SNMPD.CONF

Section: Net-SNMP (5)
Updated: 08 Feb 2002
 

NAME

/etc/snmp/snmpd.conf - configuration file for the Net-SNMP SNMP agent.  

DESCRIPTION

snmpd.conf is the configuration file which defines how the Net-SNMP SNMP agent operates. These files may contain any of the directives found in the DIRECTIVES section below. This file is not required for the agent to operate and respond to requests.  

PLEASE READ FIRST

First, make sure you have read the snmp_config(5) manual page that describes how the Net-SNMP configuration files operate, where they are located and how they all work together.

Also, you might consider looking into the snmpconf application (perl script) which can help you build an snmpd.conf file by prompting you for information. You should try it. Really. Go ahead. Right now. Run:

snmpconf -g basic_setup

to get you started. See the snmpconf(1) manual page for more information.  

EXTENSIBLE-MIB

The Net-SNMP SNMP agent reports much of its information through queries to the 1.3.6.1.4.1.2021 section of the MIB tree. Every MIB in this section has the following table entries in it.

.1 -- index
This is the table's index numbers for each of the DIRECTIVES listed below.
.2 -- name
The name of the given table entry. This should be unique, but is not required to be.
.100 -- errorFlag
This is a flag returning either the integer value 1 or 0 if an error is detected for this table entry.
.101 -- errorMsg
This is a DISPLAY-STRING describing any error triggering the errorFlag above.
.102 -- errorFix
If this entry is set to the integer value of 1 AND the errorFlag defined above is indeed a 1, a program or script will get executed with the table entry name from above as the argument. The program to be executed is configured in the config.h file at compile time.
 

Directives

proc NAME
proc NAME MAX
proc NAME MAX MIN
Checks to see if processes called NAME are running on the agent machine. An error flag (1) and a description message are then passed to the 1.3.6.1.4.1.2021.2.1.100 and 1.3.6.1.4.1.2021.2.1.101 MIB columns (respectively) if the NAME'd program is not found in the process table as reported by "/bin/ps -e".
If MAX and MIN are not specified, MAX is assumed to be infinity and MIN is assumed to be 1.
If MAX is specified but MIN is not specified, MIN is assumed to be 0.
procfix NAME PROG ARGS
This registers a command that knows how to fix errors with the given process NAME. When 1.3.6.1.4.1.2021.2.1.102 for a given NAMEd program is set to the integer value of 1, this command will be called. It defaults to a compiled value set using the PROCFIXCMD definition in the config.h file.
exec NAME PROG ARGS
exec MIBNUM NAME PROG ARGS
If MIBNUM is not specified, the agent executes the named PROG with arguments of ARGS and returns the exit status and the first line of the STDOUT output of the PROG program to queries of the 1.3.6.1.4.1.2021.8.1.100 and 1.3.6.1.4.1.2021.8.1.101 mib columns (respectively). All STDOUT output beyond the first line is silently truncated.
If MIBNUM is specified, it acts as above but returns the exit status to MIBNUM.100.0 and the entire STDOUT output to the table MIBNUM.101 in a MIB table. In this case, the MIBNUM.101 mib contains the entire STDOUT output, one MIB table entry per line of output (ie, the first line is output as MIBNUM.101.1, the second at MIBNUM.101.2, etc...).
Note:
The MIBNUM must be specified in dotted-integer notation and can not be specified as ".iso.org.dod.internet..." (should instead be .1.3.6.1...).
Note:
The agent caches the exit status and STDOUT of the executed program for 30 seconds after the initial query. This is to increase speed and maintain consistency of information for consecutive table queries. The cache can be flushed by a snmp-set request of integer(1) to 1.3.6.1.4.1.2021.100.VERCLEARCACHE.
execfix NAME PROG ARGS
This registers a command that knows how to fix errors with the given exec or sh NAME. When 1.3.6.1.4.1.2021.8.1.102 for a given NAMEd entry is set to the integer value of 1, this command will be called. It defaults to a compiled value set using the EXECFIXCMD definition in the config.h file.
disk PATH
disk PATH [ MINSPACE | MINPERCENT% ]
Checks the named disks mounted at PATH for available disk space. If the disk space is less than MINSPACE (kB) if specified or less than MINPERCENT (%) if a % sign is specified, or DEFDISKMINIMUMSPACE (kB) if not specified, the associated entry in the 1.3.6.1.4.1.2021.9.1.100 MIB table will be set to (1) and a descriptive error message will be returned to queries of 1.3.6.1.4.1.2021.9.1.101.
includeAllDisks MINPERCENT%
Adds all the disks that can be found on the system using the setmntent(3) and getmntent(3), or fopen(3) and getmntent(3), or setfsent(3) and getfsent(3) system calls. If none of the above system calls are available then it adds the root partition "/", (which is assumed to exist on any UNIX based system) using the statfs(2) system call.
There can only be one 'includeAllDisks' directive in the config- uration file. It can be used in conjunction with the 'disk' directive. They may be used in any order. The 'disk' directive overrides the disk usage specified by the 'includeAllDisks' directive, no matter in which order they are specified in the configuration file.
The 'includeAllDisks' directive only includes the disks that are mounted when the snmpd daemon is started. It cannot include disks that are dynamically loadable, such as with automount. So the preferred way is to mount all the disks that will ever need to be monitored before starting the snmpd daemon.
load MAX1
load MAX1 MAX5
load MAX1 MAX5 MAX15
Checks the load average of the machine and returns an error flag (1), and an text-string error message to queries of 1.3.6.1.4.1.2021.10.1.100 and 1.3.6.1.4.1.2021.10.1.101 (respectively) when the 1-minute, 5-minute, or 15-minute averages exceed the associated maximum values. If any of the MAX1, MAX5, or MAX15 values are unspecified, they default to a value of DEFMAXLOADAVE.
file FILE [MAXSIZE]
Monitors file sizes and makes sure they don't grow beyond a certain size (in kilobytes). MAXSIZE defaults to infinite if not specified, and only monitors the size without reporting errors about it. A maximum of 20 files can be monitored.
 

