Ubuntu Manpage: Config::Model::models::Ssh

Provided by: libconfig-model-openssh-perl_2.9.9.1-1_all

NAME

       Config::Model::models::Ssh - Configuration class Ssh

DESCRIPTION

       Configuration classes used by Config::Model

       This configuration class was generated from ssh_system documentation.  by parse-man.pl
       <https://github.com/dod38fr/config-model-openssh/contrib/parse-man.pl>

Elements

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 usually the hostname argument given on the command line (see the CanonicalizeHostname
keyword for exceptions).

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. Optional. Type hash of node of class Ssh::HostElement .

AddKeysToAgent
Specifies whether keys should be automatically added to a running ssh-agent1. If this option is set to
yes and a key is loaded from a file, the key and its passphrase are added to the agent with the default
lifetime, as if by ssh-add1. If this option is set to ask ssh(1) will require confirmation using the
SSH_ASKPASS program before adding a key (see ssh-add1 for details). If this option is set to confirm each
use of the key must be confirmed, as if the -c option was specified to ssh-add1. If this option is set to
no no keys are added to the agent. Alternately, this option may be specified as a time interval using the
format described in the TIME FORMATS section of sshd_config5 to specify the key's lifetime in ssh-agent1,
after which it will automatically be removed. The argument must be no (the default), yes confirm
(optionally followed by a time interval), ask or a time interval. Optional. Type enum. choice: 'ask',
'confirm', 'no', 'yes'.

upstream_default value :
no

AddressFamily
Specifies which address family to use when connecting. Valid arguments are any (the default), inet (use
IPv4 only), or inet6 (use IPv6 only). Optional. Type enum. choice: 'any', 'inet', 'inet6'.

upstream_default value :
any

BatchMode
If set to yes user interaction such as password prompts and host key confirmation requests will be
disabled. In addition, the ServerAliveInterval option will be set to 300 seconds by default (Debian-
specific). This option is useful in scripts and other batch jobs where no user is present to interact
with ssh(1), and where it is desirable to detect a broken network swiftly. The argument must be yes or
no (the default). Optional. Type boolean.

upstream_default value :
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. Optional. Type uniline.

BindInterface
Use the address of the specified interface on the local machine as the source address of the connection.
Optional. Type uniline.

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

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 Optional. Type boolean.

upstream_default value :
yes

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 or ProxyJump 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, then the configuration files are processed again using the new target name to
pick up any new configuration in matching Host and Match stanzas. A value of none disables the use of a
ProxyJump host. Optional. Type enum. choice: 'always', 'no', 'none', 'yes'.

upstream_default value :
no

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). Optional. Type integer.

upstream_default value :
1

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

A single argument of Qq none causes no CNAMEs to be considered for canonicalization. This is the default
behaviour. Optional. Type uniline.

CASignatureAlgorithms
Specifies which algorithms are allowed for signing of certificates by certificate authorities (CAs). The
default is: ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com, sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512, rsa-sha2-256

If the specified list begins with a '+' character, then the specified algorithms will be appended to the
default set instead of replacing them. If the specified list begins with a '-' character, then the
specified algorithms (including wildcards) will be removed from the default set instead of replacing
them.

ssh(1) will not accept host certificates signed using algorithms other than those specified. Optional.
Type uniline.

CertificateFile
Specifies a file from which the user's certificate is read. A corresponding private key must be provided
separately in order to use this certificate either from an IdentityFile directive or -i flag to ssh(1),
via ssh-agent1, or via a PKCS11Provider or SecurityKeyProvider

Arguments to CertificateFile may use the tilde syntax to refer to a user's home directory, the tokens
described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES
section.

It is possible to have multiple certificate files specified in configuration files; these certificates
will be tried in sequence. Multiple CertificateFile directives will add to the list of certificates used
for authentication. Optional. Type uniline.

ChannelTimeout
Specifies whether and how quickly ssh(1) should close inactive channels. Timeouts are specified as one
or more ''type=interval'' pairs separated by whitespace, where the ''type'' must be the special keyword
''global'' or a channel type name from the list below, optionally containing wildcard characters.

The timeout value ''interval'' is specified in seconds or may use any of the units documented in the TIME
FORMATS section. For example, ''session=5m'' would cause interactive sessions to terminate after five
minutes of inactivity. Specifying a zero value disables the inactivity timeout.

The special timeout ''global'' applies to all active channels, taken together. Traffic on any active
channel will reset the timeout, but when the timeout expires then all open channels will be closed. Note
that this global timeout is not matched by wildcards and must be specified explicitly.

The available channel type names include:

agent-connection Open connections to ssh-agent1. direct-tcpip , direct-streamlocal@openssh.com Open TCP
or Unix socket (respectively) connections that have been established from a ssh(1) local forwarding, i.e.
LocalForward or DynamicForward forwarded-tcpip , forwarded-streamlocal@openssh.com Open TCP or Unix
socket (respectively) connections that have been established to a sshd(8) listening on behalf of a ssh(1)
remote forwarding, i.e. RemoteForward session The interactive main session, including shell session,
command execution, scp(1), sftp(1), etc. tun-connection Open TunnelForward connections. x11-connection
Open X11 forwarding sessions.

