/usr.bin/ssh/ssh_config.5 - diff

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Diff for /src/usr.bin/ssh/ssh_config.5 between version 1.6 and 1.6.2.3

version 1.6, 2003/02/06 09:27:29

version 1.6.2.3, 2004/03/04 18:18:17

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given after the keyword.

.Ql \&*

and

.Ql ?

.Ql \&?

can be used as wildcards in the

patterns.

A single

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.Ar hostname

argument given on the command line (i.e., the name is not converted to

a canonicalized host name before matching).

.It Cm AFSTokenPassing

.It Cm AddressFamily

Specifies whether to pass AFS tokens to remote host.

Specifies which address family to use when connecting.

The argument to this keyword must be

Valid arguments are

.Dq yes

.Dq any ,

.Dq inet

.Dq no .

(Use IPv4 only) or

This option applies to protocol version 1 only.

.Dq inet6

(Use IPv6 only.)

.It Cm BatchMode

If set to

.Dq yes ,

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client for interoperability with legacy protocol 1 implementations

that do not support the

.Ar 3des

cipher. Its use is strongly discouraged due to cryptographic

cipher.

weaknesses.

Its use is strongly discouraged due to cryptographic weaknesses.

The default is

.Dq 3des .

.It Cm Ciphers

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in order of preference.

Multiple ciphers must be comma-separated.

The default is

.Pp

.Bd -literal

``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,

aes192-cbc,aes256-cbc''

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.It Cm ClearAllForwardings

Specifies that all local, remote and dynamic port forwardings

specified in the configuration files or on the command line be

cleared. This option is primarily useful when used from the

cleared.

This option is primarily useful when used from the

.Nm ssh

command line to clear port forwardings set in

configuration files, and is automatically set by

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The argument must be an integer.

This may be useful in scripts if the connection sometimes fails.

The default is 1.

.It Cm ConnectTimeout

Specifies the timeout (in seconds) used when connecting to the ssh

server, instead of using the default system TCP timeout.

This value is used only when the target is down or really unreachable,

not when it refuses the connection.

.It Cm DynamicForward

Specifies that a TCP/IP port on the local machine be forwarded

over the secure channel, and the application

protocol is then used to determine where to connect to from the

remote machine. The argument must be a port number.

remote machine.

Currently the SOCKS4 protocol is supported, and

The argument must be a port number.

Currently the SOCKS4 and SOCKS5 protocols are supported, and

.Nm ssh

will act as a SOCKS4 server.

will act as a SOCKS server.

Multiple forwardings may be specified, and

additional forwardings can be given on the command line. Only

additional forwardings can be given on the command line.

the superuser can forward privileged ports.

Only the superuser can forward privileged ports.

.It Cm EnableSSHKeysign

Setting this option to

.Dq yes

in the global client configuration file

.Pa /etc/ssh/ssh_config

enables the use of the helper program

.Xr ssh-keysign 8

during

.Cm HostbasedAuthentication .

The argument must be

.Dq yes

.Dq no .

The default is

.Dq no .

This option should be placed in the non-hostspecific section.

See

.Xr ssh-keysign 8

for more information.

.It Cm EscapeChar

Sets the escape character (default:

.Ql ~ ) .

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The default is

.Dq no .

.Pp

Agent forwarding should be enabled with caution. Users with the

Agent forwarding should be enabled with caution.

ability to bypass file permissions on the remote host (for the agent's

Users with the ability to bypass file permissions on the remote host

Unix-domain socket) can access the local agent through the forwarded

(for the agent's Unix-domain socket)

connection. An attacker cannot obtain key material from the agent,

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.

.It Cm ForwardX11

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The default is

.Dq no .

.Pp

X11 forwarding should be enabled with caution. Users with the ability

X11 forwarding should be enabled with caution.

to bypass file permissions on the remote host (for the user's X

Users with the ability to bypass file permissions on the remote host

authorization database) can access the local X11 display through the

(for the user's X11 authorization database)

forwarded connection. An attacker may then be able to perform

can access the local X11 display through the forwarded connection.

activities such as keystroke monitoring.

