configuration-options.txt

==========================
Configuration File Options
==========================

.. default-domain:: mongodb

.. When editing this file make sure that the man pages for the
   binaries reflect all changes that you've made.

   That is:

        - /reference/mongod.txt
        - /reference/mongos.txt

Synopsis
--------

Administrators and users can control :program:`mongod` or
:program:`mongos` instances at runtime either directly from
:doc:`mongod's command line arguments </reference/program/mongod>` or using a
configuration file.

While both methods are functionally equivalent and all settings are
similar, the configuration file method is preferable. If you
installed from a package and have started MongoDB using your system's
:term:`control script`, you're already using a configuration file.

To start :program:`mongod` or :program:`mongos` using a config file,
use one of the following forms:

.. code-block:: sh

   mongod --config /etc/mongodb.conf
   mongod -f /etc/mongodb.conf
   mongos --config /srv/mongodb/mongos.conf
   mongos -f /srv/mongodb/mongos.conf

Declare all settings in this file using the following form:

.. code-block:: sh

   <setting> = <value>

.. versionadded:: 2.0
   *Before* version 2.0, Boolean (i.e. ``true|false``) or "flag"
   parameters, register as true, if they appear in the configuration
   file, regardless of their value.

.. include:: /includes/note-configuration-file-must-be-ascii.rst

Settings
--------

.. setting:: verbose

   *Default:* false

   Increases the amount of internal reporting returned on standard
   output or in the log file generated by :setting:`logpath`. To
   enable :setting:`verbose` or to enable increased verbosity with
   :setting:`vvvv`, set these options as in the following example:

   .. code-block:: sh

      verbose = true
      vvvv = true


   MongoDB has the following levels of verbosity:

   .. setting:: v

      *Default:* false

      Alternate form of :setting:`verbose`.

   .. setting:: vv

      *Default:* false

      Additional increase in verbosity of output and logging.

   .. setting:: vvv

      *Default:* false

      Additional increase in verbosity of output and logging.

   .. setting:: vvvv

      *Default:* false

      Additional increase in verbosity of output and logging.

   .. setting:: vvvvv

      *Default:* false

      Additional increase in verbosity of output and logging.

.. setting:: port

   *Default:* 27017

   Specifies a TCP port for the :program:`mongod` or :program:`mongos`
   instance to listen for client connections. UNIX-like systems
   require root access for ports with numbers lower than 1024.

.. setting:: bind_ip

   *Default:* All interfaces.

   Set this option to configure the :program:`mongod` or
   :program:`mongos` process to bind to and listen for connections
   from applications on this address. You may attach :program:`mongod`
   or :program:`mongos` instances to any interface; however, if you
   attach the process to a publicly accessible interface, implement
   proper authentication or firewall restrictions to protect the
   integrity of your database.

   You may concatenate a list of comma separated values to bind
   :program:`mongod` to multiple IP addresses.

.. setting:: maxConns

   *Default:* depends on system (i.e. ulimit and file descriptor)
   limits. Unless set, MongoDB will not limit its own connections.

   Specifies a value to set the maximum number of simultaneous
   connections that :program:`mongod` or :program:`mongos` will
   accept. This setting has no effect if it is higher than your
   operating system's configured maximum connection tracking
   threshold.

   This is particularly useful for :program:`mongos` if you have a
   client that creates a number of connections but allows them to
   timeout rather than close the connections. When you set
   :setting:`maxConns`, ensure the value is slightly higher than the
   size of the connection pool or the total number of connections to
   prevent erroneous connection spikes from propagating to the members
   of a :term:`shard` cluster.

   .. include:: /includes/note-max-conns-max.rst

.. setting:: objcheck

   *Default:* true

   .. versionchanged:: 2.4
      The default setting for :setting:`objcheck` became ``true`` in
      2.4. In earlier versions :setting:`objcheck` was ``false`` by
      default.

   Forces the :program:`mongod` to validate all requests from clients
   upon receipt to ensure that clients never insert invalid documents
   into the database. For objects with a high degree of sub-document
   nesting, :setting:`objcheck` can have a small impact on
   performance. You can set :setting:`noobjcheck` to disable object
   checking at run-time.