Errors

Any errors in obtaining the above information are reported via the 1.3.6.1.4.1.2021.101.1.100 flag and the 1.3.6.1.4.1.2021.101.1.101 text-string description.  

AGENTX SUB-AGENTS

To enable AgentX support in the SNMP master agent, put the following line in your snmpd.conf file:
master agentx
See README.agentx for further details.
AgentXSocket addr
This defines the address the master agent listens at. The default is /var/agentx/master. By default the Unix Domain socket is accessible only to subagents which have the same userid as the agent. Another possibility is localhost:705
AgentXTimeout addr
Defines the timeout period for an AgentX request. Default is 1 second.
AgentXRetries addr
Defines the number of retries for an AgentX request. Default is 5 retries. You can also put the following in your subagent.conf file (where "subagent" is the name you used in your init_snmp("subagent") api call:
agentPingInterval NUM
This makes the subagent try and reconnect every NUM seconds to the master if it ever becomes (or starts) disconnected.
 

SMUX SUB-AGENTS

To enable and SMUX based sub-agent, such as gated, use the smuxpeer configuration entry
smuxpeer OID PASS
For gated a sensible entry might be smuxpeer .1.3.6.1.4.1.4.1.3 secret
 

DYNAMICALLY LOADABLE MODULES

If the agent is built with support for the UCD-DLMOD-MIB it is capable of loading agent MIB modules dynamically at startup through the dlmod directive and during runtime through use of the UCD-DLMOD-MIB. The following directive loads the shared object module file PATH which uses the module name prefix NAME.
dlmod NAME PATH
 

