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SSHD_CONFIG(5)		  FreeBSD File Formats Manual		SSHD_CONFIG(5)

NAME
     sshd_config -- OpenSSH SSH	daemon configuration file

SYNOPSIS
     /etc/ssh/sshd_config

DESCRIPTION
     sshd(8) reads configuration data from /etc/ssh/sshd_config	(or the	file
     specified with -f on the command line).  The file contains	keyword-argu-
     ment 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.

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

     AcceptEnv
	     Specifies what environment	variables sent by the client will be
	     copied into the session's environ(7).  See	SendEnv	in
	     ssh_config(5) for how to configure	the client.  The TERM environ-
	     ment variable is always sent whenever the client requests a
	     pseudo-terminal as	it is required by the protocol.	 Variables are
	     specified by name,	which may contain the wildcard characters `*'
	     and `?'.  Multiple	environment variables may be separated by
	     whitespace	or spread across multiple AcceptEnv directives.	 Be
	     warned that some environment variables could be used to bypass
	     restricted	user environments.  For	this reason, care should be
	     taken in the use of this directive.  The default is not to	accept
	     any environment variables.

     AddressFamily
	     Specifies which address family should be used by sshd(8).	Valid
	     arguments are any (the default), inet (use	IPv4 only), or inet6
	     (use IPv6 only).

     AllowAgentForwarding
	     Specifies whether ssh-agent(1) forwarding is permitted.  The
	     default is	yes.  Note that	disabling agent	forwarding does	not
	     improve security unless users are also denied shell access, as
	     they can always install their own forwarders.

     AllowGroups
	     This keyword can be followed by a list of group name patterns,
	     separated by spaces.  If specified, login is allowed only for
	     users whose primary group or supplementary	group list matches one
	     of	the patterns.  Only group names	are valid; a numerical group
	     ID	is not recognized.  By default,	login is allowed for all
	     groups.  The allow/deny directives	are processed in the following
	     order: DenyUsers, AllowUsers, DenyGroups, and finally
	     AllowGroups.

	     See PATTERNS in ssh_config(5) for more information	on patterns.

     AllowStreamLocalForwarding
	     Specifies whether StreamLocal (Unix-domain	socket)	forwarding is
	     permitted.	 The available options are yes (the default) or	all to
	     allow StreamLocal forwarding, no to prevent all StreamLocal for-
	     warding, local to allow local (from the perspective of ssh(1))
	     forwarding	only or	remote to allow	remote forwarding only.	 Note
	     that disabling StreamLocal	forwarding does	not improve security
	     unless users are also denied shell	access,	as they	can always
	     install their own forwarders.

     AllowTcpForwarding
	     Specifies whether TCP forwarding is permitted.  The available
	     options are yes (the default) or all to allow TCP forwarding, no
	     to	prevent	all TCP	forwarding, local to allow local (from the
	     perspective of ssh(1)) forwarding only or remote to allow remote
	     forwarding	only.  Note that disabling TCP forwarding does not
	     improve security unless users are also denied shell access, as
	     they can always install their own forwarders.

     AllowUsers
	     This keyword can be followed by a list of user name patterns,
	     separated by spaces.  If specified, login is allowed only for
	     user names	that match one of the patterns.	 Only user names are
	     valid; a numerical	user ID	is not recognized.  By default,	login
	     is	allowed	for all	users.	If the pattern takes the form
	     USER@HOST then USER and HOST are separately checked, restricting
	     logins to particular users	from particular	hosts.	HOST criteria
	     may additionally contain addresses	to match in CIDR
	     address/masklen format.  The allow/deny directives	are processed
	     in	the following order: DenyUsers,	AllowUsers, DenyGroups,	and
	     finally AllowGroups.

	     See PATTERNS in ssh_config(5) for more information	on patterns.

     AuthenticationMethods
	     Specifies the authentication methods that must be successfully
	     completed for a user to be	granted	access.	 This option must be
	     followed by one or	more comma-separated lists of authentication
	     method names, or by the single string any to indicate the default
	     behaviour of accepting any	single authentication method.  If the
	     default is	overridden, then successful authentication requires
	     completion	of every method	in at least one	of these lists.

	     For example, "publickey,password publickey,keyboard-interactive"
	     would require the user to complete	public key authentication,
	     followed by either	password or keyboard interactive authentica-
	     tion.  Only methods that are next in one or more lists are
	     offered at	each stage, so for this	example	it would not be	possi-
	     ble to attempt password or	keyboard-interactive authentication
	     before public key.

	     For keyboard interactive authentication it	is also	possible to
	     restrict authentication to	a specific device by appending a colon
	     followed by the device identifier bsdauth,	pam, or	skey, depend-
	     ing on the	server configuration.  For example,
	     "keyboard-interactive:bsdauth" would restrict keyboard interac-
	     tive authentication to the	bsdauth	device.

	     If	the publickey method is	listed more than once, sshd(8) veri-
	     fies that keys that have been used	successfully are not reused
	     for subsequent authentications.  For example,
	     "publickey,publickey" requires successful authentication using
	     two different public keys.

