Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
SSHD_CONFIG(5)		    BSD	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.  Note that envi-
	     ronment passing is	only supported for protocol 2.	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", "inet" (use IPv4 only), or "inet6" (use IPv6
	     only).  The default is "any".

     AllowAgentForwarding
	     Specifies whether ssh-agent(1) forwarding is permitted.  The de-
	     fault 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.

     AllowTcpForwarding
	     Specifies whether TCP forwarding is permitted.  The available op-
	     tions are "yes" 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.  The	default	is "yes".  Note	that disabling TCP forwarding
	     does not improve security unless users are	also denied shell ac-
	     cess, 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.	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.  Successful authentication requires completion of
	     every method in at	least one of these lists.

	     For example, an argument of "publickey,password
	     publickey,keyboard-interactive" would require the user to com-
	     plete public key authentication, followed by either password or
	     keyboard interactive authentication.  Only	methods	that are next
	     in	one or more lists are offered at each stage, so	for this exam-
	     ple, it would not be possible to attempt password or keyboard-in-
	     teractive authentication before public key.

	     This option is only available for SSH protocol 2 and will yield a
	     fatal error if enabled if protocol	1 is also enabled.  Note that
	     each authentication method	listed should also be explicitly en-
	     abled in the configuration.  The default is not to	require	multi-
	     ple authentication; successful completion of a single authentica-
	     tion method is sufficient.

     AuthorizedKeysCommand
	     Specifies a program to be used to look up the user's public keys.
	     The program will be invoked with a	single argument	of the user-
	     name being	authenticated, and 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
	     authentication 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.

     AuthorizedKeysFile
	     Specifies the file	that contains the public keys that can be used
	     for user authentication.  The format is described in the
	     AUTHORIZED_KEYS FILE FORMAT section of sshd(8).
	     AuthorizedKeysFile	may contain tokens of the form %T which	are
	     substituted during	connection setup.  The following tokens	are
	     defined: %% is replaced by	a literal '%', %h is replaced by the
	     home directory of the user	being authenticated, and %u is re-
	     placed by the username of that user.  After expansion,
	     AuthorizedKeysFile	is taken to be an absolute path	or one rela-
	     tive to the user's	home directory.	 Multiple files	may be listed,
	     separated by whitespace.  The default is ".ssh/authorized_keys
	     .ssh/authorized_keys2".

     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.

	     AuthorizedPrincipalsFile may contain tokens of the	form %T	which
	     are substituted during connection setup.  The following tokens
	     are defined: %% is	replaced by a literal '%', %h is replaced by
	     the home directory	of the user being authenticated, and %u	is re-
	     placed by the username of that user.  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 principals file -	in
	     this case,	the username of	the user must appear in	a certifi-
	     cate's principals list for	it to be accepted.  Note that
	     AuthorizedPrincipalsFile is only used when	authentication pro-
	     ceeds 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.  This option is only available for	proto-
	     col version 2.  By	default, no banner is displayed.

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

     ChrootDirectory
	     Specifies the pathname of a directory to chroot(2)	to after au-
	     thentication.  All	components of the pathname must	be root-owned
	     directories that are not writable by any other user or group.
	     After the chroot, sshd(8) changes the working directory to	the
	     user's home directory.

	     The pathname may contain the following tokens that	are expanded
	     at	runtime	once the connecting user has been authenticated: %% is
	     replaced by a literal '%',	%h is replaced by the home directory
	     of	the user being authenticated, and %u is	replaced by the	user-
	     name of that user.

	     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),
	     arandom(4)	and tty(4) devices.  For file transfer sessions	using
	     "sftp", no	additional configuration of the	environment is neces-
	     sary if the in-process sftp server	is used, though	sessions which
	     use logging do require /dev/log inside the	chroot directory (see
	     sftp-server(8) for	details).

	     The default is not	to chroot(2).

     Ciphers
	     Specifies the ciphers allowed for protocol	version	2.  Multiple
	     ciphers must be comma-separated.  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", "arcfour128",
	     "arcfour256", "arcfour", "blowfish-cbc", and "cast128-cbc".  The
	     default is:

		aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
		aes128-gcm@openssh.com,aes256-gcm@openssh.com,
		aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
		aes256-cbc,arcfour

     ClientAliveCountMax
	     Sets the number of	client alive messages (see below) which	may be
	     sent without sshd(8) receiving any	messages back from the client.
	     If	this threshold is reached while	client alive messages are be-
	     ing sent, sshd will disconnect the	client,	terminating the	ses-
	     sion.  It is important to note that the use of client alive mes-
	     sages is very different from TCPKeepAlive (below).	 The client
	     alive messages are	sent through the encrypted channel and there-
	     fore will not be spoofable.  The TCP keepalive option enabled by
	     TCPKeepAlive is spoofable.	 The client alive mechanism is valu-
	     able when the client or server depend on knowing when a connec-
	     tion has become inactive.

