snmpd.conf - Cheap VPS LLC

SNMPD.CONF


Section: Net-SNMP (5)
Updated: 08 Feb 2002
Index
Return to Main Contents

 

NAME

snmpd.conf – configuration file for the Net-SNMP SNMP agent
 

DESCRIPTION

The Net-SNMP agent uses one or more configuration files
to control its operation and the management information
provided.
These files (snmpd.conf and snmpd.local.conf)
can be located in one of several locations, as described in the
snmp_config(5)

manual page.

The (perl) application
snmpconf

can be used to generate configuration files for the
most common agent requirements. See the
snmpconf(1)

manual page for more information, or try running the
command:



snmpconf -g basic_setup


There are a large number of directives that can be specified,
but these mostly fall into four distinct categories:



those controlling who can access the agent

those configuring the information that is supplied by the agent

those controlling active monitoring of the local system

those concerned with extending the functionality of the agent.

Some directives don’t fall naturally into any of these four
categories, but this covers the majority of the contents of
a typical
snmpd.conf

file.
A full list of recognised directives can be obtained by running
the command:



snmpd -H


 

AGENT BEHAVIOUR

Although most configuration directives are concerned with the MIB
information supplied by the agent, there are a handful of directives that
control the behaviour of snmpd considered simply as a daemon
providing a network service.


agentaddress [<transport-specifier>:]<transport-address>[,...]

defines a list of listening addresses, on which to receive incoming
SNMP requests.
See the section
LISTENING ADDRESSES

in the
snmpd(8)

manual page for more information about the format of listening
addresses.


The default behaviour is to
listen on UDP port 161 on all IPv4 interfaces.
agentgroup {GROUP|#GID}

changes to the specified group after opening the listening port(s).
This may refer to a group by name (GROUP), or a numeric group ID
starting with ‘#’ (#GID).
agentuser {USER|#UID}

changes to the specified user after opening the listening port(s).
This may refer to a user by name (USER), or a numeric user ID
starting with ‘#’ (#UID).
leave_pidfile yes

instructs the agent to not remove its pid file on shutdown. Equivalent to
specifying "-U" on the command line.
maxGetbulkRepeats NUM

Sets the maximum number of responses allowed for a single variable in
a getbulk request. Set to 0 to enable the default and set it to -1 to
enable unlimited. Because memory is allocated ahead of time, sitting
this to unlimited is not considered safe if your user population can
not be trusted. A repeat number greater than this will be truncated
to this value.

This is set by default to -1.
maxGetbulkResponses NUM

Sets the maximum number of responses allowed for a getbulk request.
This is set by default to 100. Set to 0 to enable the default and set
it to -1 to enable unlimited. Because memory is allocated ahead of
time, sitting this to unlimited is not considered safe if your user
population can not be trusted.

In general, the total number of responses will not be allowed to
exceed the maxGetbulkResponses number and the total number returned
will be an integer multiple of the number of variables requested times
the calculated number of repeats allow to fit below this number.

Also not that processing of maxGetbulkRepeats is handled first.

 

SNMPv3 Configuration

SNMPv3 requires an SNMP agent to define a unique "engine ID"
in order to respond to SNMPv3 requests.
This ID will normally be determined automatically, using two reasonably
non-predictable values – a (pseudo-)random number and the current
time in seconds. This is the recommended approach. However the
capacity exists to define the engineID in other ways:


engineID STRING

specifies that the engineID should be built from the given text STRING.
engineIDType 1|2|3

specifies that the engineID should be built from the IPv4 address (1),
IPv6 address (2) or MAC address (3). Note that changing the IP address
(or switching the network interface card) may cause problems.
engineIDNic INTERFACE

defines which interface to use when determining the MAC address.
If engineIDType 3 is not specified, then this directive
has no effect.

The default is to use eth0.


 

SNMPv3 AUTHENTICATION

SNMPv3 was originally defined using the User-Based Security Model
(USM), which contains a private list of users and keys specific to the
SNMPv3 protocol. The operational community, however, declared it a
pain to manipulate yet another database and would prefer to use
existing infrastructure. To that end the IETF created the ISMS
working group to battle that problem, and the ISMS working group
decided to tunnel SNMP over SSH and DTLS to make use existing user and
authentication infrastructures.
 

SNMPv3 USM Users

To use the USM based SNMPv3-specific users, you’ll need to create
them. It is recommended you
use the net-snmp-config command

to do this, but you can also do it by directly specifying createUser
directives yourself instead:


createUser [-e ENGINEID] username (MD5|SHA) authpassphrase [DES|AES] [privpassphrase]


MD5 and SHA are the authentication types to use. DES and AES are the
privacy protocols to use. If the privacy
passphrase is not specified, it is assumed to be the same as the
authentication passphrase. Note that the users created will be
useless unless they are also added to the VACM access control tables
described above.

SHA authentication and DES/AES privacy require OpenSSL to be installed and
the agent to be built with OpenSSL support. MD5 authentication may be
used without OpenSSL.

Warning: the minimum pass phrase length is 8 characters.

SNMPv3 users can be created at runtime using the
snmpusm(1)

command.


Instead of figuring out how to use this directive and where to put it
(see below), just run "net-snmp-config –create-snmpv3-user" instead,
which will add one of these lines to the right place.

This directive should be placed into the
/var/lib/net-snmp/snmpd.conf file instead of the other normal
locations. The reason is that the information is read from the file
and then the line is removed (eliminating the storage of the master
password for that user) and replaced with the key that is derived from
it. This key is a localized key, so that if it is stolen it can not
be used to access other agents. If the password is stolen, however,
it can be.

If you need to localize the user to a particular EngineID (this is
useful mostly in the similar snmptrapd.conf file), you can use the -e
argument to specify an EngineID as a hex value (EG, "0x01020304").

If you want to generate either your master or localized keys directly,
replace the given password with a hexstring (preceeded by a "0x") and
precede the hex string by a -m or -l token (respectively). EGs:



[these keys are *not* secure but are easy to visually parse for
counting purposes. Please generate random keys instead of using
these examples]

createUser myuser SHA -l 0x0001020304050607080900010203040506070809 AES -l 0x00010203040506070809000102030405
createUser myuser SHA -m 0x0001020304050607080900010203040506070809 AES -m 0x0001020304050607080900010203040506070809


Due to the way localization happens, localized privacy keys are
expected to be the length needed by the algorithm (128 bits for all
supported algorithms). Master encryption keys, though, need to be the
length required by the authentication algorithm not the length
required by the encrypting algorithm (MD5: 16 bytes, SHA: 20 bytes).

 

SSH Support

To use SSH, you’ll need to configure sshd to invoke sshtosnmp as well
as configure the access control settings to allow access through the
tsm security model using the user name provided to snmpd by the ssh
transport.
 

DTLS Support

For DTLS,
snmpd

will need to be configured with it’s own X.509 certificate as well as
the certificates of the client users to be allowed to connect to the
agent. The access control will need to be set up as well to allow
access through the
tsm

security model. The CommonName of the Subject from the X.509
certificate will be passed to snmpd as the SNMPv3 username to use.
See the http://www.net-snmp.org/wiki/index.php/Using_DTLS web page for
more detailed instructions for setting up DTLS.


defX509ServerPub FILE

defX509ServerPriv FILE

These two directives specify the public and private key files for the
certificate that
snmpd

should present to incoming connections.

defX509ClientCerts FILE

This directive specifies a file containing all of the public keys (or
CAs of public keys) for clients to connect the server with.