.. setting:: noobjcheck

   .. versionadded:: 2.4

   *Default:* false

   Disables the default object validation that MongoDB performs on all
   incoming BSON documents.

.. setting:: logpath

   *Default:* None. (i.e. ``/dev/stdout``)

   Specify the path to a file name for the log file that will hold all
   diagnostic logging information.

   Unless specified, :program:`mongod` will output all log information
   to the standard output. Unless :setting:`logappend` is ``true``,
   the logfile will be overwritten when the process restarts.

   .. note::

      Currently, MongoDB will overwrite the contents of the log file
      if the :setting:`logappend` is not used. This behavior may
      change in the future depending on the outcome of
      :issue:`SERVER-4499`.

.. setting:: logappend

   *Default:* false

   Set to ``true`` to add new entries to the end of the logfile rather
   than overwriting the content of the log when the process restarts.

   If this setting is not specified, then MongoDB will overwrite the
   existing logfile upon start up.

   .. note::

      The behavior of the logging system may change in the near
      future in response to the :issue:`SERVER-4499` case.

.. setting:: syslog

   .. versionadded:: 2.2

   Sends all logging output to the host's :term:`syslog` system rather
   than to standard output or a log file as with :setting:`logpath`.

   .. important:: You cannot use :setting:`syslog` with :setting:`logpath`.

.. setting:: pidfilepath

   *Default:* None.

   Specify a file location to hold the :term:`PID` or process ID of the
   :program:`mongod` process. Useful for tracking the :program:`mongod` process in
   combination with the :setting:`fork` setting.

   Without a specified :setting:`pidfilepath`, :program:`mongos`
   creates no PID file.

   Without this option, :program:`mongod` creates no PID file.

.. setting:: keyFile

   *Default:* None.

   Specify the path to a key file to store authentication
   information. This option is only useful for the connection between
   replica set members.

   .. seealso:: :ref:`Replica Set Security <replica-set-security>`

.. setting:: nounixsocket

   *Default:* false

   Set to ``true`` to disable listening on the UNIX
   socket.

   MongoDB always creates and listens on the UNIX socket, unless
   :setting:`nounixsocket` is set, or :setting:`bind_ip` is *not* set,
   or :setting:`bind_ip` does *not* specify ``127.0.0.1``.

.. setting:: unixSocketPrefix

   *Default:* ``/tmp``

   Specifies a path for the UNIX socket. Unless this option has a
   value :program:`mongod` creates a socket with ``/tmp`` as a
   prefix.

   MongoDB will *always* create and listen on a UNIX socket, unless
   :setting:`nounixsocket` is set, :setting:`bind_ip` is *not* set.
   or :setting:`bind_ip` does *not* specify ``127.0.0.1``.

.. setting:: fork

   *Default:* false

   Set to ``true`` to enable a :term:`daemon` mode for
   :program:`mongod` that runs the process in the background.

.. setting:: auth

   *Default:* false

   Set to ``true`` to enable database authentication for users
   connecting from remote hosts. Configure users via the :doc:`mongo
   shell </reference/program/mongo>`. If no users exist, the localhost
   interface will continue to have access to the database until you
   create the first user.

.. setting:: cpu

   *Default:* false

   Set to ``true`` to force :program:`mongod` to report every four
   seconds CPU utilization and the amount of time that the processor
   waits for I/O operations to complete (i.e. I/O wait.) MongoDB writes
   this data to standard output, or the logfile if using the
   :setting:`logpath` option.

.. setting:: dbpath

   *Default:* ``/data/db/``

   Set this value to designate a directory for the :program:`mongod`
   instance to store its data. Typical locations include:
   ``/srv/mongodb``, ``/var/lib/mongodb`` or ``/opt/mongodb``

   Unless specified, :program:`mongod` will look for data files in the
   default ``/data/db`` directory. (Windows systems use the
   ``\data\db`` directory.) If you installed using a package
   management system. Check the ``/etc/mongodb.conf`` file provided by
   your packages to see the configuration of the :setting:`dbpath`.

