Frequently the Mongodb cluster server stopped without any instruction. I was referred the mongodb log file,

#  tail -f /var/log/mongodb/mongod.log


2015-12-02T07:10:24.466-0500 I JOURNAL  [journal writer] Journal writer thread stopped

2015-12-02T07:10:24.466-0500 I JOURNAL  [durability] Durability thread stopped

2015-12-02T07:10:24.467-0500 I STORAGE  [signalProcessingThread] shutdown: closing all files...

2015-12-02T07:10:24.472-0500 I STORAGE  [signalProcessingThread] closeAllFiles() finished

2015-12-02T07:10:24.472-0500 I STORAGE  [signalProcessingThread] shutdown: removing fs lock...

2015-12-02T07:10:24.472-0500 I CONTROL  [signalProcessingThread] dbexit:  rc: 0


Finally got the simple solutions mongodb forums, 

You can start the mongodb service with --fork option, fork for running in background.
 
# mongod --config /etc/mongod.conf --replSet rs1 --fork

Another ways is you can set  replSet and fork in configure file 
 
# vim /etc/mongod.conf 



# Replication

replication:

   replSetName: rs0



#fork

processManagement:

fork: true


Now start the mongod,
 
# mongod --config /etc/mongod.conf

To check the process status,
 
# ps aux | grep mongod



root      7530  0.0  0.0  11740   936 pts/0    S+   09:07   0:00 grep --color=auto mongod

root     19540  0.6 11.7 5405856 119856 ?      Sl    2015 312:22 mongod --config /etc/mongod.conf