Day 6 . Shell Scripting Real-Time Scenarios

Write a shell script function to find and kill all the zombie processes. when a zombie is detected a log message is generated and sent to a log directory for when the kill is successful and not successful.

 #You can create a sample zombie process using below command
 #(A=$BASHPID && ( kill -STOP $A ))
 killzombie() {

 #List PID of all zombie process
 for childid in $(ps aux | awk '$8 ~ /^[Zz]/' | awk '{print $2}')
 do
   #get parent procesid from child process 
   parentid=$(ps -o ppid= -p $childid | awk '{print $1}')

   #Send Kill SIGCHLD signal to parent process
   echo "Sending signal to parent process to kill all zombie process"
   kill -s SIGCHLD $parentid  
     #Identify process is still not killed
     if [[ $(ps -p $childid | awk 'NR > 1 {print $1}') -ge 0 ]]
     then
           #kill parent process
           echo "Kill parent process"
           kill -9 $parentid 
           logger "Kill successfull $parentid"  
     fi

  done
 }

 #call function to kill processes
 killzombie

Write a shell script to automate the process of creating new user accounts on a Linux server and setting up their permissions and SSH access.

 #!/bin/bash
 #Create new user account
 createUser() {

         userName=$1
         if id $userName
         then
                 echo "User $userName already exists"
                 exit 1
         fi

         #Create user
         useradd -m $userName

         #Set password from user
         echo "Setting password for user $userName"
         passwd $userName

         #Add users to sudoers
         usermod -aG sudo $userName
         echo "User $userName is added to sudoers"

         #enable ssh access
         enableSSHAccess $userName
 }

 enableSSHAccess() {
         userName=$1

         sshDir="/home/$userName/.ssh/"
         authkeyFile="$sshDir/authorized_keys"

         #Create ssh directory if not exist
         if [ ! -d $sshDir ];
         then
                 mkdir $sshDir #create ssh directory
                 chmod 770 $sshDir #read permission for directory
         fi

         #read authorised keys from user
         echo "Enter public key for $userName:"
         read -r publicKey

         #write public key to authorised keys
         echo $publicKey >> $authkeyFile
         chmod 070 $authkeyFile

         #set ownership for ssh directory
         chown -R $userName $sshDir
         echo "SSH access enabled for $userName"
 }

 # Prompt for the username
 echo "Enter the username for the new user:"
 read -r userName

 # Call create user function
 createUser $userName

Shell script that displays the number of failed login attempts by IP address and location.

 #!/bin/bash
 #log file
 logFile="/var/log/secure"

 #Get failed login ip addressess
 ipAddresses=$(cat $logFile | grep sshd | grep -v invalid | awk '{ print $11; }')

 #Get location of ip address
 getLocation() {
  ip=$1
  location=$(geoiplookup $ip | awk -F ', ' '{ print $2 }')
  if [[ $location == *": "* ]]
  then
     location="${location#*: }"
  fi
  echo $location
 }

 #display all ip address
 for ip in $ipAddresses
 do
     noOfFailedAttempt=$(grep -c $ip $logFile)
     location=$(getLocation $ip)
     echo "Ip address=$ip, Location=$location, Failed attempt=$noOfFailedAttempt"
 done

Shell script to Copy files recursively to remote hosts.

 #!/bin/bash
 hosts=("ec2-user@13.235.31.39" "ec2-user@13.235.31.39") # replace host with your hosts

 for host in "${hosts[@]}"
 do
   set timeout -1 #set timeout to copy all files
   scp -i linux.pem -r files $host:/home/ec2-user #copy all files recursively to remote host
   sleep 1
   echo "Files copied to $host"
 done

Write a shell script to the list of users logged in by date and write it to an output file.

  #!/bin/bash
 #output file
 outputFile="loggedinusers.txt"
 checkLoggedInUsers() {
     date=$1
     who -v d="$date" | awk '{print $3" "$1}' | sort | uniq >> $outputFile
 }

 #Enter date
 echo "Enter date in format: YYYY-MM-DD"
 read date
 checkLoggedInUsers date

Shell script parses a log file and forwards a specific value with a timestamp to an output file.

