ssh_config — OpenSSH SSH client configuration files at Linux.org

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SSH_CONFIG(5) BSD File Formats Manual SSH_CONFIG(5)

NAME
ssh_config — OpenSSH SSH client configuration files

SYNOPSIS

~/.ssh/config
/etc/ssh/ssh_config

DESCRIPTION
ssh(1) obtains configuration data from the following sources in the following order:

1. command-line options
2. user's configuration file (~/.ssh/config)
3. system-wide configuration file (/etc/ssh/ssh_config)

For each parameter, the first obtained value will be used. The configuration files contain sections separated
by “Host” specifications, and that section is only applied for hosts that match one of the patterns given in the
specification. The matched host name is the one given on the command line.

Since the first obtained value for each parameter is used, more host-specific declarations should be given near
the beginning of the file, and general defaults at the end.

The configuration file has the following format:

Empty lines and lines starting with ‘#’ are comments. Otherwise a line is of the format “keyword arguments”.
Configuration options may be separated by whitespace or optional whitespace and exactly one ‘=’; the latter for‐
mat is useful to avoid the need to quote whitespace when specifying configuration options using the ssh, scp,
and sftp -o option. Arguments may optionally be enclosed in double quotes (") in order to represent arguments
containing spaces.

The possible keywords and their meanings are as follows (note that keywords are case-insensitive and arguments
are case-sensitive):

Host Restricts the following declarations (up to the next Host or Match keyword) to be only for those hosts
that match one of the patterns given after the keyword. If more than one pattern is provided, they
should be separated by whitespace. A single ‘*’ as a pattern can be used to provide global defaults for
all hosts. The host is the hostname argument given on the command line (i.e. the name is not converted
to a canonicalized host name before matching).

A pattern entry may be negated by prefixing it with an exclamation mark (‘!’). If a negated entry is
matched, then the Host entry is ignored, regardless of whether any other patterns on the line match.
Negated matches are therefore useful to provide exceptions for wildcard matches.

See PATTERNS for more information on patterns.

Match Restricts the following declarations (up to the next Host or Match keyword) to be used only when the
conditions following the Match keyword are satisfied. Match conditions are specified using one or more
keyword/criteria pairs or the single token all which matches all criteria. The available keywords are:
exec, host, originalhost, user, and localuser.

The exec keyword executes the specified command under the user's shell. If the command returns a zero
exit status then the condition is considered true. Commands containing whitespace characters must be
quoted. The following character sequences in the command will be expanded prior to execution: ‘%L’ will
be substituted by the first component of the local host name, ‘%l’ will be substituted by the local host
name (including any domain name), ‘%h’ will be substituted by the target host name, ‘%n’ will be substi‐
tuted by the original target host name specified on the command-line, ‘%p’ the destination port, ‘%r’ by
the remote login username, and ‘%u’ by the username of the user running ssh(1).

The other keywords' criteria must be single entries or comma-separated lists and may use the wildcard
other batch jobs where no user is present to supply the password. The argument must be “yes” or “no”.
The default is “no”.

BindAddress
Use the specified address on the local machine as the source address of the connection. Only useful on
systems with more than one address. Note that this option does not work if UsePrivilegedPort is set to
“yes”.

CanonicalDomains
When CanonicalizeHostname is enabled, this option specifies the list of domain suffixes in which to
search for the specified destination host.

CanonicalizeFallbackLocal
Specifies whether to fail with an error when hostname canonicalization fails. The default, “yes”, will
attempt to look up the unqualified hostname using the system resolver's search rules. A value of “no”
will cause ssh(1) to fail instantly if CanonicalizeHostname is enabled and the target hostname cannot be
found in any of the domains specified by CanonicalDomains.

CanonicalizeHostname
Controls whether explicit hostname canonicalization is performed. The default, “no”, is not to perform
any name rewriting and let the system resolver handle all hostname lookups. If set to “yes” then, for
connections that do not use a ProxyCommand, ssh(1) will attempt to canonicalize the hostname specified
on the command line using the CanonicalDomains suffixes and CanonicalizePermittedCNAMEs rules. If
CanonicalizeHostname is set to “always”, then canonicalization is applied to proxied connections too.