	     Note that each authentication method listed should	also be
	     explicitly	enabled	in the configuration.

     AuthorizedKeysCommand
	     Specifies a program to be used to look up the user's public keys.
	     The program must be owned by root,	not writable by	group or oth-
	     ers and specified by an absolute path.  Arguments to
	     AuthorizedKeysCommand accept the tokens described in the TOKENS
	     section.  If no arguments are specified then the username of the
	     target user is used.

	     The program should	produce	on standard output zero	or more	lines
	     of	authorized_keys	output (see AUTHORIZED_KEYS in sshd(8)).  If a
	     key supplied by AuthorizedKeysCommand does	not successfully
	     authenticate and authorize	the user then public key authentica-
	     tion continues using the usual AuthorizedKeysFile files.  By
	     default, no AuthorizedKeysCommand is run.

     AuthorizedKeysCommandUser
	     Specifies the user	under whose account the	AuthorizedKeysCommand
	     is	run.  It is recommended	to use a dedicated user	that has no
	     other role	on the host than running authorized keys commands.  If
	     AuthorizedKeysCommand is specified	but AuthorizedKeysCommandUser
	     is	not, then sshd(8) will refuse to start.

     AuthorizedKeysFile
	     Specifies the file	that contains the public keys used for user
	     authentication.  The format is described in the AUTHORIZED_KEYS
	     FILE FORMAT section of sshd(8).  Arguments	to AuthorizedKeysFile
	     accept the	tokens described in the	TOKENS section.	 After expan-
	     sion, AuthorizedKeysFile is taken to be an	absolute path or one
	     relative to the user's home directory.  Multiple files may	be
	     listed, separated by whitespace.  Alternately this	option may be
	     set to none to skip checking for user keys	in files.  The default
	     is	".ssh/authorized_keys .ssh/authorized_keys2".

     AuthorizedPrincipalsCommand
	     Specifies a program to be used to generate	the list of allowed
	     certificate principals as per AuthorizedPrincipalsFile.  The pro-
	     gram must be owned	by root, not writable by group or others and
	     specified by an absolute path.  Arguments to
	     AuthorizedPrincipalsCommand accept	the tokens described in	the
	     TOKENS section.  If no arguments are specified then the username
	     of	the target user	is used.

	     The program should	produce	on standard output zero	or more	lines
	     of	AuthorizedPrincipalsFile output.  If either
	     AuthorizedPrincipalsCommand or AuthorizedPrincipalsFile is	speci-
	     fied, then	certificates offered by	the client for authentication
	     must contain a principal that is listed.  By default, no
	     AuthorizedPrincipalsCommand is run.

     AuthorizedPrincipalsCommandUser
	     Specifies the user	under whose account the
	     AuthorizedPrincipalsCommand is run.  It is	recommended to use a
	     dedicated user that has no	other role on the host than running
	     authorized	principals commands.  If AuthorizedPrincipalsCommand
	     is	specified but AuthorizedPrincipalsCommandUser is not, then
	     sshd(8) will refuse to start.

     AuthorizedPrincipalsFile
	     Specifies a file that lists principal names that are accepted for
	     certificate authentication.  When using certificates signed by a
	     key listed	in TrustedUserCAKeys, this file	lists names, one of
	     which must	appear in the certificate for it to be accepted	for
	     authentication.  Names are	listed one per line preceded by	key
	     options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)).
	     Empty lines and comments starting with `#'	are ignored.

	     Arguments to AuthorizedPrincipalsFile accept the tokens described
	     in	the TOKENS section.  After expansion, AuthorizedPrincipalsFile
	     is	taken to be an absolute	path or	one relative to	the user's
	     home directory.  The default is none, i.e.	not to use a princi-
	     pals file - in this case, the username of the user	must appear in
	     a certificate's principals	list for it to be accepted.

	     Note that AuthorizedPrincipalsFile	is only	used when authentica-
	     tion proceeds using a CA listed in	TrustedUserCAKeys and is not
	     consulted for certification authorities trusted via
	     ~/.ssh/authorized_keys, though the	principals= key	option offers
	     a similar facility	(see sshd(8) for details).

     Banner  The contents of the specified file	are sent to the	remote user
	     before authentication is allowed.	If the argument	is none	then
	     no	banner is displayed.  By default, no banner is displayed.

     ChallengeResponseAuthentication
	     Specifies whether challenge-response authentication is allowed
	     (e.g. via PAM or through authentication styles supported in
	     login.conf(5)) The	default	is yes.

     ChrootDirectory
	     Specifies the pathname of a directory to chroot(2)	to after
	     authentication.  At session startup sshd(8) checks	that all com-
	     ponents of	the pathname are root-owned directories	which are not
	     writable by any other user	or group.  After the chroot, sshd(8)
	     changes the working directory to the user's home directory.
	     Arguments to ChrootDirectory accept the tokens described in the
	     TOKENS section.

