Solr getting stopped abruptly - solr

Question

I am using Solr-4.3.1 on Ubuntu machine and it is running on default jetty server. Recently, I have observed that it gets shut down abruptly. I cant find any exception or error or warning message in the logs. Following are the logs:
org.eclipse.jetty.server.Server; Graceful shutdown
SocketConnector#0.0.0.0:8983
INFO - 2013-10-16 15:05:15.091; org.eclipse.jetty.server.Server;
Graceful shutdown
o.e.j.w.WebAppContext{/solr,file:/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr-webapp/webapp/},/home/abhijeet/project/demo/Demo/solr-4.3.1/example/webapps/solr.war
INFO - 2013-10-16 15:05:16.093; org.apache.solr.core.CoreContainer;
Shutting down CoreContainer instance=2137222734
INFO - 2013-10-16 15:05:16.236; org.apache.solr.core.SolrCore;
[collection1] CLOSING SolrCore org.apache.solr.core.SolrCore#9f07597
INFO - 2013-10-16 15:05:16.244;
org.apache.solr.update.DirectUpdateHandler2; closing
DirectUpdateHandler2{commits=9,autocommit
maxTime=15000ms,autocommits=0,soft
autocommits=0,optimizes=1,rollbacks=0,expungeDeletes=0,docsPending=0,adds=0,deletesById=0,deletesByQuery=0,errors=0,cumulative_adds=0,cumulative_deletesById=0,cumulative_deletesByQuery=0,cumulative_errors=0}
INFO - 2013-10-16 15:05:16.245; org.apache.solr.update.SolrCoreState;
Closing SolrCoreState
INFO - 2013-10-16 15:05:16.246;
org.apache.solr.update.DefaultSolrCoreState; SolrCoreState ref count
has reached 0 - closing IndexWriter
INFO - 2013-10-16 15:05:16.246;
org.apache.solr.update.DefaultSolrCoreState; closing IndexWriter with
IndexWriterCloser
INFO - 2013-10-16 15:05:16.330; org.apache.solr.core.SolrCore;
[collection1] Closing main searcher on request.
INFO - 2013-10-16 15:05:16.332;
org.apache.solr.core.CachingDirectoryFactory; Closing
NRTCachingDirectoryFactory - 2 directories currently being tracked
INFO - 2013-10-16 15:05:16.352;
org.apache.solr.core.CachingDirectoryFactory; looking to close
/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr/collection1/data
[CachedDir<>]
INFO - 2013-10-16 15:05:16.352;
org.apache.solr.core.CachingDirectoryFactory; Closing directory:
/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr/collection1/data
INFO - 2013-10-16 15:05:16.352;
org.apache.solr.core.CachingDirectoryFactory; looking to close
/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr/collection1/data/index
[CachedDir<>]
INFO - 2013-10-16 15:05:16.353;
org.apache.solr.core.CachingDirectoryFactory; Closing directory:
/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr/collection1/data/index
INFO - 2013-10-16 15:05:16.354;
org.eclipse.jetty.server.handler.ContextHandler; stopped
o.e.j.w.WebAppContext{/solr,file:/home/abhijeet/project/demo/Demo/solr-4.3.1/example/solr-webapp/webapp/},/home/abhijeet/project/demo/Demo/solr-4.3.1/example/webapps/solr.war
INFO - 2013-10-16 15:05:16.588;
org.eclipse.jetty.util.thread.ShutdownThread; shutdown already
commenced