sshd_config(4)							   File Formats 						    sshd_config(4)

NAME

       sshd_config - sshd configuration file

SYNOPSIS

       /etc/ssh/sshd_config

DESCRIPTION

       The  sshd(1M)  daemon reads configuration data from /etc/ssh/sshd_config (or the file specified with sshd -f on the command line). The file
       contains keyword-value pairs, one per line. A line starting with a hash mark (#) and empty lines are interpreted as comments.

       The sshd_config file supports the following keywords. Unless otherwise noted, keywords and their arguments are case-insensitive.

       AllowGroups

	   This keyword can be followed by a number of group names, separated by spaces. If specified, login is allowed only for users whose  pri-
	   mary  group	matches one of the patterns. Asterisk (*) and question mark (?) can be used as wildcards in the patterns. Only group names
	   are valid; a numerical group ID is not recognized. By default, login is allowed regardless of the primary group.

       AllowTcpForwarding

	   Specifies whether TCP forwarding is permitted. The default is yes. 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 number of user names, separated by spaces. If specified, login is allowed only for user names that
	   match one of the patterns. Asterisk (*) and question mark (?) can be used as wildcards in the patterns. Only user names  are  valid;  a
	   numerical user ID is not recognized. By default login is allowed regardless of the user name.

	   If  a specified pattern takes the form user@host then user and host are checked separately, restricting logins to particular users from
	   particular hosts.

       AuthorizedKeysFile

	   Specifies the file that contains the public keys that can be used for user authentication. AuthorizedKeysFile can contain tokens of the
	   form  %T,  which  are  substituted  during  connection  set-up.  The following tokens are defined: %% is replaced by a literal %, %h is
	   replaced by the home directory of the user being authenticated and %u is replaced by the username of that user. After expansion, Autho-
	   rizedKeysFile is taken to be an absolute path or one relative to the user's home directory. The default is .ssh/authorized_keys.

       Banner

	   In  some  jurisdictions,  sending a warning message before authentication can be relevant for getting legal protection. The contents of
	   the specified file are sent to the remote user before authentication is allowed. This option is only available for protocol version	2.
	   By default, no banner is displayed.

       Ciphers

	   Specifies  the  ciphers  allowed  for  protocol version 2. Cipher ordering on the server side is not relevant. Multiple ciphers must be
	   comma separated.

	   Valid ciphers are: aes128-ctr, aes192-ctr, aes256-ctr, aes128-cbc, aes192-cbc, aes256-cbc, arcfour, arcfour128,  arcfour256,  3des-cbc,
	   and blowfish-cbc.

	   The default cipher list is:

	     aes128-ctr,aes192-ctr,aes256-ctr,arcfour128,
	     arcfour256,arcfour

	   Using CBC modes on the server side is not recommended due to potential security issues in connection with the SSH protocol version 2.

       ClientAliveCountMax

	   Sets the number of client alive messages, (see ClientAliveInterval), that can be sent without sshd receiving any messages back from the
	   client. If this threshold is reached while client alive messages are being sent, sshd disconnects the client, terminating the  session.
	   The use of client alive messages is very different from KeepAlive. The client alive messages are sent through the encrypted channel and
	   therefore are not spoofable. The TCP keepalive option enabled by KeepAlive is spoofable. The client alive mechanism is valuable when  a
	   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
	   are disconnected after approximately 45 seconds.

       ClientAliveInterval

	   Sets a timeout interval in seconds after which, if no data has been received  from  the  client,  sshd  sends  a  message  through  the
	   encrypted  channel  to request a response from the client. The default is 0, indicating that these messages are not sent to the client.
	   This option applies only to protocol version 2.

       Compression

	   Controls whether the server allows the client to negotiate the use of compression. The default is yes.

       DenyGroups

	   Can be followed by a number of group names, separated by spaces. Users whose primary group matches one of the patterns are not  allowed
	   to  log  in. Asterisk (*) and question mark (?) can be used as wildcards in the patterns. Only group names are valid; a numerical group
	   ID is not recognized. By default, login is allowed regardless of the primary group.

       DenyUsers

	   Can be followed by a number of user names, separated by spaces. Login is disallowed for user names that  match  one	of  the  patterns.
	   Asterisk (*) and question mark (?) can be used as wildcards in the patterns. Only user names are valid; a numerical user ID is not rec-
	   ognized. By default, login is allowed regardless of the user name.

