How to add public key to authorized_keys ec2 instance Ubunutu Linux

 Step 1: Login into you AWS account and go to EC2 instances

Step 2: Select your instance and click connect

Step 2: Then click connect button at the bottom right corner

Step 3: Now a new tab will be opened with console as follows

Step 4: Copy your SSH public key then add the key to the following key file

Use this command in Mac/Windows powershell to copy your public key: pbcopy ~/.ssh/id_rsa.pub

nano ~/.ssh/authorized_keys

Step 5: Save and reboot then try to connect again with device from which public key generated.

Fix laravel SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when trying to get lock

Cause:

his happens when two processes or more are trying to write to the same database table at the exact same time. Solutions can be complicated. Deadlocks are usually an application problem most of the time can either be solved by:

1. changing the logic of your code (e.g. use transactions) or
2. retrying the operation

      php artisan route:list

      php artisan view:clear

      php artisan cache:clear

How to add SSH Public key to an existing Droplet or VM?

First copy your Public key using the following command: 

cat ~/.ssh/id_rsa.pub

or 

pbcopy ~/.ssh/id_rsa.pub

Now login into your Droplet or VM and open the following file then paste your public key into authorized_keys file.

nano ~/.ssh/authorized_keys

Save the file and try to login from your local terminal.

Fix Adding new SSL virtual website .. .. certificate authority file is not valid : Data does not start with line -----BEGIN CERTIFICATE-- in virtualmin

Open the file at /etc/webmin/virtual-server/domains/13694005276497

Delete including 4 lines pointing to the 4 certificate files: ssl.cert, ssl.combined, ssl.everything & ssl.key

Then re-add the ssl.

How to generate SSH keys in Windows PowerShell

 Open your PowerShell and follow the steps:

ssh

ssh-keygen -b 4096

C:\Users\WINUSER/.ssh/id_rsa.pub

notepad C:\Users\WINUSER/.ssh/id_rsa.pub

How to check TCP, UDP Domain Socket using NetCat

 Install the netcat Using the fllowing command:

$ yum install nc      [On CentOS/RHEL]

$ dnf install nc      [On Fedora 22+ and RHEL 8]

$ sudo apt-get install Netcat      [On Debian/Ubuntu]

NetCat commands:

$ nc -v -w 2 z 192.168.56.1 22     #scan a single port

OR

$ nc -v -w 2 z 192.168.56.1 22 80  #scan multiple ports

OR

$ nc -v -w 2 z 192.168.56.1 20-25  #scan range of ports

How to hide IP in header from Postal MTA

Remove  text where need using the following file in postalMTA.

For SMTP Server:

lib/postal/smtp_server/client.rb

@receiving_headers = true
received_header_content = "from #{@helo_name} (#{@hostname} [#{@ip_address}]) by #{Postal.config.dns.smtp_server_hostname} with SMTP;

For HTTP:

app/models/outgoing_message_prototype.rb

mail.header['Received'] = "from #{@source_type} (#{self.resolved_hostname} [#{@ip}]) by Postal with HTTP; #{Time.now.utc.rfc2822.to_s}"
mail.message_id = "<#{@message_id}>"