TrapReceiver(3)

📦
version 5.9.5.2 · 19 versions
, in alpine 3.23

💖 NetSNMP::TrapReceiver + TrapReceiver(3) — embedded perl trap handling, bestie 💖

okay so this is the NetSNMP::TrapReceiver module, and it's part of the User Contributed Perl Documentation. It's the whole embedded perl trap handling situation for Net-SNMP's snmptrapd. No cap, it's giving backend magic. ✨

🌸 NAME 🌸

NetSNMP::TrapReceiver — Embedded perl trap handling for Net-SNMP's snmptrapd

🎀 SYNOPSIS 🎀

Put the following lines in your snmptrapd.conf file:

perl NetSNMP::TrapReceiver::register("trapOID", \&myfunc);

🦋 ABSTRACT 🦋

The NetSNMP::TrapReceiver module is used to register perl subroutines into the Net-SNMP snmptrapd process. Net-SNMP MUST have been configured using --enable-embedded-perl. Registration of functions is then done through the snmptrapd.conf configuration file. This module can NOT be used in a normal perl script to receive traps. It is intended solely for embedded use within the snmptrapd daemon. 🫶

✨ DESCRIPTION ✨

Within the snmptrapd.conf file, the keyword perl may be used to call any perl expression. Using this ability, you can use the NetSNMP::TrapReceiver module to register functions which will be called every time a given notification (a trap or an inform) is received. 💅

Registered functions are called with 2 arguments. The first is a reference to a hash containing information about how the trap was received (what version of the SNMP protocol was used, where it came from, what SNMP user name or community name it was sent under, etc). The second argument is a reference to an array containing the variable bindings (OID and value information) that define the notification itself.

Each variable is itself a reference to an array containing four values: a NetSNMP::OID object, a string representation of the value that came associated with it, the value's numeric type (see NetSNMP::ASN for further details on SNMP typing information), and the raw value of the trap, encoded according to its type. 64-bit integer types are returned as strings, integer types as integers, strings as strings, object identifiers as NetSNMP::OID objects, and any other types as undefs.

Registered functions should return one of the following values:

  • NETSNMPTRAPD_HANDLER_OK — handling the trap succeeded, but lets the snmptrapd daemon check for further appropriate handlers.
  • NETSNMPTRAPD_HANDLER_FAIL — handling the trap failed, but lets the snmptrapd daemon check for further appropriate handlers.
  • NETSNMPTRAPD_HANDLER_BREAK — stops evaluating the list of handlers for this specific trap, but lets the snmptrapd daemon apply global handlers.
  • NETSNMPTRAPD_HANDLER_FINISH — stops searching for further appropriate handlers.

If a handler function does not return anything appropriate or even nothing at all, a return value of NETSNMPTRAPD_HANDLER_OK is assumed.

Subroutines are registered using the NetSNMP::TrapReceiver::register function, which takes two arguments. The first is a string describing the notification you want to register for (such as "linkUp" or "MyMIB::MyTrap" or ".1.3.6.1.4.1.2021...."). Two special keywords can be used in place of an OID: "default" and "all". The "default" keyword indicates you want your handler to be called in the case where no other handlers are called. The "all" keyword indicates that the handler should ALWAYS be called for every notification. 👑

🔥 EXAMPLE 🔥

As an example, put the following code into a file (say /usr/local/share/snmp/mytrapd.pl):

#!/usr/bin/perl

sub my_receiver {
    print "********** PERL RECEIVED A NOTIFICATION:\n";

    # print the PDU info (a hash reference)
    print "PDU INFO:\n";
    foreach my $k(keys(%{$_[0]})) {
      if ($k eq "securityEngineID" || $k eq "contextEngineID") {
        printf "  %-30s 0x%s\n", $k, unpack('h*', $_[0]{$k});
      }
      else {
        printf "  %-30s %s\n", $k, $_[0]{$k};
      }
    }

    # print the variable bindings:
    print "VARBINDS:\n";
    foreach my $x (@{$_[1]}) {
        printf "  %-30s type=%-2d value=%s\n", $x->[0], $x->[2], $x->[1];
    }
}

NetSNMP::TrapReceiver::register("all", \&my_receiver) ||
  warn "failed to register our perl trap handler\n";

print STDERR "Loaded the example perl snmptrapd handler\n";

Then, put the following line in your snmprapd.conf file:

perl do "/usr/local/share/snmp/mytrapd.pl";

Start snmptrapd (as root, and the following other options make it stay in the foreground and log to stderr):

snmptrapd -f -Le

You should see it start up and display the final message from the end of the above perl script:

Loaded the perl snmptrapd handler
2004-02-11 10:08:45 NET-SNMP version 5.2 Started.

Then, if you send yourself a fake trap using the following example command:

snmptrap -v 2c -c mycommunity localhost 0 linkUp ifIndex.1 i 1 \
    ifAdminStatus.1 i up ifOperStatus.1 i up ifDescr s eth0

You should see the following output appear from snmptrapd as your perl code gets executed:

********** PERL RECEIVED A NOTIFICATION:
PDU INFO:
  notificationtype               TRAP
  receivedfrom                   127.0.0.1
  version                        1
  errorstatus                    0
  messageid                      0
  community                      mycommunity
  transactionid                  2
  errorindex                     0
  requestid                      765160220
VARBINDS:
  sysUpTimeInstance              type=67 value=0:0:00:00.00
  snmpTrapOID.0                  type=6  value=linkUp
  ifIndex.1                      type=2  value=1
  ifAdminStatus.1                type=2  value=1
  ifOperStatus.1                 type=2  value=1
  ifDescr                        type=4  value="eth0"

🫶 Passing Arguments 🫶

If you need to pass arguments in to the script, you'll need to do it by one of two methods:

💅 Using Subroutines

You can either define a subroutine in the file rather than have the file itself do something. IE, in the file if you put:

sub foo {
   print "$_[0]\n";
}

and then put these lines in the snmptrapd.conf file:

perl do /path/to/script
perl foo("hello world");
perl foo("now I am passing something different");

It'd call the foo function twice, and print the results to the console where snmptrapd was started.

🌈 Using Variables

Or you could always set a variable ahead of time:

perl $myVariable = 42;
perl do /path/to/script

And have the script look for and use the $myVariable value in the script.

👑 EXPORT 👑

None by default.

⭐ Exportable constants

  • NETSNMPTRAPD_AUTH_HANDLER
  • NETSNMPTRAPD_HANDLER_BREAK
  • NETSNMPTRAPD_HANDLER_FAIL
  • NETSNMPTRAPD_HANDLER_FINISH
  • NETSNMPTRAPD_HANDLER_OK
  • NETSNMPTRAPD_POST_HANDLER
  • NETSNMPTRAPD_PRE_HANDLER

🎀 SEE ALSO 🎀

💜 AUTHOR 💜

W. Hardaker, <hardaker@users.sourceforge.net>

Copyright 2004 by W. Hardaker

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

💖 bestie sign-off: this page's source/version is perl v5.42.2, dated 2026-04-12, and it's literally TrapReceiver(3). Byeee, go register those traps 🎀✨

📦 where this page comes from