An attacker may then be able to perform activities such as keystroke monitoring

if the

.Cm ForwardX11Trusted

option is also enabled.

.It Cm ForwardX11Trusted

If the this option is set to

.Dq yes

then remote X11 clients will have full access to the original X11 display.

If this option is set to

.Dq no

then remote X11 clients will be considered untrusted and prevented

from stealing or tampering with data belonging to trusted X11

clients.

.Pp

The default is

.Dq no .

.Pp

See the X11 SECURITY extension specification for full details on

the restrictions imposed on untrusted clients.

.It Cm GatewayPorts

Specifies whether remote hosts are allowed to connect to local

forwarded ports.

By default,

.Nm ssh

binds local port forwardings to the loopback address. This

binds local port forwardings to the loopback address.

prevents other remote hosts from connecting to forwarded ports.

This prevents other remote hosts from connecting to forwarded ports.

.Cm GatewayPorts

can be used to specify that

.Nm ssh

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Specifies a file to use for the global

host key database instead of

.Pa /etc/ssh/ssh_known_hosts .

.It Cm GSSAPIAuthentication

Specifies whether user authentication based on GSSAPI is allowed.

The default is

.Dq no .

Note that this option applies to protocol version 2 only.

.It Cm GSSAPIDelegateCredentials

Forward (delegate) credentials to the server.

The default is

.Dq no .

Note that this option applies to protocol version 2 only.

.It Cm HostbasedAuthentication

Specifies whether to try rhosts based authentication with public key

authentication.

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specifications).

.It Cm IdentityFile

Specifies a file from which the user's RSA or DSA authentication identity

is read. The default is

is read.

The default is

.Pa $HOME/.ssh/identity

for protocol version 1, and

.Pa $HOME/.ssh/id_rsa

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It is possible to have

multiple identity files specified in configuration files; all these

identities will be tried in sequence.

.It Cm KeepAlive

Specifies whether the system should send TCP keepalive messages to the

other side.

If they are sent, death of the connection or crash of one

of the machines will be properly noticed.

However, this means that

connections will die if the route is down temporarily, and some people

find it annoying.

.Pp

The default is

.Dq yes

(to send keepalives), and the client will notice

if the network goes down or the remote host dies.

This is important in scripts, and many users want it too.

.Pp

To disable keepalives, the value should be set to

.Dq no .

.It Cm KerberosAuthentication

Specifies whether Kerberos authentication will be used.

The argument to this keyword must be

.Dq yes

.Dq no .

.It Cm KerberosTgtPassing

Specifies whether a Kerberos TGT will be forwarded to the server.

This will only work if the Kerberos server is actually an AFS kaserver.

The argument to this keyword must be

.Dq yes

.Dq no .

.It Cm LocalForward

Specifies that a TCP/IP port on the local machine be forwarded over

the secure channel to the specified host and port from the remote machine.

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.Nm ssh .

The possible values are:

QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.

The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2

The default is INFO.

and DEBUG3 each specify higher levels of verbose output.

DEBUG and DEBUG1 are equivalent.

DEBUG2 and DEBUG3 each specify higher levels of verbose output.

.It Cm MACs

Specifies the MAC (message authentication code) algorithms

in order of preference.

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Default is 22.

.It Cm PreferredAuthentications

Specifies the order in which the client should try protocol 2

authentication methods. This allows a client to prefer one method (e.g.

authentication methods.

This allows a client to prefer one method (e.g.

.Cm keyboard-interactive )

over another method (e.g.

.Cm password )

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Host key management will be done using the

HostName of the host being connected (defaulting to the name typed by

the user).

Setting the command to

.Dq none

disables this option entirely.

Note that

.Cm CheckHostIP

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Multiple forwardings may be specified, and additional

forwardings can be given on the command line.

Only the superuser can forward privileged ports.

.It Cm RhostsAuthentication

Specifies whether to try rhosts based authentication.

Note that this

declaration only affects the client side and has no effect whatsoever

on security.

Most servers do not permit RhostsAuthentication because it

is not secure (see

.Cm RhostsRSAAuthentication ) .

The argument to this keyword must be

.Dq yes

.Dq no .

The default is

.Dq no .