.. setting:: diaglog

   *Default:* 0

   Creates a very verbose :term:`diagnostic log` for troubleshooting and
   recording various errors. MongoDB writes these log files in the
   :setting:`dbpath` directory and names them :file:`diaglog.<time in
   hex>`, where ``<time-in-hex>`` is the initiation time of logging as a
   hexadecimal string.

   The value of this setting configures the level of
   verbosity. Possible values, and their impact are as follows.

   =========  ===================================
   **Value**  **Setting**
   ---------  -----------------------------------
      0       Off. No logging.
      1       Log write operations.
      2       Log read operations.
      3       Log both read and write operations.
      7       Log write and some read operations.
   =========  ===================================

   You can use the :program:`mongosniff` tool to replay this output
   for investigation. Given a typical diaglog file, located at
   ``/data/db/diaglog.4f76a58c``, you might use a command in the
   following form to read these files:

   .. code-block:: sh

      mongosniff --source DIAGLOG /data/db/diaglog.4f76a58c

   :setting:`diaglog` is for internal use and not intended for most
   users.

   .. include:: /includes/warning-diaglogging-off.rst

.. setting:: directoryperdb

   *Default:* false

   Set to ``true`` to modify the storage pattern of the data directory
   to store each database's files in a distinct folder. This option
   will create directories within the :setting:`dbpath` named for each
   database.

   Use this option in conjunction with your file system and device
   configuration so that MongoDB will store data on a number of
   distinct disk devices to increase write throughput or disk
   capacity.

   .. warning::

      .. |directoryperdb-option-name| replace:: :setting:`directoryperdb`
      .. include:: /includes/fact-directory-per-db-requires-migration.rst

.. _setting-journal:

.. setting:: journal

   *Default:* (on 64-bit systems) true

   *Default:* (on 32-bit systems) false

   Set to true to enable operation journaling to ensure write
   durability and data consistency.

   Set to false to prevent the overhead of journaling in situations
   where durability is not required. To reduce the impact of the
   journaling on disk usage, you can leave :setting:`journal`
   enabled, and set :setting:`smallfiles` to true to reduce the size
   of the data and journal files.

   .. note:: You must use :setting:`nojournal` to disable journaling
      on 64-bit systems.

.. setting:: journalCommitInterval

   *Default:* 100 or 30

   Set this value to specify the maximum amount of time for
   :program:`mongod` to allow between journal operations. Lower
   values increase the durability of the journal, at the possible
   expense of disk performance.

   .. include:: /includes/fact-journal-commit-interval-length.rst

   This option accepts values between 2 and 300 milliseconds.

   .. include:: /includes/fact-journal-commit-interval-with-gle.rst

.. setting:: ipv6

   *Default:* false

   Set to ``true`` to IPv6 support to allow clients to connect to
   :program:`mongod` using IPv6 networks. :program:`mongod` disables
   IPv6 support by default in :program:`mongod` and all utilities.

.. setting:: jsonp

   *Default:* false

   Set to ``true`` to permit :term:`JSONP` access via an HTTP
   interface. Consider the security implications of allowing this
   activity before setting this option.

.. setting:: noauth

   *Default:* true

   Disable authentication. Currently the default. Exists for future
   compatibility and clarity.

   For consistency use the :setting:`auth` option.

.. setting:: nohttpinterface

   *Default:* false

   Set to ``true`` to disable the HTTP interface. This command will
   override the :setting:`rest` and disable the HTTP interface if you
   specify both.

   .. include:: /includes/note-kerberos-unsupported-in-http-console.rst

   .. versionchanged:: 2.1.2
      The :setting:`nohttpinterface` option is not available for :program:`mongos` instances before 2.1.2

.. setting:: nojournal

   *Default:* (on 64-bit systems) false

   *Default:* (on 32-bit systems) true

   Set ``nojournal = true`` to disable durability journaling. By
   default, :program:`mongod` enables journaling in 64-bit versions
   after v2.0.

   .. note:: You must use :setting:`journal` to enable journaling
      on 32-bit systems.