Note that in all the above cases, terminating an inactive session does not guarantee to remove all
resources associated with the session, e.g. shell processes or X11 clients relating to the session may
continue to execute.

Moreover, terminating an inactive channel or session does not necessarily close the SSH connection, nor
does it prevent a client from requesting another channel of the same type. In particular, expiring an
inactive forwarding session does not prevent another identical forwarding from being subsequently
created.

The default is not to expire channels of any type for inactivity. Optional. Type uniline.

CheckHostIP
If set to yes ssh(1) will additionally check the host IP address in the known_hosts file. This allows it
to detect if a host key changed due to DNS spoofing and will add addresses of destination hosts to
~/.ssh/known_hosts in the process, regardless of the setting of StrictHostKeyChecking If the option is
set to no (the default), the check will not be executed. Optional. Type boolean.

upstream_default value :
no

Ciphers
Specifies the ciphers allowed and their order of preference. Multiple ciphers must be comma-separated. If
the specified list begins with a '+' character, then the specified ciphers will be appended to the
default set instead of replacing them. If the specified list begins with a '-' character, then the
specified ciphers (including wildcards) will be removed from the default set instead of replacing them.
If the specified list begins with a '^' character, then the specified ciphers will be placed at the head
of the default set.

The supported ciphers are: 3des-cbc aes128-cbc aes192-cbc aes256-cbc aes128-ctr aes192-ctr aes256-ctr
aes128-gcm@openssh.comaes256-gcm@openssh.comchacha20-poly1305@openssh.com

The default is: chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr,
aes128-gcm@openssh.com, aes256-gcm@openssh.com

The list of available ciphers may also be obtained using Qq ssh -Q cipher . Optional. Type uniline.

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). Optional. Type boolean.

upstream_default value :
no

Compression
Specifies whether to use compression. The argument must be yes or no (the default). Optional. Type
boolean.

upstream_default value :
no

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. Optional. Type
integer.

upstream_default value :
1

ConnectTimeout
Specifies the timeout (in seconds) used when connecting to the SSH server, instead of using the default
system TCP timeout. This timeout is applied both to establishing the connection and to performing the
initial SSH protocol handshake and key exchange. SetupTimeOut is a Debian-specific compatibility alias
for this option. Optional. Type integer.

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 initiating 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(1) to listen for control connections, but require confirmation using
ssh-askpass1. If the ControlPath cannot be opened, ssh(1) will continue without connecting to a master
instance.

X11 and ssh-agent1 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. Optional. Type enum. choice: 'ask', 'auto', 'autoask', 'no',
'yes'.

upstream_default value :
no

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. Arguments to ControlPath may use the
tilde syntax to refer to a user's home directory, the tokens described in the TOKENS section and
environment variables as described in the ENVIRONMENT VARIABLES section. It is recommended that any
ControlPath used for opportunistic connection sharing include at least %h, %p, and %r (or alternatively
%C) and be placed in a directory that is not writable by other users. This ensures that shared
connections are uniquely identified. Optional. Type uniline.

ControlPersist
When used in conjunction with ControlMaster specifies that the master connection should remain open in
the background (waiting for future client connections) after the initial client connection has been
closed. If set to no (the default), then the master connection will not be placed into the background,
and will close as soon as the initial client connection is closed. If set to yes or 0, then the master
connection will remain in the background indefinitely (until killed or closed via a mechanism such as the
Qq ssh -O exit ) . If set to a time in seconds, or a time in any of the formats documented in
sshd_config5, then the backgrounded master connection will automatically terminate after it has remained
idle (with no client connections) for the specified time. Optional. Type uniline.

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.
However, 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. Multiple
forwardings may be specified, and additional forwardings can be given on the command line. Only the
superuser can forward privileged ports. Optional. Type list of uniline.

EnableEscapeCommandline
Enables the command line option in the EscapeChar menu for interactive sessions (default '~C' ) . By
default, the command line is disabled. Optional. Type uniline.

EnableSSHKeysign
Setting this option to yes in the global client configuration file /etc/ssh/ssh_config enables the use of
the helper program ssh-keysign8 during HostbasedAuthentication The argument must be yes or no (the
default). This option should be placed in the non-hostspecific section. See ssh-keysign8 for more
information. Optional. Type boolean.

upstream_default value :
no

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). Optional. Type uniline.

