SMART-SNMP

smart-snmp is a lightweight program written on C and used as SNMP server. Main feature of smart-snmp is possibility to get or set values on demand by providing callbacks for small shell or Lua scripts.

Installation

TBD

Usage

smart-snmp [options]
    -4, --use-ipv4     
      Use IPv4, default
    -6, --use-ipv6
      Use IPv6
    -a, --auth
      Require client authentication, thus SNMP version 2c, default is off.
    -c, --community
      SNMP version 2c authentication, or community, string, default is "public". 
      Remeber to also enable --auth to activate authentication.
    -h, --help
      Show summary of command line options and exit.
    -m, --max-connections NUMBER
      Amount of connections concurently handled by program, default is 10.
    -p, --udp-port PORT
      UDP port to listen to for incoming connections, default is 161.
    -P, --tcp-port PORT
      TCP port to listen to for incoming connections, default is 161.
    -s, --syslog
      Use syslog for logging
    -v, --version
      Show program version and exit.

Request handlers

smart-snmp can handle some requests himself, see OIDs supported by default. Other should be handled manually, otherwise noSuchName PDU will be returned. To manage custom OIDs smart-snmp provides special callbacks what can be processed by shell and/or Lua scripts. Before starting listening for incoming requests smart-snmp scan directory with scripts and add store references to them in internal MIB database. If during scan process smart-snmp find multiple handlers for same OID it will stop with error and tell files what are wrong. Lua scripts are checked for correctness. smart-snmp stores only paths to scripts and call them if appropriate request will come.

smart-snmp if started in tcp mode can handle up to max-connections connections concurrently. In this case, to prevent race conditions all requests to the same OIDs are passed through read-write locks. This means concurrent read access and exclusive write access.

Lua scripts

TBD

Shell scripts

Shell script will be called in this way:

</path/to/script> method [argument]

Possible methods are:

oid - ask script to return OID what will be handled by this script. This method will be called once during smart-smpt start;
type - ask script to return type of OID. This method will be called once during smart-smpt start Possible types are:
- INTEGER - return value is integer value;
- STRING - return type is string;
- OID - return type is OID;
get - ask script to return actual value for OID. Script should return string value what will be converted by smart-snmp to type returned by type method call.
set - ask script to update value for OID with value passed in argument.

Simple shell script can look like this:

#!/bin/bash
# 
# smart-snmp callback script to handle 1.3.6.1.2.1.1.1 (Device Model)
#

get_oid () {
  echo -n "1.3.6.1.2.1.1.1"
}

get_type () {
  echo -n "STRING"
}

get_val () {
  echo -n "MySimpleDevice"
}

set_val () {
  local val = $3 # passed string value will be here
  exit 4; # 4 means readOnly 
}

case "$1" in
  oid)
    get_oid
  ;;
  type)
    get_type
  ;;
  get)
    get_val
  ;;
  set)
    set_val
  ;;
  *)
    exit -1;
  ;;
esac

exit 0 # 0 means noError

OIDs supported by default

TDB

Running as daemon

By default, smart-snmp is not applicable to run as daemon. Use separate wrapper like start-stop-daemon from BusyBox or other tools.

ArhiChief/snmp