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17.6.4. Retrieving Performance Data over SNMP

The Net-SNMP Agent in Fedora provides a wide variety of performance information over the SNMP protocol. In addition, the agent can be queried for a listing of the installed RPM packages on the system, a listing of currently running processes on the system, or the network configuration of the system.
This section provides an overview of OIDs related to performance tuning available over SNMP. It assumes that the net-snmp-utils package is installed and that the user is granted access to the SNMP tree as described in Section 17.6.3.2, “Configuring Authentication”.

17.6.4.1. Hardware Configuration

The Host Resources MIB included with Net-SNMP presents information about the current hardware and software configuration of a host to a client utility. Table 17.3, “Available OIDs” summarizes the different OIDs available under that MIB.
Table 17.3. Available OIDs
OID Description
HOST-RESOURCES-MIB::hrSystem Contains general system information such as uptime, number of users, and number of running processes.
HOST-RESOURCES-MIB::hrStorage Contains data on memory and file system usage.
HOST-RESOURCES-MIB::hrDevices Contains a listing of all processors, network devices, and file systems.
HOST-RESOURCES-MIB::hrSWRun Contains a listing of all running processes.
HOST-RESOURCES-MIB::hrSWRunPerf Contains memory and CPU statistics on the process table from HOST-RESOURCES-MIB::hrSWRun.
HOST-RESOURCES-MIB::hrSWInstalled Contains a listing of the RPM database.

There are also a number of SNMP tables available in the Host Resources MIB which can be used to retrieve a summary of the available information. The following example displays HOST-RESOURCES-MIB::hrFSTable:
~]$ snmptable -Cb localhost HOST-RESOURCES-MIB::hrFSTable
SNMP table: HOST-RESOURCES-MIB::hrFSTable

 Index MountPoint RemoteMountPoint                                Type
    Access Bootable StorageIndex LastFullBackupDate LastPartialBackupDate
     1        "/"               "" HOST-RESOURCES-TYPES::hrFSLinuxExt2
 readWrite     true           31      0-1-1,0:0:0.0         0-1-1,0:0:0.0
     5 "/dev/shm"               ""     HOST-RESOURCES-TYPES::hrFSOther
 readWrite    false           35      0-1-1,0:0:0.0         0-1-1,0:0:0.0
     6    "/boot"               "" HOST-RESOURCES-TYPES::hrFSLinuxExt2
 readWrite    false           36      0-1-1,0:0:0.0         0-1-1,0:0:0.0
For more information about HOST-RESOURCES-MIB, see the /usr/share/snmp/mibs/HOST-RESOURCES-MIB.txt file.

17.6.4.2. CPU and Memory Information

Most system performance data is available in the UCD SNMP MIB. The systemStats OID provides a number of counters around processor usage:
~]$ snmpwalk localhost UCD-SNMP-MIB::systemStats
UCD-SNMP-MIB::ssIndex.0 = INTEGER: 1
UCD-SNMP-MIB::ssErrorName.0 = STRING: systemStats
UCD-SNMP-MIB::ssSwapIn.0 = INTEGER: 0 kB
UCD-SNMP-MIB::ssSwapOut.0 = INTEGER: 0 kB
UCD-SNMP-MIB::ssIOSent.0 = INTEGER: 0 blocks/s
UCD-SNMP-MIB::ssIOReceive.0 = INTEGER: 0 blocks/s
UCD-SNMP-MIB::ssSysInterrupts.0 = INTEGER: 29 interrupts/s
UCD-SNMP-MIB::ssSysContext.0 = INTEGER: 18 switches/s
UCD-SNMP-MIB::ssCpuUser.0 = INTEGER: 0
UCD-SNMP-MIB::ssCpuSystem.0 = INTEGER: 0
UCD-SNMP-MIB::ssCpuIdle.0 = INTEGER: 99
UCD-SNMP-MIB::ssCpuRawUser.0 = Counter32: 2278
UCD-SNMP-MIB::ssCpuRawNice.0 = Counter32: 1395
UCD-SNMP-MIB::ssCpuRawSystem.0 = Counter32: 6826
UCD-SNMP-MIB::ssCpuRawIdle.0 = Counter32: 3383736
UCD-SNMP-MIB::ssCpuRawWait.0 = Counter32: 7629
UCD-SNMP-MIB::ssCpuRawKernel.0 = Counter32: 0
UCD-SNMP-MIB::ssCpuRawInterrupt.0 = Counter32: 434
UCD-SNMP-MIB::ssIORawSent.0 = Counter32: 266770
UCD-SNMP-MIB::ssIORawReceived.0 = Counter32: 427302
UCD-SNMP-MIB::ssRawInterrupts.0 = Counter32: 743442
UCD-SNMP-MIB::ssRawContexts.0 = Counter32: 718557
UCD-SNMP-MIB::ssCpuRawSoftIRQ.0 = Counter32: 128
UCD-SNMP-MIB::ssRawSwapIn.0 = Counter32: 0
UCD-SNMP-MIB::ssRawSwapOut.0 = Counter32: 0
In particular, the ssCpuRawUser, ssCpuRawSystem, ssCpuRawWait, and ssCpuRawIdle OIDs provide counters which are helpful when determining whether a system is spending most of its processor time in kernel space, user space, or I/O. ssRawSwapIn and ssRawSwapOut can be helpful when determining whether a system is suffering from memory exhaustion.
More memory information is available under the UCD-SNMP-MIB::memory OID, which provides similar data to the free command:
~]$ snmpwalk localhost UCD-SNMP-MIB::memory
UCD-SNMP-MIB::memIndex.0 = INTEGER: 0
UCD-SNMP-MIB::memErrorName.0 = STRING: swap
UCD-SNMP-MIB::memTotalSwap.0 = INTEGER: 1023992 kB
UCD-SNMP-MIB::memAvailSwap.0 = INTEGER: 1023992 kB
UCD-SNMP-MIB::memTotalReal.0 = INTEGER: 1021588 kB
UCD-SNMP-MIB::memAvailReal.0 = INTEGER: 634260 kB
UCD-SNMP-MIB::memTotalFree.0 = INTEGER: 1658252 kB
UCD-SNMP-MIB::memMinimumSwap.0 = INTEGER: 16000 kB
UCD-SNMP-MIB::memBuffer.0 = INTEGER: 30760 kB
UCD-SNMP-MIB::memCached.0 = INTEGER: 216200 kB
UCD-SNMP-MIB::memSwapError.0 = INTEGER: noError(0)
UCD-SNMP-MIB::memSwapErrorMsg.0 = STRING:
Load averages are also available in the UCD SNMP MIB. The SNMP table UCD-SNMP-MIB::laTable has a listing of the 1, 5, and 15 minute load averages:
~]$ snmptable localhost UCD-SNMP-MIB::laTable
SNMP table: UCD-SNMP-MIB::laTable

