Cannot perform operation: an index build is currently running for collection

Question: I'm trying to rename a MongoDB collection but getting the following warning : 

Cannot perform operation: an index build is currently running for collection

Answer: Use this command from to identify the operation 

db.adminCommand(
    {
      currentOp: true,
      $or: [
        { op: "command", "command.createIndexes": { $exists: true }  },
        { op: "none", "msg" : /^Index Build/ }
      ]
    }
)

You can also use the aggregate function

db.aggregate( [    { $currentOp : { allUsers: true, idleConnections: false } },    { $match : { client: "10.11.33.99", microsecs_running: {$gt: 10000} }}, {$project: { _id:0, host:1, opid:1, secs_running: 1, op:1, ns:1, waitingForLock: 1, numYields: 1  } } ] ).pretty()

db.aggregate( [    { $currentOp : { allUsers: true, idleConnections: false } },    { $match : { client: "10.11.33.99" }}, {$project: { _id:0, host:1, opid:1, secs_running: 1, op:1, ns:1, waitingForLock: 1, numYields: 1  } } ] ).pretty()

db.aggregate( [    { $currentOp : { allUsers: true, idleConnections: false } },   {$project: { _id:0, client:1,host:1, opid:1, secs_running: 1, op:1, ns:1, waitingForLock: 1, numYields: 1  } } ] ).pretty()

db.aggregate( [    { $currentOp : { allUsers: true, idleConnections: false } },   {$project: { _id:0, client:1,host:1, opid:1, secs_running: 1, op:1, ns:1, waitingForLock: 1, numYields: 1  } } ] ).pretty()

db.aggregate( [    { $currentOp : { allUsers: true, idleConnections: false } },  { $match : { ns: "mydb.mycollection"}}, {$project: { _id:0, client:1,host:1, command:1,opid:1, secs_running: 1, op:1, ns:1, waitingForLock: 1, numYields: 1  } } ] ).pretty()

Depending on the circumstances it may be necessary to kill the operatoiom

db.currentOp()

db.killOp(74747474)