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mongos - MongoDB Shard Utility


mongos for "MongoDB Shard," is a routing service for MongoDB shard configurations that
processes queries from the application layer, and determines the location of this data in
the sharded cluster, in order to complete these operations. From the perspective of the
application, a mongos instance behaves identically to any other MongoDB instance.

Note Changed in version 2.1.

Some aggregation operations using the aggregate will cause mongos instances to
require more CPU resources than in previous versions. This modified performance
profile may dictate alternate architecture decisions if you use the aggregation
framework extensively in a sharded environment.

See also

/sharding and /core/sharded-clusters.



--help, -h
Returns a basic help and usage text.

Returns the version of the mongod daemon.

--config <filename>, -f <filename>
Specifies a configuration file, that you can use to specify runtime-configurations.
While the options are equivalent and accessible via the other command line
arguments, the configuration file is the preferred method for runtime configuration
of mongod. See the "/reference/configuration-options" document for more information
about these options.

Not all configuration options for mongod make sense in the context of mongos.

--verbose, -v
Increases the amount of internal reporting returned on standard output or in the
log file specified by --logpath. Use the -v form to control the level of verbosity
by including the option multiple times, (e.g. -vvvvv.)

Runs the mongos instance in a quiet mode that attempts to limit the amount of

--port <port>
Specifies a TCP port for the mongos to listen for client connections. By default
mongos listens for connections on port 27017.

UNIX-like systems require root access to access ports with numbers lower than 1024.

--bind_ip <ip address>
The IP address that the mongos process will bind to and listen for connections. By
default mongos listens for connections on the localhost (i.e. address.)
You may attach mongos to any interface; however, if you attach mongos to a publicly
accessible interface you must implement proper authentication or firewall
restrictions to protect the integrity of your database.

--maxConns <number>
Specifies the maximum number of simultaneous connections that mongos will accept.
This setting will have no effect if the value of this setting is higher than your
operating system's configured maximum connection tracking threshold.

This is particularly useful for mongos if you have a client that creates a number
of collections but allows them to timeout rather than close the collections. When
you set 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 shard cluster.

Note You cannot set maxConns to a value higher than 20000.

Forces the mongos to validate all requests from clients upon receipt to ensure that
invalid objects are never inserted into the database. This option has a performance
impact, and is not enabled by default.

--logpath <path>
Specify a path for the log file that will hold all diagnostic logging information.

Unless specified, mongos will output all log information to the standard output.
Additionally, unless you also specify --logappend, the logfile will be overwritten
when the process restarts.

Specify to ensure that mongos appends additional logging data to the end of the
logfile rather than overwriting the content of the log when the process restarts.

New in version 2.1.0.

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

You cannot use --syslog with --logpath.

--pidfilepath <path>
Specify a file location to hold the "PID" or process ID of the mongos process.
Useful for tracking the mongos process in combination with the mongos --fork

Without a specified --pidfilepath option, mongos creates no PID file.

--keyFile <file>
Specify the path to a key file to store authentication information. This option is
only useful for the connection between mongos instances and components of the
sharded cluster.

See also


Disables listening on the UNIX socket. Without this option mongos creates a UNIX

--unixSocketPrefix <path>
Specifies a path for the UNIX socket. Unless specified, mongos creates a socket in
the /tmp path.

--fork Enables a daemon mode for mongod which forces the process to the background. This
is the normal mode of operation, in production and production-like environments,
but may not be desirable for testing.

--configdb <config1>,<config2><:port>,<config3>
Set this option to specify a configuration database (i.e. config database) for the
sharded cluster. You must specify either 1 configuration server or 3 configuration
servers, in a comma separated list.

Note mongos instances read from the first config server in the list provided. All mongos
instances must specify the hosts to the --configdb setting in the same order.

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

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

--test This option is for internal testing use only, and runs unit tests without starting
a mongos instance.

This option updates the meta data format used by the config database.

--chunkSize <value>
The value of the --chunkSize determines the size of each chunk, in megabytes, of
data distributed around the sharded cluster. The default value is 64 megabytes,
which is the ideal size for chunks in most deployments: larger chunk size can lead
to uneven data distribution, smaller chunk size often leads to inefficient movement
of chunks between nodes. However, in some circumstances it may be necessary to set
a different chunk size.

This option 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 "sharding-balancing-modify-chunk-size" procedure if you need to change the
chunk size on an existing sharded cluster.

--ipv6 Enables IPv6 support to allow clients to connect to mongos using IPv6 networks.
MongoDB disables IPv6 support by default in mongod and all utilities.

Permits JSONP access via an HTTP interface. Consider the security implications of
allowing this activity before enabling this option.

Disables the scripting engine.

New in version 2.1.2.

Disables the HTTP interface.

New in version 2.2.

--localThreshold affects the logic that mongos uses when selecting replica set
members to pass read operations to from clients. Specify a value to
--localThreshold in milliseconds. The default value is 15, which corresponds to the
default value in all of the client drivers.

When mongos receives a request that permits reads to secondary members, the mongos

· 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 --localThreshold, mongos will construct the list of
replica members that are within the latency allowed by this value.

· The mongos will select a member to read from at random from this list.

The ping time used for a set member compared by the --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 mongos
recalculates the average.

See the replica-set-read-preference-behavior-member-selection section of the read
preference documentation for more information.

New in version 2.0.7.

--noAutoSplit prevents mongos from automatically inserting metadata splits in a
sharded collection. If set on all mongos, this will prevent MongoDB from creating
new chunks as the data in a collection grows.

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

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

SSL Options

/administration/ssl for full documentation of MongoDB's support.

--authenticationDatabase <dbname>
New in version 2.4.

Specifies the database that holds the user's (e.g --username) credentials.

By default, mongos assumes that the database specified to the --db argument holds
the user's credentials, unless you specify --authenticationDatabase.

See userSource, /reference/privilege-documents and /reference/user-privileges for
more information about delegated authentication in MongoDB.

--authenticationMechanism <name>
New in version 2.4.

Specifies the authentication mechanism. By default, the authentication mechanism is
MONGODB-CR, which is the MongoDB challenge/response authentication mechanism. In
the MongoDB Subscriber Edition, mongos also includes support for GSSAPI to handle
Kerberos authentication.

See /tutorial/control-access-to-mongodb-with-kerberos-authentication for more
information about Kerberos authentication.

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