Script to import csv into dhcpd.conf import multiple mac bindings

make sure your csv file is in this order MAC,IP,NAME and file name of csv is ips.csv
Once that is done just run the script and check mac_out.txt which is file to be imported in dhcpd.conf

!/bin/bash

INPUT=ips.csv
OUTPUT=mac_out.txt
OLDIFS=$IFS
IFS=","
[ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
[ -f $OUTPUT ] && { rm $OUTPUT; }
[ ! -f $OUTPUT ] && { touch $OUTPUT; }
while read mac ip uname
do
echo "host $uname {" >> $OUTPUT
echo -e "\thardware ethernet $mac;" >> $OUTPUT
echo -e "\tfixed-address $ip;" >> $OUTPUT
echo "}" >> $OUTPUT
done < $INPUT

IFS=$OLDIFS

How to drop cache or in-memory cache on linux and free up some memory ?

$ echo 1 | sudo tee /proc/sys/vm/drop_caches  # drop pagecache
$ echo 2 | sudo tee /proc/sys/vm/drop_caches  # drop dentries and inodes
$ echo 3 | sudo tee /proc/sys/vm/drop_caches  # drop pagecache, dentries and inod

Also we can use 

echo 1 > /proc/sys/vm/drop_caches

echo 2 > /proc/sys/vm/drop_caches

echo 3 > /proc/sys/vm/drop_caches

This is also used when we take benchmarks of server.

Command to get linux dhcp client list

cat /var/log/messages | grep DHCPACK

What Server remote management systems called ?

These are different remote server management tools

Intel uses RMM2 (remote management 2)
Dell uses DRAC (Dell Remote Access Control)
Sun or Oracle uses ILOM (Integrated Lights Out Manager)
IBM uses IMM (Integrated Management Module)
HP uses ILO (Integrated Lights-Out).

Simple encryption and decryption of files using GPG

gpg --yes --passphrase="test" -c test1.txt

encrypted file will be test1.txt.gpg and test1.txt will still exist.

gpg --decrypt  --passphrase "test" --output "test1.txt" "test1.txt.gpg"

Sophos command to exclude directory from on-access scans

/opt/sophos-av/bin/savconfig  ExcludeFilePaths /opt/folder-exclude

Linux bash script for checking and sending email alerts on disk space issues

#!/bin/sh
FILE=/tmp/mailcontent.txt

> /tmp/mailcontent.txt

df -H | awk '{ print $5 " " $6 }'|head -6|tail -5|while read output;

do
#  echo $output
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
echo $usep
  if [ $usep -ge 90 ]; then
   echo -e "Running out of space \n\nPartition:\"$partition ($usep%)\" \nHost:$(hostname) \nDate:$(date)\n" >> /tmp/mailcontent.txt

 fi

done

if [[ -s $FILE ]] ; then

mail -s "CRITICAL ALERT:Disk space of $hostname more that 90%" disk-alert@yourcompany.com
else
echo "$FILE is empty."
fi

exit