ExitOnForwardFailure
Specifies whether ssh(1) should terminate the connection if it cannot set up all requested dynamic,
tunnel, local, and remote port forwardings, (e.g. if either end is unable to bind and listen on a
specified port). Note that ExitOnForwardFailure does not apply to connections made over port forwardings
and will not, for example, cause ssh(1) to exit if TCP connections to the ultimate forwarding destination
fail. The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :
no

FingerprintHash
Specifies the hash algorithm used when displaying key fingerprints. Valid options are: md5 and sha256
(the default). Optional. Type enum. choice: 'md5', 'sha256'.

upstream_default value :
sha256

ForkAfterAuthentication
Requests ssh to go to background just before command execution. This is useful if ssh is going to ask for
passwords or passphrases, but the user wants it in the background. This implies the StdinNull
configuration option being set to ''yes'' The recommended way to start X11 programs at a remote site is
with something like ssh -f host xterm which is the same as ssh host xterm if the ForkAfterAuthentication
configuration option is set to ''yes''

If the ExitOnForwardFailure configuration option is set to ''yes'' then a client started with the
ForkAfterAuthentication configuration option being set to ''yes'' will wait for all remote port forwards
to be successfully established before placing itself in the background. The argument to this keyword must
be yes (same as the -f option) or no (the default). Optional. Type boolean.

upstream_default value :
no

ForwardAgent
Specifies whether the connection to the authentication agent (if any) will be forwarded to the remote
machine. The argument may be yes no (the default), an explicit path to an agent socket or the name of an
environment variable (beginning with '$' in which to find the path.

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. Optional. Type
boolean.

upstream_default value :
no

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).

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. Optional. Type boolean.

upstream_default value :
no

ForwardX11Timeout
Specify a timeout for untrusted X11 forwarding using the format described in the TIME FORMATS section of
sshd_config5. X11 connections received by ssh(1) after this time will be refused. Setting
ForwardX11Timeout to zero will disable the timeout and permit X11 forwarding for the life of the
connection. The default is to disable untrusted X11 forwarding after twenty minutes has elapsed.
Optional. Type integer.

ForwardX11Trusted
If this option is set to yes (the Debian-specific default), remote X11 clients will have full access to
the original X11 display.

If this option is set to no (the upstream default), remote X11 clients will be considered untrusted and
prevented from stealing or tampering with data belonging to trusted X11 clients. Furthermore, the
xauth(1) token used for the session will be set to expire after 20 minutes. Remote clients will be
refused access after this time.

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

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). Optional. Type boolean.

upstream_default value :
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. Optional. Type uniline.

default value :
/etc/ssh/ssh_known_hosts /etc/ssh/ssh_known_hosts2

GSSAPIAuthentication
Specifies whether user authentication based on GSSAPI is allowed. The default is no Optional. Type
boolean.

upstream_default value :
no

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. Optional. Type uniline.

GSSAPIDelegateCredentials
Forward (delegate) credentials to the server. The default is no Optional. Type boolean.

upstream_default value :
no

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'' Optional. Type uniline.

GSSAPIRenewalForcesRekey
If set to ''yes'' then renewal of the client's GSSAPI credentials will force the rekeying of the ssh
connection. With a compatible server, this will delegate the renewed credentials to a session on the
server.

Checks are made to ensure that credentials are only propagated when the new credentials match the old
ones on the originating client and where the receiving server still has the old set in its cache.

The default is ''no''

For this to work GSSAPIKeyExchange needs to be enabled in the server and also used by the client.
Optional. Type uniline.

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 target
hostname. Optional. Type uniline.

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'' Optional. Type uniline.

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-, gss-group14-sha256-, gss-group16-sha512-,

gss-nistp256-sha256-, gss-curve25519-sha256-
The default is ''gss-group14-sha256-, gss-group16-sha512-, gss-nistp256-sha256-, gss-curve25519-sha256-,
gss-gex-sha1-, gss-group14-sha1-'' This option only applies to connections using GSSAPI. Optional. Type
uniline.

HashKnownHosts
Indicates that ssh(1) should hash host names and addresses when they are added to ~/.ssh/known_hosts
These hashed names may be used normally by ssh(1) and sshd(8), but they do not visually reveal
identifying information if the file's contents are disclosed. The default is no Note that existing names
and addresses in known hosts files will not be converted automatically, but may be manually hashed using
ssh-keygen1. Use of this option may break facilities such as tab-completion that rely on being able to
read unhashed host names from ~/.ssh/known_hosts. Optional. Type boolean.

upstream_default value :
no

HostbasedAcceptedAlgorithms
Specifies the signature algorithms that will be used for hostbased authentication as a comma-separated
list of patterns. Alternately if the specified list begins with a '+' character, then the specified
signature algorithms will be appended to the default set instead of replacing them. If the specified list
begins with a '-' character, then the specified signature algorithms (including wildcards) will be
removed from the default set instead of replacing them. If the specified list begins with a '^'
character, then the specified signature algorithms will be placed at the head of the default set. The
default for this option is: ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-ed25519, ecdsa-sha2-nistp256,
ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com, sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512, rsa-sha2-256

The -Q option of ssh(1) may be used to list supported signature algorithms. This was formerly named
HostbasedKeyTypes. Optional. Type uniline.

Note: HostbasedAcceptedAlgorithms is migrated with '$old' and with:

• $old => "- HostbasedKeyTypes"

HostbasedAuthentication
Specifies whether to try rhosts based authentication with public key authentication. The argument must be
yes or no (the default). Optional. Type boolean.

upstream_default value :
no

HostKeyAlgorithms
Specifies the host key signature algorithms that the client wants to use in order of preference.
Alternately if the specified list begins with a '+' character, then the specified signature algorithms
will be appended to the default set instead of replacing them. If the specified list begins with a '-'
character, then the specified signature algorithms (including wildcards) will be removed from the default
set instead of replacing them. If the specified list begins with a '^' character, then the specified
signature algorithms will be placed at the head of the default set. The default for this option is:
ssh-ed25519-cert-v01@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com, sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com, rsa-sha2-256-cert-v01@openssh.com, ssh-ed25519, ecdsa-sha2-nistp256,
ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com,
rsa-sha2-512, rsa-sha2-256

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

The list of available signature algorithms may also be obtained using Qq ssh -Q HostKeyAlgorithms .
Optional. Type uniline.

