SSH_CONFIG(5) File Formats and Configurations SSH_CONFIG(5)

NAME

ssh_config - OpenSSH client configuration file

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)

Unless noted otherwise, 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
usually the one given on the command line (see the CanonicalizeHostname
option for exceptions).

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 file contains keyword-argument pairs, one per line. Lines starting
with `#' and empty lines are interpreted as comments. Arguments may
optionally be enclosed in double quotes (") in order to represent arguments
containing spaces. Configuration options may be separated by whitespace or
optional whitespace and exactly one `='; the latter format is useful to
avoid the need to quote whitespace when specifying configuration options
using the ssh, scp, and sftp -o option.

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
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.

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, Tag, 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).

AddKeysToAgent
Specifies whether keys should be automatically added to a running
ssh-agent(1). 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-add(1). If this option is set
to ask, ssh(1) will require confirmation using the SSH_ASKPASS
program before adding a key (see ssh-add(1) 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-add(1). 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_config(5) to specify
the key's lifetime in ssh-agent(1), 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.

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

BatchMode
If set to yes, user interaction such as password prompts and host
key confirmation requests will be disabled. This option is useful
in scripts and other batch jobs where no user is present to
interact with ssh(1). The argument must be yes or no (the
default).

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.

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

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 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.

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.

A single argument of "none" causes no CNAMEs to be considered for
canonicalization. This is the default behaviour.

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.

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-agent(1), 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.

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 a channel
type name (as described in the table 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 the interactive session to terminate after
five minutes of inactivity. Specifying a zero value disables the
inactivity timeout.

The available channel types include:

agent-connection
Open connections to ssh-agent(1).

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.

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.

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.com
aes256-gcm@openssh.com
chacha20-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 "ssh -Q
cipher".

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).

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

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
timeout is applied both to establishing the connection and to
performing the initial SSH protocol handshake and key exchange.

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-askpass(1). If the
ControlPath cannot be opened, ssh(1) 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. 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.

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
"ssh -O exit"). 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.

DisableBanner
If set to yes, disables the display of the banner message. If
set to in-exec-mode, disables the display of banner message when in
remote command mode only.

The default value is no, which means that the banner is displayed
unless the log level is QUIET, FATAL, or ERROR. See also the
Banner option in sshd_config(4). This option applies to protocol
version 2 only.

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.

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

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). 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, 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).

FingerprintHash
Specifies the hash algorithm used when displaying key fingerprints.
Valid options are: md5 and sha256 (the default).

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).

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.

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.

ForwardX11Timeout
Specify a timeout for untrusted X11 forwarding using the format
described in the TIME FORMATS section of sshd_config(5). 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.

ForwardX11Trusted
If this option is set to yes, remote X11 clients will have full
access to the original X11 display.

If this option is set to no (the 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.

The default on Solaris is "yes".

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).

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 on Solaris is "yes".

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

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-keygen(1).

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.

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

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 "ssh -Q HostKeyAlgorithms".

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.

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.

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-agent(1) 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.

IdentityAgent
Specifies the UNIX-domain 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
"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.

IdentityFile
Specifies a file from which the user's DSA, 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-agent(1) 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, ~/.ssh/id_ed25519_sk and ~/.ssh/id_dsa.
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.

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.

Include
Include the specified configuration file(s). Multiple pathnames
may be specified and each pathname may contain glob(7) wildcards
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.

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 af21 (Low-Latency Data) for interactive sessions and cs1 (Lower
Effort) for non-interactive sessions.

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.

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.

KexAlgorithms
Specifies the available KEX (Key Exchange) algorithms. 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 default is:

sntrup761x25519-sha512@openssh.com,
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 available key exchange algorithms may also be obtained
using "ssh -Q kex".

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.

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.

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.

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.

LogVerbose
Specify one or more overrides to LogLevel. An override consists of
a 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 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.

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 "-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
"ssh -Q mac".

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

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

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

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).

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.

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.

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 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

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

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.

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.

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 "ssh -Q PubkeyAcceptedAlgorithms".

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-agent(1) forwarding.

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_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.

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.

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_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).

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.

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-keygen(1). For more information on
KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
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.

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.

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_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.

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.

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.

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.

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).

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.

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).

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.

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).

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.

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.