	     The default value is 3.  If ClientAliveInterval (see below) is
	     set to 15,	and ClientAliveCountMax	is left	at the default,	unre-
	     sponsive SSH clients will be disconnected after approximately 45
	     seconds.  This option applies to protocol version 2 only.

     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.	 This option applies to	protocol ver-
	     sion 2 only.

     Compression
	     Specifies whether compression is allowed, or delayed until	the
	     user has authenticated successfully.  The argument	must be	"yes",
	     "delayed",	or "no".  The default is "delayed".

     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 al-
	     low/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.  The allow/deny directives are pro-
	     cessed in the following order: DenyUsers, AllowUsers, DenyGroups,
	     and finally AllowGroups.

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

     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.

     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".  Note	that this option applies to protocol
	     version 2 only.

     GSSAPICleanupCredentials
	     Specifies whether to automatically	destroy	the user's credentials
	     cache on logout.  The default is "yes".  Note that	this option
	     applies to	protocol version 2 only.

     HostbasedAuthentication
	     Specifies whether rhosts or /etc/hosts.equiv authentication to-
	     gether with successful public key client host authentication is
	     allowed (host-based authentication).  This	option is similar to
	     RhostsRSAAuthentication and applies to protocol version 2 only.
	     The default is "no".

     HostbasedUsesNameFromPacketOnly
	     Specifies whether or not the server will attempt to perform a re-
	     verse 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
	     default is	/etc/ssh/ssh_host_key for protocol version 1, and
	     /etc/ssh/ssh_host_dsa_key,	/etc/ssh/ssh_host_ecdsa_key and
	     /etc/ssh/ssh_host_rsa_key for protocol version 2.	Note that
	     sshd(8) will refuse to use	a file if it is	group/world-accessi-
	     ble.  It is possible to have multiple host	key files.  "rsa1"
	     keys are used for version 1 and "dsa", "ecdsa" or "rsa" are used
	     for version 2 of the SSH protocol.

     IgnoreRhosts
	     Specifies that .rhosts and	.shosts	files will not be used in
	     RhostsRSAAuthentication or	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 RhostsRSAAuthentication or
	     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 white-
	     space.  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 in-
	     teractive sessions	and "throughput" for non-interactive sessions.

     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.  The default is
	     "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
	     "diffie-hellman-group-exchange-sha256",
	     "diffie-hellman-group-exchange-sha1",
	     "diffie-hellman-group14-sha1", "diffie-hellman-group1-sha1".

     KeyRegenerationInterval
	     In	protocol version 1, the	ephemeral server key is	automatically
	     regenerated after this many seconds (if it	has been used).	 The
	     purpose of	regeneration is	to prevent decrypting captured ses-
	     sions by later breaking into the machine and stealing the keys.
	     The key is	never stored anywhere.	If the value is	0, the key is
	     never regenerated.	 The default is	3600 (seconds).

     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
	     prior Port	options	specified.  The	default	is to listen on	all
	     local addresses.  Multiple	ListenAddress options are permitted.
	     Additionally, any Port options must precede this option for non-
	     port qualified addresses.

     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	in protocol version 2 for data
	     integrity protection.  Multiple algorithms	must be	comma-sepa-
	     rated.  The algorithms that contain "-etm"	calculate the MAC af-
	     ter encryption (encrypt-then-mac).	 These are considered safer
	     and their use recommended.	 The default is:

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

     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, un-
	     til either	another	Match line or the end of the file.

	     The arguments to Match are	one or more criteria-pattern pairs.
	     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 operators	described in the PATTERNS section of
	     ssh_config(5).

	     The patterns in an	Address	criteria may additionally contain ad-
	     dresses to	match in CIDR address/masklen format, e.g.
	     "192.0.2.0/24" or "3ffe:ffff::/32".  Note that the	mask length
	     provided 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,	AllowTcpForwarding,
	     AllowUsers, AuthenticationMethods,	AuthorizedKeysCommand,
	     AuthorizedKeysCommandUser,	AuthorizedKeysFile,
	     AuthorizedPrincipalsFile, Banner, ChrootDirectory,	DenyGroups,
	     DenyUsers,	ForceCommand, GatewayPorts, GSSAPIAuthentication,
	     HostbasedAuthentication, HostbasedUsesNameFromPacketOnly,
	     KbdInteractiveAuthentication, KerberosAuthentication,
	     MaxAuthTries, MaxSessions,	PasswordAuthentication,
	     PermitEmptyPasswords, PermitOpen, PermitRootLogin,	PermitTunnel,
	     PubkeyAuthentication, RhostsRSAAuthentication, RSAAuthentication,
	     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 sessions permitted per net-
	     work connection.  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 ex-
	     pires 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) unauthenti-
	     cated connections.	 The probability increases linearly and	all
	     connection	attempts are refused if	the number of unauthenticated
	     connections 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 restric-
	     tions and permit any forwarding requests.	An argument of "none"
	     can be used to prohibit all forwarding requests.  By default all
	     port forwarding requests are permitted.

