Unable to start node manager because of java.io.IOException: Could not obtain exclusive lock with lockFile

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Applies to:
Weblogic Server: 12.2.1.1
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Problem Summary:
Unable to start node manager because of java.io.IOException: Could not obtain exclusive lock with lockFile.

Error Message:
Feb 11, 2017 12:38:05 PM weblogic.nodemanager.server.NMServer main
SEVERE: Fatal error in NodeManager server
java.io.IOException: Could not obtain exclusive lock with lockFile '/u01/domain/poc/osb/osb_poc_dit/nodemanager/nodemanager.process.lck'. This most likely indicates another NodeManager process is already running in this NodeManaagerHome.
        at weblogic.nodemanager.server.NMServer.getNMFileLock(NMServer.java:228)
        at weblogic.nodemanager.server.NMServer.<init>(NMServer.java:127)
        at weblogic.nodemanager.server.NMServer.main(NMServer.java:527)
        at weblogic.NodeManager.main(NodeManager.java:31)

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Root Cause:
Error clearly states that NodeManager process is already running in this NodeManaagerHome.

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How to verify:
Login to host and verify if node manager is running using below commands,
/usr/sbin/lsof -i:NM_PORT
OR
ps -ef | grep weblogic.NodeManager

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Resolution:
1. Node manager is already running. No action needed and it's expected behaviour.
Try to perform intended activities like server restart/shutdown/start using node manager.
2. If you would like to restart node manager then shutdown node manager first and restart.