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Run-time Database Configuration

On this page

  • Configure the Database
  • Security Considerations
  • Replication and Sharding Configuration
  • Run Multiple Database Instances on the Same System
  • Diagnostic Configurations

The command line and configuration file interfaces provide MongoDB administrators with a large number of options and settings for controlling the operation of the database system. This document provides an overview of common configurations and examples of best-practice configurations for common use cases.

While both interfaces provide access to the same collection of options and settings, this document primarily uses the configuration file interface.

  • If you installed MongoDB with a package manager such as yum or apt on Linux or brew on macOS, or with the MSI installer on Windows, a default configuration file has been provided as part of your installation:

    Configuration File
    apt, yum, or zypper Package Manager
    brew Package Manager

    /usr/local/etc/mongod.conf (on Intel processors), or

    /opt/homebrew/etc/mongod.conf (on Apple M1 processors)

    MSI Installer
    <install directory>\bin\mongod.cfg
  • If you installed MongoDB via a downloaded TGZ or ZIP file, you will need to create your own configuration file. The basic example configuration is a good place to start.

For package installations of MongoDB on Linux or macOS, an initialization script which uses this default configuration file is also provided. This initialization script can be used to start the mongod on these platforms in the following manner:

  • On Linux systems that use the systemd init system (the systemctl command):

    sudo systemctl start mongod
  • On Linux systems that use the SystemV init init system (the service command):

    sudo service mongod start
  • On macOS, using the brew package manger:

    brew services start mongodb-community@4.4

If you installed MongoDB using a TGZ or ZIP file, you will need to create your own configuration file. A basic example configuration can be found later in this document. Once you have created a configuration file, you can start a MongoDB instance with this configuration file by using either the --config or -f options to mongod. For example, on Linux:

mongod --config /etc/mongod.conf
mongod -f /etc/mongod.conf

Modify the values in the mongod.conf file on your system to control the configuration of your database instance.

Consider the following basic configuration:

fork: true
bindIp: localhost
port: 27017
dbPath: /var/lib/mongo
destination: file
path: "/var/log/mongodb/mongod.log"
logAppend: true
enabled: true

For most standalone servers, this is a sufficient base configuration. It makes several assumptions, but consider the following explanation:

  • fork is true, which enables a daemon mode for mongod, which detaches (i.e. "forks") the MongoDB from the current session and allows you to run the database as a conventional server.

  • bindIp is localhost, which forces the server to only listen for requests on the localhost IP. Only bind to secure interfaces that the application-level systems can access with access control provided by system network filtering (i.e. "firewall").

  • port is 27017, which is the default MongoDB port for database instances. MongoDB can bind to any port. You can also filter access based on port using network filtering tools.


    UNIX-like systems require superuser privileges to attach processes to ports lower than 1024.

  • quiet is true. This disables all but the most critical entries in output/log file, and is not recommended for production systems. If you do set this option, you can use setParameter to modify this setting during run time.

  • dbPath is /var/lib/mongo, which specifies where MongoDB will store its data files.

    If you installed MongoDB on Linux using a package manager, such as yum or apt, the /etc/mongod.conf file provided with your MongoDB installation sets the following default dbPath, depending on your Linux distro:

    Package Manager
    Default dbPath
    RHEL / CentOS and Amazon
    Ubuntu and Debian

    The user account that mongod runs under will need read and write access to this directory.

  • systemLog.path is /var/log/mongodb/mongod.log which is where mongod will write its output. If you do not set this value, mongod writes all output to standard output (e.g. stdout.)

  • logAppend is true, which ensures that mongod does not overwrite an existing log file following the server start operation.

  • storage.journal.enabled is true, which enables journaling. Journaling ensures single instance write-durability. 64-bit builds of mongod enable journaling by default. Thus, this setting may be redundant.

Given the default configuration, some of these values may be redundant. However, in many situations explicitly stating the configuration increases overall system intelligibility.

The following configuration options are useful for limiting access to a mongod instance:

bindIp: localhost,,,/tmp/mongod.sock
authorization: enabled

This example provides four values to the bindIp option:

  • localhost, the localhost interface;

  •, a private IP address typically used for local networks and VPN interfaces;

  •, a private network interface typically used for local networks; and

  • /tmp/mongod.sock, a Unix domain socket path.

Because production MongoDB instances need to be accessible from multiple database servers, it is important to bind MongoDB to multiple interfaces that are accessible from your application servers. At the same time it's important to limit these interfaces to interfaces controlled and protected at the network layer.