     PermitRootLogin
	     Specifies whether root can	log in using ssh(1).  The argument
	     must be "yes", "without-password",	"forced-commands-only",	or
	     "no".  The	default	is "no".  Note that if
	     ChallengeResponseAuthentication is	"yes", the root	user may be
	     allowed in	with its password even if PermitRootLogin is set to
	     "without-password".

	     If	this option is set to "without-password", password authentica-
	     tion is 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.

     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".

     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.

     PidFile
	     Specifies the file	that contains the process ID of	the SSH	dae-
	     mon.  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".

     Protocol
	     Specifies the protocol versions sshd(8) supports.	The possible
	     values are	`1' and	`2'.  Multiple versions	must be	comma-sepa-
	     rated.  The default is `2'.  Note that the	order of the protocol
	     list does not indicate preference,	because	the client selects
	     among multiple protocol versions offered by the server.  Specify-
	     ing "2,1" is identical to "1,2".

     PubkeyAuthentication
	     Specifies whether public key authentication is allowed.  The de-
	     fault is "yes".  Note that	this option applies to protocol	ver-
	     sion 2 only.

     RevokedKeys
	     Specifies revoked public keys.  Keys listed in this file will be
	     refused for public	key authentication.  Note that if this file is
	     not readable, then	public key authentication will be refused for
	     all users.	 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).

     RhostsRSAAuthentication
	     Specifies whether rhosts or /etc/hosts.equiv authentication to-
	     gether with successful RSA	host authentication is allowed.	 The
	     default is	"no".  This option applies to protocol version 1 only.

     RSAAuthentication
	     Specifies whether pure RSA	authentication is allowed.  The	de-
	     fault is "yes".  This option applies to protocol version 1	only.

     ServerKeyBits
	     Defines the number	of bits	in the ephemeral protocol version 1
	     server key.  The minimum value is 512, and	the default is 1024.

     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(8)	implements the "sftp" file transfer
	     subsystem.

	     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.  Note that this option ap-
	     plies to protocol version 2 only.

     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 de-
	     fault 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.  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 authentication 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 us-
	     ing TrustedUserCAKeys.  For more details on certificates, see the
	     CERTIFICATES section in ssh-keygen(1).

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

     UseLogin
	     Specifies whether login(1)	is used	for interactive	login ses-
	     sions.  The default is "no".  Note	that login(1) is never used
	     for remote	command	execution.  Note also, that if this is en-
	     abled, X11Forwarding will be disabled because login(1) does not
	     know how to handle	xauth(1) cookies.  If UsePrivilegeSeparation
	     is	specified, it will be disabled after authentication.

     UsePAM  Enables the Pluggable Authentication Module interface.  If	set to
	     "yes" this	will enable PAM	authentication using
	     ChallengeResponseAuthentication and PasswordAuthentication	in ad-
	     dition to PAM account and session module processing for all au-
	     thentication 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".

     UsePrivilegeSeparation
	     Specifies whether sshd(8) separates privileges by creating	an un-
	     privileged	child process to deal with incoming network traffic.
	     After successful authentication, another process will be created
	     that has the privilege of the authenticated user.	The goal of
	     privilege separation is to	prevent	privilege escalation by	con-
	     taining any corruption within the unprivileged processes.	The
	     default is	"yes".	If UsePrivilegeSeparation is set to "sandbox"
	     then the pre-authentication unprivileged process is subject to
	     additional	restrictions.

     VersionAddendum
	     Optionally	specifies additional text to append to the SSH proto-
	     col banner	sent by	the server upon	connection.  The default is
	     "FreeBSD-20130515".

     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 below), though this is not	the default.  Addi-
	     tionally, the authentication spoofing and authentication data
	     verification and substitution occur on the	client side.  The se-
	     curity risk of using X11 forwarding is that the client's X11 dis-
	     play server may be	exposed	to attack when the SSH client requests
	     forwarding	(see the warnings for ForwardX11 in ssh_config(5)).  A
	     system administrator may have a stance in which they want to pro-
	     tect 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.  X11 forwarding is automatically disabled if UseLogin
	     is	enabled.

     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.  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)

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
     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.

BSD			       February	6, 2013				   BSD

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

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=sshd_config&sektion=5&manpath=FreeBSD+9.2-RELEASE>

home | help