	   If a specified pattern takes the form user@host then user and host are checked separately, disallowing logins to particular users  from
	   particular hosts.

       GatewayPorts

	   Specifies whether remote hosts are allowed to connect to ports forwarded for the client. By default, sshd 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 bind remote port forwardings to the wildcard address, thus allowing remote hosts to connect to forwarded ports.

	   The argument can 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. See also RemoteForward in ssh_config(4).

       GSSAPIAuthentication

	   Enables/disables GSS-API user authentication. The default is yes.

	   Currently sshd authorizes client user principals to user accounts as follows: if the principal name matches the requested user account,
	   then the principal is authorized. Otherwise, GSS-API authentication fails.

       GSSAPIKeyExchange

	   Enables/disables GSS-API-authenticated key exchanges. The default is yes.

	   This option also enables the use of the GSS-API to authenticate the user to server after the key exchange.  GSS-API	key  exchange  can
	   succeed  but the subsequent authentication using the GSS-API fail if the server does not authorize the user's GSS principal name to the
	   target user account.

	   Currently sshd authorizes client user principals to user accounts as follows: if the principal name matches the requested user account,
	   then the principal is authorized. Otherwise, GSS-API authentication fails.

       GSSAPIStoreDelegatedCredentials

	   Enables/disables the use of delegated GSS-API credentials on the server-side. The default is yes.

	   Specifically, this option, when enabled, causes the server to store delegated GSS-API credentials in the user's default GSS-API creden-
	   tial store (which for the Kerberos V mechanism means /tmp/krb5cc_<uid>).

	   Note -

	     sshd does not take any steps to explicitly destroy stored delegated GSS-API credentials upon logout. It is the responsibility of  PAM
	     modules to destroy credentials associated with a session.

       HostbasedAuthentication

	   Specifies whether to try rhosts-based authentication with public key authentication. The argument must be yes or no. The default is no.
	   This option applies to protocol version 2 only and is similar to RhostsRSAAuthentication. See sshd(1M) for  guidelines  on  setting	up
	   host-based authentication.

       HostbasedUsesNameFromPacketOnly

	   Controls  which  hostname  is searched for in the files ~/.shosts, /etc/shosts.equiv, and /etc/hosts.equiv. If this parameter is set to
	   yes, the server uses the name the client claimed for itself and signed with that host's key. If set to no, the default, the server uses
	   the name to which the client's IP address resolves.

	   Setting this parameter to no disables host-based authentication when using NAT or when the client gets to the server indirectly through
	   a port-forwarding firewall.

       HostKey

	   Specifies the file containing the private host key used by SSH. The default	is  /etc/ssh/ssh_host_key  for	protocol  version  1,  and
	   /etc/ssh/ssh_host_rsa_key  and /etc/ssh/ssh_host_dsa_key for protocol version 2. sshd refuses to use a file if it is group/world-acces-
	   sible. It is possible to have multiple host key files. rsa1 keys are used for version 1 and dsa or rsa are used for version	2  of  the
	   SSH protocol.

       IgnoreRhosts

	   Specifies  that  .rhosts  and  .shosts files are not used in authentication. /etc/hosts.equiv and /etc/shosts.equiv are still used. The
	   default is yes. This parameter applies to both protocol versions 1 and 2.

       IgnoreUserKnownHosts

	   Specifies whether sshd should ignore the user's $HOME/.ssh/known_hosts during RhostsRSAAuthentication. The default is no. This  parame-
	   ter applies to both protocol versions 1 and 2.

       KbdInteractiveAuthentication

	   Specifies  whether  authentication  by means of the "keyboard-interactive" authentication method (and PAM) is allowed. Defaults to yes.
	   (Deprecated: this parameter can only be set to yes.)

       KeepAlive

	   Specifies whether the system should send keepalive messages to the other side. If they are sent, death of the connection  or  crash	of
	   one	of  the  machines  is properly noticed. However, this means that connections die if the route is down temporarily, which can be an
	   annoyance. On the other hand, if keepalives are not sent, sessions can hang indefinitely on the server, leaving ghost users and consum-
	   ing server resources.

	   The default is yes (to send keepalives), and the server notices if the network goes down or the client host reboots. This avoids infin-
	   itely hanging sessions.

	   To disable keepalives, the value should be set to no in both the server and the client configuration files.