 

ACCESS CONTROL

snmpd

supports the View-Based Access Control Model (VACM) as defined in RFC
2575, to control who can retrieve or update information. To this end,
it recognizes various directives relating to access control.
 

Traditional Access Control

Most simple access control requirements can be specified using the
directives rouser/rwuser (for SNMPv3) or
rocommunity/rwcommunity (for SNMPv1 or SNMPv2c).


rouser [-s SECMODEL] USER [noauth|auth|priv [OID | -V VIEW [CONTEXT]]]

rwuser [-s SECMODEL] USER [noauth|auth|priv [OID | -V VIEW [CONTEXT]]]

specify an SNMPv3 user that will be allowed read-only (GET and GETNEXT)
or read-write (GET, GETNEXT and SET) access respectively.
By default, this will provide access to the full OID tree for authenticated
(including encrypted) SNMPv3 requests, using the default context.
An alternative minimum security level can be specified using noauth
(to allow unauthenticated requests), or priv (to enforce use of
encryption). The OID field restricts access for that
user to the subtree rooted at the given OID, or the named view.
An optional context can also be specified, or "context*" to denote a context
prefix. If no context field is specified (or the token "*" is used), the
directive will match all possible contexts.

If SECMODEL is specified then it will be the security model required
for that user (note that identical user names may come in over
different security models and will be appropriately separated via the
access control settings). The default security model is "usm" and the
other common security models are likely "tsm" when using SSH or DTLS
support and "ksm" if the Kerberos support has been compiled in.
rocommunity COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]

rwcommunity COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]

specify an SNMPv1 or SNMPv2c community that will be allowed read-only
(GET and GETNEXT) or read-write (GET, GETNEXT and SET) access respectively.
By default, this will provide access to the full OID tree for such requests,
regardless of where they were sent from. The SOURCE token can be used to
restrict access to requests from the specified system(s) – see
com2sec for the full details. The OID field restricts access for
that community to the subtree rooted at the given OID, or named view.
Contexts are typically less relevant to community-based SNMP versions,
but the same behaviour applies here.
rocommunity6 COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]

rwcommunity6 COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]

are directives relating to requests received using IPv6
(if the agent supports such transport domains).
The interpretation of the SOURCE, OID, VIEW and CONTEXT tokens are exactly
the same as for the IPv4 versions.

In each case, only one directive should be specified for a given SNMPv3 user,
or community string.
It is not appropriate to specify both rouser
and rwuser directives referring to the same SNMPv3 user (or equivalent
community settings). The rwuser directive provides all the access
of rouser (as well as allowing SET support).
The same holds true for the community-based directives.

More complex access requirements (such as access to two
or more distinct OID subtrees, or different views for GET and SET requests)
should use one of the other access control mechanisms.
Note that if several distinct communities or SNMPv3 users need to be granted
the same level of access, it would also be more efficient to use the main VACM
configuration directives.
 

VACM Configuration

The full flexibility of the VACM is available using four configuration
directives – com2sec, group, view and access.
These provide direct configuration of the underlying VACM tables.


com2sec [-Cn CONTEXT] SECNAME SOURCE COMMUNITY

com2sec6 [-Cn CONTEXT] SECNAME SOURCE COMMUNITY

map an SNMPv1 or SNMPv2c community string to a security name – either from
a particular range of source addresses, or globally ("default").
A restricted source can either be a specific hostname (or address), or
a subnet – represented as IP/MASK (e.g. 10.10.10.0/255.255.255.0), or
IP/BITS (e.g. 10.10.10.0/24), or the IPv6 equivalents.

The same community string can be specified in several separate directives
(presumably with different source tokens), and the first source/community
combination that matches the incoming request will be selected.
Various source/community combinations can also map to the same security name.

If a CONTEXT is specified (using -Cn), the community string will be
mapped to a security name in the named SNMPv3 context. Otherwise the
default context ("") will be used.
com2secunix [-Cn CONTEXT] SECNAME SOCKPATH COMMUNITY

is the Unix domain sockets version of com2sec.
group GROUP {v1|v2c|usm|tsm|ksm} SECNAME

maps a security name (in the specified security model) into
a named group. Several group directives can specify the
same group name, allowing a single access setting to apply to several
users and/or community strings.

Note that groups must be set up for the two community-based models separately –
a single com2sec (or equivalent) directive will typically be
accompanied by two group directives.
view VNAME TYPE OID [MASK]

defines a named "view" – a subset of the overall OID tree. This is most
commonly a single subtree, but several view directives can be given
with the same view name (VNAME), to build up a more complex collection of OIDs.
TYPE is either included or excluded, which can again define
a more complex view (e.g by excluding certain sensitive objects
from an otherwise accessible subtree).

MASK is a list of hex octets (optionally separated by ‘.’ or ‘:’) with
the set bits indicating which subidentifiers in the view OID to match
against. If not specified, this defaults to matching the OID exactly
(all bits set), thus defining a simple OID subtree. So:


view iso1 included .iso 0xf0

view iso2 included .iso

view iso3 included .iso.org.dod.mgmt 0xf0


would all define the same view, covering the whole of the ‘iso(1)’ subtree
(with the third example ignoring the subidentifiers not covered by the mask).

More usefully, the mask can be used to define a view covering a particular
row (or rows) in a table, by matching against the appropriate table index
value, but skipping the column subidentifier:



view ifRow4 included .1.3.6.1.2.1.2.2.1.0.4 0xff:a0



Note that a mask longer than 8 bits must use ‘:’ to separate the individual
octets.
access GROUP CONTEXT {any|v1|v2c|usm|tsm|ksm} LEVEL PREFX READ WRITE NOTIFY

maps from a group of users/communities (with a particular security model
and minimum security level, and in a specific context) to one of three views,
depending on the request being processed.

LEVEL is one of noauth, auth, or priv.
PREFX specifies how CONTEXT should be matched against the context of
the incoming request, either exact or prefix.
READ, WRITE and NOTIFY specifies the view to be used for GET*, SET
and TRAP/INFORM requests (althought the NOTIFY view is not currently used).
For v1 or v2c access, LEVEL will need to be noauth.

