Adding upstream version 1:7.9p1.upstream/1%7.9p1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1092 insertions, 0 deletions

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+SSHD_CONFIG(5)                File Formats Manual               SSHD_CONFIG(5)
+
+NAME
+     sshd_config M-bM-^@M-^S OpenSSH SSH daemon configuration file
+
+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-
+     argument pairs, one per line.  For each keyword, the first obtained value
+     will be used.  Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y 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
+     keywords 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 and SetEnv in
+             ssh_config(5) for how to configure the client.  The TERM
+             environment variable is always accepted 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 M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^X?M-bM-^@M-^Y.  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
+             forwarding, 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 lists of comma-separated 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
+             authentication.  Only methods that are next in one or more lists
+             are offered at each stage, so for this example it would not be
+             possible 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 or pam.  depending on
+             the server configuration.  For example,
+             "keyboard-interactive:bsdauth" would restrict keyboard
+             interactive authentication to the bsdauth device.
+
+             If the publickey method is listed more than once, sshd(8)
+             verifies 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.
+
+             The available authentication methods are: "gssapi-with-mic",
+             "hostbased", "keyboard-interactive", "none" (used for access to
+             password-less accounts when PermitEmptyPasswords is enabled),
+             "password" and "publickey".
+
+     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
+             others 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
+             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.  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
+             expansion, 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
+             program 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
+             specified, 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 M-bM-^@M-^X#M-bM-^@M-^Y 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
+             principals file M-bM-^@M-^S 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
+             authentication 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.
+
+     CASignatureAlgorithms
+             Specifies which algorithms are allowed for signing of
+             certificates by certificate authorities (CAs).  The default is:
+
+                   ecdsa-sha2-nistp256.ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
+                   ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
+
+             Certificates signed using other algorithms will not be accepted
+             for public key or host-based authentication.
+
+     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
+             components 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
+             directories 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
+             operating 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 M-bM-^@M-^X+M-bM-^@M-^Y character,
+             then the specified ciphers will be appended to the default set
+             instead of replacing them.  If the specified value begins with a
+             M-bM-^@M-^X-M-bM-^@M-^Y 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
+                   chacha20-poly1305@openssh.com
+
+             The default is:
+
+                   chacha20-poly1305@openssh.com,
+                   aes128-ctr,aes192-ctr,aes256-ctr,
+                   aes128-gcm@openssh.com,aes256-gcm@openssh.com
+
+             The list of available ciphers may also be obtained using "ssh -Q
+             cipher".
+
+     ClientAliveCountMax
+             Sets the number of client alive messages which may be sent
+             without 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
+             spoofable.  The TCP keepalive option enabled by TCPKeepAlive is
+             spoofable.  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
+             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.
+
+     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
+             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.
+
+     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.
+
+     ExposeAuthInfo
+             Writes a temporary file containing a list of authentication
+             methods and public credentials (e.g. keys) used to authenticate
+             the user.  The location of the file is exposed to the user
+             session through the SSH_USER_AUTH environment variable.  The
+             default is no.
+
+     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
+             connect.  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 list of comma-separated patterns.
+             Alternately if the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
+             then the specified key types will be appended to the default set
+             instead of replacing them.  If the specified value begins with a
+             M-bM-^@M-^X-M-bM-^@M-^Y character, 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,
+                rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
+                ssh-rsa-cert-v01@openssh.com,
+                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
+                ssh-ed25519,rsa-sha2-512,rsa-sha2-256,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
+             certificate's public key must match a private host key already
+             specified 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_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
+             possible 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,
+                rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
+                ssh-rsa-cert-v01@openssh.com,
+                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
+                ssh-ed25519,rsa-sha2-512,rsa-sha2-256,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/shosts.equiv are still used.  The
+             default is yes.
+
+     IgnoreUserKnownHosts
+             Specifies whether sshd(8) should ignore the user's
+             ~/.ssh/known_hosts during HostbasedAuthentication and use only
+             the system-wide known hosts file /etc/ssh/known_hosts.  The
+             default is no.