 #!/bin/bash
 logFile="path/logfile" #replace with your log file
 outputFile="/path/output.txt" #output file

 #pattern to be searched in file
 pattern="pattern"

 #parse file search pattern and save it to output file
 grep "$pattern" "$logFile" | awk '{ print $1, $2, $3 }' > "$outputFile"

 echo "Parsing complete, saved to #outputFile"

Shell script to monitor CPU, Memory, and Disk usage and send the output to a file in table format and send an alert if either of them exceeds a certain threshold.

 #!/bin/bash
 ALERT=80
 computestats() {
 printf "Memory\t\tDisk\t\tCPU\n"
 end=$((SECONDS+3600))
 while [ $SECONDS -lt $end ]; do
 MEMORY=$(free -m | awk 'NR==2{printf "%.2f%%\t\t", $3*100/$2 }')
 if [[ $MEMORY -ge $ALERT ]] #ALert for out of memory
 then
     echo "Out of memory $MEMORY"
 fi

 DISK=$(df -h | awk '$NF=="/"{printf "%s\t\t", $5}')
 if [[ $DISK -ge $ALERT ]] #ALert for out of memory
 then
     echo "Disk out of space $DISK"
 fi
 CPU=$(top -bn1 | grep load | awk '{printf "%.2f%%\t\t\n", $(NF-2)}')
 if [[ $CPU -ge $ALERT ]] #ALert for out of memory
 then
     echo "More CPU utilization $CPU"
 fi
 echo "$MEMORY$DISK$CPU"
 sleep 5
 done
 }

 #copy output to file
 computestats >> stats.txt

Write a shell script to check the status of a list of URLs and send an email notification if any of them are down.

 #!/bin/bash
 sendEmail() {
     MSG_FROM=zac@server.it #Enter your mail id
     MSG_TO="zac@gmail.com" #Enter recepient email id
     MSG_SUBJ="Website down" #Enter email subject 
     SMTP_HOST="relay.zac.it" #Enter your smtp host
     SMTP_PORT="487" #Enter your smtp port
     MSG_BODY=("Following websites are down:\n\n $1")  #Enter email message body

 echo -e $MSG_BODY | mailx -s "$MSG_SUBJ" -r "$MSG_FROM" -S smtp="$SMTP_HOST:$SMTP_PORT" "$MSG_TO"
 }
 downUrls=""
 checkUrlStatus() {
     for url in $1
     do
         response= $(curl -is $url | head -n 1)
         if [[ ! $response =~ "200 OK" ]]; then
             downUrls+="$url\n"
         fi
     done
 }
 #Read urls from user
 echo "Enter list of Urls:"
 readarray -t urls
 checkUrlStatus urls

 #send email
 if [[ -n $downUrls ]]; then
     sendEmail $downUrls
     echo "Email sent for down website"
 else
     echo "Websites are up"
 fi

Write a shell script to automate the process of updating a list of servers with the latest security patches.

 #!/bin/bash
 updateServer() {
     server=$1

     echo "Enter ssh user:"
     read sshuser
     echo "Enter path of sshkey for user:$sshuser"
     read sshkey
     #ssh into server
     ssh -i "$sshkey" "$sshuser" 
       #Download the latest software packages from the repositories.
       sudo apt update && sudo apt upgrade -y 

       #Will install only the security updates
       sudo apt-get -s dist-upgrade  

       #Eliminates the need for unplanned maintenance
       sudo pro enable livepatch 

       #Cleanup unused packages
       sudo apt autoremove -y 
 }

 echo "Enter list of servers:"
 readarray -t servers
 for server in $servers
 do
     updateServer $server
 done

Shell script to find the files created and their sizes. It should accept the number of days as input. Or a from and to date format as inputs.

#!/bin/bash
#Enter start date
echo "Enter start date:"
read startdate
startdate=$(date -d $startdate +%Y-%m-%d) # format in YYYY-MM-DD

#Enter end date
echo "Enter end date:"
read enddate
enddate=$(date -d $enddate +%Y-%m-%d)
echo "Size\ttDate"
find /home/ec2-user -type f -newermt $startdate ! -newermt $enddate -ls | awk '{print $7" "$8" "$9}'Write a shell script to automate the process of updating a list of servers with the latest security patches.