 

Typed-View Configuration

The final group of directives extend the VACM approach into a more flexible
mechanism, which can be applied to other access control requirements. Rather than
the fixed three views of the standard VACM mechanism, this can be used to
configure various different view types. As far as the main SNMP agent is
concerned, the two main view types are read and write,
corresponding to the READ and WRITE views of the main access directive.
See the ‘snmptrapd.conf(5)’ man page for discussion of other view types.


authcommunity TYPES COMMUNITY [SOURCE [OID | -V VIEW [CONTEXT]]]

is an alternative to the rocommunity/rwcommunity directives.
TYPES will usually be read or read,write respectively.
The view specification can either be an OID subtree (as before),
or a named view (defined using the
view directive) for greater flexibility. If this is omitted,
then access will be allowed to the full OID tree.
If CONTEXT is specified, access is configured within this SNMPv3 context.
Otherwise the default context ("") is used.
authuser TYPES [-s MODEL] USER [LEVEL [OID | -V VIEW [CONTEXT]]]

is an alternative to the rouser/rwuser directives.
The fields TYPES, OID, VIEW and CONTEXT have the same meaning as for
authcommunity.
authgroup TYPES [-s MODEL] GROUP [LEVEL [OID | -V VIEW [CONTEXT]]]

is a companion to the authuser directive, specifying access
for a particular group (defined using the group directive as usual).
Both authuser and authgroup default to authenticated requests –
LEVEL can also be specified as noauth or priv to allow
unauthenticated requests, or require encryption respectively.
Both authuser and authgroup directives also default to configuring
access for SNMPv3/USM requests – use the ‘-s’ flag to specify an alternative
security model (using the same values as for access above).
authaccess TYPES [-s MODEL] GROUP VIEW [LEVEL [CONTEXT]]

also configures the access for a particular group,
specifying the name and type of view to apply. The MODEL and LEVEL fields
are interpreted in the same way as for authgroup.
If CONTEXT is specified, access is configured within this SNMPv3 context
(or contexts with this prefix if the CONTEXT field ends with ‘*’).
Otherwise the default context ("") is used.
setaccess GROUP CONTEXT MODEL LEVEL PREFIX VIEW TYPES

is a direct equivalent to the original access directive, typically
listing the view types as read or read,write as appropriate.
(or see ‘snmptrapd.conf(5)’ for other possibilities).
All other fields have the same interpretation as with access.

 

SYSTEM INFORMATION

Most of the information reported by the Net-SNMP agent is retrieved
from the underlying system, or dynamically configured via SNMP SET requests
(and retained from one run of the agent to the next).
However, certain MIB objects can be configured or controlled via
the snmpd.conf(5) file.
 

System Group

Most of the scalar objects in the ‘system’ group can be configured
in this way:


sysLocation STRING

sysContact STRING

sysName STRING

set the system location, system contact or system name
(sysLocation.0, sysContact.0 and sysName.0) for the agent respectively.
Ordinarily these objects are writeable via suitably authorized SNMP SET
requests. However, specifying one of these directives makes the
corresponding object read-only, and attempts to SET it will result in
a notWritable error response.
sysServices NUMBER

sets the value of the sysServices.0 object.
For a host system, a good value is 72 (application + end-to-end layers).
If this directive is not specified, then no value will be reported
for the sysServices.0 object.
sysDescr STRING

sysObjectID OID

sets the system description or object ID for the agent.
Although these MIB objects are not SNMP-writable, these directives can be
used by a network administrator to configure suitable values for them.

 

Interfaces Group


interface NAME TYPE SPEED

can be used to provide appropriate type and speed settings for
interfaces where the agent fails to determine this information correctly.
TYPE is a type value as given in the IANAifType-MIB,
and can be specified numerically or by name (assuming this MIB is loaded).
interface_fadeout TIMEOUT

specifies, for how long the agent keeps entries in ifTable after
appropriate interfaces have been removed from system (typically various ppp,
tap or tun interfaces). Timeout value is in seconds. Default value is 300
(=5 minutes).
interface_replace_old yes

can be used to remove already existing entries in ifTable when an
interface with the same name appears on the system. E.g. when ppp0 interface
is removed, it is still listed in the table for interface_fadeout
seconds. This option ensures, that the old ppp0 interface is removed even
before the interface_fadeout timeour when new ppp0 (with different
ifIndex) shows up.

 

Host Resources Group

This requires that the agent was built with support for the
host module (which is now included as part of the default build
configuration on the major supported platforms).


ignoreDisk STRING

controls which disk devices are scanned as part of populating the
hrDiskStorageTable (and hrDeviceTable).
The HostRes implementation code includes a list of disk device patterns
appropriate for the current operating system, some of which may cause
the agent to block when trying to open the corresponding disk devices.
This might lead to a timeout when walking these tables, possibly
resulting in inconsistent behaviour. This directive can be used
to specify particular devices (either individually or wildcarded)
that should not be checked.


Note:

Please consult the source (host/hr_disk.c) and check for the
Add_HR_Disk_entry calls relevant for a particular O/S
to determine the list of devices that will be scanned.


The pattern can include one or more wildcard expressions.
See snmpd.examples(5) for illustration of the wildcard syntax.
skipNFSInHostResources true

controls whether NFS and NFS-like file systems should be omitted
from the hrStorageTable (true or 1) or not (false or 0, which is the default).
If the Net-SNMP agent gets hung on NFS-mounted filesystems, you
can try setting this to ‘1’.
storageUseNFS [1|2]

controls how NFS and NFS-like file systems should be reported
in the hrStorageTable.
as ‘Network Disks’ (1) or ‘Fixed Disks’ (2)
Historically, the Net-SNMP agent has reported such file systems
as ‘Fixed Disks’, and this is still the default behaviour.
Setting this directive to ‘1’ reports such file systems as
‘Network Disks’, as required by the Host Resources MIB.
realStorageUnits

controlls how the agent reports hrStorageAllocationUnits, hrStorageSize and
hrStorageUsed in hrStorageTable.
With this option set to ‘0’, the agent re-calculates these values for
big storage drives with small allocation units so
hrStorageAllocationUnits x hrStorageSize
gives real size of the storage.


Example:

Linux xfs 16TB filesystem with 4096 bytes large blocks will be
reported as hrStorageAllocationUnits = 8192 and hrStorageSize = 2147483647,
so 8192 x 2147483647 gives real size of the filesystem (=16 TB).


Setting this directive to ‘1’ (=default) turns off
this calculation and the agent reports real hrStorageAllocationUnits, but it
might report wrong hrStorageSize for big drives because the value won’t fit into
Integer32. In this case, hrStorageAllocationUnits x hrStorageSize won’t give
real size of the storage.

 

Process Monitoring

The hrSWRun group of the Host Resources MIB provides
information about individual processes running on the local system.
The prTable of the UCD-SNMP-MIB complements this by reporting
on selected services (which may involve multiple processes).
This requires that the agent was built with support for the
ucd-snmp/proc module (which is included as part of the
default build configuration).


proc NAME [MAX [MIN]]

monitors the number of processes called NAME (as reported by "/bin/ps -e")
running on the local system.

If the number of NAMEd processes is less than MIN or greater than MAX,
then the corresponding prErrorFlag instance will be
set to 1, and a suitable description message reported via the
prErrMessage instance.


Note:

This situation will not automatically trigger a trap to report
the problem – see the DisMan Event MIB section later.


If neither MAX nor MIN are specified (or are both 0), they will
default to infinity and 1 respectively ("at least one").
If only MAX is specified, MIN will default to 0 ("no more than MAX").
procfix NAME PROG ARGS

registers a command that can be run to fix errors with the given
process NAME. This will be invoked when the corresponding
prErrFix instance is set to 1.


Note:

This command will not be invoked automatically.



The procfix directive must be specified after the matching
proc directive, and cannot be used on its own.

If no proc directives are defined, then walking the
prTable will fail (noSuchObject).
 

Disk Usage Monitoring

This requires that the agent was built with support for the
ucd-snmp/disk module (which is included as part of the
default build configuration).


disk PATH [ MINSPACE | MINPERCENT% ]

monitors the disk mounted at PATH for available disk space.
Disks mounted after the agent has started will not be monitored,
unless includeAllDisks option is specified.