If this option is enabled and canonicalisation results in the target hostname changing, then the config‐
uration files are processed again using the new target name to pick up any new configuration in matching
Host stanzas.

CanonicalizeMaxDots
Specifies the maximum number of dot characters in a hostname before canonicalization is disabled. The
default, “1”, allows a single dot (i.e. hostname.subdomain).

CanonicalizePermittedCNAMEs
Specifies rules to determine whether CNAMEs should be followed when canonicalizing hostnames. The rules
consist of one or more arguments of source_domain_list:target_domain_list, where source_domain_list is a
pattern-list of domains that may follow CNAMEs in canonicalization, and target_domain_list is a pattern-
list of domains that they may resolve to.

For example, “*.a.example.com:*.b.example.com,*.c.example.com” will allow hostnames matching
“*.a.example.com” to be canonicalized to names in the “*.b.example.com” or “*.c.example.com” domains.

ChallengeResponseAuthentication
Specifies whether to use challenge-response authentication. The argument to this keyword must be “yes”
or “no”. The default is “yes”.

CheckHostIP
If this flag is set to “yes”, ssh(1) will additionally check the host IP address in the known_hosts
file. This allows ssh to detect if a host key changed due to DNS spoofing. If the option is set to
“no”, the check will not be executed. The default is “yes”.

Cipher Specifies the cipher to use for encrypting the session in protocol version 1. Currently, “blowfish”,
“3des”, and “des” are supported. des is only supported in the ssh(1) client for interoperability with
legacy protocol 1 implementations that do not support the 3des cipher. Its use is strongly discouraged

aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
[email protected],[email protected],
[email protected],
aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
aes256-cbc,arcfour

The list of available ciphers may also be obtained using the -Q option of ssh(1).

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 ssh(1) command line
to clear port forwardings set in configuration files, and is automatically set by scp(1) and sftp(1).
The argument must be “yes” or “no”. The default is “no”.

Compression
Specifies whether to use compression. The argument must be “yes” or “no”. The default is “no”.

CompressionLevel
Specifies the compression level to use if compression is enabled. The argument must be an integer from
1 (fast) to 9 (slow, best). The default level is 6, which is good for most applications. The meaning
of the values is the same as in gzip(1). Note that this option applies to protocol version 1 only.

ConnectionAttempts
Specifies the number of tries (one per second) to make before exiting. The argument must be an integer.
This may be useful in scripts if the connection sometimes fails. The default is 1.

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.

ControlMaster
Enables the sharing of multiple sessions over a single network connection. When set to “yes”, ssh(1)
will listen for connections on a control socket specified using the ControlPath argument. Additional
sessions can connect to this socket using the same ControlPath with ControlMaster set to “no” (the
default). These sessions will try to reuse the master instance's network connection rather than initi‐
ating new ones, but will fall back to connecting normally if the control socket does not exist, or is
not listening.

Setting this to “ask” will cause ssh to listen for control connections, but require confirmation using
the SSH_ASKPASS program before they are accepted (see ssh-add(1) for details). If the ControlPath can‐
not be opened, ssh will continue without connecting to a master instance.

X11 and ssh-agent(1) forwarding is supported over these multiplexed connections, however the display and
agent forwarded will be the one belonging to the master connection i.e. it is not possible to forward
multiple displays or agents.

Two additional options allow for opportunistic multiplexing: try to use a master connection but fall
back to creating a new one if one does not already exist. These options are: “auto” and “autoask”. The
latter requires confirmation like the “ask” option.

ControlPath
Specify the path to the control socket used for connection sharing as described in the ControlMaster
section above or the string “none” to disable connection sharing. In the path, ‘%L’ will be substituted
will remain in the background indefinitely (until killed or closed via a mechanism such as the ssh(1)
“-O exit” option). If set to a time in seconds, or a time in any of the formats documented in
sshd_config(5), then the backgrounded master connection will automatically terminate after it has
remained idle (with no client connections) for the specified time.