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.
See also ServerAliveInterval for protocol-level keepalives.

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

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.

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.

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
"hostkeys@openssh.com" protocol extension used to inform the client
of all the server's hostkeys.

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. 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.

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).

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.

XAuthLocation
Specifies the full pathname of the xauth(1) program. The default
is /opt/local/bin/xauth.

PATTERNS

A pattern consists of zero or more non-whitespace characters, `*' (a
wildcard that matches zero or more characters), or `?' (a wildcard that
matches exactly one character). For example, to specify a set of
declarations for any host in the ".co.uk" set of domains, the following
pattern could be used:

Host *.co.uk

The following pattern would match any host in the 192.168.0.[0-9] network
range:

Host 192.168.0.?

A pattern-list is a comma-separated list of patterns. Patterns within
pattern-lists may be negated by preceding them with an exclamation mark
(`!'). For example, to allow a key to be used from anywhere within an
organization except from the "dialup" pool, the following entry (in
authorized_keys) could be used:

from="!*.dialup.example.com,*.example.com"

Note that a negated match will never produce a positive result by itself.
For example, attempting to match "host3" against the following pattern-list
will fail:

from="!host1,!host2"

The solution here is to include a term that will yield a positive match,
such as a wildcard:

from="!host1,!host2,*"

TOKENS

Arguments to some keywords can make use of tokens, which are expanded at
runtime:

%% A literal `%'.
%C Hash of %l%h%p%r%j.
%d Local user's home directory.
%f The fingerprint of the server's host key.
%H The known_hosts hostname or address that is being searched for.
%h The remote hostname.
%I A string describing the reason for a KnownHostsCommand
execution: either ADDRESS when looking up a host by address
(only when CheckHostIP is enabled), HOSTNAME when searching by
hostname, or ORDER when preparing the host key algorithm
preference list to use for the destination host.
%i The local user ID.
%j The contents of the ProxyJump option, or the empty string if
this option is unset.
%K The base64 encoded host key.
%k The host key alias if specified, otherwise the original remote
hostname given on the command line.
%L The local hostname.
%l The local hostname, including the domain name.
%n The original remote hostname, as given on the command line.
%p The remote port.
%r The remote username.
%T The local tun(4) or tap(4) network interface assigned if tunnel
forwarding was requested, or "NONE" otherwise.
%t The type of the server host key, e.g. ssh-ed25519.
%u The local username.

CertificateFile, ControlPath, IdentityAgent, IdentityFile,
KnownHostsCommand, LocalForward, Match exec, RemoteCommand, RemoteForward,
RevokedHostKeys, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
%i, %j, %k, %L, %l, %n, %p, %r, and %u.

KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.

Hostname accepts the tokens %% and %h.

LocalCommand accepts all tokens.

ProxyCommand and ProxyJump accept the tokens %%, %h, %n, %p, and %r.

Note that some of these directives build commands for execution via the
shell. Because ssh(1) performs no filtering or escaping of characters that
have special meaning in shell commands (e.g. quotes), it is the user's
responsibility to ensure that the arguments passed to ssh(1) do not contain
such characters and that tokens are appropriately quoted when used.

ENVIRONMENT VARIABLES

Arguments to some keywords can be expanded at runtime from environment
variables on the client by enclosing them in ${}, for example ${HOME}/.ssh
would refer to the user's .ssh directory. If a specified environment
variable does not exist then an error will be returned and the setting for
that keyword will be ignored.

The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
KnownHostsCommand, and UserKnownHostsFile support environment variables.
The keywords LocalForward and RemoteForward support environment variables
only for Unix domain socket paths.

FILES

~/.ssh/config
This is the per-user configuration file. The format of this file
is described above. This file is used by the SSH client. Because
of the potential for abuse, this file must have strict permissions:
read/write for the user, and not writable by others.

/etc/ssh/ssh_config
Systemwide configuration file. This file provides defaults for
those values that are not specified in the user's configuration
file, and for those users who do not have a configuration file.
This file must be world-readable.

SEE ALSO

ssh(1)

AUTHORS

OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu
Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de
Raadt and Dug Song removed many bugs, re-added newer features and created
OpenSSH. Markus Friedl contributed the support for SSH protocol versions
1.5 and 2.0.

illumos October 12, 2023 illumos