	     The ChrootDirectory must contain the necessary files and directo-
	     ries to support the user's	session.  For an interactive session
	     this requires at least a shell, typically sh(1), and basic	/dev
	     nodes such	as null(4), zero(4), stdin(4), stdout(4), stderr(4),
	     and tty(4)	devices.  For file transfer sessions using SFTP	no
	     additional	configuration of the environment is necessary if the
	     in-process	sftp-server is used, though sessions which use logging
	     may require /dev/log inside the chroot directory on some operat-
	     ing systems (see sftp-server(8) for details).

	     For safety, it is very important that the directory hierarchy be
	     prevented from modification by other processes on the system
	     (especially those outside the jail).  Misconfiguration can	lead
	     to	unsafe environments which sshd(8) cannot detect.

	     The default is none, indicating not to chroot(2).

     Ciphers
	     Specifies the ciphers allowed.  Multiple ciphers must be comma-
	     separated.	 If the	specified value	begins with a `+' character,
	     then the specified	ciphers	will be	appended to the	default	set
	     instead of	replacing them.	 If the	specified value	begins with a
	     `-' character, then the specified ciphers (including wildcards)
	     will be removed from the default set instead of replacing them.

	     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
		   arcfour
		   arcfour128
		   arcfour256
		   blowfish-cbc
		   cast128-cbc
		   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,
		   aes128-cbc,aes192-cbc,aes256-cbc

	     The list of available ciphers may also be obtained	using "ssh -Q
	     cipher".

     ClientAliveCountMax
	     Sets the number of	client alive messages which may	be sent	with-
	     out sshd(8) receiving any messages	back from the client.  If this
	     threshold is reached while	client alive messages are being	sent,
	     sshd will disconnect the client, terminating the session.	It is
	     important to note that the	use of client alive messages is	very
	     different from TCPKeepAlive.  The client alive messages are sent
	     through the encrypted channel and therefore will not be spoofa-
	     ble.  The TCP keepalive option enabled by TCPKeepAlive is spoofa-
	     ble.  The client alive mechanism is valuable when the client or
	     server depend on knowing when a connection	has become inactive.

	     The default value is 3.  If ClientAliveInterval is	set to 15, and
	     ClientAliveCountMax is left at the	default, unresponsive SSH
	     clients will be disconnected after	approximately 45 seconds.

     ClientAliveInterval
	     Sets a timeout interval in	seconds	after which if no data has
	     been received from	the client, sshd(8) will send a	message
	     through the encrypted channel to request a	response from the
	     client.  The default is 0,	indicating that	these messages will
	     not be sent to the	client.

     Compression
	     Specifies whether compression is enabled after the	user has
	     authenticated successfully.  The argument must be yes, delayed (a
	     legacy synonym for	yes) or	no.  The default is yes.

     DenyGroups
	     This keyword can be followed by a list of group name patterns,
	     separated by spaces.  Login is disallowed for users whose primary
	     group or supplementary group list matches one of the patterns.
	     Only group	names are valid; a numerical group ID is not recog-
	     nized.  By	default, login is allowed for all groups.  The
	     allow/deny	directives are processed in the	following order:
	     DenyUsers,	AllowUsers, DenyGroups,	and finally AllowGroups.

	     See PATTERNS in ssh_config(5) for more information	on patterns.

     DenyUsers
	     This keyword can be followed by a list of user name patterns,
	     separated by spaces.  Login is disallowed for user	names that
	     match one of the patterns.	 Only user names are valid; a numeri-
	     cal user ID is not	recognized.  By	default, login is allowed for
	     all users.	 If the	pattern	takes the form USER@HOST then USER and
	     HOST are separately checked, restricting logins to	particular
	     users from	particular hosts.  HOST	criteria may additionally con-
	     tain addresses to match in	CIDR address/masklen format.  The
	     allow/deny	directives are processed in the	following order:
	     DenyUsers,	AllowUsers, DenyGroups,	and finally AllowGroups.

	     See PATTERNS in ssh_config(5) for more information	on patterns.

     DisableForwarding
	     Disables all forwarding features, including X11, ssh-agent(1),
	     TCP and StreamLocal.  This	option overrides all other forwarding-
	     related options and may simplify restricted configurations.

     FingerprintHash
	     Specifies the hash	algorithm used when logging key	fingerprints.
	     Valid options are:	md5 and	sha256.	 The default is	sha256.

     ForceCommand
	     Forces the	execution of the command specified by ForceCommand,
	     ignoring any command supplied by the client and ~/.ssh/rc if
	     present.  The command is invoked by using the user's login	shell
	     with the -c option.  This applies to shell, command, or subsystem
	     execution.	 It is most useful inside a Match block.  The command
	     originally	supplied by the	client is available in the
	     SSH_ORIGINAL_COMMAND environment variable.	 Specifying a command
	     of	internal-sftp will force the use of an in-process SFTP server
	     that requires no support files when used with ChrootDirectory.
	     The default is none.

