dummy port listener linux

Sometimes we need to test the network port and make sure that there is connectivity between servers.

In many cases, the app that might be listening on the port might not be ready yet. For such use cases, you can create a port listener on any port using netcat.

nc -l 3000

This will create a listener at the port 3000 on the server. To create who has connected to the port, use the verbose mode.

nc -lv  3000


Connection from x.x.x.x port 3000 [tcp/hbci] accepted

Create Basic Auth

You might need to generate basic authentication string when trying to use apache htaccess or for restricting web access.

The simple way to generate it is by using openssl.

echo -n username:password | openssl base64

How to make subject lines appear in maillog

Klog syslog
HSubject: $>+CheckSubject

R$*     $: $(log Subject: $1 $) $1

Make sure that the blank spaces after R$8 is a tab and not 4 spaces.

Build the macro

    m4 sendmail.mc > sendmail.cf

Restart sendmail

/etc/init.d/sendmail restart

You should now start to see the subject as a separate line in the log. Use the unique id to find the subject line

sendmail[21030]: w182kQTv021030: Subject:test123


Port check script

NC=’\033[0m’ # No Color

function checkport {
if nc -zv -w30 $1 $2 <<< ” &> /dev/null
echo “${GREEN}[O]${NC} $1:$2”
echo “${RED}[C]${NC} $1:$2”

printf “server list:”;
read server
printf “ports list[enter for default]:”
read ports_to_check

if [[ $ports_to_check = “” ]]; then
echo “using default port list”;
ports_to_check=”22 389 3306 8080″; #enter your default list of ports here
echo “$ports_to_check”;

for i in $server;do
echo “==========================================”
for j in $ports_to_check ; do
checkport $i $j
}; done

Create a md5 hash password

Here are the steps to create an MD5 hash password

To use in linux shadow file or when you want to update the password somewhere

You will need “mkpasswd”

If your server seem to be missing the mkpasswd command, install it using yum.

yum install expect

Create the password and update for the user in /etc/shadow file.

mkpasswd -l 8 -d 3 -C 1 -s 1 maugustine

l – minimum length of password

d – minimum number of digits in password

C – number of uppercase characters

s – special characters.


The user you specify in mkpasswd should exist on the system

Grep command for windows

Here is how you do grep in windows using powershell.

PS G:\> Get-ChildItem -Path G:\messages\processed | Select-String -Pattern “string pattern” | Measure-Object -Line

Find your tomcat version

Sometimes you might need to figure out your tomcat version from within the folder where you run tomcat from. The below command will help you get the details.

java -cp lib/catalina.jar org.apache.catalina.util.ServerInfo

/usr/share/tomcat7$ java -cp lib/catalina.jar org.apache.catalina.util.ServerInfo
Server version: Apache Tomcat/7.0.81
Server built: Aug 11 2017 10:21:27 UTC
Server number:
OS Name: Linux
OS Version: 3.13.0-95-generic
Architecture: amd64
JVM Version: 1.7.0_75-b13
JVM Vendor: Oracle Corporation

how to wget from a site with authentication

when you got to download from a site that ask for authentication details use the below flags to specify the user and password details


wget  –user=’yourusernamehere’ –password=’yourpasswordhere’ –auth-no-challenge  https://yoururlhere.com