how to change sysman and dbsnmp password for Oracle 11g under Linux

• emctl stop dbconsole
• emctl status dbconsole and emctl status agent to make sure it's stopped
• ORACLE_SID=orcl
• sqlplus / as sysdba
• alter user sysman identified by sysman (change new password to 'sysman')
• conn sysman/sysman
• alter user sysman account unlock (if above command shows 'locked')
• cd $ORACLE_HOME/hostname_sid/sysman/config
• vi emoms.properties
• change orcle.sysman.eml.mntr.emdRepPwd=newplaintextpassword
• change orcle.sysman.eml.mntr.emdRepPwdEncrypted=FALSE (from true to false)
• emctl start dbconsole
  
• now the plain text password will be encrypted, and false will become true

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for dbsnmp password change, same thing except for the below.

• modify the file targets.xml under sysman/emd folder
  

  Just like before, change encryptedpassword to new plaintext password and change TRUE to FALSE.