     GatewayPorts
	     Specifies whether remote hosts are	allowed	to connect to ports
	     forwarded for the client.	By default, sshd(8) binds remote port
	     forwardings to the	loopback address.  This	prevents other remote
	     hosts from	connecting to forwarded	ports.	GatewayPorts can be
	     used to specify that sshd should allow remote port	forwardings to
	     bind to non-loopback addresses, thus allowing other hosts to con-
	     nect.  The	argument may be	no to force remote port	forwardings to
	     be	available to the local host only, yes to force remote port
	     forwardings to bind to the	wildcard address, or clientspecified
	     to	allow the client to select the address to which	the forwarding
	     is	bound.	The default is no.

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

     GSSAPICleanupCredentials
	     Specifies whether to automatically	destroy	the user's credentials
	     cache on logout.  The default is yes.

     GSSAPIStrictAcceptorCheck
	     Determines	whether	to be strict about the identity	of the GSSAPI
	     acceptor a	client authenticates against.  If set to yes then the
	     client must authenticate against the host service on the current
	     hostname.	If set to no then the client may authenticate against
	     any service key stored in the machine's default store.  This
	     facility is provided to assist with operation on multi homed
	     machines.	The default is yes.

     HostbasedAcceptedKeyTypes
	     Specifies the key types that will be accepted for hostbased
	     authentication as a comma-separated pattern list.	Alternately if
	     the specified value begins	with a `+' character, then the speci-
	     fied key types will be appended to	the default set	instead	of
	     replacing them.  If the specified value begins with a `-' charac-
	     ter, then the specified key types (including wildcards) will be
	     removed from the default set instead of replacing them.  The
	     default for this option is:

		ecdsa-sha2-nistp256-cert-v01@openssh.com,
		ecdsa-sha2-nistp384-cert-v01@openssh.com,
		ecdsa-sha2-nistp521-cert-v01@openssh.com,
		ssh-ed25519-cert-v01@openssh.com,
		ssh-rsa-cert-v01@openssh.com,
		ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
		ssh-ed25519,ssh-rsa

	     The list of available key types may also be obtained using	"ssh
	     -Q	key".

     HostbasedAuthentication
	     Specifies whether rhosts or /etc/hosts.equiv authentication
	     together with successful public key client	host authentication is
	     allowed (host-based authentication).  The default is no.

     HostbasedUsesNameFromPacketOnly
	     Specifies whether or not the server will attempt to perform a
	     reverse name lookup when matching the name	in the ~/.shosts,
	     ~/.rhosts,	and /etc/hosts.equiv files during
	     HostbasedAuthentication.  A setting of yes	means that sshd(8)
	     uses the name supplied by the client rather than attempting to
	     resolve the name from the TCP connection itself.  The default is
	     no.

     HostCertificate
	     Specifies a file containing a public host certificate.  The cer-
	     tificate's	public key must	match a	private	host key already spec-
	     ified by HostKey.	The default behaviour of sshd(8) is not	to
	     load any certificates.

     HostKey
	     Specifies a file containing a private host	key used by SSH.  The
	     defaults are /etc/ssh/ssh_host_dsa_key,
	     /etc/ssh/ssh_host_ecdsa_key, /etc/ssh/ssh_host_ed25519_key	and
	     /etc/ssh/ssh_host_rsa_key.

	     Note that sshd(8) will refuse to use a file if it is group/world-
	     accessible	and that the HostKeyAlgorithms option restricts	which
	     of	the keys are actually used by sshd(8).

	     It	is possible to have multiple host key files.  It is also pos-
	     sible to specify public host key files instead.  In this case
	     operations	on the private key will	be delegated to	an
	     ssh-agent(1).

     HostKeyAgent
	     Identifies	the UNIX-domain	socket used to communicate with	an
	     agent that	has access to the private host keys.  If the string
	     "SSH_AUTH_SOCK" is	specified, the location	of the socket will be
	     read from the SSH_AUTH_SOCK environment variable.

     HostKeyAlgorithms
	     Specifies the host	key algorithms that the	server offers.	The
	     default for this option is:

		ecdsa-sha2-nistp256-cert-v01@openssh.com,
		ecdsa-sha2-nistp384-cert-v01@openssh.com,
		ecdsa-sha2-nistp521-cert-v01@openssh.com,
		ssh-ed25519-cert-v01@openssh.com,
		ssh-rsa-cert-v01@openssh.com,
		ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
		ssh-ed25519,ssh-rsa

	     The list of available key types may also be obtained using	"ssh
	     -Q	key".

     IgnoreRhosts
	     Specifies that .rhosts and	.shosts	files will not be used in
	     HostbasedAuthentication.

	     /etc/hosts.equiv and /etc/ssh/shosts.equiv	are still used.	 The
	     default is	yes.

     IgnoreUserKnownHosts
	     Specifies whether sshd(8) should ignore the user's
	     ~/.ssh/known_hosts	during HostbasedAuthentication.	 The default
	     is	no.

     IPQoS   Specifies the IPv4	type-of-service	or DSCP	class for the connec-
	     tion.  Accepted values are	af11, af12, af13, af21,	af22, af23,
	     af31, af32, af33, af41, af42, af43, cs0, cs1, cs2,	cs3, cs4, cs5,
	     cs6, cs7, ef, lowdelay, throughput, reliability, or a numeric
	     value.  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.