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 and when validating host certificates. This option is useful for
tunneling SSH connections or for multiple servers running on a single host. Optional. Type uniline.

Hostname
Specifies the real host name to log into. This can be used to specify nicknames or abbreviations for
hosts. Arguments to Hostname accept the tokens described in the TOKENS section. Numeric IP addresses are
also permitted (both on the command line and in Hostname specifications). The default is the name given
on the command line. Optional. Type uniline.

IdentitiesOnly
Specifies that ssh(1) should only use the configured authentication identity and certificate files
(either the default files, or those explicitly configured in the ssh_config files or passed on the ssh(1)
command-line), even if ssh-agent1 or a PKCS11Provider or SecurityKeyProvider offers more identities. The
argument to this keyword must be yes or no (the default). This option is intended for situations where
ssh-agent offers many different identities. Optional. Type boolean.

upstream_default value :
no

IdentityAgent
Specifies the UNIX socket used to communicate with the authentication agent.

This option overrides the SSH_AUTH_SOCK environment variable and can be used to select a specific agent.
Setting the socket name to none disables the use of an authentication agent. If the string Qq
SSH_AUTH_SOCK is specified, the location of the socket will be read from the SSH_AUTH_SOCK environment
variable. Otherwise if the specified value begins with a '$' character, then it will be treated as an
environment variable containing the location of the socket.

Arguments to IdentityAgent may use the tilde syntax to refer to a user's home directory, the tokens
described in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES
section. Optional. Type uniline.

IdentityFile
Specifies a file from which the user's ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted
Ed25519 or RSA authentication identity is read. You can also specify a public key file to use the
corresponding private key that is loaded in ssh-agent1 when the private key file is not present locally.
The default is ~/.ssh/id_rsa ~/.ssh/id_ecdsa ~/.ssh/id_ecdsa_sk ~/.ssh/id_ed25519 and
~/.ssh/id_ed25519_sk Additionally, any identities represented by the authentication agent will be used
for authentication unless IdentitiesOnly is set. If no certificates have been explicitly specified by
CertificateFile ssh(1) will try to load certificate information from the filename obtained by appending
-cert.pub to the path of a specified IdentityFile

Arguments to IdentityFile may use the tilde syntax to refer to a user's home directory or the tokens
described in the TOKENS section. Alternately an argument of none may be used to indicate no identity
files should be loaded.

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. IdentityFile may also be used in conjunction with CertificateFile in order
to provide any certificate also needed for authentication with the identity. Optional. Type list of
uniline.

IgnoreUnknown
Specifies a pattern-list of unknown options to be ignored if they are encountered in configuration
parsing. This may be used to suppress errors if ssh_config contains options that are unrecognised by
ssh(1). It is recommended that IgnoreUnknown be listed early in the configuration file as it will not be
applied to unknown options that appear before it. Optional. Type uniline.

Include
Include the specified configuration file(s). Multiple pathnames may be specified and each pathname may
contain glob(7) wildcards, tokens as described in the TOKENS section, environment variables as described
in the ENVIRONMENT VARIABLES section and, for user configurations, shell-like '~' references to user home
directories. Wildcards will be expanded and processed in lexical order. Files without absolute paths are
assumed to be in ~/.ssh if included in a user configuration file or /etc/ssh if included from the system
configuration file. Include directive may appear inside a Match or Host block to perform conditional
inclusion. Optional. Type list of uniline.

IPQoS
Specifies the IPv4 type-of-service or DSCP class for connections. Accepted values are af11 af12 af13 af21
af22 af23 af31 af32 af33 af41 af42 af43 cs0 cs1 cs2 cs3 cs4 cs5 cs6 cs7 ef le lowdelay throughput
reliability a numeric value, or none to use the operating system default. This option may take one or two
arguments, separated by whitespace. If one argument is specified, it is used as the packet class
unconditionally. If two values are specified, the first is automatically selected for interactive
sessions and the second for non-interactive sessions. The default is lowdelay for interactive sessions
and throughput for non-interactive sessions. Optional. Type uniline.

upstream_default value :
af21 cs1

KbdInteractiveAuthentication
Specifies whether to use keyboard-interactive authentication. The argument to this keyword must be yes
(the default) or no ChallengeResponseAuthentication is a deprecated alias for this. Optional. Type
boolean.

upstream_default value :
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 and pam Optional.
Type list of uniline.

KexAlgorithms
Specifies the permitted KEX (Key Exchange) algorithms that will be used and their preference order. The
selected algorithm will be the first algorithm in this list that the server also supports. Multiple
algorithms must be comma-separated.

