How to Monitor Swap Space with net-snmp

Procedure

  1. Determine how much total swap space is available on your server (any of these methods will work):
    • RHEL: 
      
% free
             total       used       free     shared    buffers     cached
Mem:       1922236    1798148     124088          0     220632    1184504
-/+ buffers/cache:     393012    1529224
Swap:     16383992          0   16383992


      
% cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/sda3                               partition       16383992        0       -1


      
% snmpwalk -c public -v2c highgate HOST-RESOURCES-MIB::hrStorageDescr
HOST-RESOURCES-MIB::hrStorageDescr.1 = STRING: Physical memory
HOST-RESOURCES-MIB::hrStorageDescr.3 = STRING: Virtual memory
HOST-RESOURCES-MIB::hrStorageDescr.6 = STRING: Memory buffers
HOST-RESOURCES-MIB::hrStorageDescr.7 = STRING: Cached memory
HOST-RESOURCES-MIB::hrStorageDescr.10 = STRING: Swap space
HOST-RESOURCES-MIB::hrStorageDescr.31 = STRING: /
HOST-RESOURCES-MIB::hrStorageDescr.35 = STRING: /dev/shm
HOST-RESOURCES-MIB::hrStorageDescr.36 = STRING: /boot
HOST-RESOURCES-MIB::hrStorageDescr.37 = STRING: /opt
HOST-RESOURCES-MIB::hrStorageDescr.38 = STRING: /tmp
HOST-RESOURCES-MIB::hrStorageDescr.39 = STRING: /usr
HOST-RESOURCES-MIB::hrStorageDescr.40 = STRING: /var
HOST-RESOURCES-MIB::hrStorageDescr.42 = STRING: /var/tmp

% snmpwalk -c public -v2c highgate HOST-RESOURCES-MIB::hrStorageSize.10
HOST-RESOURCES-MIB::hrStorageSize.10 = INTEGER: 16383992
  2. net-snmp requires us to configure the minimum amount of swap space that needs to be available (below which it sends a trap): 
    
swap MIN
    monitors the amount of swap space available on the local system. If this falls
below the specified threshold (MIN kB), then the memErrorSwap object will be set to 1,
and a suitable description message reported via memSwapErrorMsg.

        Note:
            This situation will not automatically trigger a trap to report the problem
- see the DisMan Event MIB section later. 

    If this directive is not specified, the default threshold is 16 MB.

    As a local rule of thumb, assume we want an alert if < 15% of swap space is free: 

    
16383992 bytes * 15% threshold factor = 2457599 bytes
2457599 bytes * 1 kB/1000 bytes = 2458 kB
  3. Add a swap entry to snmpd.conf: 
    
swap 2458
  4. Restart snmpd: 
    
% sudo /etc/init.d/snmpd restart
Stopping snmpd:                                            [  OK  ]
Starting snmpd:                                            [  OK  ]
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