.. setting:: noprealloc

   *Default:* false

   Set ``noprealloc = true`` to disable the preallocation of data
   files. This will shorten the start up time in some cases, but can
   cause significant performance penalties during normal operations.

.. setting:: noscripting

   *Default:* false

   Set ``noscripting = true`` to disable the scripting engine.

.. setting:: notablescan

   *Default:* false

   Set ``notablescan = true`` to forbid operations that require a
   table scan.

.. setting:: nssize

   *Default:* 16

   Specify this value in megabytes. The maximum size is 2047 megabytes.

   Use this setting to control the default size for all newly created
   namespace files (i.e ``.ns``). This option has no impact on the
   size of existing namespace files.

   See :limit:`Limits on namespaces <Number of Namespaces>`.

.. setting:: profile

   *Default:* 0

   Modify this value to changes the level of database profiling, which
   inserts information about operation performance into output of
   :program:`mongod` or the log file if specified by
   :setting:`logpath`. The following levels are available:

   =========  ==================================
   **Level**  **Setting**
   ---------  ----------------------------------
      0       Off. No profiling.
      1       On. Only includes slow operations.
      2       On. Includes all operations.
   =========  ==================================

   By default, :program:`mongod` disables profiling. Database profiling
   can impact database performance because the profiler must record
   and process all database operations. Enable this option only after
   careful consideration.

.. setting:: quota

   *Default:* false

   Set to ``true`` to enable a maximum limit for the number data files
   each database can have. The default quota is 8 data files, when
   ``quota`` is true. Adjust the quota size with the with the
   :setting:`quotaFiles` setting.

.. setting:: quotaFiles

   *Default:* 8

   Modify limit on the number of data files per database. This option
   requires the :setting:`quota` setting.

.. setting:: rest

   *Default:* false

   Set to ``true`` to enable a simple :term:`REST` interface.

.. setting:: repair

   *Default:* false

   Set to ``true`` to run a repair routine on all databases following
   start up. In general you should set this option on the command line
   and *not* in the :doc:`configuration file
   </administration/configuration>` or in a :term:`control script`.

   Use the :option:`mongod --repair` option to access this
   functionality.

   .. note::

      Because :program:`mongod` rewrites all of the database files
      during the repair routine, if you do not run :setting:`repair`
      under the same user account as :program:`mongod` usually runs,
      you will need to run ``chown`` on your database files to correct
      the permissions before starting :program:`mongod` again.

.. setting:: repairpath

   *Default:* A ``_tmp`` directory in the :setting:`dbpath`.

   Specify the path to the directory containing MongoDB data files, to
   use in conjunction with the :setting:`repair` setting or
   :option:`mongod --repair` operation. Defaults to a ``_tmp``
   directory within the :setting:`dbpath`.

.. setting:: slowms

   *Default:* 100

   Specify values in milliseconds.

   Sets the threshold for :program:`mongod` to consider a query "slow"
   for the database profiler. The database logs all slow queries to
   the log, even when the profiler is not turned on. When the database
   profiler is on, :program:`mongod` the profiler writes to the
   ``system.profile`` collection.

   .. seealso:: :setting:`profile`

.. setting:: smallfiles

   *Default:* false

   Set to ``true`` to modify MongoDB to use a smaller default data
   file size. Specifically, :setting:`smallfiles` reduces the initial
   size for data files and limits them to 512
   megabytes. The :setting:`smallfiles` setting also reduces the size of each
   :term:`journal` files from 1 gigabyte to 128 megabytes.

   Use the :setting:`smallfiles` setting if you have a large number of databases
   that each hold a small quantity of data. The :setting:`smallfiles` setting can
   lead :program:`mongod` to create many files,
   which may affect performance for larger databases.

.. setting:: syncdelay

   *Default:* 60

   :program:`mongod` writes data very quickly to the journal, and
   lazily to the data files. :setting:`syncdelay` controls how much
   time can pass before MongoDB flushes data to the *database files* via an
   :term:`fsync` operation. The default setting is 60 seconds.  In
   almost every situation you should not set this value and use the
   default setting.