This option applies to protocol version 1 only and requires

.Nm ssh

to be setuid root and

.Cm UsePrivilegedPort

to be set to

.Dq yes .

.It Cm RhostsRSAAuthentication

Specifies whether to try rhosts based authentication with RSA host

authentication.

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The default is

.Dq yes .

Note that this option applies to protocol version 1 only.

.It Cm ServerAliveInterval

Sets a timeout interval in seconds after which if no data has been received

from the server,

.Nm ssh

will send a message through the encrypted

channel to request a response from the server.

The default

is 0, indicating that these messages will not be sent to the server.

This option applies to protocol version 2 only.

.It Cm ServerAliveCountMax

Sets the number of server alive messages (see above) which may be

sent without

.Nm ssh

receiving any messages back from the server.

If this threshold is reached while server alive messages are being sent,

.Nm ssh

will disconnect from the server, terminating the session.

It is important to note that the use of server alive messages is very

different from

.Cm TCPKeepAlive

(below).

The server alive messages are sent through the encrypted channel

and therefore will not be spoofable.

The TCP keepalive option enabled by

.Cm TCPKeepAlive

is spoofable.

The server alive mechanism is valuable when the client or

server depend on knowing when a connection has become inactive.

.Pp

The default value is 3.

If, for example,

.Cm ServerAliveInterval

(above) is set to 15, and

.Cm ServerAliveCountMax

is left at the default, if the server becomes unresponsive ssh

will disconnect after approximately 45 seconds.

.It Cm SmartcardDevice

Specifies which smartcard device to use. The argument to this keyword is

Specifies which smartcard device to use.

the device

The argument to this keyword is the device

.Nm ssh

should use to communicate with a smartcard used for storing the user's

private RSA key. By default, no device is specified and smartcard support

private RSA key.

is not activated.

By default, no device is specified and smartcard support is not activated.

.It Cm StrictHostKeyChecking

If this flag is set to

.Dq yes ,

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.Dq ask .

The default is

.Dq ask .

.It Cm TCPKeepAlive

Specifies whether the system should send TCP keepalive messages to the

other side.

If they are sent, death of the connection or crash of one

of the machines will be properly noticed.

However, this means that

connections will die if the route is down temporarily, and some people

find it annoying.

.Pp

The default is

.Dq yes

(to send TCP keepalive messages), and the client will notice

if the network goes down or the remote host dies.

This is important in scripts, and many users want it too.

.Pp

To disable TCP keepalive messages, the value should be set to

.Dq no .

.It Cm UsePrivilegedPort

Specifies whether to use a privileged port for outgoing connections.

The argument must be

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must be setuid root.

Note that this option must be set to

.Dq yes

for

.Cm RhostsAuthentication

and

.Cm RhostsRSAAuthentication

authentications are needed with older servers.

with older servers.

.It Cm User

Specifies the user to log in as.

This can be useful when a different user name is used on different machines.

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Specifies a file to use for the user

host key database instead of

.Pa $HOME/.ssh/known_hosts .

.It Cm VerifyHostKeyDNS

Specifies whether to verify the remote key using DNS and SSHFP resource

records.

If this option is set to

.Dq yes ,

the client will implicitly trust keys that match a secure fingerprint

from DNS.

Insecure fingerprints will be handled as if this option was set to

.Dq ask .

If this option is set to

.Dq ask ,

information on fingerprint match will be displayed, but the user will still

need to confirm new host keys according to the

.Cm StrictHostKeyChecking

option.

The argument must be

.Dq yes ,

.Dq no

.Dq ask .

The default is

.Dq no .

Note that this option applies to protocol version 2 only.

.It Cm XAuthLocation

Specifies the full pathname of the

.Xr xauth 1

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for those users who do not have a configuration file.

This file must be world-readable.

.El

.Sh SEE ALSO

.Xr ssh 1

.Sh AUTHORS

OpenSSH is a derivative of the original and free

ssh 1.2.12 release by Tatu Ylonen.

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created OpenSSH.

Markus Friedl contributed the support for SSH

protocol versions 1.5 and 2.0.

.Sh SEE ALSO

.Xr ssh 1