Couldn't connect to server 127.0.0.1:27017 connection attempt failed MongoDB

mongod --repair worked for me ,

sudo mongod --repair
sudo mongod

Then open a different tab/terminal:

mongo

After this your local setup will work properly

This worked for me (MAC):

Step 1 : Check the status if MongoDB is running or not

brew services list | grep mongo

Step 2 : if you get something like :

Name           Status  User    Plist
mongodb        stopped

Step 3: : start the service:

brew services start mongodb 

else :

if you get like this after step 2:

Name           Status  User    Plist
mongodb        started u1 /Users/u1/Library/LaunchAgents/homebrew.mxcl.mongodb.plist

then it is already running then you can restart your service by

brew services restart mongodb

This error occurs when your mongodb server is not running on 27017 port. Try the below command to start the mongodb server.

sudo systemctl start mongod

And after running this command run the mongo command.