Complete Guide to Listing All Databases in MongoDB Shell

Overview of MongoDB Database Listing Methods

In MongoDB database management, viewing all databases present in the current instance is a fundamental yet crucial operation. Unlike relational databases, MongoDB provides specialized built-in commands to accomplish this task.

Basic Command: show dbs

In the MongoDB Shell environment, the most straightforward way to list all databases is using the show dbs command. This command returns a list of all non-empty databases in the current MongoDB instance, along with the disk space occupied by each database.

> show dbs
admin   0.000GB
config  0.000GB
local   0.000GB
test    0.000GB

It's important to note that the show databases command is functionally identical to show dbs, and both can be used interchangeably. This design considers different user preferences and provides better user experience.

Alternative Command: show databases

Besides show dbs, MongoDB also provides the more semantically explicit show databases command. These two commands are functionally equivalent and produce identical output results.

> show databases
admin   0.000GB
config  0.000GB
local   0.000GB
test    0.000GB

This command alias design reflects MongoDB's emphasis on user-friendliness, allowing users to choose command syntax that feels more natural based on their preferences.

Programming Interface: listDatabases Command

For scenarios requiring database list retrieval in scripts or applications, MongoDB provides the more powerful listDatabases database command. This command is invoked through JavaScript API and offers richer output information and more flexible query options.

Basic Usage

To use the listDatabases command, it must be executed in the admin database context:

> db.adminCommand({ listDatabases: 1 })
{
  "databases": [
    { "name": "admin", "sizeOnDisk": 83886080, "empty": false },
    { "name": "local", "sizeOnDisk": 83886080, "empty": false },
    { "name": "test", "sizeOnDisk": 83886080, "empty": false }
  ],
  "totalSize": 251658240,
  "totalSizeMb": 251,
  "ok": 1
}

Database Names Only

If only database names are needed without size information, use the nameOnly parameter:

> db.adminCommand({ listDatabases: 1, nameOnly: true })
{
  "databases": [
    { "name": "admin" },
    { "name": "local" },
    { "name": "test" }
  ],
  "ok": 1
}

Permission Control and Security Considerations

In environments with authentication enabled, the behavior of the listDatabases command varies based on user privileges:

• If the user has listDatabases action permission on cluster resources, the command returns all databases
• If the user lacks this permission, the command returns only databases for which the user has access privileges
• The authorizedDatabases option provides additional control over the scope of returned results

Advanced Filtering Capabilities

The listDatabases command supports using filters to screen returned databases. For example, returning only databases whose names start with a specific prefix:

> db.adminCommand({ 
    listDatabases: 1, 
    filter: { "name": /^test/ } 
  })
{
  "databases": [
    { "name": "test", "sizeOnDisk": 83886080, "empty": false }
  ],
  "totalSize": 83886080,
  "totalSizeMb": 80,
  "ok": 1
}

Special Handling in Sharded Cluster Environments

When executing the listDatabases command in sharded cluster environments, the output includes additional sharding information:

• When nameOnly is false, each database's summary document includes an embedded shards document
• The shards document displays size information of collections on various shards
• The local database is excluded from output in sharded clusters

Command Selection Recommendations

Based on different usage scenarios, appropriate command selection is recommended:

• Interactive Queries: Use show dbs or show databases for simplicity and intuitiveness
• Script Programming: Use listDatabases command for easier result processing and automation
• Filtering or Custom Output Needs: Use listDatabases with appropriate parameters
• Permission-Restricted Environments: Use listDatabases to ensure only accessible databases are returned

Error Handling and Important Notes

When executing database listing queries, the following considerations are important:

• In replica set environments, commands can only be executed on PRIMARY or SECONDARY state members
• If client disconnects during execution, the operation is marked for termination
• Ensure sufficient permissions to execute corresponding commands
• Note the empty field in output, which identifies whether databases are empty

Conclusion

MongoDB provides multiple flexible ways to list databases, ranging from simple show dbs to feature-rich listDatabases command, meeting requirements across different scenarios. Understanding the characteristics and applicable scenarios of these commands helps developers perform database management and monitoring more efficiently.