 laIndex laNames laLoad laConfig laLoadInt laLoadFloat laErrorFlag laErrMessage
       1  Load-1   0.00    12.00         0    0.000000     noError
       2  Load-5   0.00    12.00         0    0.000000     noError
       3 Load-15   0.00    12.00         0    0.000000     noError

17.6.4.3. File System and Disk Information

The Host Resources MIB provides information on file system size and usage. Each file system (and also each memory pool) has an entry in the HOST-RESOURCES-MIB::hrStorageTable table:
~]$ snmptable -Cb localhost HOST-RESOURCES-MIB::hrStorageTable
SNMP table: HOST-RESOURCES-MIB::hrStorageTable

 Index                                         Type           Descr
AllocationUnits    Size   Used AllocationFailures
     1           HOST-RESOURCES-TYPES::hrStorageRam Physical memory
1024 Bytes 1021588 388064                  ?
     3 HOST-RESOURCES-TYPES::hrStorageVirtualMemory  Virtual memory
1024 Bytes 2045580 388064                  ?
     6         HOST-RESOURCES-TYPES::hrStorageOther  Memory buffers
1024 Bytes 1021588  31048                  ?
     7         HOST-RESOURCES-TYPES::hrStorageOther   Cached memory
1024 Bytes  216604 216604                  ?
    10 HOST-RESOURCES-TYPES::hrStorageVirtualMemory      Swap space
1024 Bytes 1023992      0                  ?
    31     HOST-RESOURCES-TYPES::hrStorageFixedDisk               /
4096 Bytes 2277614 250391                  ?
    35     HOST-RESOURCES-TYPES::hrStorageFixedDisk        /dev/shm
4096 Bytes  127698      0                  ?
    36     HOST-RESOURCES-TYPES::hrStorageFixedDisk           /boot
1024 Bytes  198337  26694                  ?
The OIDs under HOST-RESOURCES-MIB::hrStorageSize and HOST-RESOURCES-MIB::hrStorageUsed can be used to calculate the remaining capacity of each mounted file system.
I/O data is available both in UCD-SNMP-MIB::systemStats (ssIORawSent.0 and ssIORawRecieved.0) and in UCD-DISKIO-MIB::diskIOTable. The latter provides much more granular data. Under this table are OIDs for diskIONReadX and diskIONWrittenX, which provide counters for the number of bytes read from and written to the block device in question since the system boot:
~]$ snmptable -Cb localhost UCD-DISKIO-MIB::diskIOTable
SNMP table: UCD-DISKIO-MIB::diskIOTable

 Index Device     NRead  NWritten Reads Writes LA1 LA5 LA15    NReadX NWrittenX
...
    25    sda 216886272 139109376 16409   4894   ?   ?    ? 216886272 139109376
    26   sda1   2455552      5120   613      2   ?   ?    ?   2455552      5120
    27   sda2   1486848         0   332      0   ?   ?    ?   1486848         0
    28   sda3 212321280 139104256 15312   4871   ?   ?    ? 212321280 139104256

17.6.4.4. Network Information

Information on network devices is provided by the Interfaces MIB. IF-MIB::ifTable provides an SNMP table with an entry for each interface on the system, the configuration of the interface, and various packet counters for the interface. The following example shows the first few columns of ifTable on a system with two physical network interfaces:
~]$ snmptable -Cb localhost IF-MIB::ifTable
SNMP table: IF-MIB::ifTable

 Index Descr             Type   Mtu    Speed      PhysAddress AdminStatus
     1    lo softwareLoopback 16436 10000000                           up
     2  eth0   ethernetCsmacd  1500        0 52:54:0:c7:69:58          up
     3  eth1   ethernetCsmacd  1500        0 52:54:0:a7:a3:24        down
Network traffic is available under the OIDs IF-MIB::ifOutOctets and IF-MIB::ifInOctets. The following SNMP queries will retrieve network traffic for each of the interfaces on this system:
~]$ snmpwalk localhost IF-MIB::ifDescr
IF-MIB::ifDescr.1 = STRING: lo
IF-MIB::ifDescr.2 = STRING: eth0
IF-MIB::ifDescr.3 = STRING: eth1
~]$ snmpwalk localhost IF-MIB::ifOutOctets
IF-MIB::ifOutOctets.1 = Counter32: 10060699
IF-MIB::ifOutOctets.2 = Counter32: 650
IF-MIB::ifOutOctets.3 = Counter32: 0
~]$ snmpwalk localhost IF-MIB::ifInOctets
IF-MIB::ifInOctets.1 = Counter32: 10060699
IF-MIB::ifInOctets.2 = Counter32: 78650
IF-MIB::ifInOctets.3 = Counter32: 0