Linux Server Hacks, Volume Two

Hack #81. Remotely Monitor and Configure a Variety of Networked Equipment

Using SNMP, you can collect information about almost any device attached to your network.

For everything that has a network interface, chances are there's some form of Simple Network Management Protocol (SNMP) daemon that can run on it. Over the years, SNMP daemons have been added to everything from environmental sensors to UPSs to soda vending machines. The point of all of this is to be able to remotely access as much information about the host as humanly possible. As an added bonus, proper configuration can allow administrators to change values on the host remotely as well.

SNMP daemon packages are available for all of the widely used distributions, along with possibly separate packages containing a suite of SNMP command-line tools. You might have come across the snmpwalk or snmpget commands before in your travels, or you might've seen similarly named functions in scripting languages such as Perl and PHP.

Let's have a look at a small bit of a "walk" on an SNMP-enabled Linux host and use it to explain how this works:

$ snmpwalk -v2c -c public livid interfaces IF-MIB::ifNumber.0 = INTEGER: 4 IF-MIB::ifIndex.1 = INTEGER: 1 IF-MIB::ifIndex.2 = INTEGER: 2 IF-MIB::ifIndex.3 = INTEGER: 3 IF-MIB::ifIndex.4 = INTEGER: 4 IF-MIB::ifDescr.1 = STRING: lo IF-MIB::ifDescr.2 = STRING: eth0 IF-MIB::ifDescr.3 = STRING: eth1 IF-MIB::ifDescr.4 = STRING: sit0 IF-MIB::ifType.1 = INTEGER: softwareLoopback(24) IF-MIB::ifType.2 = INTEGER: ...