The default is: sntrup761x25519-sha512, sntrup761x25519-sha512@openssh.com, mlkem768x25519-sha256,
curve25519-sha256, curve25519-sha256@libssh.org, ecdh-sha2-nistp256, ecdh-sha2-nistp384,
ecdh-sha2-nistp521, diffie-hellman-group-exchange-sha256, diffie-hellman-group16-sha512,
diffie-hellman-group18-sha512, diffie-hellman-group14-sha256

The list of supported key exchange algorithms may also be obtained using Qq ssh -Q kex . Optional. Type
uniline.

KnownHostsCommand
Specifies a command to use to obtain a list of host keys, in addition to those listed in
UserKnownHostsFile and GlobalKnownHostsFile This command is executed after the files have been read. It
may write host key lines to standard output in identical format to the usual files (described in the
VERIFYING HOST KEYS section in ssh(1)). Arguments to KnownHostsCommand accept the tokens described in the
TOKENS section. The command may be invoked multiple times per connection: once when preparing the
preference list of host key algorithms to use, again to obtain the host key for the requested host name
and, if CheckHostIP is enabled, one more time to obtain the host key matching the server's address. If
the command exits abnormally or returns a non-zero exit status then the connection is terminated.
Optional. Type uniline.

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. Arguments to
LocalCommand accept the tokens described in the TOKENS section.

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. Optional. Type uniline.

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 specifies the listener and may be [bind_address :
port ] or a Unix domain socket path. The second argument is the destination and may be host : hostport
or a Unix domain socket path if the remote host supports it.

IPv6 addresses can be specified by enclosing addresses in square brackets. 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 accordance with the GatewayPorts setting.
However, 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. Unix domain socket paths
may use the tokens described in the TOKENS section and environment variables as described in the
ENVIRONMENT VARIABLES section. Optional. Type list of node of class Ssh::PortForward .

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. Optional. Type
enum. choice: 'DEBUG', 'DEBUG1', 'DEBUG2', 'DEBUG3', 'ERROR', 'FATAL', 'INFO', 'QUIET', 'VERBOSE'.

upstream_default value :
INFO

LogVerbose
Specify one or more overrides to LogLevel. An override consists of one or more pattern lists that matches
the source file, function and line number to force detailed logging for. For example, an override pattern
of: kex.c:*:1000,*:kex_exchange_identification():*, packet.c:*

would enable detailed logging for line 1000 of kex.c everything in the Fn kex_exchange_identification
function, and all code in the packet.c file. This option is intended for debugging and no overrides are
enabled by default. Optional. Type uniline.

MACs
Specifies the MAC (message authentication code) algorithms

in order of preference. The MAC algorithm is used for data integrity protection. Multiple algorithms must
be comma-separated. If the specified list begins with a '+' character, then the specified algorithms will
be appended to the default set instead of replacing them. If the specified list begins with a '-'
character, then the specified algorithms (including wildcards) will be removed from the default set
instead of replacing them. If the specified list begins with a '^' character, then the specified
algorithms will be placed at the head of the default set.

The algorithms that contain Qq -etm calculate the MAC after encryption (encrypt-then-mac). These are
considered safer and their use recommended.

The default is: umac-64-etm@openssh.com, umac-128-etm@openssh.com, hmac-sha2-256-etm@openssh.com,
hmac-sha2-512-etm@openssh.com, hmac-sha1-etm@openssh.com, umac-64@openssh.com, umac-128@openssh.com,
hmac-sha2-256, hmac-sha2-512, hmac-sha1

The list of available MAC algorithms may also be obtained using Qq ssh -Q mac . Optional. Type uniline.

NoHostAuthenticationForLocalhost
Disable host authentication for localhost (loopback addresses). The argument to this keyword must be yes
or no (the default). Optional. Type boolean.

upstream_default value :
no

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

upstream_default value :
3

ObscureKeystrokeTiming
Specifies whether ssh(1) should try to obscure inter-keystroke timings from passive observers of network
traffic. If enabled, then for interactive sessions, ssh(1) will send keystrokes at fixed intervals of a
few tens of milliseconds and will send fake keystroke packets for some time after typing ceases. The
argument to this keyword must be yes no or an interval specifier of the form interval:milliseconds (e.g.
interval:80 for 80 milliseconds). The default is to obscure keystrokes using a 20ms packet interval. Note
that smaller intervals will result in higher fake keystroke packet rates. Optional. Type uniline.

upstream_default value :
interval:20

PasswordAuthentication
Specifies whether to use password authentication. The argument to this keyword must be yes (the default)
or no Optional. Type boolean.

upstream_default value :
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). Optional. Type boolean.

upstream_default value :
no

PermitRemoteOpen
Specifies the destinations to which remote TCP port forwarding is permitted when RemoteForward is used as
a SOCKS proxy. The forwarding specification must be one of the following forms:

PermitRemoteOpen host : port PermitRemoteOpen IPv4_addr : port PermitRemoteOpen [ IPv6_addr ] : port

Multiple forwards may be specified by separating them with whitespace. An argument of any can be used to
remove all restrictions and permit any forwarding requests. An argument of none can be used to prohibit
all forwarding requests. The wildcard '*' can be used for host or port to allow all hosts or ports
respectively. Otherwise, no pattern matching or address lookups are performed on supplied names.
Optional. Type list of uniline.

