The Net-SNMP notification receiver (trap daemon) uses one or more configuration files to control its operation and how incoming traps (and INFORM requests) should be processed. This file (snmptrapd.conf) can be located in one of several locations, as described in the snmp_config(5) manual page.
Previously, snmptrapd would accept all incoming notifications, and log them automatically (even if no explicit configuration was provided). Starting with release 5.3, access control checks will be applied to incoming notifications. If snmptrapd is run without a suitable configuration file (or equivalent access control settings), then such traps WILL NOT be processed. See the section Access Control for more details.
As with the agent configuration, the snmptrapd.conf directives can be divided into four distinct groups.
- snmpTrapdAddr [<transport-specifier>:]<transport-address>[,...]
defines a list of listening addresses, on which to receive incoming SNMP notifications. 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 162 on all IPv4 interfaces.
- doNotRetainNotificationLogs yes
disables support for the NOTIFICATION-LOG-MIB. Normally the snmptrapd program keeps a record of the traps received, which can be retrieved by querying the
nlmLogvariableTabletables. This directive can be used to suppress this behaviour.
See the snmptrapd(8) manual page and the NOTIFICATION-LOG-MIB for details.
- doNotLogTraps yes
disables the logging of notifications altogether. This is useful if the snmptrapd application should only run traphandle hooks and should not log traps to any location.
- doNotFork yes
do not fork from the calling shell.
- pidFile PATH
defines a file in which to store the process ID of the notification receiver. By default, this ID is not saved.
Starting with release 5.3, it is necessary to explicitly specify who is authorised to send traps and informs to the notification receiver (and what types of processing these are allowed to trigger). This uses an extension of the VACM model, used in the main SNMP agent.
There are currently three types of processing that can be specified:
log the details of the notification - either in a specified file, to standard output (or stderr), or via syslog (or similar).
pass the details of the trap to a specified handler program, including embedded perl.
forward the trap to another notification receiver.
In the following directives, TYPES will be a (comma-separated) list of one or more of these tokens. Most commonly, this will typically be log,execute,net to cover any style of processing for a particular category of notification. But it is perfectly possible (even desirable) to limit certain notification sources to selected processing only.
- authCommunity TYPES COMMUNITY [SOURCE [OID | -v VIEW ]]
authorises traps (and SNMPv2c INFORM requests) with the specified community to trigger the types of processing listed. By default, this will allow any notification using this community to be processed. The SOURCE field can be used to specify that the configuration should only apply to notifications received from particular sources - see snmpd.conf(5) for more details.
- authUser TYPES [-s MODEL] USER [LEVEL [OID | -v VIEW ]]
authorises SNMPv3 notifications with the specified user to trigger the types of processing listed. By default, this will accept authenticated requests. (authNoPriv or authPriv). The LEVEL field can be used to allow unauthenticated notifications (noauth), or to require encryption (priv), just as for the SNMP agent.
With both of these directives, the OID (or -v VIEW) field can be used to retrict this configuration to the processing of particular notifications.
Unlike the VACM processing described in RFC 3415, this view is only matched against the
snmpTrapOIDvalue of the incoming notification. It is not applied to the payload varbinds held within that notification.
- authGroup TYPES [-s MODEL] GROUP [LEVEL [OID | -v VIEW ]]
- authAccess TYPES [-s MODEL] GROUP VIEW [LEVEL [CONTEXT]]
- setAccess GROUP CONTEXT MODEL LEVEL PREFIX VIEW TYPES
authorise notifications in the specified GROUP (configured using the group directive) to trigger the types of processing listed. See snmpd.conf(5) for more details.
- createUser [-e ENGINEID] username (MD5|SHA|SHA-512|SHA-384|SHA-256|SHA-224) authpassphrase [AES]
See the snmpd.conf(5) manual page for a description of how to create SNMPv3 users. This is roughly the same, but the file name changes to snmptrapd.conf from snmpd.conf.
- disableAuthorization yes
will disable the above access control checks, and revert to the previous behaviour of accepting all incoming notifications.
- format1 FORMAT
- format2 FORMAT
specify the format used to display SNMPv1 TRAPs and SNMPv2 notifications respectively. Note that SNMPv2c and SNMPv3 both use the same SNMPv2 PDU format.
- format DESTINATION FORMAT
specify the format used for different destinations. DESTINATION is one of: print, print1, print2, syslog, syslog1, syslog2, execute, execute1, execute2. print1 is used for printing SNMPv1 traps, print2 is for SNMPv2. print is used for both versions. syslog is similarly used when sending traps to syslog, and execute used when sending traps to a program such as traptoemail(1).