DynamicForward
Specifies that a TCP 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 [bind_address:]port. IPv6 addresses can be specified by enclosing addresses in
square brackets. By default, the local port is bound in accordance with the GatewayPorts setting. How‐
ever, an explicit bind_address may be used to bind the connection to a specific address. The
bind_address of “localhost” indicates that the listening port be bound for local use only, while an
empty address or ‘*’ indicates that the port should be available from all interfaces.

Currently the SOCKS4 and SOCKS5 protocols are supported, and ssh(1) will act as a SOCKS server. Multi‐
ple forwardings may be specified, and additional forwardings can be given on the command line. Only the
superuser can forward privileged ports.

EnableSSHKeysign
Setting this option to “yes” in the global client configuration file /etc/ssh/ssh_config enables the use
of the helper program ssh-keysign(8) during HostbasedAuthentication. The argument must be “yes” or
“no”. The default is “no”. This option should be placed in the non-hostspecific section. See
ssh-keysign(8) for more information.

EscapeChar
Sets the escape character (default: ‘~’). The escape character can also be set on the command line.
The argument should be a single character, ‘^’ followed by a letter, or “none” to disable the escape
character entirely (making the connection transparent for binary data).

ExitOnForwardFailure
Specifies whether ssh(1) should terminate the connection if it cannot set up all requested dynamic, tun‐
nel, local, and remote port forwardings. The argument must be “yes” or “no”. The default is “no”.

ForwardAgent
Specifies whether the connection to the authentication agent (if any) will be forwarded to the remote
machine. The argument must be “yes” or “no”. The default is “no”.

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. 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.

ForwardX11
Specifies whether X11 connections will be automatically redirected over the secure channel and DISPLAY
set. The argument must be “yes” or “no”. The default is “no”.

X11 forwarding should be enabled with caution. Users with the ability to bypass file permissions on the
remote host (for the user's X11 authorization database) can access the local X11 display through the
forwarded connection. An attacker may then be able to perform activities such as keystroke monitoring
if the ForwardX11Trusted option is also enabled.

ForwardX11Timeout
Specify a timeout for untrusted X11 forwarding using the format described in the TIME FORMATS section of

See the X11 SECURITY extension specification for full details on the restrictions imposed on untrusted
clients.

GatewayPorts
Specifies whether remote hosts are allowed to connect to local forwarded ports. By default, ssh(1)
binds local port forwardings to the loopback address. This prevents other remote hosts from connecting
to forwarded ports. GatewayPorts can be used to specify that ssh should bind local port forwardings to
the wildcard address, thus allowing remote hosts to connect to forwarded ports. The argument must be
“yes” or “no”. The default is “no”.

GlobalKnownHostsFile
Specifies one or more files to use for the global host key database, separated by whitespace. The
default is /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.

GSSAPIAuthentication
Specifies whether user authentication based on GSSAPI is allowed. The default is “no”. Note that this
option applies to protocol version 2 only.

GSSAPIKeyExchange
Specifies whether key exchange based on GSSAPI may be used. When using GSSAPI key exchange the server
need not have a host key. The default is “no”. Note that this option applies to protocol version 2
only.

GSSAPIClientIdentity
If set, specifies the GSSAPI client identity that ssh should use when connecting to the server. The
default is unset, which means that the default identity will be used.

GSSAPIServerIdentity
If set, specifies the GSSAPI server identity that ssh should expect when connecting to the server. The
default is unset, which means that the expected GSSAPI server identity will be determined from the tar‐
get hostname.

GSSAPIDelegateCredentials
Forward (delegate) credentials to the server. The default is “no”. Note that this option applies to
protocol version 2 connections using GSSAPI.

GSSAPIRenewalForcesRekey
If set to “yes” then renewal of the client's GSSAPI credentials will force the rekeying of the ssh con‐
nection. With a compatible server, this can delegate the renewed credentials to a session on the server.
The default is “no”.

GSSAPITrustDns
Set to “yes to indicate that the DNS is trusted to securely canonicalize” the name of the host being
connected to. If “no, the hostname entered on the” command line will be passed untouched to the GSSAPI
library. The default is “no”. This option only applies to protocol version 2 connections using GSSAPI.

GSSAPIKexAlgorithms
The list of key exchange algorithms that are offered for GSSAPI key exchange. Possible values are

gss-gex-sha1-,
gss-group1-sha1-,
gss-group14-sha1-

be “yes” or “no”. The default is “no”. This option applies to protocol version 2 only and is similar
to RhostsRSAAuthentication.