PKCS11Provider
Specifies which PKCS#11 provider to use or none to indicate that no provider should be used (the
default). The argument to this keyword is a path to the PKCS#11 shared library ssh(1) should use to
communicate with a PKCS#11 token providing keys for user authentication. Optional. Type uniline.

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

PreferredAuthentications
Specifies the order in which the client should try 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. Optional. Type list of uniline.

ProxyCommand
Specifies the command to use to connect to the server. The command string extends to the end of the line,
and is executed using the user's shell 'exec' directive to avoid a lingering shell process.

Arguments to ProxyCommand accept the tokens described in the TOKENS section. 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. Optional. Type uniline.

ProxyJump
Specifies one or more jump proxies as either [user @ ] host [: port ] or an ssh URI . Multiple proxies
may be separated by comma characters and will be visited sequentially. Setting this option will cause
ssh(1) to connect to the target host by first making a ssh(1) connection to the specified ProxyJump host
and then establishing a TCP forwarding to the ultimate target from there. Setting the host to none
disables this option entirely.

Note that this option will compete with the ProxyCommand option - whichever is specified first will
prevent later instances of the other from taking effect.

Note also that the configuration for the destination host (either supplied via the command-line or the
configuration file) is not generally applied to jump hosts. ~/.ssh/config should be used if specific
configuration is required for jump hosts. Optional. Type list of uniline.

ProxyUseFdpass
Specifies that ProxyCommand will pass a connected file descriptor back to ssh(1) instead of continuing to
execute and pass data. The default is no Optional. Type boolean.

upstream_default value :
no

PubkeyAcceptedAlgorithms
Specifies the signature algorithms that will be used for public key authentication as a comma-separated
list of patterns. If the specified list begins with a '+' character, then the algorithms after it will be
appended to the default instead of replacing it. If the specified list begins with a '-' character, then
the specified algorithms (including wildcards) will be removed from the default set instead of replacing
them. If the specified list begins with a '^' character, then the specified algorithms will be placed at
the head of the default set. The default for this option is: ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com, ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com, sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, rsa-sha2-512-cert-v01@openssh.com,
rsa-sha2-256-cert-v01@openssh.com, ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384,
ecdsa-sha2-nistp521, sk-ssh-ed25519@openssh.com, sk-ecdsa-sha2-nistp256@openssh.com, rsa-sha2-512,
rsa-sha2-256

The list of available signature algorithms may also be obtained using Qq ssh -Q PubkeyAcceptedAlgorithms
. Optional. Type uniline.

Note: PubkeyAcceptedAlgorithms is migrated with '$old' and with:

• $old => "- PubkeyAcceptedKeyTypes"

PubkeyAuthentication
Specifies whether to try public key authentication. The argument to this keyword must be yes (the
default), no unbound or host-bound The final two options enable public key authentication while
respectively disabling or enabling the OpenSSH host-bound authentication protocol extension required for
restricted ssh-agent1 forwarding. Optional. Type enum. choice: 'host-bound', 'no', 'unbound', 'yes'.

upstream_default value :
yes

RekeyLimit
Specifies the maximum amount of data that may be transmitted or received before the session key is
renegotiated, optionally followed by a maximum amount of time that may pass before the session key is
renegotiated. The first argument is specified in bytes and may have a suffix of 'K' 'M' or 'G' to
indicate Kilobytes, Megabytes, or Gigabytes, respectively. The default is between '1G' and '4G' depending
on the cipher. The optional second value is specified in seconds and may use any of the units documented
in the TIME FORMATS section of sshd_config5. 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. Optional. Type uniline.

RemoteCommand
Specifies a command to execute on the remote 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. Arguments to
RemoteCommand accept the tokens described in the TOKENS section. Optional. Type uniline.

RemoteForward
Specifies that a TCP port on the remote machine be forwarded over the secure channel. The remote port may
either be forwarded to a specified host and port from the local machine, or may act as a SOCKS 4/5 proxy
that allows a remote client to connect to arbitrary destinations from the local machine. The first
argument is the listening specification and may be [bind_address : port ] or, if the remote host supports
it, a Unix domain socket path. If forwarding to a specific destination then the second argument must be
host : hostport or a Unix domain socket path, otherwise if no destination argument is specified then the
remote forwarding will be established as a SOCKS proxy. When acting as a SOCKS proxy, the destination of
the connection can be restricted by PermitRemoteOpen

IPv6 addresses can be specified by enclosing addresses in square brackets. 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. Unix domain socket paths may use the tokens described
in the TOKENS section and environment variables as described in the ENVIRONMENT VARIABLES section.

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_config5). Optional. Type list of node of class Ssh::PortForward .

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).
Optional. Type enum. choice: 'auto', 'force', 'no', 'yes'.

