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Faacy Farook edited this page Jan 23, 2016 · 15 revisions

Frequently Asked Questions (FAQs) - Course 3 Module 1

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Q: The data directory not found or permission denied

A: Creating the data directory C:\data\db (windows) or /data/db (linux) In windows:

C:\>mkdir -p C:\data\db

In Linx or Mac, as root user:

$ mkdir -p /data/db
$ chown -R mongod:mongod /data/db

Otherwise:

$ sudo mkdir -p /data/db
$ sudo chown -R mongod:mongod /data/db

See also:

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Q: WARNING: soft rlimits too low. Number of files is 256, should be at least 1000

After installing and running the mongo server,

$ mongod

Then in a another terminal, when running the mongo client,

$ mongo

The following warnings are shown:

Server has startup warnings:

2016-01-19T20:59:55.320-0800 I CONTROL [initandlisten]

2016-01-19T20:59:55.320-0800 I CONTROL [initandlisten] ** WARNING: soft rlimits too low. Number of files is 256, should be at least 1000

What to do?

A: In Linux, set the resource limit just before starting mongod with this:

$ ulimit -n 1024
$ mongod

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Q: mongod waiting for connections on port 27017

After doing mongod it shows:

[initandlisten] waiting for connections on port 27017

In the video a connection was accepted, that line is missing on my computer. Is this a problem?

A: No, this is not a problem. That was probably because a client running was already running in the video.

When you start clean, mongod should just come and wait for connections. This is the MongoDB database server.

When you start mongo then you should see the connection accepted message since this is the client connecting to the database server.

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Q: Error connecting to db server: no reachable servers

This error shows up when try to run mongoimport:

mongoimport --db test --collection zips --drop --file zips.json

A: This happens if MongoDB Server (mongod) is not running. In a different terminal, go ahead and start mongod and then do an import.

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Q: NameError: uninitialized constant Mongo::Client

In irb,

rb(main):001:0> require 'mongo'
=> true
irb(main):002:0> db = Mongo::Client.new('mongodb://localhost:27017')
NameError: uninitialized constant Mongo::Client
    from (irb):2
    ...

A: This error is because the `mongo`` ruby driver was not loaded properly.

First in the command shell ensure that you have installed the ruby gems by running:

      C:\>gem install mongo
      C:\>gem install bson_ext

Now start irb and run the command:

C:\>irb

irb(main):001:0> require 'mongo'
=> true

irb(main):004:0> db = Mongo::Client.new('mongodb://localhost:27017')
D, [2016-01-23T09:33:16.963650 #4156] DEBUG -- : MONGODB | Adding localhost:27017 to the cluster.
=> #<Mongo::Client:0x24416640 cluster=localhost:27017>

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Q: Hash Rocket Notation vs. JSON Notation

Is there any particular reason for choosing to use the :symbol => "value"`` (Hash Rocket) notation or symbol: "value"` (JSON) notation?

A: The GitHub Ruby style guide suggests just to use the hash-rocket syntax for Hash literals and Rails style guide prefers JSON.

So it really comes down to your preference and in which side of the fence you are on.

See also:

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