The minimum threshold can either be specified in kB (MINSPACE) or
as a percentage of the total disk (MINPERCENT% with a ‘%’ character),
defaulting to 100kB if neither are specified.
If the free disk space falls below this threshold,
then the corresponding dskErrorFlag instance will be
set to 1, and a suitable description message reported via the
dskErrorMsg instance.


Note:

This situation will not automatically trigger a trap to report
the problem – see the DisMan Event MIB section later.

includeAllDisks MINPERCENT%

configures monitoring of all disks found on the system,
using the specified (percentage) threshold.
The dskTable is dynamically updated, unmounted disks
disappear from the table and newly mounted disks are
added to the table.
The threshold for individual disks can be adjusted using suitable
disk directives (which can come either before or after the
includeAllDisks directive).


Note:

Whether disk directives appears before or after includeAllDisks
may affect the indexing of the dskTable.


Only one includeAllDisks directive should be specified – any
subsequent copies will be ignored.

The list of mounted disks will be determined from
HOST-RESOURCES-MIB::hrFSTable.


If neither any disk directives or includeAllDisks are defined,
then walking the dskTable will fail (noSuchObject).
 

Disk I/O Monitoring

This requires that the agent was built with support for the
ucd-snmp/diskio module (which is not included as part of the
default build configuration).

By default, all block devices known to the operating system are
included in the diskIOTable. On platforms other than Linux, this module
has no configuration directives.

On Linux systems, it is possible to report only explicitly whitelisted
devices. It may take significant amount of time to process diskIOTable data
on systems with tens of thousands of block devices and whitelisting only the
important ones avoids large CPU consumption.


diskio <device>

Enables whitelisting of devices and adds the device to the whitelist. Only
explicitly whitelisted devices will be reported. This option may be used
multiple times.

 

System Load Monitoring

This requires that the agent was built with support for either the
ucd-snmp/loadave module or the ucd-snmp/memory module
respectively (both of which are included as part of the
default build configuration).


load MAX1 [MAX5 [MAX15]]

monitors the load average of the local system, specifying
thresholds for the 1-minute, 5-minute and 15-minute averages.
If any of these loads exceed the associated maximum value,
then the corresponding laErrorFlag instance will be
set to 1, and a suitable description message reported via the
laErrMessage instance.


Note:

This situation will not automatically trigger a trap to report
the problem – see the DisMan Event MIB section later.


If the MAX15 threshold is omitted, it will default to the MAX5 value.
If both MAX5 and MAX15 are omitted, they will default to the MAX1 value.
If this directive is not specified, all three thresholds will
default to a value of DEFMAXLOADAVE.

If a threshold value of 0 is given, the agent will not report errors
via the relevant laErrorFlag or laErrMessage instances,
regardless of the current load.

Unlike the proc and disk directives, walking the
walking the laTable will succeed (assuming the
ucd-snmp/loadave module was configured into the agent),
even if the load directive is not present.


swap MIN

monitors the amount of swap space available on the local system.
If this falls below the specified threshold (MIN kB),
then the memErrorSwap object will be set to 1,
and a suitable description message reported via memSwapErrorMsg.


Note:

This situation will not automatically trigger a trap to report
the problem – see the DisMan Event MIB section later.

If this directive is not specified, the default threshold is 16 MB.


 

Log File Monitoring

This requires that the agent was built with support for either the
ucd-snmp/file or ucd-snmp/logmatch modules respectively
(both of which are included as part of the
default build configuration).


file FILE [MAXSIZE]

monitors the size of the specified file (in kB).
If MAXSIZE is specified, and the size of the file exceeds
this threshold, then the corresponding fileErrorFlag
instance will be set to 1, and a suitable description message reported
via the fileErrorMsg instance.


Note:

This situation will not automatically trigger a trap to report
the problem – see the DisMan Event MIB section later.


Note: A maximum of 20 files can be monitored.

Note: If no file directives are defined, then walking the
fileTable will fail (noSuchObject).
logmatch NAME FILE CYCLETIME REGEX

monitors the specified file for occurances of the specified
pattern REGEX. The file position is stored internally so the entire file
is only read initially, every subsequent pass will only read the new lines
added to the file since the last read.


NAME

name of the logmatch instance (will appear as logMatchName under
logMatch/logMatchTable/logMatchEntry/logMatchName in the ucd-snmp MIB tree)
FILE

absolute path to the logfile to be monitored. Note that this path
can contain date/time directives (like in the UNIX ‘date’ command). See the
manual page for ‘strftime’ for the various directives accepted.
CYCLETIME

time interval for each logfile read and internal variable update in seconds.
Note: an SNMPGET* operation will also trigger an immediate logfile read and
variable update.
REGEX

the regular expression to be used. Note: DO NOT enclose the regular expression
in quotes even if there are spaces in the expression as the quotes will also
become part of the pattern to be matched!


Example:



logmatch apache-GETs /usr/local/apache/logs/access.log-%Y-%m-%d 60 GET.*HTTP.*

This logmatch instance is named ‘apache-GETs’, uses ‘GET.*HTTP.*’ as its
regular expression and it will monitor the file named
(assuming today is May 6th 2009): ‘/usr/local/apache/logs/access.log-2009-05-06′,
tomorrow it will look for ‘access.log-2009-05-07′. The logfile is read every 60
seconds.


Note: A maximum of 250 logmatch directives can be specified.

Note: If no logmatch directives are defined, then walking the
logMatchTable will fail (noSuchObject).

 

ACTIVE MONITORING

The usual behaviour of an SNMP agent is to wait for incoming SNMP requests
and respond to them – if no requests are received, an agent will typically
not initiate any actions. This section describes various directives that
can configure snmpd to take a more active role.
 

Notification Handling


trapcommunity STRING

defines the default community string to be used when sending traps.
Note that this directive must be used prior to any community-based
trap destination directives that need to use it.
trapsink HOST [COMMUNITY [PORT]]

trap2sink HOST [COMMUNITY [PORT]]

informsink HOST [COMMUNITY [PORT]]

define the address of a notification receiver that should be sent
SNMPv1 TRAPs, SNMPv2c TRAP2s, or SNMPv2 INFORM notifications respectively.
See the section
LISTENING ADDRESSES

in the
snmpd(8)

manual page for more information about the format of listening
addresses.
If COMMUNITY is not specified, the most recent trapcommunity
string will be used.


If the transport address does not include an explicit
port specification, then PORT will be used.
If this is not specified, the well known SNMP trap
port (162) will be used.


Note:

This mechanism is being deprecated, and the listening port
should be specified via the transport specification HOST instead.


If several sink directives are specified, multiple
copies of each notification (in the appropriate formats)
will be generated.


Note:

It is not normally appropriate to list two (or all three)
sink directives with the same destination.

trapsess [SNMPCMD_ARGS] HOST

provides a more generic mechanism for defining notification destinations.
SNMPCMD_ARGS

should be the command-line options required for an equivalent
snmptrap (or snmpinform) command to send the desired notification.
The option -Ci can be used (with -v2c or -v3) to generate
an INFORM notification rather than an unacknowledged TRAP.