       KeyRegenerationInterval

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

       ListenAddress

	   Specifies what local address sshd should listen on. The following forms can be used:

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

	   If port is not specified, sshd listens on the address and all prior Port options specified. The default  is	to  listen  on	all  local
	   addresses. Multiple ListenAddress options are permitted. Additionally, any Port options must precede this option for non-port qualified
	   addresses.

	   The default is to listen on all local addresses. Multiple options of this type are permitted. Additionally, the Ports options must pre-
	   cede this option.

       LoginGraceTime

	   The	server	disconnects  after  this time (in seconds) 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. The possible values are: QUIET, FATAL,  ERROR,  INFO,  VERBOSE,
	   DEBUG,  DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG2 and DEBUG3 each specify higher levels of debugging output. Logging with
	   level DEBUG violates the privacy of users and is not recommended.

       LookupClientHostnames

	   Specifies whether or not to lookup the names of client's addresses. Defaults to yes.

       MACs

	   Specifies the available MAC (message authentication code) algorithms. The MAC  algorithm  is  used  in  protocol  version  2  for  data
	   integrity protection. Multiple algorithms must be comma-separated. The default is hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96.

       MaxStartups

	   Specifies  the  maximum  number  of concurrent unauthenticated connections to the sshd daemon. Additional connections are dropped until
	   authentication succeeds or the LoginGraceTime expires for a connection. The default is 10.

	   Alternatively, random early drop can be enabled by specifying the three colon-separated values start:rate:full (for example, 10:30:60).
	   Referring  to  this example, sshd refuse connection attempts with a probability of rate/100 (30% in our example) if there are currently
	   10 (from the start field) unauthenticated connections. The probability increases linearly and all connection attempts  are  refused	if
	   the number of unauthenticated connections reaches full (60 in our example).

       PasswordAuthentication

	   Specifies whether password authentication is allowed. The default is yes. This option applies to both protocol versions 1 and 2.

       PermitEmptyPasswords

	   When  password  or  keyboard-interactive authentication is allowed, it specifies whether the server allows login to accounts with empty
	   password strings.

	   If not set then the /etc/default/login PASSREQ value is used instead.

	   PASSREQ=no is equivalent to PermitEmptyPasswords yes. PASSREQ=yes is equivalent to PermitEmptyPasswords no. If neither PermitEmptyPass-
	   words or PASSREQ are set the default is no.

       PermitRootLogin

	   Specifies  whether  the root can log in using ssh(1). The argument must be yes, without-password, forced-commands-only, or no. without-
	   password means that root cannot be authenticated using the "password" or "keyboard-interactive" methods (see description of KbdInterac-
	   tiveAuthentication).  forced-commands-only  means  that authentication is allowed only for publickey (for SSHv2, or RSA, for SSHv1) and
	   only if the matching authorized_keys entry for root has a command=<cmd> option.

	   In Solaris, the default /etc/ssh/sshd_config file is shipped with PermitRootLogin set to no. If unset by the administrator,	then  CON-
	   SOLE  parameter  from  /etc/default/login  supplies the default value as follows: if the CONSOLE parameter is not commented out (it can
	   even be empty, that is, "CONSOLE="), then without-password is used as default value. If CONSOLE is commented out, then the default  for
	   PermitRootLogin is yes.

	   The	without-password and forced-commands-only settings are useful for, for example, performing remote administration and backups using
	   trusted public keys for authentication of the remote client, without allowing access to the root account using passwords.

       PermitUserEnvironment

	   Specifies whether a user's ~/.ssh/environment on the server side and environment options in the AuthorizedKeysFile file  are  processed
	   by sshd. The default is no. Enabling environment processing can enable users to bypass access restrictions in some configurations using
	   mechanisms such as LD_PRELOAD.

	   Environment setting from a relevant entry in AuthorizedKeysFile file is processed only if the user was authenticated using  the  public
	   key authentication method. Of the two files used, values of variables set in ~/.ssh/environment are of higher priority.

       PidFile

	   Allows  you to specify an alternative to /var/run/sshd.pid, the default file for storing the PID of the sshd listening for connections.
	   See sshd(1M).

       Port

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

       PrintLastLog

	   Specifies whether sshd should display the date and time when the user last logged in. The default is yes.