   The :dbcommand:`serverStatus` command reports the background flush
   thread's status via the :data:`~serverStatus.backgroundFlushing` field.

   :setting:`syncdelay` has no effect on the :setting:`journal`
   files or :doc:`journaling </core/journaling>`.

   .. warning::

      If you set :setting:`syncdelay` to ``0``, MongoDB will not sync
      the memory mapped files to disk. Do not set this value on
      production systems.

.. setting:: sysinfo

   *Default:* false

   When set to ``true``, :program:`mongod` returns diagnostic system
   information regarding the page size, the number of physical pages,
   and the number of available physical pages to standard output.

   More typically, run this operation by way of the :option:`mongod --sysinfo`
   command. When running with the :setting:`sysinfo`, only
   :program:`mongod` only outputs the page information and no database
   process will start.

.. setting:: upgrade

   *Default:* false

   When set to ``true`` this option upgrades the on-disk data format
   of the files specified by the :setting:`dbpath` to the latest
   version, if needed.

   This option only affects the operation of :program:`mongod` if the
   data files are in an old format.

   When specified for a :program:`mongos` instance, this option updates
   the meta data format used by the :term:`config database`.

   .. note::

      In most cases you should **not** set this value, so you can
      exercise the most control over your upgrade process. See the MongoDB
      `release notes <http://www.mongodb.org/downloads>`_ (on the
      download page) for more information about the upgrade process.

.. setting:: traceExceptions

   *Default:* false

   For internal diagnostic use only.

.. setting:: quiet

   *Default:* false

   Runs the :program:`mongod` or :program:`mongos` instance in a quiet
   mode that attempts to limit the amount of output. This option suppresses:

   - output from :term:`database commands <database command>`,
     including :dbcommand:`drop`, :dbcommand:`dropIndexes`,
     :dbcommand:`diagLogging`, :dbcommand:`validate`, and
     :dbcommand:`clean`.

   - replication activity.

   - connection accepted events.

   - connection closed events.

   .. note::

      For production systems this option is **not** recommended as it may make
      tracking problems during particular connections much more difficult.

.. setting:: setParameter

   .. versionadded:: 2.4

   Specifies an option to configure on startup.  Specify multiple
   options with multiple :setting:`setParameter` options.  See
   :doc:`/reference/parameters` for full documentation of these
   parameters. The :dbcommand:`setParameter` database command provides
   access to many of these parameters.

   Declare all :dbcommand:`setParameter` settings in this file using the following form:

   .. code-block:: sh

      setParameter = <parameter>=<value>

   For :program:`mongod` the following options are available using
   :setting:`setParameter`:

   .. include:: /includes/list-set-parameters-mongod.rst

   For :program:`mongos` the following options are available using
   :setting:`setParameter`:

   .. include:: /includes/list-set-parameters-mongos.rst

.. setting:: noIndexBuildRetry

   By default, :program:`mongod` will attempt to rebuild indexes upon
   start-up *if* :program:`mongod` shuts down or stops in the middle
   of an index build. When you specify :option:`--noIndexBuildRetry`,
   :program:`mongod` will not attempt to rebuild the index.

