Ubuntu – Can’t start MongoDB, mongod is always stop/waiting

I try to run MongoDB 3.2.4 on Ubuntu 14.04:

sudo service mongod start

And get the result:

mongod start/running, process 67725

But when I check the status I get:

mongod stop/waiting

I tried to reinstall MongoDB or to define the permissions for Mongo's folders (lib & log) as root or as mongodb. I also tried to repair the mongod.conf but nothing helps.

The content of log:

2016-04-09T23:56:28.349+0300 I CONTROL  [main] ***** SERVER RESTARTED *****
2016-04-09T23:56:28.359+0300 I CONTROL  [initandlisten] MongoDB starting : pid=69120 port=27017 dbpath=/var/lib/mongodb 64-bit host=is-infomedia
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] db version v3.2.4
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] git version: e2ee9ffcf9f5a94fad76802e28cc978718bb7a30
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] OpenSSL version: OpenSSL 1.0.1f 6 Jan 2014
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] allocator: tcmalloc
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] modules: none
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] build environment:
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten]     distmod: ubuntu1404
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten]     distarch: x86_64
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten]     target_arch: x86_64
2016-04-09T23:56:28.360+0300 I CONTROL  [initandlisten] options: { config: "/etc/mongod.conf", net: { bindIp: "127.0.0.1", port: 27017 }, storage: { dbPath: "/var/lib/mongodb", journal: { enabled: true } }, systemLog: { destination: "file", logAppend: true, path: "/var/log/mongodb/mongod.log" } }
2016-04-09T23:56:28.393+0300 E NETWORK  [initandlisten] Failed to unlink socket file /tmp/mongodb-27017.sock errno:1 Operation not permitted
2016-04-09T23:56:28.393+0300 I -        [initandlisten] Fatal Assertion 28578
2016-04-09T23:56:28.393+0300 I -        [initandlisten] 

***aborting after fassert() failure

Update:

After editing of /etc/mongod.conf:

#security:
authorization: enabled
enableEncryption: true
javascriptEnabled: false

and saving the file, and try to restart the mongod, I get the same error but MongoDB doesn't write any log file. I checked the permissions of /etc/mongod.conf, it is assigned to mongodb group. How can I restart mongod after editing its config file?

My questions:

1. How can I run MongoDB as a service in Ubuntu?
2. What I miss or do wrong?