Keep PuTTY SSH Sessions from Disconnecting

If you are using PuTTY to interact with your Linux Server(s) for extensive period of time and are frustrated due to disconnecting, when the SSH session turns idle for a certain amount of time (usually ~10 min). To overcome this problem, just use the keepalive feature of PuTTY!

Click on the Connection and enter the 30 (or whatever value which indicates the number of seconds) in Seconds between keepalives (0 to turn off) text box.

You are done, from now onward, the keepalive feature will prevent your SSH session from disconnecting.

Hope this will help you!

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How to Fix Postfix File too large error

Today, I was getting an error from my Postfix mail server, when trying to send mysqldump file which is about 8 MB attachment. I checked the /var/log/maillog and found this:

sudo tail -f  /var/log/maillog

To view the default settings for all the parameters of Postfix:

postconf -d | grep size

Public-Key Authentication in SecureCRT

Public-key authentication is a proven, it’s better then allowing password authentication.As long as you keep your private key file safe, you’re less likely to encounter a break-in of your Unix/Linux servers. In this tutorial, I’ll try to show you the steps that you need to create public/private key using SecureCRT and use it with Ubuntu Server.

To create a public/private key pair in SecureCRT, open up SecureCRT, click on “Quick Connect“, from there click on the “Properties“:

Note: Uncheck all other options

Click “Create Identity File…” and the key generation wizard starts:

 Click “Next” to get started:

Select RSA as the Key Type and click “Next“:

Next, you are prompted to enter a passphrase twice (I leave it blank, but you should use something pretty long phrase, that you’re going to remember):

Next, it will ask you for your desired key length in bits. Take the default “1024” and click “Next“:

Now, you need to move your mouse randomly to generate some data to encrypt the key pairs:

Once it has been generated, click “Next” then you will need to save the public key and private key to your computer. Save it in a safe place!

Click “Finish” When asked whether or not you want to upload the following key, say NO!

Copy the public key into your home directory using WinSCP:

Login to your Linux server with your username and password and cat the content of the public key:

cat Identity.pub

First you need to format the public key properly, for this you need to delete the first four lines as well as delete the last line, and get JUST the key on a single line with “ssh-rsa” in front:

cat Identity.pub

Note: Open the file with “nano <public key filename>” and you will be able to edit it properly.

Create the “authorized_keys” file inside .ssh folder and set the permission on it:

touch .ssh/authorized_keys
chmod 750 .ssh/authorized_keys

Important Note: If .ssh folder doesn’t exist then you can use these command to create it!

mkdir ~/.ssh
chmod 700 ~/.ssh

Now that the RSA key is properly formatted, you can add it to the “authorized_keys” file.

cat Identity.pub >> .ssh/authorized_keys

Remove the public key (In this case, it is Identity.pub):

rm Identity.pub

Connecting via SecureCRT using your key pair:

If this is the same session you were already working with above, your identity file should already be filled in…if not, just click the browse button “…” and find your private key. Click “OK“. (You can also refer this link for more help):

It will not ask for the username and password

Hope this will help you!

Please Remember me in your prayers!

Enjoy 🙂

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How to add 2nd Hard drive to Ubuntu

To add/mount the second hard drive into Ubuntu, open up the terminal window and type:

sudo fdisk -l

Where sdb is our newly added Secondary Harddisk!

To create the partition on the second Hard drive, use the following command and follow the “on screen” instructions:

sudo fdisk /dev/sdb

Use the partprobe command to update the kernel with the changes:

sudo partprobe /dev/sdb

Where /dev/sdb is my device name, you can use your’s!

Now we need to format our newly created partition using the following command:

sudo mkfs /dev/sdb1 -t ext4

Verify the newly created partition:

sudo fdisk -l

Next you need to create a directory for a mount point:

cd /mnt/
sudo mkdir 2ndHDD 
sudo chmod 0777 2ndHDD
ls -l

Next, mount the newly created sdb1 parition into 2ndHDD directory:

sudo mount /dev/sdb1 /mnt/2ndHDD -t ext4

Updated: Run this command once more:

sudo chmod 0777 2ndHDD

Now, we make a test that we can write a file on to the new drive:

touch /mnt/2ndHDD/test.txt
ls /mnt/2ndHDD/* 

Next time, when we will reboot the computer, it will be gone. If we want to mount new hard drive permanently then we need to edit the fstab file:

sudo nano /etc/fstab

Add this line at the end of the fstab file(you can adjust it according to your requirement):

/dev/sdb1 /mnt/2ndHDD ext4 defaults 0 0

Use this command or else reboot your computer:

sudo mount –a

Hope this will help you!

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Key-based ssh logins with PuTTY

Open your PuTTY Key Generator, it was installed when you installed PuTTY!

Click Generate:

You will need to move your mouse randomly to generate some data to encrypt the key pairs:

When the private/public key pair has been generated then you will need to save the public key and private key to your computer. Save it in a safe place!

Login to your Linux server with your username and password and enter the following commands:

mkdir ~/.ssh
chmod 700 ~/.ssh
nano ~/.ssh/authorized_keys2 

Paste the public key into your file. It may paste over in 3 lines, make sure its on a single line, this is very important!

Now to make that file accessible by only the user:

chmod 600 ~/.ssh/authorized_keys2

Now we shall create & save the session in PuTTY:

Select the Data and fill in the Auto-login username field, with the username for which you created the key:

We need to tell PuTTY to use a Private Key File. Select SSH->Auth-> Browse and point it to your private key:

Now we shall try to connecting via PuTTY using the saved session:

It will not ask for the username and password 🙂

Hope this will help you!

Please Remember me in your prayers!

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