Replication Options
~~~~~~~~~~~~~~~~~~~

.. setting:: replSet

   *Default:* <none>

   *Form:* <setname>

   Use this setting to configure replication with replica
   sets. Specify a replica set name as an argument to this set. All
   hosts must have the same set name.

   .. seealso:: :doc:`/replication`,
      :doc:`/administration/replica-set-deployment`, and
      :doc:`/reference/replica-configuration`

.. setting:: oplogSize

   Specifies a maximum size in megabytes for the replication operation
   log (e.g. :term:`oplog`.) :program:`mongod` creates an oplog
   based on the maximum amount of space available. For 64-bit systems,
   the oplog is typically 5% of available disk space.

   Once the :program:`mongod` has created the oplog for the first
   time, changing :setting:`oplogSize` will not affect the size of the
   oplog.

.. setting:: fastsync

   *Default:* false

   In the context of :term:`replica set` replication, set this option
   to ``true`` if you have seeded this member with a snapshot of the
   :term:`dbpath` of another member of the set. Otherwise the
   :program:`mongod` will attempt to perform an initial sync, as though the member were a new member.

   .. warning::

      If the data is not perfectly synchronized *and*
      :program:`mongod` starts with :setting:`fastsync`, then the
      secondary or slave will be permanently out of sync with the
      primary, which may cause significant consistency problems.

.. setting:: replIndexPrefetch

   .. versionadded:: 2.2

   *Default:* ``all``

   *Values:* ``all``, ``none``, and ``_id_only``

   You can only use :setting:`replIndexPrefetch` in conjunction with
   :setting:`replSet`.

   By default :term:`secondary` members of a :term:`replica set` will
   load all indexes related to an operation into memory before
   applying operations from the oplog. You can modify this behavior so
   that the secondaries will only load the ``_id`` index. Specify
   ``_id_only`` or ``none`` to prevent the :program:`mongod` from
   loading *any* index into memory.

Master/Slave Replication
~~~~~~~~~~~~~~~~~~~~~~~~

.. setting:: master

   *Default:* false

   Set to ``true`` to configure the current instance to act as
   :term:`master` instance in a replication configuration.

.. setting:: slave

   *Default:* false

   Set to ``true`` to configure the current instance to act as
   :term:`slave` instance in a replication configuration.

.. setting:: source

   *Default:* <>

   *Form:* <host><:port>

   Used with the :setting:`slave` setting to specify the
   :term:`master` instance from which this :term:`slave` instance will
   replicate

.. setting:: only

   *Default:* <>

   Used with the :setting:`slave` option, :setting:`only`
   specifies only a single :term:`database` to replicate.

.. setting:: slaveDelay

   *Default:* 0

   Used with the :setting:`slave` setting, :setting:`slaveDelay`
   configures a "delay" in seconds, for this slave to wait to apply
   operations from the :term:`master` instance.

.. setting:: autoresync

   *Default:* false

   Used with the :setting:`slave` setting, set :setting:`autoresync` to
   ``true`` to force the :term:`slave` to automatically resync if it
   is more than 10 seconds behind the master. This setting may be
   problematic if the :setting:`oplogSize` of the
   :term:`oplog` is too small.
   If the :term:`oplog` is not large
   enough to store the difference in changes between the master's
   current state and the state of the slave, this instance will forcibly
   resync itself unnecessarily. When you set the :setting:`autoresync`
   option to ``false``, the slave will not attempt an automatic resync more than
   once in a ten minute period.

