Why can't I start mongodb server? - mongodb

Question

I try to start mongodb server, but it exists immediatly. Is it because it tried to use a port already in use? How shall I run it correctly? Thanks.
I am on Ubuntu 14.04, and installed mongodb following the guideline in mongodb website.
$ mongod
2016-08-04T11:06:39.947-0400 I CONTROL [initandlisten] MongoDB starting : pid=15947 port=27017 dbpath=/data/db 64-bit host=ocean
2016-08-04T11:06:39.947-0400 I CONTROL [initandlisten] db version v3.2.8
2016-08-04T11:06:39.951-0400 I CONTROL [initandlisten] git version: ed70e33130c977bda0024c125b56d159573dbaf0
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] OpenSSL version: OpenSSL 1.0.1f 6 Jan 2014
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] allocator: tcmalloc
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] modules: none
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] build environment:
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] distmod: ubuntu1404
2016-08-04T11:06:39.952-0400 I CONTROL [initandlisten] distarch: x86_64
2016-08-04T11:06:39.953-0400 I CONTROL [initandlisten] target_arch: x86_64
2016-08-04T11:06:39.953-0400 I CONTROL [initandlisten] options: {}
2016-08-04T11:06:40.015-0400 E NETWORK [initandlisten] listen(): bind() failed errno:98 Address already in use for socket: 0.0.0.0:27017
2016-08-04T11:06:40.016-0400 E NETWORK [initandlisten] addr already in use
2016-08-04T11:06:40.016-0400 E STORAGE [initandlisten] Failed to set up sockets during startup.
2016-08-04T11:06:40.016-0400 I CONTROL [initandlisten] dbexit: rc: 48

Answer 1

It tells you that Address already in use for socket: 0.0.0.0:27017.
Try on another port with mongod --port 27018.
To kill process that uses port 27017 on ubuntu you can use lsof -i :27017 to find PID of that process and then kill -9 <PID>.

Answer 2

The error is shown pretty clearly here:
listen(): bind() failed errno:98 Address already in use for socket: 0.0.0.0:27017
This is saying that the socket is already bound by something else - that is, there is another service already running on port 27017; most likely, an instance of your mongo server already ( only one process can bind to a port at a time )
Use this
ps aux | grep mongod
To find any mongod processes that are already running. Use kill <pid> to end the process.
If you want to start a second instance of mongo, then you need to have it bind to a new port, you can do this using
mongod --port 27015
Note, that if you start a second instance, you will also need to provide a second data directory - you should not have two running instances using the same database files.