     KbdInteractiveAuthentication
	     Specifies whether to allow	keyboard-interactive authentication.
	     The argument to this keyword must be yes or no.  The default is
	     to	use whatever value ChallengeResponseAuthentication is set to
	     (by default yes).

     KerberosAuthentication
	     Specifies whether the password provided by	the user for
	     PasswordAuthentication will be validated through the Kerberos
	     KDC.  To use this option, the server needs	a Kerberos servtab
	     which allows the verification of the KDC's	identity.  The default
	     is	no.

     KerberosGetAFSToken
	     If	AFS is active and the user has a Kerberos 5 TGT, attempt to
	     acquire an	AFS token before accessing the user's home directory.
	     The default is no.

     KerberosOrLocalPasswd
	     If	password authentication	through	Kerberos fails then the	pass-
	     word will be validated via	any additional local mechanism such as
	     /etc/passwd.  The default is yes.

     KerberosTicketCleanup
	     Specifies whether to automatically	destroy	the user's ticket
	     cache file	on logout.  The	default	is yes.

     KexAlgorithms
	     Specifies the available KEX (Key Exchange)	algorithms.  Multiple
	     algorithms	must be	comma-separated.  Alternately if the specified
	     value begins with a `+' character,	then the specified methods
	     will be appended to the default set instead of replacing them.
	     If	the specified value begins with	a `-' character, then the
	     specified methods (including wildcards) will be removed from the
	     default set instead of replacing them.  The supported algorithms
	     are:

		   curve25519-sha256
		   curve25519-sha256@libssh.org
		   diffie-hellman-group1-sha1
		   diffie-hellman-group14-sha1
		   diffie-hellman-group-exchange-sha1
		   diffie-hellman-group-exchange-sha256
		   ecdh-sha2-nistp256
		   ecdh-sha2-nistp384
		   ecdh-sha2-nistp521

	     The default is:

		   curve25519-sha256,curve25519-sha256@libssh.org,
		   ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
		   diffie-hellman-group-exchange-sha256,
		   diffie-hellman-group14-sha1

	     The list of available key exchange	algorithms may also be
	     obtained using "ssh -Q kex".

     ListenAddress
	     Specifies the local addresses sshd(8) should listen on.  The fol-
	     lowing forms may be used:

		   ListenAddress host|IPv4_addr|IPv6_addr
		   ListenAddress host|IPv4_addr:port
		   ListenAddress [host|IPv6_addr]:port

	     If	port is	not specified, sshd will listen	on the address and all
	     Port options specified.  The default is to	listen on all local
	     addresses.	 Multiple ListenAddress	options	are permitted.

     LoginGraceTime
	     The server	disconnects after this time if the user	has not	suc-
	     cessfully logged in.  If the value	is 0, there is no time limit.
	     The default is 120	seconds.

     LogLevel
	     Gives the verbosity level that is used when logging messages from
	     sshd(8).  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 debugging	output.	 Logging with a	DEBUG level
	     violates the privacy of users and is not recommended.

     MACs    Specifies the available MAC (message authentication code) algo-
	     rithms.  The MAC algorithm	is used	for data integrity protection.
	     Multiple algorithms must be comma-separated.  If the specified
	     value begins with a `+' character,	then the specified algorithms
	     will be appended to the default set instead of replacing them.
	     If	the specified value begins with	a `-' character, then the
	     specified algorithms (including wildcards)	will be	removed	from
	     the default set instead of	replacing them.

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

		   hmac-md5
		   hmac-md5-96
		   hmac-ripemd160
		   hmac-sha1
		   hmac-sha1-96
		   hmac-sha2-256
		   hmac-sha2-512
		   umac-64@openssh.com
		   umac-128@openssh.com
		   hmac-md5-etm@openssh.com
		   hmac-md5-96-etm@openssh.com
		   hmac-ripemd160-etm@openssh.com
		   hmac-sha1-etm@openssh.com
		   hmac-sha1-96-etm@openssh.com
		   hmac-sha2-256-etm@openssh.com
		   hmac-sha2-512-etm@openssh.com
		   umac-64-etm@openssh.com
		   umac-128-etm@openssh.com

	     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".

     Match   Introduces	a conditional block.  If all of	the criteria on	the
	     Match line	are satisfied, the keywords on the following lines
	     override those set	in the global section of the config file,
	     until either another Match	line or	the end	of the file.  If a
	     keyword appears in	multiple Match blocks that are satisfied, only
	     the first instance	of the keyword is applied.

	     The arguments to Match are	one or more criteria-pattern pairs or
	     the single	token All which	matches	all criteria.  The available
	     criteria are User,	Group, Host, LocalAddress, LocalPort, and
	     Address.  The match patterns may consist of single	entries	or
	     comma-separated lists and may use the wildcard and	negation oper-
	     ators described in	the PATTERNS section of	ssh_config(5).