Sharded Cluster Options
~~~~~~~~~~~~~~~~~~~~~~~

.. setting:: configsvr

   *Default:* false

   Set this value to ``true`` to configure this :program:`mongod`
   instance to operate as the :term:`config database` of a shard
   cluster. When running with this option, clients will not be able to
   write data to any database other than ``config`` and ``admin``. The
   default port for a :program:`mongod` with this option is ``27019``
   and the default :setting:`dbpath` directory is ``/data/configdb``,
   unless specified.

   .. versionchanged:: 2.2
      :setting:`configsvr` also sets :setting:`smallfiles`.

   .. versionchanged:: 2.4
      :setting:`configsvr` creates a local :term:`oplog`.

   Do not use :setting:`configsvr` with :setting:`replSet` or
   :setting:`shardsvr`. Config servers cannot be a shard
   server or part of a :term:`replica set`.

   default port for :program:`mongod` with this option is ``27019``
   and :program:`mongod` writes all data files to the ``/configdb``
   sub-directory of the :setting:`dbpath` directory.

.. setting:: shardsvr

   *Default:* false

   Set this value to ``true`` to configure this :program:`mongod`
   instance as a shard in a partitioned cluster. The default port for
   these instances is ``27018``. The only effect of
   :setting:`shardsvr` is to change the port number.

.. setting:: configdb

   *Default:* None.

   *Format:* ``<config1>,<config2><:port>,<config3>``

   Set this option to specify a configuration database
   (i.e. :term:`config database`) for the :term:`sharded cluster`. You
   must specify either 1 configuration server or 3 configuration
   servers, in a comma separated list.

   This setting only affects :program:`mongos` processes.

   .. note::

      :program:`mongos` instances read from the first :term:`config
      server <config database>` in the list provided. All
      :program:`mongos` instances **must** specify the hosts to the
      :setting:`configdb` setting in the same order.

      If your configuration databases reside in more that one data
      center, order the hosts in the :setting:`configdb` setting so
      that the config database that is closest to the majority of your
      :program:`mongos` instances is first servers in the list.

   .. warning::

      Never remove a config server from the :setting:`configdb` parameter, even if
      the config server or servers are not available, or offline.

.. setting:: test

   *Default:* false

   Only runs unit tests and does not start a :program:`mongos` instance.

   This setting only affects :program:`mongos` processes and is for
   internal testing use only.

.. setting:: chunkSize

   *Default:* 64

   The value of this option determines the size of each :term:`chunk`
   of data distributed around the :term:`sharded cluster`. The default
   value is 64 megabytes. Larger chunks may lead to an uneven
   distribution of data, while smaller chunks may lead to frequent and
   unnecessary migrations. However, in some circumstances it may be
   necessary to set a different chunk size.

   This setting only affects :program:`mongos` processes. Furthermore,
   :setting:`chunkSize` *only* sets the chunk size when initializing
   the cluster for the first time. If you modify the run-time option
   later, the new value will have no effect. See the
   :doc:`/tutorial/modify-chunk-size-in-sharded-cluster` procedure if you
   need to change the chunk size on an existing sharded cluster.

.. setting:: localThreshold

   .. versionadded:: 2.2

   :setting:`localThreshold` affects the logic that :program:`mongos`
   uses when selecting :term:`replica set` members to pass reads
   operations to from clients. Specify a value to
   :setting:`localThreshold` in milliseconds. The default value is
   ``15``, which corresponds to the default value in all of the client
   :doc:`drivers </applications/drivers>`.

   This setting only affects :program:`mongos` processes.

   When :program:`mongos` receives a request that permits reads to
   :term:`secondary` members, the :program:`mongos` will:

    - find the member of the set with the lowest ping time.

    - construct a list of replica set members that is within a ping
      time of 15 milliseconds of the nearest suitable member of the
      set.

      If you specify a value for :setting:`localThreshold`,
      :program:`mongos` will construct the list of replica members
      that are within the latency allowed by this value.

    - The :program:`mongos` will select a member to read from at
      random from this list.

   The ping time used for a set member compared by the
   :setting:`localThreshold` setting is a moving average of recent
   ping times, calculated, at most, every 10 seconds. As a result,
   some queries may reach members above the threshold until the
   :program:`mongos` recalculates the average.

   See the :ref:`replica-set-read-preference-behavior-member-selection`
   section of the :doc:`read preference </core/read-preference>`
   documentation for more information.

.. setting:: noAutoSplit

   :setting:`noAutoSplit` is for internal use and is only available on
   :program:`mongos` instances.

   .. versionadded:: 2.0.7

   :setting:`noAutoSplit` prevents :program:`mongos` from
   automatically inserting metadata splits in a :term:`sharded
   collection <sharding>`. If set on all :program:`mongos`, this will prevent
   MongoDB from creating new chunks as the data in a collection
   grows.

   Because any :program:`mongos` in a cluster can create a split,
   to totally disable splitting in a cluster you must
   set :setting:`noAutoSplit` on all :program:`mongos`.

   .. warning::

      With :setting:`noAutoSplit` enabled, the data in your sharded
      cluster may become imbalanced over time. Enable with caution.

.. setting:: moveParanoia

   .. |move-paranoia-opt| replace:: :setting:`moveParanoia`

   .. versionadded:: 2.4

   .. include:: /includes/setting-moveparanoia.rst

SSL Options
~~~~~~~~~~~

.. |binary-name| replace:: :program:`mongod` or :program:`mongos`
.. include:: /includes/manpage-options-ssl-settings.rst