• To set the memory online in RHEL and CentOS:

1. Look for memory that appears offline.
   
   Run this command to check the state of the memory:
   
   grep line /sys/devices/system/memory/*/state
    
2. When memory appears offline, run this command to set it to online:
   
   echo online >/sys/devices/system/memory/memory[number]/state
    

• To set the memory online in SLES OS:

1. 1. Run this command to load the acpiphp module for SLES to detect hot add devices:
      
      modprobe acpiphp
       
   2. Run this command to enable acpi_memhotplug within the SLES virtual machine:
      
      modprobe acpi_memhotplug
       
   3. Using vSphere Client edit the virtual machine settings to increase the memory assigned. For more information, see Increasing the amount of memory assigned to a virtual machine (1004059).
   4. Run this command to bring the memory online in /sys/devices/system/:
      
      echo online >/sys/devices/system/memory/memory[number]/state
       
   5. Run this command to check the state of the memory.
      
      Look for memory that appears offline:
      
      grep line /sys/devices/system/memory/*/state
       
   6. When memory appears offline, run this command to set it to online:
      
      echo online >/sys/devices/system/memory/memory[number]/state
       
   7. Verify you can see the extra memory by running this command:
      
      free -m