HostKeyAlgorithms
Specifies the protocol version 2 host key algorithms that the client wants to use in order of prefer‐
ence. The default for this option is:

[email protected],
[email protected],
[email protected],
[email protected],
[email protected],[email protected],
[email protected],[email protected],
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
ssh-ed25519,ssh-rsa,ssh-dss

If hostkeys are known for the destination host then this default is modified to prefer their algorithms.

HostKeyAlias
Specifies an alias that should be used instead of the real host name when looking up or saving the host
key in the host key database files. This option is useful for tunneling SSH connections or for multiple
servers running on a single host.

HostName
Specifies the real host name to log into. This can be used to specify nicknames or abbreviations for
hosts. If the hostname contains the character sequence ‘%h’, then this will be replaced with the host
name specified on the command line (this is useful for manipulating unqualified names). The default is
the name given on the command line. Numeric IP addresses are also permitted (both on the command line
and in HostName specifications).

IdentitiesOnly
Specifies that ssh(1) should only use the authentication identity files configured in the ssh_config
files, even if ssh-agent(1) or a PKCS11Provider offers more identities. The argument to this keyword
must be “yes” or “no”. This option is intended for situations where ssh-agent offers many different
identities. The default is “no”.

IdentityFile
Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA authentication identity is read. The
default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519
and ~/.ssh/id_rsa for protocol version 2. Additionally, any identities represented by the authentica‐
tion agent will be used for authentication unless IdentitiesOnly is set. ssh(1) will try to load cer‐
tificate information from the filename obtained by appending -cert.pub to the path of a specified
IdentityFile.

The file name may use the tilde syntax to refer to a user's home directory or one of the following
escape characters: ‘%d’ (local user's home directory), ‘%u’ (local user name), ‘%l’ (local host name),
‘%h’ (remote host name) or ‘%r’ (remote user name).

It is possible to have multiple identity files specified in configuration files; all these identities
will be tried in sequence. Multiple IdentityFile directives will add to the list of identities tried
(this behaviour differs from that of other configuration directives).

IdentityFile may be used in conjunction with IdentitiesOnly to select which identities in an agent are
offered during authentication.
selected for interactive sessions and the second for non-interactive sessions. The default is
“lowdelay” for interactive sessions and “throughput” for non-interactive sessions.

KbdInteractiveAuthentication
Specifies whether to use keyboard-interactive authentication. The argument to this keyword must be
“yes” or “no”. The default is “yes”.

KbdInteractiveDevices
Specifies the list of methods to use in keyboard-interactive authentication. Multiple method names must
be comma-separated. The default is to use the server specified list. The methods available vary
depending on what the server supports. For an OpenSSH server, it may be zero or more of: “bsdauth”,
“pam”, and “skey”.

KexAlgorithms
Specifies the available KEX (Key Exchange) algorithms. Multiple algorithms must be comma-separated.
The default is:

[email protected],
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
diffie-hellman-group-exchange-sha256,
diffie-hellman-group-exchange-sha1,
diffie-hellman-group14-sha1,
diffie-hellman-group1-sha1

LocalCommand
Specifies a command to execute on the local machine after successfully connecting to the server. The
command string extends to the end of the line, and is executed with the user's shell. The following
escape character substitutions will be performed: ‘%d’ (local user's home directory), ‘%h’ (remote host
name), ‘%l’ (local host name), ‘%n’ (host name as provided on the command line), ‘%p’ (remote port),
‘%r’ (remote user name) or ‘%u’ (local user name).

The command is run synchronously and does not have access to the session of the ssh(1) that spawned it.
It should not be used for interactive commands.

This directive is ignored unless PermitLocalCommand has been enabled.

