SNMP Subagent

Preparation

Firstly, be sure your have downloaded several libraries:

• libsnmp-base
• libsnmp-dev
• libsnmp40

and SNMP tools itself with daemon:

• snmp
• snmpd

Secondly, for this example to work, you should edit your snmpd.conf file, which default location is /etc/snmp/snmpd.conf. Minimum setup is persented below:

sysServices    72

# using AgentX
master  agentx
agentXSocket /var/agentx/master

# address to call for master agent
agentaddress  udp:localhost:8888

# access control setup
view   systemonly  included   .1.3.6.1.2.1.1
view   systemonly  included   .1.3.6.1.2.1.25.4.2  # hrSWRunTable
view   systemonly  included   .1.3.6.1.2.1.25.5.1  # hrSWRunPerfTable

# setup read-only SNMPv2 community string access
rocommunity  public default -V systemonly

# include other .conf files
includeDir /etc/snmp/snmpd.conf.d

As this example overrides default internal tables hrSWRunTable and hrSWRunPerfTable, you should disable them on daemon start. This should be done in daemon init settings, defaultly settled in directory /lib/systemd/system/snmpd.service (for Debian).

You need to modify ExecStart line like

...
ExecStart=/usr/sbin/snmpd -LOw -u Debian-snmp -g Debian-snmp -I -{EXCLUDED_MODULES} -f -M {MIB_FILE_DIRECTORIES} -m {IMPORTED_MIB_FILES}
...

where

• {EXCLUDED_MODULES} - comma-separated excluded modules, in our case - internal tables hrSWRunTable and hrSWRunPerfTable
• {MIB_FILE_DIRECTORIES} - colon-separated directories, where the MIB files are located (in this projects is {SOURCE_DIR}/mibs)
• {IMPORTED_MIB_FILES} - colon-separed imported MIB file names without .txt extensions or ALL

Example (in this project):

...
ExecStart=/usr/sbin/snmpd -LOw -u Debian-snmp -g Debian-snmp -I -smux,hrSWRunTable,hrSWRunPerfTable -f -M /home/user/snmp_test/mibs -m ALL
...

After this, daemon should be reloaded

systemctl daemon-reload
systemctl restart snmpd

Build

To build this masterpiece you can type

make all

There are several targets:

• load/apt - this target installs required packages using APT
• configure - this target call configure.sh script
• build - this target creates CMake directory with Unix Makefiles
• install - this target moves program to ./out/ folder
• test - some snmpget, snmpwalk and snmptable testing

Running

Running a program is simple. Considering that you passed the install target:

out/snmp_test

sudo is also can be important, if your agentx socket is owned by root.

If you want to include MIB-files, override some environment variables as follows:

export MIBDIRS=$(pwd)/mibs
export MIBS=ALL

To perform some testing you should run target test.

make test