+
+     IPQoS   Specifies the IPv4 type-of-service or DSCP class for the
+             connection.  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, a
+             numeric value, or none to use the operating system default.  This
+             option may take one or two arguments, separated by whitespace.
+             If one argument is specified, it is used as the packet class
+             unconditionally.  If two values are specified, the first is
+             automatically selected for interactive sessions and the second
+             for non-interactive sessions.  The default is af21 (Low-Latency
+             Data) for interactive sessions and cs1 (Lower Effort) for non-
+             interactive sessions.
+
+     KbdInteractiveAuthentication
+             Specifies whether to 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
+             password 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 M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods
+             will be appended to the default set instead of replacing them.
+             If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y 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-group14-sha256
+                   diffie-hellman-group16-sha512
+                   diffie-hellman-group18-sha512
+                   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-group16-sha512,diffie-hellman-group18-sha512,
+                   diffie-hellman-group14-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
+             following forms may be used:
+
+                   ListenAddress hostname|address [rdomain domain]
+                   ListenAddress hostname:port [rdomain domain]
+                   ListenAddress IPv4_address:port [rdomain domain]
+                   ListenAddress [hostname|address]:port [rdomain domain]
+
+             The optional rdomain qualifier requests sshd(8) listen in an
+             explicit routing domain.  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 on the current
+             default routing domain.  Multiple ListenAddress options are
+             permitted.  For more information on routing domains, see
+             rdomain(4).
+
+     LoginGraceTime
+             The server disconnects after this time if the user has not
+             successfully 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)
+             algorithms.  The MAC algorithm is used for data integrity
+             protection.  Multiple algorithms must be comma-separated.  If the
+             specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified
+             algorithms will be appended to the default set instead of
+             replacing them.  If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y
+             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-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-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, RDomain,
+             and Address (with RDomain representing the rdomain(4) on which
+             the connection was received.)
+
+             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
+             addresses to match in CIDR address/masklen format, such as
+             192.0.2.0/24 or 2001:db8::/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, 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, LogLevel,
+             MaxAuthTries, MaxSessions, PasswordAuthentication,
+             PermitEmptyPasswords, PermitListen, PermitOpen, PermitRootLogin,
+             PermitTTY, PermitTunnel, PermitUserRC, PubkeyAcceptedKeyTypes,
+             PubkeyAuthentication, RekeyLimit, RevokedKeys, RDomain, SetEnv,
+             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
+             forwarding.  The default is 10.
+
+     MaxStartups
+             Specifies the maximum number of concurrent unauthenticated
+             connections 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
+             connection attempts are refused if the number of unauthenticated
+             connections 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.
+
+     PermitListen
+             Specifies the addresses/ports on which a remote TCP port
+             forwarding may listen.  The listen specification must be one of
+             the following forms:
+
+                   PermitListen port
+                   PermitListen host:port
+
+             Multiple permissions may be specified by separating them with
+             whitespace.  An argument of any can be used to remove all
+             restrictions and permit any listen requests.  An argument of none
+             can be used to prohibit all listen requests.  The host name may
+             contain wildcards as described in the PATTERNS section in
+             ssh_config(5).  The wildcard M-bM-^@M-^X*M-bM-^@M-^Y can also be used in place of a
+             port number to allow all ports.  By default all port forwarding
+             listen requests are permitted.  Note that the GatewayPorts option
+             may further restrict which addresses may be listened on.  Note
+             also that ssh(1) will request a listen host of M-bM-^@M-^\localhostM-bM-^@M-^] if no
+             listen host was specifically requested, and this this name is
+             treated differently to explicit localhost addresses of
+             M-bM-^@M-^\127.0.0.1M-bM-^@M-^] and M-bM-^@M-^\::1M-bM-^@M-^].