LocalForward
Specifies that a TCP port on the local machine be forwarded over the secure channel to the specified
host and port from the remote machine. The first argument must be [bind_address:]port and the second
argument must be host:hostport. IPv6 addresses can be specified by enclosing addresses in square brack‐
ets. Multiple forwardings may be specified, and additional forwardings can be given on the command
line. Only the superuser can forward privileged ports. By default, the local port is bound in accor‐
dance with the GatewayPorts setting. However, an explicit bind_address may be used to bind the connec‐
tion to a specific address. The bind_address of “localhost” indicates that the listening port be bound
for local use only, while an empty address or ‘*’ indicates that the port should be available from all
interfaces.

LogLevel
Gives the verbosity level that is used when logging messages from ssh(1). The possible values are:
QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG and
DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of verbose output.

MACs Specifies the MAC (message authentication code) algorithms in order of preference. The MAC algorithm is
used in protocol version 2 for data integrity protection. Multiple algorithms must be comma-separated.

NoHostAuthenticationForLocalhost
This option can be used if the home directory is shared across machines. In this case localhost will
refer to a different machine on each of the machines and the user will get many warnings about changed
host keys. However, this option disables host authentication for localhost. The argument to this key‐
word must be “yes” or “no”. The default is to check the host key for localhost.

NumberOfPasswordPrompts
Specifies the number of password prompts before giving up. The argument to this keyword must be an
integer. The default is 3.

PasswordAuthentication
Specifies whether to use password authentication. The argument to this keyword must be “yes” or “no”.
The default is “yes”.

PermitLocalCommand
Allow local command execution via the LocalCommand option or using the !command escape sequence in
ssh(1). The argument must be “yes” or “no”. The default is “no”.

PKCS11Provider
Specifies which PKCS#11 provider to use. The argument to this keyword is the PKCS#11 shared library
ssh(1) should use to communicate with a PKCS#11 token providing the user's private RSA key.

Port Specifies the port number to connect on the remote host. The default is 22.

PreferredAuthentications
Specifies the order in which the client should try protocol 2 authentication methods. This allows a
client to prefer one method (e.g. keyboard-interactive) over another method (e.g. password). The
default is:

gssapi-with-mic,hostbased,publickey,
keyboard-interactive,password

Protocol
Specifies the protocol versions ssh(1) should support in order of preference. The possible values are
‘1’ and ‘2’. Multiple versions must be comma-separated. When this option is set to “2,1” ssh will try
version 2 and fall back to version 1 if version 2 is not available. The default is ‘2’.

ProxyCommand
Specifies the command to use to connect to the server. The command string extends to the end of the
line, and is executed with the user's shell. In the command string, any occurrence of ‘%h’ will be sub‐
stituted by the host name to connect, ‘%p’ by the port, and ‘%r’ by the remote user name. The command
can be basically anything, and should read from its standard input and write to its standard output. It
should eventually connect an sshd(8) server running on some machine, or execute sshd -i somewhere. 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 “none” disables this option entirely. Note that CheckHostIP is
not available for connects with a proxy command.

This directive is useful in conjunction with nc(1) and its proxy support. For example, the following
directive would connect via an HTTP proxy at 192.0.2.0:

ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p

ProxyUseFdpass
Specifies that ProxyCommand will pass a connected file descriptor back to ssh(1) instead of continuing
FORMATS section of sshd_config(5). The default value for RekeyLimit is “default none”, which means that
rekeying is performed after the cipher's default amount of data has been sent or received and no time
based rekeying is done. This option applies to protocol version 2 only.

RemoteForward
Specifies that a TCP port on the remote machine be forwarded over the secure channel to the specified
host and port from the local machine. The first argument must be [bind_address:]port and the second
argument must be host:hostport. IPv6 addresses can be specified by enclosing addresses in square brack‐
ets. Multiple forwardings may be specified, and additional forwardings can be given on the command
line. Privileged ports can be forwarded only when logging in as root on the remote machine.

If the port argument is ‘0’, the listen port will be dynamically allocated on the server and reported to
the client at run time.

If the bind_address is not specified, the default is to only bind to loopback addresses. If the
bind_address is ‘*’ or an empty string, then the forwarding is requested to listen on all interfaces.
Specifying a remote bind_address will only succeed if the server's GatewayPorts option is enabled (see
sshd_config(5)).

RequestTTY
Specifies whether to request a pseudo-tty for the session. The argument may be one of: “no” (never
request a TTY), “yes” (always request a TTY when standard input is a TTY), “force” (always request a
TTY) or “auto” (request a TTY when opening a login session). This option mirrors the -t and -T flags
for ssh(1).

