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C.2. Common Command-Line Arguments

For the most part, the Net-SNMP commands follow a similar command structure; they share many options and use roughly the same syntax. For example, in the abstract, an snmpget command looks like this:

snmpget options hostname community objectID...
In other words, the command name is followed by a series of options, the hostname of the system you want to poll, the community string, and one or more object IDs. (Note that you can use the -c community option instead of placing the community string after the hostname. You can also provide a default hostname in your snmp.conf file.) The syntax of snmpset is only slightly different; because snmpset changes object values, it requires you to specify the object's datatype and the new value:

snmpset options hostname community objectID type value...
Table C-1 summarizes some of the most useful options that are common to all Net-SNMP commands. See the snmpcmd(1) manpage for a complete list.

Table C-1. Summary of Command-Line Options

Option

Description

-m

Specifies which MIB modules you would like the command to load. If you want the command to parse the MIB file for a particular vendor, copy the MIB file to /usr/local/share/snmp/mibs and invoke the command with the option -m ALL. The argument ALL forces the command to read all the MIB files in the directory. Setting the environment variable $MIBS to ALL achieves the same thing. If you don't want the command to read all the MIB files, you can follow the -m option with a colon-separated list of the MIB files you want parsed.

-M

Allows you to specify a colon-separated list of directories to search for MIB files. This option is useful if you don't want to copy MIB files into the default MIB location. Setting the shell variable $MIBDIRS has the same effect.

-IR

Performs a random-access search through the MIB database for an OID label. By default, the commands assume that you specify an object ID relative to .iso.org.dod.internet.mgmt.mib-2. In practice, this option allows you to avoid typing long OIDs for objects that aren't under the mib-2 subtree. For example, there's a group of objects in the Cisco MIB named lcpu. If you use the -IR option, you can retrieve objects in this group without typing the entire OID; the following command is sufficient:

snmpget -IR hostname community lcpu.2
If there is more than one object with the given name, the Net-SNMP tools will access the first object they find. Since this feature is billed as a random-access search, there's no way to predict which object the tools will find first. Within the standard MIBs, objects rarely (if ever) have the same name, but there's no guarantee that any name will be unique, particularly if you're using vendor-specific MIBs.

-On

Prints OIDs numerically (e.g., .1.3.6.1.2.1.1.3.0). Note that the -O options can be combined, as long as the combination makes sense.

-Of

Prints the entire OID (i.e., starting with .1).

-Os

Displays only the final part of the OID, in symbolic form (e.g., sysUpTime.0).

-OS

Same as -Os, but prefixes the object name with the name of the MIB file from which the object is taken (e.g., SNMPv2-MIB::sysUpTime.0).

-T

Specifies whether the command should use TCP or UDP as the transport-layer protocol. UDP is the default; -T tcp uses TCP.

-v

Specifies which version of SNMP to use. By default, the commands use Version 1. Valid options are -v 1, -v 2c, and -v 3. Note that some commands, such as snmpbulkget, are available only for Versions 2c and 3.

-h

Displays help information for the command.

-c

Specifies the community string for the command. Alternately, you can place the community string after the hostname and omit the -c option.



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