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Most system performance data is available in the `UCD SNMP MIB`. The `systemStats` OID provides a number of counters around processor usage:
~]$ [command]#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 [command]#free# command:
~]$ [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:
~]$ [command]#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
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:
~]$ [command]#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:
~]$ [command]#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
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:
~]$ [command]#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:
~]$ [command]#snmpwalk localhost IF-MIB::ifDescr#
IF-MIB::ifDescr.1 = STRING: lo
IF-MIB::ifDescr.2 = STRING: eth0
IF-MIB::ifDescr.3 = STRING: eth1
~]$ [command]#snmpwalk localhost IF-MIB::ifOutOctets#
IF-MIB::ifOutOctets.1 = Counter32: 10060699
IF-MIB::ifOutOctets.2 = Counter32: 650
IF-MIB::ifOutOctets.3 = Counter32: 0
~]$ [command]#snmpwalk localhost IF-MIB::ifInOctets#
IF-MIB::ifInOctets.1 = Counter32: 10060699
IF-MIB::ifInOctets.2 = Counter32: 78650
IF-MIB::ifInOctets.3 = Counter32: 0
Extending Net-SNMP
The Net-SNMP Agent can be extended to provide application metrics in addition to raw system metrics. This allows for capacity planning as well as performance issue troubleshooting. For example, it may be helpful to know that an email system had a 5-minute load average of 15 while being tested, but it is more helpful to know that the email system has a load average of 15 while processing 80,000 messages a second. When application metrics are available via the same interface as the system metrics, this also allows for the visualization of the impact of different load scenarios on system performance (for example, each additional 10,000 messages increases the load average linearly until 100,000).
A number of the applications that ship with {MAJOROS} extend the Net-SNMP Agent to provide application metrics over SNMP. There are several ways to extend the agent for custom applications as well. This section describes extending the agent with shell scripts and Perl plug-ins. It assumes that the [package]*net-snmp-utils* and [package]*net-snmp-perl* packages are installed, and that the user is granted access to the SNMP tree as described in xref:System_Monitoring_Tools.adoc#sect-System_Monitoring_Tools-Net-SNMP-Configuring-Authentication[Configuring Authentication].
Extending Net-SNMP with Shell Scripts
The Net-SNMP Agent provides an extension MIB (`NET-SNMP-EXTEND-MIB`) that can be used to query arbitrary shell scripts. To specify the shell script to run, use the [option]`extend` directive in the `/etc/snmp/snmpd.conf` file. Once defined, the Agent will provide the exit code and any output of the command over SNMP. The example below demonstrates this mechanism with a script which determines the number of `httpd` processes in the process table.
Using the proc directive
The Net-SNMP Agent also provides a built-in mechanism for checking the process table via the [option]`proc` directive. See the *snmpd.conf*(5) manual page for more information.
The exit code of the following shell script is the number of [command]#httpd# processes running on the system at a given point in time:
#!/bin/sh

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  1. fedora-docs-l10n/fedora-system-administrat
  2. f28/pages/monitoring-and-automation/System_Monitoring_Tools
  3. English
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
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
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Source string description
type: delimited block -
Flags
no-wrap, read-only
Source string location
./pages/monitoring-and-automation/System_Monitoring_Tools.adoc:1186
String age
a year ago
Last updated
10 months ago
Source string age
a year ago
Translation file
pot/f28/pages/monitoring-and-automation/System_Monitoring_Tools.pot, string 275