The default formats are
format print1 %.4y-%.2m-%.2l %.2h:%.2j:%.2k %B [%b] (via %A [%a]): %N\n\t%W Trap (%q) Uptime: %#T\n%v\n
format print2 %.4y-%.2m-%.2l %.2h:%.2j:%.2k %B [%b]:\n%v\n
format syslog1 %a: %W Trap (%q) Uptime: %#T%#v\n
format syslog2 %B [%b]: Trap %#v\n
format execute %B\n%b\n%V\n%v\n
See snmptrapd(8) for the layout characters available.
- ignoreAuthFailure yes
instructs the receiver to ignore authenticationFailure traps.
This currently only affects the logging of such notifications. authenticationFailure traps will still be passed to trap handler scripts, and forwarded to other notification receivers. This behaviour should not be relied on, as it is likely to change in future versions.
- logOption string
specifies where notifications should be logged - to standard output, standard error, a specified file or via syslog. See the section LOGGING OPTIONS in the snmpcmd(1) manual page for details.
- outputOption string
specifies various characteristics of how OIDs and other values should be displayed. See the section OUTPUT OPTIONS in the snmpcmd(1) manual page for details.
There are two configuration variables that work together to control when queued traps are logged to the MySQL database. A non-zero value must be specified for sqlSaveInterval to enable MySQL logging.
- sqlMaxQueue max
specifies the maximum number of traps to queue before a forced flush to the MySQL database.
- sqlSaveInterval seconds
specified the number of seconds between periodic queue flushes. A value of 0 for will disable MySQL logging.
As well as logging incoming notifications, they can also be forwarded on to another notification receiver, or passed to an external program for specialised processing.
- traphandle OID|default PROGRAM [ARGS ...]
invokes the specified program (with the given arguments) whenever a notification is received that matches the OID token. For SNMPv2c and SNMPv3 notifications, this token will be compared against the
snmpTrapOIDvalue taken from the notification. For SNMPv1 traps, the generic and specific trap values and the enterprise OID will be converted into the equivalent OID (following RFC 2576).
Typically, the OID token will be the name (or numeric OID) of a NOTIFICATION-TYPE object, and the specified program will be invoked for notifications that match this OID exactly. However this token also supports a simple form of wildcard suffixing. By appending the character ´*' to the OID token, the corresponding program will be invoked for any notification based within subtree rooted at the specified OID. For example, an OID token of
.220.127.116.11.4.1*would match any enterprise specific notification (including the specified OID itself). An OID token of
.18.104.22.168.4.1.*would would work in much the same way, but would not match this exact OID - just notifications that lay strictly below this root. Note that this syntax does not support full regular expressions or wildcards - an OID token of the form
If the OID field is the token default then the program will be invoked for any notification not matching another (OID specific) traphandle entry.
Details of the notification are fed to the program via its standard input. Note that this will always use the SNMPv2-style notification format, with SNMPv1 traps being converted as per RFC 2576, before being passed to the program. The input format is, if you use the default set by the "format execute %B\n%b\n%V\n%v\n", one entry per line:
The name of the host that sent the notification, as determined by gethostbyaddr(3).
The transport address, like
A list of variable bindings describing the contents of the notification, one per line. The first token on each line (up until a space) is the OID of the varind, and the remainder of the line is its value. The format of both of these are controlled by the outputOption directive (or similar configuration).
The first OID should always be
SNMPv2-MIB::sysUpTime.0, and the second should be
SNMPv2-MIB::snmpTrapOID.0. The remaining lines will contain the payload varbind list. For SNMPv1 traps, the final OID will be
A traptoemail script has been included in the Net-SNMP package that can be used within a traphandle directive:
traphandle default /usr/bin/perl /usr/bin/traptoemail -s mysmtp.somewhere.com -f firstname.lastname@example.org email@example.com
- forward OID|default DESTINATION
forwards notifications that match the specified OID to another receiver listening on DESTINATION. The interpretation of OID (and default) is the same as for the traphandle directive).
See the section LISTENING ADDRESSES in the snmpd(8) manual page for more information about the format of listening addresses.
Each time a trap is forwarded, add an OID with the IP address of the system from which the trap has been received. The following OID is added: .22.214.171.124.126.96.36.199.3.x (SNMP-COMMUNITY-MIB::snmpTrapAddress.x) where x is the lowest index >= 0 that does not yet occur in the trap payload. The end recipient (i.e. the monitoring system) can determine the IPv4 address of the original sender by looking for the varbind with OID snmpTrapAddress.0. If that OID is not populated it means that the trap has been sent directly or in other words that it has not been forwarded.
- The daemon blocks while executing the traphandle commands. (This should be fixed in the future with an appropriate signal catch and wait() combination).
- 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.
snmp_config(5), snmptrapd(8), syslog(8), traptoemail(1), variables(5), netsnmp_config_api(3).
snmpd.conf(5), snmptrapd(8), snmpvacm(1).