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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.  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.  All of the specified user and group tests must suc-
	     ceed, before user is allowed to log in.

	     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.  All of the specified user and group tests
	     must succeed, before user is allowed to log in.

	     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.

	     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,
		   blowfish-cbc,cast128-cbc,3des-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.  All
	     of the specified user and group tests must succeed, before user
	     is allowed to log in.

	     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.  All
	     of the specified user and group tests must succeed, before user
	     is allowed to log in.

	     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.

     ExposeAuthenticationMethods
	     When using SSH2, this option controls the exposure of the list of
	     successful authentication methods to PAM during the authentica-
	     tion and to the shell environment via the SSH_USER_AUTH variable.
	     See the description of this variable for more details.  Valid
	     options are: never (Do not expose successful authentication meth-
	     ods), pam-only (Only expose them to PAM during authentication,
	     not afterwards), pam-and-env (Expose them to PAM and keep them in
	     the shell environment).  The default is never.

     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.

     GSSAPIKeyExchange
	     Specifies whether key exchange based on GSSAPI is allowed. GSSAPI
	     key exchange doesn't rely on ssh keys to verify host identity.
	     The default is ``no''.

     GSSAPIEnablek5users
	     Specifies whether to look at .k5users file for GSSAPI authentica-
	     tion access control. Further details are described in ksu(1).
	     The default is no.

     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.

     GSSAPIStoreCredentialsOnRekey
	     Controls whether the user's GSSAPI credentials should be updated
	     following a successful connection rekeying. This option can be
	     used to accepted renewed or updated credentials from a compatible
	     client. The default is ``no''.

     GSSAPIKexAlgorithms
	     The list of key exchange algorithms that are accepted by GSSAPI
	     key exchange. Possible values are

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

	     The default is
	     ``gss-gex-sha1-,gss-group1-sha1-,gss-group14-sha1-''.  This
	     option only applies to protocol version 2 connections using GSS-
	     API.

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

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

	     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.

     KerberosUseKuserok
	     Specifies whether to look at .k5login file for user's aliases.
	     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.
	     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,
		   diffie-hellman-group1-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.

	     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,
		   hmac-sha1-etm@openssh.com

	     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,
	     KerberosUseKuserok, MaxAuthTries, MaxSessions,
	     PasswordAuthentication, PermitEmptyPasswords, PermitOpen,
	     PermitRootLogin, PermitTTY, PermitTunnel, PermitUserRC,
	     PubkeyAcceptedKeyTypes, PubkeyAuthentication, RekeyLimit,
	     RevokedKeys, StreamLocalBindMask, StreamLocalBindUnlink,
	     TrustedUserCAKeys, X11DisplayOffset, X11MaxDisplays,
	     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.  The
	     default is yes.

     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 yes.

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

	     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).

     ShowPatchLevel
	     Specifies whether sshd will display the patch level of the binary
	     in the identification string.  The patch level is set at compile-
	     time.  The default is ``no''.  This option applies to protocol
	     version 1 only.

     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, AUTHPRIV,
	     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).

     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 (the default) then only addresses and
	     not host names may be used in ~/.ssh/authorized_keys from and
	     sshd_config Match Host directives.

     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 no.

     UsePrivilegeSeparation
	     Specifies whether sshd(8) separates privileges by creating an
	     unprivileged 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
	     argument must be yes, no, or sandbox.  If UsePrivilegeSeparation
	     is set to sandbox then the pre-authentication unprivileged
	     process is subject to additional restrictions.  The default is
	     sandbox.

     VersionAddendum
	     Optionally specifies additional text to append to the SSH proto-
	     col banner sent by the server upon connection.  The default is
	     none.

     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.

     X11MaxDisplays
	     Specifies the maximum number of displays available for sshd(8)'s
	     X11 forwarding.  This prevents sshd from exhausting local ports.
	     The default is 1000.

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

	     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/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, %t, and %u.

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

     AuthorizedPrincipalsCommand accepts the tokens %%, %F, %f, %K, %k, %h,
     %i, %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.

BSD			       October 19, 2017				   BSD