ACCESS CONTROL

snmpd supports the View-Based Access Control Model (VACM) as defined in RFC 2575. To this end, it recognizes the following keywords in the configuration file: com2sec, group, access, and view as well as some easier-to-use wrapper directives: rocommunity, rwcommunity, rouser, rwuser. If IPv6 support has been enabled, the rocommunity6 and rwcommunity6 tokens will also be available. This section defines how to configure the snmpd program to accept various types and levels of access.
rouser USER [noauth|auth|priv [OID]]
rwuser USER [noauth|auth|priv [OID]]
Creates a SNMPv3 USM user in the VACM access configuration tables. It is more efficient (and powerful) to use the combined group, access, and view directives instead, but these wrapper directives are much simpler.
The minimum level of authentication and privacy the user must use is specified by the first token (which defaults to "auth"). The OID parameter restricts access for that user to everything below the given OID.
rocommunity COMMUNITY [SOURCE [OID]]
rwcommunity COMMUNITY [SOURCE [OID]]
These create read-only and read-write communities that can be used to access the agent. They are a quick wrapper around the more complex and powerful com2sec, group, access, and view directive lines. They are not as efficient either, as groups aren't created so the tables are possibly larger. In other words: don't use these if you have complex situations to set up. If your setup is simple or you don't mind a small performance hit, use these directives.
The format of the SOURCE is token is described in the com2sec directive section below. The OID token restricts access for that community to everything below that given OID.
rocommunity6 COMMUNITY [SOURCE [OID]]
rwcommunity6 COMMUNITY [SOURCE [OID]]
They are the alternative directives to the rocommunity, rwcommunity for the transport domain UDPIPv6. They are only valid in specifing UDPIPv6 as transport domain.
The format of the SOURCE is token is described in the com2sec6 directive section below. The OID token restricts access for that community to everything below that given OID.
com2sec NAME SOURCE COMMUNITY
This directive specifies the mapping from a source/community pair to a security name. SOURCE can be a hostname, a subnet, or the word "default". A subnet can be specified as IP/MASK or IP/BITS. For example, given a directive "com2sec myLocal 10.10.10.0/24 public" then this would match requests from IP addresses 10.10.10.0 through to 10.10.10.255, but not one from 10.10.11.1 or similar. The first source/community combination that matches the incoming packet is selected.
com2sec6 NAME SOURCE COMMUNITY
This directive is the IPv6 version of com2sec. A subnet can be specified as IPv6/IPv6MASK or IPv6/BITS. It is only valid in specifing UDPIPv6 as transport domain.
group NAME MODEL SECURITY
This directive defines the mapping from securitymodel/securityname to group. MODEL is one of v1, v2c, or usm.
access NAME CONTEXT MODEL LEVEL PREFX READ WRITE NOTIFY
The access directive maps from group/security model/security level to a view. MODEL is one of any, v1, v2c, or usm. LEVEL is one of noauth, auth, or priv. PREFX specifies how CONTEXT should be matched against the context of the incoming pdu, either exact or prefix. READ, WRITE and NOTIFY specifies the view to be used for the corresponding access. For v1 or v2c access, LEVEL will be noauth, and CONTEXT will be empty.
view NAME TYPE SUBTREE [MASK]
This defines the named view. TYPE is either included or excluded. MASK is a list of hex octets, separated by '.' or ':'. The MASK defaults to "ff" if not specified.
The reason for the mask is, that it allows you to control access to one row in a table, in a relatively simple way. As an example, as an ISP you might consider giving each customer access to his or her own interface:
view cust1 included interfaces.ifTable.ifEntry.ifIndex.1 ff.a0
view cust2 included interfaces.ifTable.ifEntry.ifIndex.2 ff.a0
(interfaces.ifTable.ifEntry.ifIndex.1 == .1.3.6.1.2.1.2.2.1.1.1, ff.a0 == 11111111.10100000. which nicely covers up and including the row index, but lets the user vary the field of the row)
VACM Examples:
# sec.name source community com2sec local localhost private com2sec mynet 10.10.10.0/24 public com2sec public default public com2sec6 mynet fec0::/64 public # sec.model sec.name group mygroup v1 mynet group mygroup v2c mynet group mygroup usm mynet group local v1 local group local v2c local group local usm local group public v1 public group public v2c public group public usm public # incl/excl subtree mask view all included .1 80 view system included system fe view mib2 included .iso.org.dod.internet.mgmt.mib-2 fc # context sec.model sec.level prefix read write notify access mygroup "" any noauth exact mib2 none none access public "" any noauth exact system none none access local "" any noauth exact all all all
Default VACM model
The default configuration of the agent, as shipped, is functionally equivalent to the following entries: com2sec public default public group public v1 public group public v2c public group public usm public view all included .1 access public "" any noauth exact all none none
 

