check_snmp_active_router.sh

#! /bin/bash
 
# Creative Commons CC0 Public Domain Licence
 
set -euo pipefail
IFS=$' \t\n'
export LC_ALL=C
 
OID_HOSTNAME=.1.3.6.1.2.1.1.5.0
LABEL="ACTIVE_ROUTER"
 
ALL_ARGS=("$@")
 
exec 6>&1 # Link file descriptor #6 with stdout. Saves stdout.
 
# FIX IGNORED ~/.snmp/snmp.conf WHEN 'sudo -u nagios check_snmp_host.sh'
HOME=$(getent passwd "$(whoami)" | cut -d: -f6)
 
PATH="/sbin:/usr/sbin:$PATH"
 
exit_malfunction() {
	exec 1>&6 6>&- # Restore stdout and close file descriptor #6
	echo "${LABEL} ${STATUS_MSG} - ERROR $*"
	exit 3
}
 
# NAGIOS EXIT STATUS
# STATE_OK=0 ; STATE_WARNING=1 ; STATE_CRITICAL=2 ; STATE_UNKNOWN=3; STATE_DEPENDENT=4
STATUS_MSG=UNKNOWN
typeset -i STATUS_CODE=3
trap 'if [ $STATUS_CODE -eq 3 ] && [ $? -ne 0 ] ; then
  exit_malfunction "Unexpected error"
fi' EXIT ERR
 
command_exists() {
	command -v "$1" >/dev/null 2>&1 || (
		exit_malfunction "I require $1 but it's not installed. Aborting."
	)
}
 
command_exists snmpget
 
get_defaultgw() {
	ip -4 route show default | awk '/^default/ { print $3 }' || exit_malfunction "Can't get default gateway"
}
 
get_hostname() {
	local REMOTE_HOST=$1
	ROUTER_NAME=$(snmpget -r 2 "${ALL_ARGS[@]}" "$REMOTE_HOST" "${OID_HOSTNAME}" | cut -d= -f2 | cut -d: -f2 | xargs) || exit_malfunction "SNMP failed"
}
 
main() {
	local DEFAULTGW
	local -i ROUTER_NB
	DEFAULTGW=$(get_defaultgw)
	get_hostname "$DEFAULTGW"
	ROUTER_NB=$(echo "$ROUTER_NAME" | grep -o -e '[0-9]\+$') || exit_malfunction "Hostname error in '$ROUTER_NAME' for $DEFAULTGW"
	if [ "$ROUTER_NB" -eq 1 ]; then
		STATUS_CODE=0
		STATUS_MSG=OK
	elif [ "$ROUTER_NB" -eq 2 ]; then
		STATUS_CODE=1
		STATUS_MSG=WARNING
	else
		STATUS_CODE=2
		STATUS_MSG=CRITICAL
	fi
	echo "${LABEL} ${STATUS_MSG} - $ROUTER_NAME is active router"
 
}
 
main
exit $STATUS_CODE