This is the appropriate directive for defining SNMPv3 trap receivers.
See
http://www.net-snmp.org/tutorial/tutorial-5/commands/snmptrap-v3.html
for more information about SNMPv3 notification behaviour.
authtrapenable {1|2}

determines whether to generate authentication failure traps
(enabled(1)) or not (disabled(2) – the default).
Ordinarily the corresponding MIB
object (snmpEnableAuthenTraps.0) is read-write, but specifying
this directive makes this object read-only, and attempts to set the
value via SET requests will result in a notWritable error response.

v1trapaddress HOST

defines the agent address, which is inserted into SNMPv1 TRAPs. Arbitrary local
IPv4 address is chosen if this option is ommited. This option is useful mainly
when the agent is visible from outside world by specific address only (e.g.
because of network address translation or firewall).

 

DisMan Event MIB

The previous directives can be used to configure where traps should
be sent, but are not concerned with when to send such traps
(or what traps should be generated). This is the domain of the
Event MIB – developed by the Distributed Management (DisMan)
working group of the IETF.

This requires that the agent was built with support for the
disman/event module (which is now included as part of the
default build configuration for the most recent distribution).



Note:

The behaviour of the latest implementation differs in some minor
respects from the previous code – nothing too significant, but
existing scripts may possibly need some minor adjustments.


iquerySecName NAME

agentSecName NAME

specifies the default SNMPv3 username, to be used when making internal
queries to retrieve any necessary information (either for evaluating
the monitored expression, or building a notification payload).
These internal queries always use SNMPv3, even if normal querying
of the agent is done using SNMPv1 or SNMPv2c.

Note that this user must also be explicitly created (createUser)
and given appropriate access rights (e.g. rouser). This
directive is purely concerned with defining which user should
be used – not with actually setting this user up.

monitor [OPTIONS] NAME EXPRESSION

defines a MIB object to monitor.
If the EXPRESSION condition holds (see below), then this will trigger
the corresponding event, and either send a notification or apply
a SET assignment (or both).
Note that the event will only be triggered once, when the expression
first matches. This monitor entry will not fire again until the
monitored condition first becomes false, and then matches again.
NAME is an administrative name for this expression, and is used for
indexing the mteTriggerTable (and related tables).
Note also that such monitors use an internal SNMPv3 request to retrieve
the values being monitored (even if normal agent queries typically use
SNMPv1 or SNMPv2c). See the iquerySecName token described above.
EXPRESSION

There are three types of monitor expression supported by the Event MIB –
existence, boolean and threshold tests.


OID | ! OID | != OID

defines an existence(0) monitor test.
A bare OID specifies a present(0) test, which will fire when
(an instance of) the monitored OID is created.
An expression of the form ! OID specifies an absent(1) test,
which will fire when the monitored OID is delected.
An expression of the form != OID specifies a changed(2) test,
which will fire whenever the monitored value(s) change.
Note that there must be whitespace before the OID token.
OID OP VALUE

defines a boolean(1) monitor test.
OP should be one of the defined
comparison operators (!=, ==, <, <=, >, >=) and VALUE should be an
integer value to compare against.
Note that there must be whitespace around the OP token.
A comparison such as OID !=0 will not be handled correctly.
OID MIN MAX [DMIN DMAX]

defines a threshold(2) monitor test.
MIN and MAX are integer values, specifying lower and upper thresholds.
If the value of the monitored OID falls below the lower threshold (MIN)
or rises above the upper threshold (MAX), then the monitor entry will
trigger the corresponding event.

Note that the rising threshold event will only be re-armed when
the monitored value falls below the lower threshold (MIN).
Similarly, the falling threshold event will be re-armed by
the upper threshold (MAX).

The optional parameters DMIN and DMAX configure a pair of
similar threshold tests, but working with the delta
differences between successive sample values.

OPTIONS

There are various options to control the behaviour of the monitored
expression. These include:


-D

indicates that the expression should be evaluated using delta differences
between sample values (rather than the values themselves).
-d OID

-di OID

specifies a discontinuity marker for validating delta differences.
A -di object instance will be used exactly as given.
A -d object will have the instance subidentifiers from the
corresponding (wildcarded) expression object appended.
If the -I flag is specified, then there is no difference
between these two options.

This option also implies -D.
-e EVENT

specifies the event to be invoked when this monitor entry is triggered.
If this option is not given, the monitor entry will generate one
of the standard notifications defined in the DISMAN-EVENT-MIB.
-I

indicates that the monitored expression should be applied to the
specified OID as a single instance. By default, the OID will
be treated as a wildcarded object, and the monitor expanded
to cover all matching instances.
-i OID

-o OID

define additional varbinds to be added to the notification payload
when this monitor trigger fires.
For a wildcarded expression, the suffix of the matched instance
will be added to any OIDs specified using -o, while OIDs
specified using -i will be treated as exact instances.
If the -I flag is specified, then there is no difference
between these two options.

See strictDisman for details of the ordering of notification payloads.
-r FREQUENCY

monitors the given expression every FREQUENCY seconds.
By default, the expression will be evaluated every 600s (10 minutes).
-S

indicates that the monitor expression should not be evaluated
when the agent first starts up. The first evaluation will be done
once the first repeat interval has expired.
-s

indicates that the monitor expression should be evaluated when the
agent first starts up. This is the default behaviour.


Note:

Notifications triggered by this initial evaluation will be sent
before the coldStart trap.

-u SECNAME

specifies a security name to use for scanning the local host,
instead of the default iquerySecName.
Once again, this user must be explicitly created and given
suitable access rights.

notificationEvent ENAME NOTIFICATION [-m] [-i OID | -o OID ]*

defines a notification event named ENAME.
This can be triggered from a given monitor entry by specifying
the option -e ENAME (see above).
NOTIFICATION should be the OID of the NOTIFICATION-TYPE definition
for the notification to be generated.

If the -m option is given, the notification payload will
include the standard varbinds as specified in the OBJECTS clause
of the notification MIB definition.
This option must come after the NOTIFICATION OID
(and the relevant MIB file must be available and loaded by the agent).
Otherwise, these varbinds must
be listed explicitly (either here or in the corresponding
monitor directive).

The -i OID and -o OID options specify additional
varbinds to be appended to the notification payload, after the
standard list.
If the monitor entry that triggered this event involved a
wildcarded expression, the suffix of the matched instance
will be added to any OIDs specified using -o, while OIDs
specified using -i will be treated as exact instances.
If the -I flag was specified to the monitor directive,
then there is no difference between these two options.
setEvent ENAME [-I] OID = VALUE

defines a set event named ENAME, assigning the (integer) VALUE
to the specified OID.
This can be triggered from a given monitor entry by specifying
the option -e ENAME (see above).

If the monitor entry that triggered this event involved a
wildcarded expression, the suffix of the matched instance
will normally be added to the OID.
If the -I flag was specified to either of the
monitor or setEvent directives, the
specified OID will be regarded as an exact single instance.
strictDisman yes

The definition of SNMP notifications states that the
varbinds defined in the OBJECT clause should come first
(in the order specified), followed by any "extra" varbinds
that the notification generator feels might be useful.
The most natural approach would be to associate these
mandatory varbinds with the notificationEvent entry,
and append any varbinds associated with the monitor entry
that triggered the notification to the end of this list.
This is the default behaviour of the Net-SNMP Event MIB implementation.

Unfortunately, the DisMan Event MIB specifications actually
state that the trigger-related varbinds should come first,
followed by the event-related ones. This directive can be used to
restore this strictly-correct (but inappropriate) behaviour.


