The recommended nagios plugin to use to monitor a router with a public ip

Why not make a static entry in fstab instead using automount so it is always mounted?

In the GNU df manual:

This version of df cannot show the space available on unmounted file systems, because on most kinds of systems doing so requires very nonportable intimate knowledge of file system structures.

So I would guess if GNU df is not going to show the free space of a partition that is not mounted, a Nagios plugin probably won't either. But I could be wrong :-)

Maybe if you are using ext2/3 , by parsing out free blocks, block count, and block size out of tune2f you might be able to quickly write a plugin that will accomplish this:

sudo tune2fs -l /dev/sdb1

i found a plugin for this (can't remember where), which seems to work well in production.

define command{
    command_name    check_numfiles
    command_line    $USER1$/check_numoffiles.sh $ARG1$
    }

and

check_command           check_numfiles!-d /var/spool/sms/failed -w 1 -c 2

it goes warning if the directory contains one or more files, critical if two or more. the plugin uses find, so modifying it with a -mtime xxx to check only for files over a certain age would be trivial.

the plugin itself is:

#!/bin/sh
#
# ## Plugin for Nagios to monitor how man files a directory contain
# ## Written by Bernd Mueller (http://www.lisega.de/)
# ##
# ## - 20070426 coded and tested for Linux
# ## - no jet published on NagiosExchange
#
#
# ## You are free to use this script under the terms of the Gnu Public License.
# ## No guarantee - use at your own risc.
#
#
# Usage: ./check_nomoffiles -d <path> -w <warn> -c <crit>
#
# ## Description:
#
# This plugin determines the number of files in a directory
# and compares it with the supplied thresholds.
#
# ## Output: 
#
# The plugin prints the Count of Files in the directory followed by "ok" or
# either "warning" or "critical" if the corresponing threshold is reached.
#
# Exit Codes
# 0 OK       Directory Count of files checked and everything is ok
# 1 Warning  Directory Count of files above "warning" threshold
# 2 Critical Directory Count of files above "critical" threshold
# 3 Unknown  Invalid command line arguments or could not determine directory size
#
# Example: check_numoffiles -d . -w 1000 -c 1400
#
# 121 Files - ok         (exit code 0)
# 1234 Files - warning   (exit code 1)
# 1633 Files - critical  (exit code 2)


# Paths to commands used in this script.  These
# may have to be modified to match your system setup.

PATH=""

find="/usr/bin/find"
xargs="/usr/bin/xargs"
tail="/usr/bin/tail"
awk="/usr/bin/awk"
cut="/usr/bin/cut"
wc="/usr/bin/wc"

PROGNAME=`/bin/basename $0`
PROGPATH=`echo $0 | /bin/sed -e 's,[\\/][^\\/][^\\/]*$,,'`
REVISION="Revision 1.0"
AUTHOR="(c) 2007 Bernd Mueller (http://www.lisega.de/)"

# Exit codes
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
STATE_DEPENDENT=4

print_revision() {
    echo "$REVISION $AUTHOR"
}

print_usage() {
    echo "Usage: $PROGNAME -d <path> -w <warn> -c <crit>"
    echo "Usage: $PROGNAME --help"
    echo "Usage: $PROGNAME --version"
}

print_help() {
    print_revision $PROGNAME $REVISION
    echo ""
    echo "Directory Files monitor plugin for Nagios"
    echo ""
    print_usage
    echo ""
}

# Make sure the correct number of command line
# arguments have been supplied

if [ $# -lt 1 ]; then
    print_usage
    exit $STATE_UNKNOWN
fi

# Grab the command line arguments

thresh_warn=""
thresh_crit=""
exitstatus=$STATE_WARNING #default
while test -n "$1"; do
    case "$1" in
        --help)
            print_help
            exit $STATE_OK
            ;;
        -h)
            print_help
            exit $STATE_OK
            ;;
        --version)
            print_revision $PROGNAME $VERSION
            exit $STATE_OK
            ;;
        -V)
            print_revision $PROGNAME $VERSION
            exit $STATE_OK
            ;;
        --dirname)
            dirpath=$2
            shift
            ;;
        -d)
            dirpath=$2
            shift
            ;;
        --warning)
            thresh_warn=$2
            shift
            ;;
        -w)
            thresh_warn=$2
            shift
            ;;
        --critical)
            thresh_crit=$2
            shift
            ;;
        -c)
            thresh_crit=$2
            shift
            ;;
        *)
            echo "Unknown argument: $1"
            print_usage
            exit $STATE_UNKNOWN
            ;;
    esac
    shift
done

##### Get size of specified directory

error=""
statresult=`$find $dirpath -maxdepth 1 -type f | $wc -l |$tail -1`
dirsize=`echo $statresult`
result="ok"
exitstatus=$STATE_OK

##### Compare with thresholds

if [ "$thresh_warn" != "" ]; then
    if [ $dirsize -ge $thresh_warn ]; then
        result="warning"
        exitstatus=$STATE_WARNING
    fi
fi
if [ "$thresh_crit" != "" ]; then
    if [ $dirsize -ge $thresh_crit ]; then
        result="critical"
        exitstatus=$STATE_CRITICAL
    fi
fi

echo "$dirsize Files - $result"
exit $exitstatus