	     The patterns in an	Address	criteria may additionally contain
	     addresses to match	in CIDR	address/masklen	format,	such as
	     192.0.2.0/24 or 2001:db8::/32.  Note that the mask	length pro-
	     vided must	be consistent with the address - it is an error	to
	     specify a mask length that	is too long for	the address or one
	     with bits set in this host	portion	of the address.	 For example,
	     192.0.2.0/33 and 192.0.2.0/8, respectively.

	     Only a subset of keywords may be used on the lines	following a
	     Match keyword.  Available keywords	are AcceptEnv,
	     AllowAgentForwarding, AllowGroups,	AllowStreamLocalForwarding,
	     AllowTcpForwarding, AllowUsers, AuthenticationMethods,
	     AuthorizedKeysCommand, AuthorizedKeysCommandUser,
	     AuthorizedKeysFile, AuthorizedPrincipalsCommand,
	     AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile,
	     Banner, ChrootDirectory, ClientAliveCountMax,
	     ClientAliveInterval, DenyGroups, DenyUsers, ForceCommand,
	     GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedKeyTypes,
	     HostbasedAuthentication, HostbasedUsesNameFromPacketOnly, IPQoS,
	     KbdInteractiveAuthentication, KerberosAuthentication,
	     MaxAuthTries, MaxSessions,	PasswordAuthentication,
	     PermitEmptyPasswords, PermitOpen, PermitRootLogin,	PermitTTY,
	     PermitTunnel, PermitUserRC, PubkeyAcceptedKeyTypes,
	     PubkeyAuthentication, RekeyLimit, RevokedKeys,
	     StreamLocalBindMask, StreamLocalBindUnlink, TrustedUserCAKeys,
	     X11DisplayOffset, X11Forwarding and X11UseLocalHost.

     MaxAuthTries
	     Specifies the maximum number of authentication attempts permitted
	     per connection.  Once the number of failures reaches half this
	     value, additional failures	are logged.  The default is 6.

     MaxSessions
	     Specifies the maximum number of open shell, login or subsystem
	     (e.g. sftp) sessions permitted per	network	connection.  Multiple
	     sessions may be established by clients that support connection
	     multiplexing.  Setting MaxSessions	to 1 will effectively disable
	     session multiplexing, whereas setting it to 0 will	prevent	all
	     shell, login and subsystem	sessions while still permitting	for-
	     warding.  The default is 10.

     MaxStartups
	     Specifies the maximum number of concurrent	unauthenticated	con-
	     nections to the SSH daemon.  Additional connections will be
	     dropped until authentication succeeds or the LoginGraceTime
	     expires for a connection.	The default is 10:30:100.

	     Alternatively, random early drop can be enabled by	specifying the
	     three colon separated values start:rate:full (e.g.	"10:30:60").
	     sshd(8) will refuse connection attempts with a probability	of
	     rate/100 (30%) if there are currently start (10) unauthenticated
	     connections.  The probability increases linearly and all connec-
	     tion attempts are refused if the number of	unauthenticated	con-
	     nections reaches full (60).

     PasswordAuthentication
	     Specifies whether password	authentication is allowed.  See	also
	     UsePAM.  The default is no.

     PermitEmptyPasswords
	     When password authentication is allowed, it specifies whether the
	     server allows login to accounts with empty	password strings.  The
	     default is	no.

     PermitOpen
	     Specifies the destinations	to which TCP port forwarding is	per-
	     mitted.  The forwarding specification must	be one of the follow-
	     ing forms:

		   PermitOpen host:port
		   PermitOpen IPv4_addr:port
		   PermitOpen [IPv6_addr]:port

	     Multiple forwards may be specified	by separating them with	white-
	     space.  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, respec-
	     tively.  By default all port forwarding requests are permitted.

     PermitRootLogin
	     Specifies whether root can	log in using ssh(1).  The argument
	     must be yes, prohibit-password, without-password,
	     forced-commands-only, or no.  The default is no.  Note that if
	     ChallengeResponseAuthentication and UsePAM	are both yes, this
	     setting may be overridden by the PAM policy.

	     If	this option is set to prohibit-password	or without-password,
	     password and keyboard-interactive authentication are disabled for
	     root.

	     If	this option is set to forced-commands-only, root login with
	     public key	authentication will be allowed,	but only if the
	     command option has	been specified (which may be useful for	taking
	     remote backups even if root login is normally not allowed).  All
	     other authentication methods are disabled for root.

	     If	this option is set to no, root is not allowed to log in.

     PermitTTY
	     Specifies whether pty(4) allocation is permitted.	The default is
	     yes.

     PermitTunnel
	     Specifies whether tun(4) device forwarding	is allowed.  The argu-
	     ment must be yes, point-to-point (layer 3), ethernet (layer 2),
	     or	no.  Specifying	yes permits both point-to-point	and ethernet.
	     The default is no.

	     Independent of this setting, the permissions of the selected
	     tun(4) device must	allow access to	the user.