Note:

Strict DisMan ordering may result in generating invalid notifications
payload lists if the notificationEvent -n flag is used together
with monitor -o (or -i) varbind options.


If no monitor entries specify payload varbinds,
then the setting of this directive is irrelevant.
linkUpDownNotifications yes

will configure the Event MIB tables to monitor the ifTable
for network interfaces being taken up or down, and triggering
a linkUp or linkDown notification as appropriate.

This is exactly equivalent to the configuration:




notificationEvent linkUpTrap linkUp ifIndex ifAdminStatus ifOperStatus
notificationEvent linkDownTrap linkDown ifIndex ifAdminStatus ifOperStatus

monitor -r 60 -e linkUpTrap "Generate linkUp" ifOperStatus != 2
monitor -r 60 -e linkDownTrap "Generate linkDown" ifOperStatus == 2


defaultMonitors yes

will configure the Event MIB tables to monitor the various
UCD-SNMP-MIB tables for problems (as indicated by
the appropriate xxErrFlag column objects).

This is exactly equivalent to the configuration:




monitor -o prNames -o prErrMessage "process table" prErrorFlag != 0
monitor -o memErrorName -o memSwapErrorMsg "memory" memSwapError != 0
monitor -o extNames -o extOutput "extTable" extResult != 0
monitor -o dskPath -o dskErrorMsg "dskTable" dskErrorFlag != 0
monitor -o laNames -o laErrMessage "laTable" laErrorFlag != 0
monitor -o fileName -o fileErrorMsg "fileTable" fileErrorFlag != 0



In both these latter cases, the snmpd.conf must also contain a
iquerySecName directive, together with a corresponding
createUser entry and suitable access control configuration.
 

DisMan Schedule MIB

The DisMan working group also produced a mechanism for scheduling
particular actions (a specified SET assignment) at given times.
This requires that the agent was built with support for the
disman/schedule module (which is included as part of the
default build configuration for the most recent distribution).

There are three ways of specifying the scheduled action:


repeat FREQUENCY OID = VALUE

configures a SET assignment of the (integer) VALUE to the MIB instance
OID, to be run every FREQUENCY seconds.
cron MINUTE HOUR DAY MONTH WEEKDAY OID = VALUE

configures a SET assignment of the (integer) VALUE to the MIB instance
OID, to be run at the times specified by the fields MINUTE to WEEKDAY.
These follow the same pattern as the equivalent crontab(5) fields.


Note:

These fields should be specified as a (comma-separated) list of numeric
values. Named values for the MONTH and WEEKDAY fields are not supported,
and neither are value ranges. A wildcard match can be specified as ‘*’.


The DAY field can also accept negative values, to indicate days counting
backwards from the end of the month.
at MINUTE HOUR DAY MONTH WEEKDAY OID = VALUE

configures a one-shot SET assignment, to be run at the first matching
time as specified by the fields MINUTE to WEEKDAY. The interpretation
of these fields is exactly the same as for the cron directive.

 

EXTENDING AGENT FUNCTIONALITY

One of the first distinguishing features of the original UCD suite was
the ability to extend the functionality of the agent – not just by
recompiling with code for new MIB modules, but also by configuring the running agent to
report additional information. There are a number of techniques to
support this, including:



running external commands (exec, extend, pass)

loading new code dynamically (embedded perl, dlmod)

communicating with other agents (proxy, SMUX, AgentX)

 

Arbitrary Extension Commands

The earliest extension mechanism was the ability to run arbitrary
commands or shell scripts. Such commands do not need to be aware of
SNMP operations, or conform to any particular behaviour – the MIB
structures are designed to accommodate any form of command output.
Use of this mechanism requires that the agent was built with support for the
ucd-snmp/extensible and/or agent/extend modules (which
are both included as part of the default build configuration).


exec [MIBOID] NAME PROG ARGS

sh [MIBOID] NAME PROG ARGS

invoke the named PROG with arguments of ARGS. By default the exit
status and first line of output from the command will be reported via
the extTable, discarding any additional output.


Note:

Entries in this table appear in the order they are read from the
configuration file. This means that adding new exec (or sh)
directives and restarting the agent, may affect the indexing of other
entries.


The PROG argument for exec directives must be a full path
to a real binary, as it is executed via the exec() system call.
To invoke a shell script, use the sh directive instead.

If MIBOID is specified, then the results will be rooted at this point
in the OID tree, returning the exit statement as MIBOID.100.0
and the entire command output in a pseudo-table based at
MIBNUM.101 – with one ‘row’ for each line of output.


Note:

The layout of this "relocatable" form of exec (or sh) output
does not strictly form a valid MIB structure. This mechanism is being
deprecated – please see the extend directive (described below) instead.


The agent does not cache the exit status or output of the executed program.

execfix NAME PROG ARGS

registers a command that can be invoked on demand – typically to respond
to or fix errors with the corresponding exec or sh entry.
When the extErrFix instance for a given NAMEd entry is set to the
integer value of 1, this command will be called.


Note:

This directive can only be used in combination with a corresponding
exec or sh directive, which must be defined first.
Attempting to define an unaccompanied execfix directive will fail.


exec and sh extensions can only be configured via the
snmpd.conf file. They cannot be set up via SNMP SET requests.


extend [MIBOID] NAME PROG ARGS

works in a similar manner to the exec directive, but with a number
of improvements. The MIB tables (nsExtendConfigTable
etc) are indexed by the NAME token, so are unaffected by the order in
which entries are read from the configuration files.
There are two result tables – one (nsExtendOutput1Table)
containing the exit status, the first line and full output (as a single string)
for each extend entry, and the other (nsExtendOutput2Table)
containing the complete output as a series of separate lines.

If MIBOID is specified, then the configuration and result tables will be rooted
at this point in the OID tree, but are otherwise structured in exactly
the same way. This means that several separate extend
directives can specify the same MIBOID root, without conflicting.

The exit status and output is cached for each entry individually, and
can be cleared (and the caching behaviour configured)
using the nsCacheTable.
extendfix NAME PROG ARGS

registers a command that can be invoked on demand, by setting the
appropriate nsExtendRunType instance to the value
run-command(3). Unlike the equivalent execfix,
this directive does not need to be paired with a corresponding
extend entry, and can appear on its own.

Both extend and extendfix directives can be configured
dynamically, using SNMP SET requests to the NET-SNMP-EXTEND-MIB.
 

MIB-Specific Extension Commands

The first group of extension directives invoke arbitrary commands,
and rely on the MIB structure (and management applications) having
the flexibility to accommodate and interpret the output. This is a
convenient way to make information available quickly and simply, but
is of no use when implementing specific MIB objects, where the extension
must conform to the structure of the MIB (rather than vice versa).
The remaining extension mechanisms are all concerned with such
MIB-specific situations – starting with "pass-through" scripts.
Use of this mechanism requires that the agent was built with support for the
ucd-snmp/pass and ucd-snmp/pass_persist modules (which
are both included as part of the default build configuration).


pass [-p priority] MIBOID PROG

will pass control of the subtree rooted at MIBOID to the specified
PROG command. GET and GETNEXT requests for OIDs within this tree will
trigger this command, called as:



PROG -g OID

PROG -n OID


respectively, where OID is the requested OID.
The PROG command should return the response varbind as three separate
lines printed to stdout – the first line should be the OID of the returned
value, the second should be its TYPE (one of the text strings
integer, gauge, counter, timeticks, ipaddress, objectid,

or
string

), and the third should be the value itself.