+
+     PermitOpen
+             Specifies the destinations to which TCP port forwarding is
+             permitted.  The forwarding specification must be one of the
+             following forms:
+
+                   PermitOpen host:port
+                   PermitOpen IPv4_addr:port
+                   PermitOpen [IPv6_addr]:port
+
+             Multiple forwards may be specified by separating them with
+             whitespace.  An argument of any can be used to remove all
+             restrictions and permit any forwarding requests.  An argument of
+             none can be used to prohibit all forwarding requests.  The
+             wildcard M-bM-^@M-^X*M-bM-^@M-^Y can be used for host or port to allow all hosts or
+             ports, respectively.  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, forced-commands-only, or no.  The
+             default is prohibit-password.
+
+             If this option is set to prohibit-password (or its deprecated
+             alias, 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
+             argument 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).  Valid options
+             are yes, no or a pattern-list specifying which environment
+             variable names to accept (for example "LANG,LC_*").  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
+             daemon, 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 list of comma-separated patterns.
+             Alternately if the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
+             then the specified key types will be appended to the default set
+             instead of replacing them.  If the specified value begins with a
+             M-bM-^@M-^X-M-bM-^@M-^Y character, 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,
+                rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
+                ssh-rsa-cert-v01@openssh.com,
+                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
+                ssh-ed25519,rsa-sha2-512,rsa-sha2-256,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 M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes,
+             Megabytes, or Gigabytes, respectively.  The default is between
+             M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher.  The optional second
+             value is specified in seconds and may use any of the units
+             documented in the TIME FORMATS section.  The default value for
+             RekeyLimit is default none, which means that rekeying is
+             performed after the cipher's default amount of data has been sent
+             or received and no time based rekeying is done.
+
+     RevokedKeys
+             Specifies revoked public keys file, or none to not use one.  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).
+
+     RDomain
+             Specifies an explicit routing domain that is applied after
+             authentication has completed.  The user session, as well and any
+             forwarded or listening IP sockets, will be bound to this
+             rdomain(4).  If the routing domain is set to %D, then the domain
+             in which the incoming connection was received will be applied.
+
+     SetEnv  Specifies one or more environment variables to set in child
+             sessions started by sshd(8) as M-bM-^@M-^\NAME=VALUEM-bM-^@M-^].  The environment
+             value may be quoted (e.g. if it contains whitespace characters).
+             Environment variables set by SetEnv override the default
+             environment and any variables specified by the user via AcceptEnv
+             or PermitUserEnvironment.
+
+     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
+             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.
+
+     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
+             temporarily, 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
+             authorities that are trusted to sign user certificates for
+             authentication, or none to not use one.  Keys are listed one per
+             line; empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y 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 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.
+
+     VersionAddendum
+             Optionally specifies additional text to append to the SSH
+             protocol 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.
+
+     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
+             administrator 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
+             wildcard 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/X11R6/bin/xauth.
+
+TIME FORMATS
+     sshd(8) command-line arguments and configuration file options that
+     specify 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 following:
+
+           M-bM-^_M-(noneM-bM-^_M-)  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 M-bM-^@M-^X%M-bM-^@M-^Y.
+           %D    The routing domain in which the incoming connection was
+                 received.
+           %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 numeric user ID of the target user.
+           %u    The username.
+
+     AuthorizedKeysCommand accepts the tokens %%, %f, %h, %k, %t, %U, and %u.
+
+     AuthorizedKeysFile accepts the tokens %%, %h, %U, and %u.
+
+     AuthorizedPrincipalsCommand accepts the tokens %%, %F, %f, %h, %i, %K,
+     %k, %s, %T, %t, %U, and %u.
+
+     AuthorizedPrincipalsFile accepts the tokens %%, %h, %U, and %u.
+
+     ChrootDirectory accepts the tokens %%, %h, %U, and %u.
+
+     RoutingDomain accepts the token %D.
+
+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
+             necessary) 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
+     created 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.
+
+OpenBSD 6.4                   September 20, 2018                   OpenBSD 6.4