RequiredRSASize
Specifies the minimum RSA key size (in bits) that ssh(1) will accept. User authentication keys smaller
than this limit will be ignored. Servers that present host keys smaller than this limit will cause the
connection to be terminated. The default is 1024 bits. Note that this limit may only be raised from the
default. Optional. Type integer.

upstream_default value :
1024

RevokedHostKeys
Specifies revoked host public keys. Keys listed in this file will be refused for host authentication.
Note that if this file does not exist or is not readable, then host authentication will be refused for
all hosts. Keys may be specified as a text file, listing one public key per line, or as an OpenSSH Key
Revocation List (KRL) as generated by ssh-keygen1. For more information on KRLs, see the KEY REVOCATION
LISTS section in ssh-keygen1. Arguments to RevokedHostKeys may use the tilde syntax to refer to a user's
home directory, the tokens described in the TOKENS section and environment variables as described in the
ENVIRONMENT VARIABLES section. Optional. Type uniline.

SecurityKeyProvider
Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys,
overriding the default of using the built-in USB HID support.

If the specified value begins with a '$' character, then it will be treated as an environment variable
containing the path to the library. Optional. Type uniline.

SendEnv
Specifies what variables from the local environ(7) should be sent to the server. The server must also
support it, and the server must be configured 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_config5 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.

See PATTERNS for more information on patterns.

It is possible to clear previously set SendEnv variable names by prefixing patterns with - The default is
not to send any environment variables. Optional. Type list of uniline.

ServerAliveCountMax
Sets the number of server alive messages (see below) which may be sent without ssh(1) receiving any
messages 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 unresponsive.

The default value is 3. If, for example, ServerAliveInterval (see below) is set to 15 and
ServerAliveCountMax is left at the default, if the server becomes unresponsive, ssh will disconnect after
approximately 45 seconds. Optional. Type integer.

upstream_default value :
3

ServerAliveInterval
Sets a timeout interval in seconds after which if no data has been received from the server, ssh(1) 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, or 300 if the BatchMode option is set
(Debian-specific). ProtocolKeepAlives is a Debian-specific compatibility alias for this option.
Optional. Type integer.

upstream_default value :
0

SessionType
May be used to either request invocation of a subsystem on the remote system, or to prevent the execution
of a remote command at all. The latter is useful for just forwarding ports. The argument to this keyword
must be none (same as the -N option), subsystem (same as the -s option) or default (shell or command
execution). Optional. Type enum. choice: 'default', 'none', 'subsystem'.

SetEnv
Directly specify one or more environment variables and their contents to be sent to the server. Similarly
to SendEnv with the exception of the TERM variable, the server must be prepared to accept the environment
variable. Optional. Type uniline.

StdinNull
Redirects stdin from /dev/null (actually, prevents reading from stdin). Either this or the equivalent -n
option must be used when ssh is run in the background. The argument to this keyword must be yes (same as
the -n option) or no (the default). Optional. Type boolean.

upstream_default value :
no

StreamLocalBindMask
Sets the octal file creation mode mask (umask) used when creating a Unix-domain socket file for local or
remote port forwarding. This option is only used for port forwarding to a Unix-domain socket file.

The default value is 0177, which creates a Unix-domain socket file that is readable and writable only by
the owner. Note that not all operating systems honor the file mode on Unix-domain socket files.
Optional. Type uniline.

StreamLocalBindUnlink
Specifies whether to remove an existing Unix-domain socket file for local or remote port forwarding
before creating a new one. If the socket file already exists and StreamLocalBindUnlink is not enabled,
ssh will be unable to forward the port to the Unix-domain socket file. This option is only used for port
forwarding to a Unix-domain socket file.

The argument must be yes or no (the default). Optional. Type boolean.

upstream_default value :
no

StrictHostKeyChecking
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 man-
in-the-middle (MITM) 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 manually
add all new hosts.

If this flag is set to accept-new then ssh will automatically add new host keys to the user's known_hosts
file, but will not permit connections to hosts with changed host keys. If this flag is set to no or off
ssh will automatically add new host keys to the user known hosts files and allow connections to hosts
with changed hostkeys to proceed, subject to some restrictions. If this flag is set to ask (the default),
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 automatically in all cases. Optional. Type enum. choice: 'yes',
'accept-new', 'no', 'off', 'ask'.

upstream_default value :
ask

SyslogFacility
Gives the facility code that is used when logging messages from ssh(1). The possible values are: DAEMON,
USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is USER.
Optional. Type enum. choice: 'AUTH', 'DAEMON', 'LOCAL0', 'LOCAL1', 'LOCAL2', 'LOCAL3', 'LOCAL4',
'LOCAL5', 'LOCAL6', 'LOCAL7', 'USER'.

upstream_default value :
USER

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. This option only uses
TCP keepalives (as opposed to using ssh level keepalives), so takes a long time to notice when the
connection dies. As such, you probably want the ServerAliveInterval option as well. 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 See also ServerAliveInterval for
protocol-level keepalives. Optional. Type boolean.

upstream_default value :
yes

Tag
Specify a configuration tag name that may be later used by a Match directive to select a block of
configuration. Optional. Type uniline.