SNMPv3 CONFIGURATION

engineID STRING
The snmpd agent needs to be configured with an engineID to be able to respond to SNMPv3 messages. With this configuration file line, the engineID will be configured from STRING. The default value of the engineID is configured with the first IP address found for the hostname of the machine.
createUser [-e ENGINEID] username (MD5|SHA) authpassphrase [DES] [privpassphrase]
MD5 and SHA are the authentication types to use, but you must have built the package with openssl installed in order to use SHA. The only privacy protocol currently supported is DES. 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.
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/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").
 

SETTING SYSTEM INFORMATION

syslocation STRING
syscontact STRING
sysname STRING
Sets the system location, system contact or system name for the agent. This information is reported in the 'system' group the mibII tree. Ordinarily these objects (sysLocation.0, sysContact.0 and sysName.0) are read-write. However, specifying the value for one of these objects by giving the appropriate token makes the corresponding object read-only, and attempts to set the value of the object will result in a notWritable error response.
sysservices NUMBER
Sets the value of the system.sysServices.0 object. For a host, a good value is 72.
sysdescr STRING
sysobjectid OID
Sets the system description or object ID for the agent. Although these values are not SNMP-writable, it is conceivable that a network administrator may wish to configure them to something other than the default values.
agentaddress [<transport-specifier>:]<transport-address>[,...]
Makes the agent list on the specified comma-separated list of listening addresses instead of the default behaviour, which is to listen on UDP port 161 on all IPv4 interfaces. See the section LISTENING ADDRESSES in the snmpd(8) manual page for more information about the format of listening addresses. For example, specifying agentaddress 161,tcp:161,localhost:9161 will make the agent listen on UDP port 161 on all IPv4 interfaces, TCP port 161 on all IPv4 interfaces and UDP port 9161 only on the interface associated with the localhost address.
agentgroup groupid
Change to this gid after opening port. The groupid may refer to a group by name or a number if the group number starts with '#'. For example, specifying agentgroup snmp will cause the agent to run as the snmp group or agentgroup #10 will cause the agent to run as the group with groupid 10.
agentuser uid
Change to this uid after opening port. The userid may refer to a user by name or a number if the user number starts with '#'. For example, specifying agentuser snmp will cause the agent to run as the snmp user or agentuser #10 will cause the agent to run as the user with userid 10.
interface NAME TYPE SPEED
For interfaces where the agent fails to guess correctly on the type and speed, this directive can supply additional information. TYPE is a type value as given in the IANAifType-MIB.
ignoredisk STRING
When scanning for available disk devices the agent might block in trying to open all possible disk devices. This might lead to a timeout when walking the device tree. Sometimes the next walk will run without timeout, sometimes it will timeout every time you try it.
If you experience such behaviour you might add this directive and give all device names not to be checked (i.e. opened). You might have more than one such directive in your configuration file stating all devices not to be opened. You might also specify those devices using wildcards similar to the syntax you can use in a bourne shell (see examples below).
Note: For a list of devices scanned for every system please consult the sources (host/hr_disk.c) and check for the Add_HR_Disk_entry() calls relevant for your type of OS.
Examples:
ignoredisk /dev/rdsk/c0t2d0
This directive prevents the device /dev/rdsk/c0t2d0 from being scanned.
ignoredisk /dev/rdsk/c0t[!6]d0
This directive prevents all devices /dev/rdsk/c0tXd0 except .../c0t6d0 from being scanned. For most systems similar is the following directive:
ignoredisk /dev/rdsk/c0t[0-57-9a-f]d0
ignoredisk /dev/rdsk/c1*
This directive prevents all devices whose device names start with /dev/rdsk/c1 from being scanned.
ignoredisk /dev/rdsk/c?t0d0
This directive prevents all devices /dev/rdsk/cXt0d0 ('X' might be any char) from being scanned.
You might use more than one such wildcard expression in any such directive.
storageUseNFS NUMBER
Setting storageUseNFS to 1 causes all NFS and NFS-like file systems to be marked as 'Network Disks' in the hrStorageTable. This is according to RFC 2790. Not setting storageUseNFS or setting it to 2 causes NFS and NFS-like file systems to be marked as 'Fixed Disks' as it has been in previous versions of the ucd-snmp SNMP agent.
authtrapenable NUMBER
Setting authtrapenable to 1 enables generation of authentication failure traps. The default value is disabled(2). Ordinarily the corresponding object (snmpEnableAuthenTraps.0) is read-write, but setting its value via this token makes the object read-only, and attempts to set the value of the object will result in a notWritable error response.
override OID TYPE VALUE
This directive allows you to override a particular OID with a different value (and possibly a different type of value). 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, bit_str, object_id, counter, gauge, null. 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, as well as writable object support.
 

