[oracle@oratest1 bin]$ ./emctl start oms
Oracle Enterprise Manager Cloud Control 12c Release 3 
Copyright (c) 1996, 2013 Oracle Corporation.  All rights reserved.
Starting Oracle Management Server...
Starting WebTier...
WebTier Successfully Started
Oracle Management Server Could Not Be Started
Check EM Server log file for details: /oracle/oemcc/gc_inst/user_projects/domains/GCDomain/servers/EMGC_OMS1/logs/EMGC_OMS1.out
Oracle Management Server is Down
WARNING: Limit of open file descriptors is found to be 1024.
For proper functioning of OMS, please set "ulimit -n" to be at least 4096.
[oracle@oratest1 bin]$ ./emctl stop oms -all -force
Oracle Enterprise Manager Cloud Control 12c Release 3 
Copyright (c) 1996, 2013 Oracle Corporation.  All rights reserved.
Stopping WebTier...
WebTier Successfully Stopped
Stopping Oracle Management Server...
Oracle Management Server Already Stopped
AdminServer Successfully Stopped
Oracle Management Server is Down
[oracle@oratest1 bin]$ ulimit -n 4096
[oracle@oratest1 bin]$ ./emctl start oms
Oracle Enterprise Manager Cloud Control 12c Release 3 
Copyright (c) 1996, 2013 Oracle Corporation.  All rights reserved.
Starting Oracle Management Server...
[oracle@oratest1 bin]$ ./emctl start oms
Oracle Enterprise Manager Cloud Control 12c Release 3 
Copyright (c) 1996, 2013 Oracle Corporation.  All rights reserved.
Starting Oracle Management Server...

Starting WebTier...
WebTier Successfully Started
Oracle Management Server Successfully Started
Oracle Management Server is Up
[oracle@oratest1 bin]$
[oracle@oratest1 bin]$
[oracle@oratest1 bin]$
[oracle@oratest1 bin]$
[oracle@oratest1 bin]$
[oracle@oratest1 bin]$ ./emctl  status oms
Oracle Enterprise Manager Cloud Control 12c Release 3 
Copyright (c) 1996, 2013 Oracle Corporation.  All rights reserved.
WebTier is Up
Oracle Management Server is Up