     PermitUserEnvironment
	     Specifies whether ~/.ssh/environment and environment= options in
	     ~/.ssh/authorized_keys are	processed by sshd(8).  The default is
	     no.  Enabling environment processing may enable users to bypass
	     access restrictions in some configurations	using mechanisms such
	     as	LD_PRELOAD.

     PermitUserRC
	     Specifies whether any ~/.ssh/rc file is executed.	The default is
	     yes.

     PidFile
	     Specifies the file	that contains the process ID of	the SSH	dae-
	     mon, or none to not write one.  The default is /var/run/sshd.pid.

     Port    Specifies the port	number that sshd(8) listens on.	 The default
	     is	22.  Multiple options of this type are permitted.  See also
	     ListenAddress.

     PrintLastLog
	     Specifies whether sshd(8) should print the	date and time of the
	     last user login when a user logs in interactively.	 The default
	     is	yes.

     PrintMotd
	     Specifies whether sshd(8) should print /etc/motd when a user logs
	     in	interactively.	(On some systems it is also printed by the
	     shell, /etc/profile, or equivalent.)  The default is yes.

     PubkeyAcceptedKeyTypes
	     Specifies the key types that will be accepted for public key
	     authentication as a comma-separated pattern list.	Alternately if
	     the specified value begins	with a `+' character, then the speci-
	     fied key types will be appended to	the default set	instead	of
	     replacing them.  If the specified value begins with a `-' charac-
	     ter, then the specified key types (including wildcards) will be
	     removed from the default set instead of replacing them.  The
	     default for this option is:

		ecdsa-sha2-nistp256-cert-v01@openssh.com,
		ecdsa-sha2-nistp384-cert-v01@openssh.com,
		ecdsa-sha2-nistp521-cert-v01@openssh.com,
		ssh-ed25519-cert-v01@openssh.com,
		ssh-rsa-cert-v01@openssh.com,
		ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
		ssh-ed25519,ssh-rsa

	     The list of available key types may also be obtained using	"ssh
	     -Q	key".

     PubkeyAuthentication
	     Specifies whether public key authentication is allowed.  The
	     default is	yes.

     RekeyLimit
	     Specifies the maximum amount of data that may be transmitted
	     before the	session	key is renegotiated, optionally	followed 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	docu-
	     mented in the TIME	FORMATS	section.  The default value for
	     RekeyLimit	is default none, which means that rekeying is per-
	     formed after the cipher's default amount of data has been sent or
	     received and no time based	rekeying is done.

     RevokedKeys
	     Specifies revoked public keys file, or none to not	use one.  Keys
	     listed in this file will be refused for public key	authentica-
	     tion.  Note that if this file is not readable, then public	key
	     authentication will be refused for	all users.  Keys may be	speci-
	     fied 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	sec-
	     tion in ssh-keygen(1).

     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, sshd 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 is no.

     StrictModes
	     Specifies whether sshd(8) should check file modes and ownership
	     of	the user's files and home directory before accepting login.
	     This is normally desirable	because	novices	sometimes accidentally
	     leave their directory or files world-writable.  The default is
	     yes.  Note	that this does not apply to ChrootDirectory, whose
	     permissions and ownership are checked unconditionally.

     Subsystem
	     Configures	an external subsystem (e.g. file transfer daemon).
	     Arguments should be a subsystem name and a	command	(with optional
	     arguments)	to execute upon	subsystem request.

	     The command sftp-server implements	the SFTP file transfer subsys-
	     tem.

	     Alternately the name internal-sftp	implements an in-process SFTP
	     server.  This may simplify	configurations using ChrootDirectory
	     to	force a	different filesystem root on clients.

	     By	default	no subsystems are defined.

     SyslogFacility
	     Gives the facility	code that is used when logging messages	from
	     sshd(8).  The possible values are:	DAEMON,	USER, AUTH, LOCAL0,
	     LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.  The
	     default is	AUTH.

     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 tempo-
	     rarily, and some people find it annoying.	On the other hand, if
	     TCP keepalives are	not sent, sessions may hang indefinitely on
	     the server, leaving "ghost" users and consuming server resources.

	     The default is yes	(to send TCP keepalive messages), and the
	     server will notice	if the network goes down or the	client host
	     crashes.  This avoids infinitely hanging sessions.

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

     TrustedUserCAKeys
	     Specifies a file containing public	keys of	certificate authori-
	     ties that are trusted to sign user	certificates for authentica-
	     tion, or none to not use one.  Keys are listed one	per line;
	     empty lines and comments starting with `#'	are allowed.  If a
	     certificate is presented for authentication and has its signing
	     CA	key listed in this file, then it may be	used for authentica-
	     tion for any user listed in the certificate's principals list.
	     Note that certificates that lack a	list of	principals will	not be
	     permitted for authentication using	TrustedUserCAKeys.  For	more
	     details on	certificates, see the CERTIFICATES section in
	     ssh-keygen(1).

     UseBlacklist
	     Specifies whether sshd(8) attempts	to send	authentication success
	     and failure messages to the blacklistd(8) daemon.	The default is
	     no.

     UseDNS  Specifies whether sshd(8) should look up the remote host name,
	     and to check that the resolved host name for the remote IP
	     address maps back to the very same	IP address.