SETTING UP TRAP AND/OR INFORM DESTINATIONS

trapcommunity STRING
This defines the default community string to be used when sending traps. Note that this command must be used prior to any of the following three commands that are intended use this community string.
trapsink HOST [COMMUNITY [PORT]]
trap2sink HOST [COMMUNITY [PORT]]
informsink HOST [COMMUNITY [PORT]]
These commands define the hosts to receive traps (and/or inform notifications). The daemon sends a Cold Start trap when it starts up. If enabled, it also sends traps on authentication failures. Multiple trapsink, trap2sink and informsink lines may be specified to specify multiple destinations. Use trap2sink to send SNMPv2 traps and informsink to send inform notifications. If COMMUNITY is not specified, the string from a preceding trapcommunity directive will be used. If PORT is not specified, the well known SNMP trap port (162) will be used.
trapsess [SNMPCMD_ARGS] HOST
This is a more generic trap configuration token that allows any type of trap destination to be specified with any version of SNMP. See the snmpcmd(1) manual page for further details on the arguments that can be passed as SNMPCMD ARGS. In addition to the arguments listed there, the special argument -Ci specifies that you want inform notifications to be used instead of unacknowledged traps (this requires that you also specify a version number of v2c or v3 as well).
 

PROXY SUPPORT

proxy [-Cn CONTEXTNAME] [SNMPCMD ARGS] HOST OID [REMOTEOID]
This token specifies that any incoming requests under OID should be proxied on to another HOST instead. If a CONTEXTNAME is specified, it assigns the proxied tree to a particular context name within the local agent. This is the proper way to query multiple agents through a single proxy. Assign each remote agent to a different context name. Then you can use "snmpwalk -n contextname1" to walk one remote proxied agent and "snmpwalk -n contextname2" to walk another, assuming you are using SNMPv3 to talk to the proxy (snmpv1 and snmpv2c context mappings aren't currently supported but might be in the future). Optionally, relocate the local OID tree to the new location at the REMOTEOID. To authenticate to HOST you should use the appropriate set of SNMPCMD ARGS. See the snmpcmd(1) manual page for details.
Examples:
# assigns the entire mib tree on remotehost1 to the context of the
# same name:
proxy -Cn remotehost1 -v 1 -c public remotehost1 .1.3
# ditto, but for remotehost 2
proxy -Cn remotehost2 -v 1 -c public remotehost2 .1.3
# proxies only the ucdavis enterprises tree to the remote host using snmpv1
proxy -v 1 -c public remotehost .1.3.6.1.4.1.2021
# uses v3 to access remotehost and converts the remote .1.3.6.1.2.1.1
# oid to local .1.3.6.1.3.10 oid (another way to access mulitple hosts
# without using contexts)
proxy -v 3 -l noAuthNoPriv -u user remotehost .1.3.6.1.3.10 .1.3.6.1.2.1.1
 

