#!/bin/bash

#
# This is a script to log (and eventually monitor) diskusage on a filesystem.
# It will write **THE USER SPECIFIED FILESYSTEM** disk usage to a logfile.
# The logfile will never grow larger than MAX_LINES number of lines.
#
# To be used together with a cron job and optionally a GNUPLOT.
#

# **SPECIFY THE FILESYSTEM YOU WANT TO MONITOR**
# (Running df on the system will reveal all currently mounted filesystems)
FILE_SYSTEM="/dev/disk1s1"

## This var holds the name of the logfile
FILE_NAME="example.log"

# This var holds the name of a temporary logfile
TEMP_FILE_NAME=${FILE_NAME}.temp

# Format Current Date Time
CURRENT_DATETIME=$(date "+%Y-%m-%d %H:%M:%S %Z")

# Extract SIZE, USED, AVAILABLE and CAPACITY for the given filesystem
# and append to file
df -H | awk -v datetime="$CURRENT_DATETIME" -v filesystem="$FILE_SYSTEM" \
	    '$1 == filesystem {print datetime, $2, $3, $4, $5}' >> ${FILE_NAME}

# If diskusage file does not exist, something went wrong. Better exit.
if [ ! -f "$FILE_NAME" ]; then
    exit 1
fi


#
# Make sure this file doesn't grow larger than MAX_LINES lines.
# Delete oldest entries.
#

# Maximum number of lines the logfile may hold
MAX_LINES=10000

# Number of lines the logfile currently holds
CURRENT_LINES=$(cat ${FILE_NAME} | wc -l)

if [ "$CURRENT_LINES" -gt "$MAX_LINES" ]; then

    # Tail MAX_LINES to tempfile and (force) copy back to original logfile

    tail -n${MAX_LINES} ${FILE_NAME} > ${TEMP_FILE_NAME}
    cp -f ${TEMP_FILE_NAME} ${FILE_NAME}
    rm -f ${TEMP_FILE_NAME}

fi

exit 0