	     If	this option is set to no, then only addresses and not host
	     names may be used in ~/.ssh/authorized_keys from and sshd_config
	     Match Host	directives.  The default is ``yes''.

     UsePAM  Enables the Pluggable Authentication Module interface.  If	set to
	     yes this will enable PAM authentication using
	     ChallengeResponseAuthentication and PasswordAuthentication	in
	     addition to PAM account and session module	processing for all
	     authentication types.

	     Because PAM challenge-response authentication usually serves an
	     equivalent	role to	password authentication, you should disable
	     either PasswordAuthentication or ChallengeResponseAuthentication.

	     If	UsePAM is enabled, you will not	be able	to run sshd(8) as a
	     non-root user.  The default is yes.

     VersionAddendum
	     Optionally	specifies additional text to append to the SSH proto-
	     col banner	sent by	the server upon	connection.  The default is
	     "FreeBSD-20170903".  The value none may be	used to	disable	this.

     X11DisplayOffset
	     Specifies the first display number	available for sshd(8)'s	X11
	     forwarding.  This prevents	sshd from interfering with real	X11
	     servers.  The default is 10.

     X11Forwarding
	     Specifies whether X11 forwarding is permitted.  The argument must
	     be	yes or no.  The	default	is yes.

	     When X11 forwarding is enabled, there may be additional exposure
	     to	the server and to client displays if the sshd(8) proxy display
	     is	configured to listen on	the wildcard address (see
	     X11UseLocalhost), though this is not the default.	Additionally,
	     the authentication	spoofing and authentication data verification
	     and substitution occur on the client side.	 The security risk of
	     using X11 forwarding is that the client's X11 display server may
	     be	exposed	to attack when the SSH client requests forwarding (see
	     the warnings for ForwardX11 in ssh_config(5)).  A system adminis-
	     trator may	have a stance in which they want to protect clients
	     that may expose themselves	to attack by unwittingly requesting
	     X11 forwarding, which can warrant a no setting.

	     Note that disabling X11 forwarding	does not prevent users from
	     forwarding	X11 traffic, as	users can always install their own
	     forwarders.

     X11UseLocalhost
	     Specifies whether sshd(8) should bind the X11 forwarding server
	     to	the loopback address or	to the wildcard	address.  By default,
	     sshd binds	the forwarding server to the loopback address and sets
	     the hostname part of the DISPLAY environment variable to
	     localhost.	 This prevents remote hosts from connecting to the
	     proxy display.  However, some older X11 clients may not function
	     with this configuration.  X11UseLocalhost may be set to no	to
	     specify that the forwarding server	should be bound	to the wild-
	     card address.  The	argument must be yes or	no.  The default is
	     yes.

     XAuthLocation
	     Specifies the full	pathname of the	xauth(1) program, or none to
	     not use one.  The default is /usr/local/bin/xauth.

TIME FORMATS
     sshd(8) command-line arguments and	configuration file options that	spec-
     ify time may be expressed using a sequence	of the form: time[qualifier],
     where time	is a positive integer value and	qualifier is one of the	fol-
     lowing:

	   <none>  seconds
	   s | S   seconds
	   m | M   minutes
	   h | H   hours
	   d | D   days
	   w | W   weeks

     Each member of the	sequence is added together to calculate	the total time
     value.

     Time format examples:

	   600	   600 seconds (10 minutes)
	   10m	   10 minutes
	   1h30m   1 hour 30 minutes (90 minutes)

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

	   %%	 A literal `%'.
	   %F	 The fingerprint of the	CA key.
	   %f	 The fingerprint of the	key or certificate.
	   %h	 The home directory of the user.
	   %i	 The key ID in the certificate.
	   %K	 The base64-encoded CA key.
	   %k	 The base64-encoded key	or certificate for authentication.
	   %s	 The serial number of the certificate.
	   %T	 The type of the CA key.
	   %t	 The key or certificate	type.
	   %u	 The username.

     AuthorizedKeysCommand accepts the tokens %%, %f, %h, %k, %t, and %u.

     AuthorizedKeysFile	accepts	the tokens %%, %h, and %u.

     AuthorizedPrincipalsCommand accepts the tokens %%,	%F, %f,	%h, %i,	%K,
     %k, %s, %T, %t, and %u.

     AuthorizedPrincipalsFile accepts the tokens %%, %h, and %u.

     ChrootDirectory accepts the tokens	%%, %h,	and %u.

FILES
     /etc/ssh/sshd_config
	     Contains configuration data for sshd(8).  This file should	be
	     writable by root only, but	it is recommended (though not neces-
	     sary) that	it be world-readable.

SEE ALSO
     sftp-server(8), sshd(8)

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 cre-
     ated OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.  Niels Provos and Markus Friedl contributed support
     for privilege separation.

FreeBSD	11.2			 June 20, 2018			  FreeBSD 11.2

NAME | SYNOPSIS | DESCRIPTION | TIME FORMATS | TOKENS | FILES | SEE ALSO | AUTHORS

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