If the command cannot return an appropriate varbind – e.g the specified
OID did not correspond to a valid instance for a GET request, or there
were no following instances for a GETNEXT – then it should exit without
producing any output. This will result in an SNMP noSuchName
error, or a noSuchInstance exception.



Note:

The SMIv2 type counter64
and SNMPv2 noSuchObject exception are not supported.


A SET request will result in the command being called as:



PROG -s OID TYPE VALUE


where TYPE is one of the tokens listed above, indicating the type of the
value passed as the third parameter.


If the assignment is successful, the PROG command should exit without producing
any output. Errors should be indicated by writing one of the strings
not-writable,

or
wrong-type

to stdout,
and the agent will generate the appropriate error response.




Note:

The other SNMPv2 errors are not supported.


In either case, the command should exit once it has finished processing.
Each request (and each varbind within a single request) will trigger
a separate invocation of the command.

The default registration priority is 127. This can be
changed by supplying the optional -p flag, with lower priority
registrations being used in preference to higher priority values.
pass_persist [-p priority] MIBOID PROG

will also pass control of the subtree rooted at MIBOID to the specified
PROG command. However this command will continue to run after the initial
request has been answered, so subsequent requests can be processed without
the startup overheads.

Upon initialization, PROG will be passed the string "PINGn" on stdin,
and should respond by printing "PONGn" to stdout.

For GET and GETNEXT requests, PROG will be passed two lines on stdin,
the command (get or getnext) and the requested OID.
It should respond by printing three lines to stdout –
the OID for the result varbind, the TYPE and the VALUE itself –
exactly as for the pass directive above.
If the command cannot return an appropriate varbind,
it should print print "NONEn" to stdout (but continue running).

For SET requests, PROG will be passed three lines on stdin,
the command (set) and the requested OID,
followed by the type and value (both on the same line).
If the assignment is successful, the command should print
"DONEn" to stdout.
Errors should be indicated by writing one of the strings
not-writable,

wrong-type,

wrong-length,

wrong-value

or
inconsistent-value

to stdout,
and the agent will generate the appropriate error response.
In either case, the command should continue running.


The registration priority can be changed using the optional
-p flag, just as for the pass directive.

pass and pass_persist extensions can only be configured via the
snmpd.conf file. They cannot be set up via SNMP SET requests.

 

Embedded Perl Support

Programs using the previous extension mechanisms can be written in any convenient
programming language – including perl, which is a common choice for
pass-through extensions in particular. However the Net-SNMP agent
also includes support for embedded perl technology (similar to
mod_perl for the Apache web server). This allows the agent
to interpret perl scripts directly, thus avoiding the overhead of
spawning processes and initializing the perl system when a request is received.

Use of this mechanism requires that the agent was built with support for the embedded
perl mechanism, which is not part of the default build environment. It
must be explicitly included by specifying the ‘–enable-embedded-perl’
option to the configure script when the package is first built.

If enabled, the following directives will be recognised:


disablePerl true

will turn off embedded perl support entirely (e.g. if there are problems
with the perl installation).
perlInitFile FILE

loads the specified initialisation file (if present)
immediately before the first perl directive is parsed.
If not explicitly specified, the agent will look for the default
initialisation file /usr/share/snmp/snmp_perl.pl.

The default initialisation file
creates an instance of a NetSNMP::agent object – a variable
$agent which can be used to register perl-based MIB handler routines.
perl EXPRESSION

evaluates the given expression. This would typically register a
handler routine to be called when a section of the OID tree was
requested:



perl use Data::Dumper;
perl sub myroutine { print "got called: ",Dumper(@_),"n"; }
perl $agent->register(‘mylink’, ‘.1.3.6.1.8765′, &myroutine);


This expression could also source an external file:


perl ‘do /path/to/file.pl';


or perform any other perl-based processing that might be required.


 

Dynamically Loadable Modules

Most of the MIBs supported by the Net-SNMP agent are implemented as
C code modules, which were compiled and linked into the agent libraries
when the suite was first built. Such implementation modules can also be
compiled independently and loaded into the running agent once it has
started. Use of this mechanism requires that the agent was built with support for the
ucd-snmp/dlmod module (which is included as part of the default
build configuration).


dlmod NAME PATH

will load the shared object module from the file PATH (an absolute
filename), and call the initialisation routine init_NAME.


Note:

If the specified PATH is not a fully qualified filename, it will
be interpreted relative to /usr/lib(64)/snmp/dlmod, and .so
will be appended to the filename.


This functionality can also be configured using SNMP SET requests
to the UCD-DLMOD-MIB.
 

Proxy Support

Another mechanism for extending the functionality of the agent
is to pass selected requests (or selected varbinds) to another
SNMP agent, which can be running on the same host (presumably
listening on a different port), or on a remote system.
This can be viewed either as the main agent delegating requests to
the remote one, or acting as a proxy for it.
Use of this mechanism requires that the agent was built with support for the
ucd-snmp/proxy module (which is included as part of the
default build configuration).


proxy [-Cn CONTEXTNAME] [SNMPCMD_ARGS] HOST OID [REMOTEOID]

will pass any incoming requests under OID to the agent listening
on the port specified by the transport address HOST.
See the section
LISTENING ADDRESSES

in the
snmpd(8)

manual page for more information about the format of listening
addresses.



Note:

To proxy the entire MIB tree, use the OID .1.3
(not the top-level .1)


The SNMPCMD_ARGS should provide sufficient version and
administrative information to generate a valid SNMP request
(see snmpcmd(1)).


Note:

The proxied request will not use the administrative
settings from the original request.


If a CONTEXTNAME is specified, this will register the proxy
delegation within the named context in the local agent.
Defining multiple proxy directives for the same OID but
different contexts can be used to query several remote agents
through a single proxy, by specifying the appropriate SNMPv3
context in the incoming request (or using suitable configured
community strings – see the com2sec directive).

Specifying the REMOID parameter will map the local MIB tree
rooted at OID to an equivalent subtree rooted at REMOID
on the remote agent.
 

SMUX Sub-Agents

The Net-SNMP agent supports the SMUX protocol (RFC 1227) to communicate
with SMUX-based subagents (such as gated, zebra or quagga).
Use of this mechanism requires that the agent was built with support for the
smux module, which is not part of the default build environment, and
must be explicitly included by specifying the ‘–with-mib-modules=smux’
option to the configure script when the package is first built.



Note:

This extension protocol has been officially deprecated in
favour of AgentX (see below).


smuxpeer OID PASS

will register a subtree for SMUX-based processing, to be
authenticated using the password PASS. If a subagent
(or "peer") connects to the agent and registers this subtree

then requests for OIDs within it will be passed to that
SMUX subagent for processing.


A suitable entry for an OSPF routing daemon (such as gated,
zebra or quagga) might be something like


smuxpeer .1.3.6.1.2.1.14 ospf_pass

smuxsocket <IPv4-address>

defines the IPv4 address for SMUX peers to communicate with the Net-SNMP agent.
The default is to listen on all IPv4 interfaces ("0.0.0.0"), unless the
package has been configured with "–enable-local-smux" at build time, which
causes it to only listen on 127.0.0.1 by default. SMUX uses the well-known
TCP port 199.