RhostsRSAAuthentication
Specifies whether to try rhosts based authentication with RSA host authentication. The argument must be
“yes” or “no”. The default is “no”. This option applies to protocol version 1 only and requires ssh(1)
to be setuid root.

RSAAuthentication
Specifies whether to try RSA authentication. The argument to this keyword must be “yes” or “no”. RSA
authentication will only be attempted if the identity file exists, or an authentication agent is run‐
ning. The default is “yes”. Note that this option applies to protocol version 1 only.

SendEnv
Specifies what variables from the local environ(7) should be sent to the server. Note that environment
passing is only supported for protocol 2. The server must also support it, and the server must be con‐
figured to accept these environment variables. Note that the TERM environment variable is always sent
whenever a pseudo-terminal is requested as it is required by the protocol. Refer to AcceptEnv in
sshd_config(5) for how to configure the server. Variables are specified by name, which may contain
wildcard characters. Multiple environment variables may be separated by whitespace or spread across
multiple SendEnv directives. The default is not to send any environment variables.

See PATTERNS for more information on patterns.

ServerAliveCountMax
Sets the number of server alive messages (see below) which may be sent without ssh(1) receiving any mes‐
sages back from the server. If this threshold is reached while server alive messages are being sent,
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 TCPKeepAlive (below). The server alive messages are sent
through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by
TCPKeepAlive is spoofable. The server alive mechanism is valuable when the client or server depend on
knowing when a connection has become inactive.
If this flag is set to “yes”, ssh(1) will never automatically add host keys to the ~/.ssh/known_hosts
file, and refuses to connect to hosts whose host key has changed. This provides maximum protection
against trojan horse attacks, though it can be annoying when the /etc/ssh/ssh_known_hosts file is poorly
maintained or when connections to new hosts are frequently made. This option forces the user to manu‐
ally add all new hosts. If this flag is set to “no”, ssh will automatically add new host keys to the
user known hosts files. If this flag is set to “ask”, new host keys will be added to the user known
host files only after the user has confirmed that is what they really want to do, and ssh will refuse to
connect to hosts whose host key has changed. The host keys of known hosts will be verified automati‐
cally in all cases. The argument must be “yes”, “no”, or “ask”. The default is “ask”.

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.

The default is “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.

To disable TCP keepalive messages, the value should be set to “no”.

Tunnel Request tun(4) device forwarding between the client and the server. The argument must be “yes”,
“point-to-point” (layer 3), “ethernet” (layer 2), or “no”. Specifying “yes” requests the default tunnel
mode, which is “point-to-point”. The default is “no”.

TunnelDevice
Specifies the tun(4) devices to open on the client (local_tun) and the server (remote_tun).

The argument must be local_tun[:remote_tun]. The devices may be specified by numerical ID or the key‐
word “any”, which uses the next available tunnel device. If remote_tun is not specified, it defaults to
“any”. The default is “any:any”.

UsePrivilegedPort
Specifies whether to use a privileged port for outgoing connections. The argument must be “yes” or
“no”. The default is “no”. If set to “yes”, ssh(1) must be setuid root. Note that this option must be
set to “yes” for RhostsRSAAuthentication with older servers.

User Specifies the user to log in as. This can be useful when a different user name is used on different
machines. This saves the trouble of having to remember to give the user name on the command line.

UserKnownHostsFile
Specifies one or more files to use for the user host key database, separated by whitespace. The default
is ~/.ssh/known_hosts, ~/.ssh/known_hosts2.

VerifyHostKeyDNS
Specifies whether to verify the remote key using DNS and SSHFP resource records. If this option is set
to “yes”, the client will implicitly trust keys that match a secure fingerprint from DNS. Insecure fin‐
gerprints will be handled as if this option was set to “ask”. If this option is set to “ask”, informa‐
tion on fingerprint match will be displayed, but the user will still need to confirm new host keys
according to the StrictHostKeyChecking option. The argument must be “yes”, “no”, or “ask”. The default
is “no”. Note that this option applies to protocol version 2 only.