Setting this option to true enables the authorization system within MongoDB. If enabled you will need to log in by connecting over the localhost interface for the first time to create user credentials.


See also:

replica set configuration is straightforward, and only requires that the replSetName have a value that is consistent among all members of the set. Consider the following:

replSetName: set0

Use descriptive names for sets. Once configured, use the mongo shell to add hosts to the replica set.

To enable authentication for the replica set using keyfiles , add the following keyFile option [1]:

keyFile: /srv/mongodb/keyfile

Setting keyFile enables authentication and specifies a keyfile for the replica set member to use when authenticating to each other.


See also:

The Replica Set Security section for information on configuring authentication with replica sets.

The Replication document for more information on replication in MongoDB and replica set configuration in general.

[1] Sharded clusters and replica sets can use x.509 for membership verification instead of keyfiles. For details, see x.509.

Sharding requires mongod instances with different mongod configurations for the config servers and the shards. The config servers store the cluster's metadata, while the shards store the data.

To configure the config server mongod instances, in the configuration file, specify configsvr for the sharding.clusterRole setting.

Changed in version 3.4: Starting in version 3.4, MongoDB removes support for mirrored config servers and config servers must be deployed as a replica set.

clusterRole: configsvr
port: 27001
replSetName: csRS

To deploy config servers as a replica set, the config servers must run the WiredTiger Storage Engine. Initiate the replica set and add members.

To configure the shard mongod instances, specify shardsvr for the sharding.clusterRole setting, and if running as a replica set, the replica set name:

clusterRole: shardsvr
replSetName: shardA

If running as a replica set, initiate the shard replica set and add members.

For the router (i.e. mongos), configure at least one mongos process with the following setting:

configDB: csRS/

You can specify additional members of the config server replica set by specifying hostnames and ports in the form of a comma separated list after the replica set name.


See also:

The Sharding section of the manual for more information on sharding and cluster configuration.

In many cases running multiple instances of mongod on a single system is not recommended. On some types of deployments [2] and for testing purposes you may need to run more than one mongod on a single system.

In these cases, use a base configuration for each instance, but consider the following configuration values:

dbPath: /var/lib/mongo/db0/
pidFilePath: /var/lib/mongo/

The dbPath value controls the location of the mongod instance's data directory. Ensure that each database has a distinct and well labeled data directory. The pidFilePath controls where mongod process places it's process ID (PID) file. As this tracks the specific mongod file, it is crucial that file be unique and well labeled to make it easy to start and stop these processes.

Create additional init scripts and/or adjust your existing MongoDB configuration and init script as needed to control these processes.

[2] Single-tenant systems with SSD or other high performance disks may provide acceptable performance levels for multiple mongod instances. Additionally, you may find that multiple databases with small working sets may function acceptably on a single system.

The following configuration options control various mongod behaviors for diagnostic purposes:

  • operationProfiling.mode sets the database profiler level. The profiler is not active by default because of the possible impact on the profiler itself on performance. Unless this setting is on, queries are not profiled.

  • operationProfiling.slowOpThresholdMs configures the threshold which determines whether a query is "slow" for the purpose of the logging system and the profiler. The default value is 100 milliseconds. Set to a lower value if the logging system and the database profiler do not return useful results or set to a higher value to only log the longest running queries.

    Starting in version 4.2, secondary members of a replica set now log oplog entries that take longer than the slow operation threshold to apply. These slow oplog messages:

    • Are logged for the secondaries in the diagnostic log.

    • Are logged under the REPL component with the text applied op: <oplog entry> took <num>ms.

    • Do not depend on the log levels (either at the system or component level)

    • Do not depend on the profiling level.

    • May be affected by slowOpSampleRate, depending on your MongoDB version:

      • In MongoDB 4.2, these slow oplog entries are not affected by the slowOpSampleRate. MongoDB logs all slow oplog entries regardless of the sample rate.

      • In MongoDB 4.4 and later, these slow oplog entries are affected by the slowOpSampleRate.

    The profiler does not capture slow oplog entries.

  • systemLog.verbosity controls the amount of logging output that mongod write to the log. Only use this option if you are experiencing an issue that is not reflected in the normal logging level.

    Starting in MongoDB 3.0, you can also specify verbosity level for specific components using the systemLog.component.<name>.verbosity setting. For the available components, see component verbosity settings.

For more information, see also Database Profiling and MongoDB Performance.

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