Note the Net-SNMP agent will only operate as a SMUX master
agent. It does not support acting in a SMUX subagent role.
 

AgentX Sub-Agents

The Net-SNMP agent supports the AgentX protocol (RFC 2741) in
both master and subagent roles.
Use of this mechanism requires that the agent was built with support for the
agentx module (which is included as part of the
default build configuration), and also that this support is
explicitly enabled (e.g. via the snmpd.conf file).

There are two directives specifically relevant to running as
an AgentX master agent:


master agentx

will enable the AgentX functionality and cause the agent to
start listening for incoming AgentX registrations.
This can also be activated by specifying the ‘-x’ command-line
option (to specify an alternative listening socket).
agentXPerms SOCKPERMS [DIRPERMS [USER|UID [GROUP|GID]]]

Defines the permissions and ownership of the AgentX Unix Domain socket,
and the parent directories of this socket.
SOCKPERMS and DIRPERMS must be octal digits (see
chmod(1)

). By default this socket will only be accessible to subagents which
have the same userid as the agent.


There is one directive specifically relevant to running as
an AgentX sub-agent:


agentXPingInterval NUM

will make the subagent try and reconnect every NUM seconds to the
master if it ever becomes (or starts) disconnected.

The remaining directives are relevant to both AgentX master
and sub-agents:


agentXSocket [<transport-specifier>:]<transport-address>[,...]

defines the address the master agent listens at, or the subagent
should connect to.
The default is the Unix Domain socket "/var/agentx/master".
Another common alternative is tcp:localhost:705.
See the section
LISTENING ADDRESSES

in the
snmpd(8)

manual page for more information about the format of addresses.



Note:

Specifying an AgentX socket does not automatically enable
AgentX functionality (unlike the ‘-x’ command-line option).

agentXTimeout NUM

defines the timeout period (NUM seconds) for an AgentX request.
Default is 1 second.
agentXRetries NUM

defines the number of retries for an AgentX request.
Default is 5 retries.

net-snmp ships with both C and Perl APIs to develop your own AgentX
subagent.
 

OTHER CONFIGURATION


override [-rw] OID TYPE VALUE

This directive allows you to override a particular OID with a
different value (and possibly a different type of value). The -rw
flag will allow snmp SETs to modify it’s value as well. (note that if
you’re overriding original functionality, that functionality will be
entirely lost. Thus SETS will do nothing more than modify the
internal overridden value and will not perform any of the original
functionality intended to be provided by the MIB object. It’s an
emulation only.) An example:



override sysDescr.0 octet_str "my own sysDescr"


That line will set the sysDescr.0 value to "my own sysDescr" as well
as make it modifiable with SNMP SETs as well (which is actually
illegal according to the MIB specifications).

Note that care must be taken when using this. For example, if you try
to override a property of the 3rd interface in the ifTable with a new
value and later the numbering within the ifTable changes it’s index
ordering you’ll end up with problems and your modified value won’t
appear in the right place in the table.

Valid TYPEs are: integer, uinteger, octet_str, object_id, counter,
null (for gauges, use "uinteger"; for bit strings, use "octet_str").
Note that setting an object to "null" effectively delete’s it as being
accessible. No VALUE needs to be given if the object type is null.

More types should be available in the future.

If you’re trying to figure out aspects of the various mib modules
(possibly some that you’ve added yourself), the following may help you
spit out some useful debugging information. First off, please read
the snmpd manual page on the -D flag. Then the following
configuration snmpd.conf token, combined with the -D flag, can produce
useful output:


injectHandler HANDLER modulename

This will insert new handlers into the section of the mib tree
referenced by "modulename". The types of handlers available for
insertion are:


stash_cache

Caches information returned from the lower level. This
greatly help the performance of the agent, at the cost
of caching the data such that its no longer "live" for
30 seconds (in this future, this will be configurable).
Note that this means snmpd will use more memory as well
while the information is cached. Currently this only
works for handlers registered using the table_iterator
support, which is only a few mib tables. To use it,
you need to make sure to install it before the
table_iterator point in the chain, so to do this:



                  injectHandler stash_cache NAME table_iterator


If you want a table to play with, try walking the
nsModuleTable with and without this injected.


debug

Prints out lots of debugging information when
the -Dhelper:debug flag is passed to the snmpd
application.


read_only

Forces turning off write support for the given module.


serialize

If a module is failing to handle multiple requests
properly (using the new 5.0 module API), this will force
the module to only receive one request at a time.


bulk_to_next

If a module registers to handle getbulk support, but
for some reason is failing to implement it properly,
this module will convert all getbulk requests to
getnext requests before the final module receives it.

dontLogTCPWrappersConnects

If the snmpd was compiled with TCP Wrapper support, it
logs every connection made to the agent. This setting disables
the log messages for accepted connections. Denied connections will
still be logged.
Figuring out module names

To figure out which modules you can inject things into,
run snmpwalk on the nsModuleTable which will give
a list of all named modules registered within the agent.

 

Internal Data tables


table NAME

add_row NAME INDEX(ES) VALUE(S)


 

NOTES


o

The Net-SNMP agent can be instructed to re-read the various configuration files,
either via an snmpset assignment of integer(1) to
UCD-SNMP-MIB::versionUpdateConfig.0 (.1.3.6.1.4.1.2021.100.11.0),
or by sending a kill -HUP signal to the agent process.
o

All directives listed with a value of "yes" actually accept a range
of boolean values. These will accept any of 1, yes or
true to enable the corresponding behaviour,
or any of 0, no or false to disable it.
The default in each case is for the feature to be turned off, so these
directives are typically only used to enable the appropriate behaviour.

 

EXAMPLE CONFIGURATION FILE

See the EXAMPLE.CONF file in the top level source directory for a more
detailed example of how the above information is used in real
examples.
 

FILES

/etc/snmp/snmpd.conf
 

SEE ALSO

snmpconf(1), snmpusm(1), snmp.conf(5), snmp_config(5), snmpd(8), EXAMPLE.conf, read_config(3).



 

Index



NAME

DESCRIPTION

AGENT BEHAVIOUR


SNMPv3 Configuration


SNMPv3 AUTHENTICATION


SNMPv3 USM Users

SSH Support

DTLS Support


ACCESS CONTROL


Traditional Access Control

VACM Configuration

Typed-View Configuration


SYSTEM INFORMATION


System Group

Interfaces Group

Host Resources Group

Process Monitoring

Disk Usage Monitoring

Disk I/O Monitoring

System Load Monitoring

Log File Monitoring


ACTIVE MONITORING


Notification Handling

DisMan Event MIB

DisMan Schedule MIB


EXTENDING AGENT FUNCTIONALITY


Arbitrary Extension Commands

MIB-Specific Extension Commands

Embedded Perl Support

Dynamically Loadable Modules

Proxy Support

SMUX Sub-Agents

AgentX Sub-Agents


OTHER CONFIGURATION


Internal Data tables


NOTES

EXAMPLE CONFIGURATION FILE

FILES

SEE ALSO



Back to Top

PayPal Logo┬ęCheap VPS LLC - Leader of affordable VPS Hosting Services