PASS-THROUGH CONTROL

pass MIBOID EXEC
(If you're writing perl scripts, please see the embedded perl support information later in this manual page). Passes entire control of MIBOID to the EXEC program. The EXEC program is called in one of the following three ways:
EXEC -g MIBOID
EXEC -n MIBOID
These call lines match to SNMP get and getnext requests. It is expected that the EXEC program will take the arguments passed to it and return the appropriate response through it's stdout.
The first line of stdout should be the MIB OID of the returning value. The second line should be the TYPE of value returned, where TYPE is one of the text strings: string, integer, unsigned, objectid, timeticks, ipaddress, counter, or gauge. The third line of stdout should be the VALUE corresponding with the returned TYPE.
For instance, if a script was to return the value integer value "42" when a request for .1.3.6.1.4.100 was requested, the script should return the following 3 lines:

  .1.3.6.1.4.100

  integer

  42
To indicate that the script is unable to comply with the request due to an end-of-mib condition or an invalid request, simple exit and return no output to stdout at all. An SNMP error will be generated corresponding to the SNMP noSuchName response.
EXEC -s MIBOID TYPE VALUE
For SNMP set requests, the above call method is used. The TYPE passed to the EXEC program is one of the text strings: integer, counter, gauge, timeticks, ipaddress, objid, or string, indicating the type of value passed in the next argument.
Return nothing to stdout, and the set will assumed to have been successful. Otherwise, return one of the following error strings to signal an error: not-writable, or wrong-type and the appropriate error response will be generated instead.
Note:
By default, the only community allowed to write (ie snmpset) to your script will be the "private" community,or community #2 if defined differently by the "community" token discussed above. Which communities are allowed write access are controlled by the RWRITE definition in the snmplib/snmp_impl.h source file.
Example (in snmpd.conf):
pass .1.3.6.1.4.1.2021.255 /path/to/local/passtest
pass_persist MIBOID EXEC
Passes entire control of MIBOID to the EXEC program. Similar to pass, but the EXEC program continues to run after the initial request is answered. Also, pass and pass_persist block till they return.
Upon initialization, EXEC is passed the string "PING\n" in stdin, and it should respond by printing "PONG\n" to stdout.
For get and getnext requests, EXEC program is passed two lines, the command (get or getnext) and the MIB OID. It should return three lines, the MIB OID, the TYPE of value returned, the VALUE corresponding with the returned TYPE.
For example, if the value for .1.3.6.1.4.100 was requested, the following 2 lines would be passed in to stdin:

  get

  .1.3.6.1.4.100  
To return the value, say, 42, the script would write to stdout:

  .1.3.6.1.4.100

  integer

  42
To indicate that the script is unable to comply with the request due to an end-of-mib condition or an invalid request, print "NONE\n" to stdout.
Example (in snmpd.conf):
pass_persist .1.3.6.1.4.1.2021.255 /path/to/local/pass_persisttest
 

EMBEDDED PERL SUPPORT

Warning: though embedded perl is working, not much functionality has been implemented yet and thus writing mib module pieces for the agent within perl is not trivial at this point. It should get better in future releases.

The net-snmp package has ability to call perl scripts directly inside the agent through embedded perl technology (similar to mod_perl for the apache web server). This must be turned on at compile time by passing --enable-embedded-perl to the configure script when the package is built. To see if your package was built with embedded perl, run "net-snmp-config --configure-options" and see if that flag was used.