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 (the default). Specifying yes requests the default tunnel
mode, which is point-to-point Optional. Type enum. choice: 'ethernet', 'no', 'point-to-point', 'yes'.

upstream_default value :
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
keyword any which uses the next available tunnel device. If remote_tun is not specified, it defaults to
any The default is any:any Optional. Type uniline.

upstream_default value :
any:any

UpdateHostKeys
Specifies whether ssh(1) should accept notifications of additional hostkeys from the server sent after
authentication has completed and add them to UserKnownHostsFile The argument must be yes no or ask This
option allows learning alternate hostkeys for a server and supports graceful key rotation by allowing a
server to send replacement public keys before old ones are removed.

Additional hostkeys are only accepted if the key used to authenticate the host was already trusted or
explicitly accepted by the user, the host was authenticated via UserKnownHostsFile (i.e. not
GlobalKnownHostsFile and the host was authenticated using a plain key and not a certificate.

UpdateHostKeys is enabled by default if the user has not overridden the default UserKnownHostsFile
setting and has not enabled VerifyHostKeyDNS otherwise UpdateHostKeys will be set to no

If UpdateHostKeys is set to ask then the user is asked to confirm the modifications to the known_hosts
file. Confirmation is currently incompatible with ControlPersist and will be disabled if it is enabled.

Presently, only sshd(8) from OpenSSH 6.8 and greater support the Qq hostkeys@openssh.com protocol
extension used to inform the client of all the server's hostkeys. Optional. Type enum. choice: 'ask',
'no', 'yes'.

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.
Optional. Type uniline.

UserKnownHostsFile
Specifies one or more files to use for the user host key database, separated by whitespace. Each filename
may use tilde notation to refer to the user's home directory, the tokens described in the TOKENS section
and environment variables as described in the ENVIRONMENT VARIABLES section. A value of none causes
ssh(1) to ignore any user-specific known hosts files. The default is ~/.ssh/known_hosts
~/.ssh/known_hosts2. Optional. Type list of uniline.

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 fingerprints
will be handled as if this option was set to ask If this option is set to ask information on fingerprint
match will be displayed, but the user will still need to confirm new host keys according to the
StrictHostKeyChecking option. The default is no

See also VERIFYING HOST KEYS in ssh(1). Optional. Type enum. choice: 'ask', 'no', 'yes'.

upstream_default value :
no

VisualHostKey
If this flag is set to yes an ASCII art representation of the remote host key fingerprint is printed in
addition to the fingerprint string at login and for unknown host keys. If this flag is set to no (the
default), no fingerprint strings are printed at login and only the fingerprint string will be printed for
unknown host keys. Optional. Type uniline.

upstream_default value :
no

XAuthLocation
Specifies the full pathname of the xauth(1) program. The default is /usr/bin/xauth. Optional. Type
uniline.

upstream_default value :
/usr/bin/xauth

FallBackToRsh
This parameter is now ignored by Ssh. Deprecated Optional. Type uniline.

HostbasedKeyTypes
This parameter is now ignored by Ssh. Deprecated Optional. Type uniline.

PubkeyAcceptedKeyTypes
This parameter is now ignored by Ssh. Deprecated Optional. Type uniline.

UseRsh
This parameter is now ignored by Ssh. Deprecated Optional. Type uniline.

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
criteria or the single token all which always matches. The available criteria keywords are: canonical
final exec localnetwork host originalhost tagged user and localuser The all criteria must appear alone or
immediately after canonical or final Other criteria may be combined arbitrarily. All criteria but all
canonical and final require an argument. Criteria may be negated by prepending an exclamation mark ('!' )

The canonical keyword matches only when the configuration file is being re-parsed after hostname
canonicalization (see the CanonicalizeHostname option). This may be useful to specify conditions that
work with canonical host names only.

The final keyword requests that the configuration be re-parsed (regardless of whether
CanonicalizeHostname is enabled), and matches only during this final pass. If CanonicalizeHostname is
enabled, then canonical and final match during the same pass.

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. Arguments to exec accept the tokens described in the TOKENS section.

The localnetwork keyword matches the addresses of active local network interfaces against the supplied
list of networks in CIDR format. This may be convenient for varying the effective configuration on
devices that roam between networks. Note that network address is not a trustworthy criteria in many
situations (e.g. when the network is automatically configured using DHCP) and so caution should be
applied if using it to control security-sensitive configuration.

The other keywords' criteria must be single entries or comma-separated lists and may use the wildcard and
negation operators described in the PATTERNS section. The criteria for the host keyword are matched
against the target hostname, after any substitution by the Hostname or CanonicalizeHostname options. The
originalhost keyword matches against the hostname as it was specified on the command-line. The tagged
keyword matches a tag name specified by a prior Tag directive or on the ssh(1) command-line using the -P
flag. The user keyword matches against the target username on the remote host. The localuser keyword
matches against the name of the local user running ssh(1) (this keyword may be useful in system-wide
ssh_config files). Optional. Type hash of node of class Ssh::HostElement .

LICENSE

       LGPL2

perl v5.40.1                                       2025-04-09                    Config::Model::models::Ssh(3pm)

NAME

DESCRIPTION

Elements

SEE ALSO

LICENSE