       PrintMotd

	   Specifies whether sshd should display the contents of /etc/motd when a user logs in interactively. (On some systems	it  is	also  dis-
	   played by the shell or a shell startup file, such as /etc/profile.) The default is yes.

       Protocol

	   Specifies  the protocol versions sshd should support in order of preference. The possible values are 1 and 2. Multiple versions must be
	   comma-separated. The default is 2,1. This means that ssh tries version 2 and falls back to version 1 if version 2 is not available.

       PubkeyAuthentication

	   Specifies whether public key authentication is allowed. The default is yes. This option applies to protocol version 2 only.

       RhostsAuthentication

	   Specifies whether authentication using rhosts or /etc/hosts.equiv files is sufficient. Normally, this method should	not  be  permitted
	   because  it	is insecure. RhostsRSAAuthentication should be used instead, because it performs RSA-based host authentication in addition
	   to normal rhosts or /etc/hosts.equiv authentication. The default is no. This parameter applies only to protocol version 1.

       RhostsRSAAuthentication

	   Specifies whether rhosts or /etc/hosts.equiv authentication together with successful RSA host authentication is allowed. The default is
	   no. This parameter applies only to protocol version 1.

       RSAAuthentication

	   Specifies whether pure RSA authentication is allowed. The default is yes. This option applies to protocol version 1 only.

       ServerKeyBits

	   Defines the number of bits in the ephemeral protocol version 1 server key. The minimum value is 512, and the default is 768.

       StrictModes

	   Specifies  whether  sshd  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.

       Subsystem

	   Configures an external subsystem (for example, a file transfer daemon). Arguments should be a subsystem name and a command  to  execute
	   upon subsystem request. The command sftp-server(1M) implements the sftp file transfer subsystem. By default, no subsystems are defined.
	   This option applies to protocol version 2 only.

       SyslogFacility

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

       UseOpenSSLEngine

	   Specifies  whether  ssh  should use the OpenSSL PKCS#11 engine for off loading cryptographic operations to the Cryptographic Framework.
	   Cryptographic operations are accelerated according to the available installed plug-ins. When no  suitable  plug-ins	are  present  this
	   option does not have an effect. The default is yes.

       VerifyReverseMapping

	   Specifies  whether  sshd should try to verify the remote host name and check that the resolved host name for the remote IP address maps
	   back to the very same IP address. (A yes setting means "verify".) Setting this parameter to no can be useful where DNS servers might be
	   down  and  thus cause sshd to spend much time trying to resolve the client's IP address to a name. This feature is useful for Internet-
	   facing servers. The default is no.

       X11DisplayOffset

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

       X11Forwarding

	   Specifies  whether  X11  forwarding is permitted. The default is yes. Disabling X11 forwarding does not improve security in any way, as
	   users can always install their own forwarders.

	   When X11 forwarding is enabled, there can be additional exposure to the server and to client displays if the sshd proxy display is con-
	   figured  to	listen	on  the wildcard address (see X11UseLocalhost). However, 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 can be exposed to attack when the ssh client requests forwarding (see the warnings for ForwardX11
	   in ssh_config(4)). A system administrator who wants to protect clients that expose themselves to attack by unwittingly  requesting  X11
	   forwarding, should specify a no setting.

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

       X11UseLocalhost

	   Specifies whether sshd 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  pre-
	   vents  remote  hosts  from connecting to the proxy display. However, some older X11 clients might not function with this configuration.
	   X11UseLocalhost can 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 location of the xauth(1) program. The default is /usr/openwin/bin/xauth and sshd attempts to open it when X11 forwarding
	   is enabled.

   Time Formats
       sshd command-line arguments and configuration file options that specify time can be expressed using a sequence  of  the	form:  time[quali-
       fier,] where time is a positive integer value and qualifier is one of the following:

       <none>	 seconds

       s | S	 seconds

       m | M	 minutes

       h | H	 hours

       d | D	 days

       w |	 weeks

       Each element of the sequence is added together to calculate the total time value. For example:

       600	600 seconds (10 minutes)

       10m	10 minutes

       1h30m	1 hour, 30 minutes (90 minutes)

FILES

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

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWsshu			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Uncommitted		   |
       +-----------------------------+-----------------------------+

SEE ALSO

       login(1), sshd(1M), ssh_config(4), attributes(5), kerberos(5)

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 recent 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.

SunOS 5.11							    5 Mar 2009							    sshd_config(4)