If compiled in, it defines the following snmpd.conf configuration directives:

disablePerl true
This will turn off perl support entirely. If the embedded perl support stops working due to a change in perl, etc, this will stop any calls to the perl core.

perlInitFile FILE
Use FILE as the initialization file. This file is normally /usr/share/snmp/snmp_perl.pl but this token can override that default. This file performs any in-perl initialization that is needed before the rest of the perl directives (below) are called. It is sourced once just before the first perl directive is parsed. See the default file for an example of the initialization it performs.
perl EXPRESSION
Calls perl to evaluate an expression. Normally you'd want to do something like register a function to call when an OID is requested, but you can really do anything perl related you want. For example:
perl print "hello world\n";
is the most basic hello world example.
The init script by default initializes a $agent variable which is a pointer to a NetSnmp::agent object through which you can register callbacks when a section of the OID tree is hit:
perl use Data::Dumper;
perl sub myroutine  { print "got called: ",Dumper(@_),"\n"; }
perl $agent->register('mylink', '.1.3.6.1.8765', \&myroutine);
Sourcing an external file:
perl 'do /path/to/file.pl';
No better examples exist at the moment, unfortunately. Look for improved support in future releases. Comments on how this looks as an architecture are certainly appreciated now.
 

DISMAN-EVENT-MIB SUPPORT (READ: SENDING TRAPS ON ERRORS)

Warning: this implementation has not been extensively tested and is additionally not known to be entirely complete. The concepts defined here should function appropriately, however, but no promises are made at this time.

If your agent was compiled with support for the DISMAN-EVENT-MIB (you can enable this by running the net-snmp configure script with the --with-mib-modules=disman/event-mib argument) you have support for having the agent check its own data at regular intervals and to send out traps when certain conditions occur. Traps are sent when expressions are first noticed, not once per evaluation. Once a test expression fires a trap, the test will have to fail again before a new trap is sent. See the DISMAN-EVENT-MIB documentation for more details. This can be configured either using the MIB tables themselves or by using these special key words:

agentSecName NAME
The DISMAN-EVENT-MIB support requires a valid user name for which to scan your agent with. This can either be specified using the agentSecName token or by explicitly list one on the "monitor" lines described below using the -u switch. Either way, a "rouser" line (or equivalent access control settings) must also be specified with the same security name name. If you need an example, just do something like this:
agentSecName internal
rouser internal
And everything below should work just fine.
monitor [OPTIONS] NAME EXPRESSION
This token tells the agent to monitor itself for problems based on EXPRESSION. Expression is a simple expression based on an oid, a comparison operator (!=, ==, <, <=, >, >=) and an integer value (see the examples below). NAME is merely an arbitrary name of your choosing for administrative purposes only. OPTIONS include the following possibilities:
-t
Use a threshold monitor instead of a boolean monitor. This means that expression should be a low and high value. If the given OID passes beyond the high value, a rising alarm will triggered. A falling alarm will then be triggered after it falls below the low value.
-r FREQUENCY
Monitors the given expression every FREQUENCY seconds. The default is 600 (10 minutes).
-u SECNAME
Use the SECNAME security name for scanning the local host. Specifically, this SECNAME must then be given access control rights via something like the "rouser" snmpd.conf token for this expression to be valid at all. If not specified, it uses the default security name specified by the agentsecname snmpd.conf token. Either the -u flag or a valid agentsecname token must be specified (and that name must be given proper access control rights via a "rouser" token).
-o OID
Specifies additional object values to be delivered with in the resulting trap in addition to the normal trap objects. This is useful for obtaining other columns in the table for the row that triggered the expression. See the examples below for more details.
-e EVENTNAME
Specifies an event name that describes what to do when the trigger is fired. Currently, this must be the name of a notificationEvent event as described below.
The following example configuration checks the hrSWRunPerfTable table (listing running processes) for any process which is consuming > 10Mb of memory. It performs this check every 600 seconds (the default). For every process it finds exceeding the limit, it will end out exactly one notification. In addition to the normal hrSWRunPerfMem oid and value sent in the trap, the hrSWRunName object will also be sent. Note that the hrSWRunName object actually occurs in a different table, but since the indexes to the two tables are the same this works out alright.
rouser me
monitor -u me -o sysUpTime.0 -o hrSWRunName "high process memory" hrSWRunPerfMem > 10000
The above line would produce a trap which, when formated by snmptrapd, would look like:
2002-04-05 13:33:53 localhost.localdomain [udp:127.0.0.1:32931]:
        sysUpTimeInstance = Timeticks: (1629) 0:00:16.29        snmpTrapOID.0 = OID: mteTriggerFired    mteHotTrigger = high process memory     mteHotTargetName =      mteHotContextName =     mteHotOID = OID: hrSWRunPerfMem.1968    mteHotValue = 28564     hrSWRunName.1968 = "xemacs"
This shows my xemacs process using 28Mb of resident memory. Which, considering it's xemacs, is not that surprising.
Threshold example:
monitor -t -r 15 -o prNames -o prErrMessage "process table" prErrorFlag 0 1
notificationEvent NAME NOTIFICATION [[-w] OID_OBJECT ...]
This will create a notification event, which can be fired by attaching it to a monitor using a monitor's -e switch and an identical NAME field. The NOTIFICATION to be sent should be the OID of a notification. Additional objects can be included, and by default the suffix of the row/object being monitored will be appended to the object identifier unless it's told not to be a wild-card object by prefixing it with the -w switch. EG, if you're monitoring the ifTable and you want your trap to include the ifDescr object for the row that was discovered, don't add the -w switch and the .INDEX field will be appended. If the OID is fully qualified (EG, "sysContact.0") and no instance suffix should be appended to it then add a -w switch before it. See the linkUpDownNotifications token below for example usage of this token to send the linkUp and linkDown traps.
linkUpDownNotifications yes
This will make the DISMAN-EVENT-MIB support watch the ifTable to determine when a network interface is taken up or down. When this happens, a linkUp or linkDown notification will be triggered. This is exactly equivalent to doing:
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
By default, the agent and the DISMAN-EVENT-MIB support do nothing until configured. Typically people wish to watch a bunch of tables within the UCD-SNMP-MIB which are designed specifically for reporting problems. If the "defaultMonitors yes" line is put into the snmpd.conf file (which must be accompanied by an appropriate agentSecName line and a rouser line), the following monitoring conditions will be installed:
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
 

DEBUGGING AND OTHER EXTENSIBILITY NOTES

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

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.  

RE-READING snmpd.conf AND snmpd.local.conf

The Net-SNMP agent can be forced to re-read its configuration files. It can be told to do so by one of two ways:
1.
An snmpset of integer(1) to UCD-SNMP-MIB::versionUpdateConfig.0 (.1.3.6.1.4.1.2021.100.11.0)
2.
A "kill -HUP" signal sent to the snmpd agent process.
 

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
PLEASE READ FIRST
EXTENSIBLE-MIB
Directives
Errors
AGENTX SUB-AGENTS
SMUX SUB-AGENTS
DYNAMICALLY LOADABLE MODULES
ACCESS CONTROL
SNMPv3 CONFIGURATION
SETTING SYSTEM INFORMATION
SETTING UP TRAP AND/OR INFORM DESTINATIONS
PROXY SUPPORT
PASS-THROUGH CONTROL
EMBEDDED PERL SUPPORT
DISMAN-EVENT-MIB SUPPORT (READ: SENDING TRAPS ON ERRORS)
DEBUGGING AND OTHER EXTENSIBILITY NOTES
EXAMPLE CONFIGURATION FILE
RE-READING snmpd.conf AND snmpd.local.conf
FILES
SEE ALSO
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