SSHd is by default configured to perform DNS Lookup everytime you connect to the server. This is especially true for CentOS/Red Hat and could significantly increase login time.

To fix this you’ll have to disable the UseDNS option on the server via the following steps;

1. Open SSHd config file.

   /etc/ssh/sshd_config

2. Look for UseDNS and set the value to no

   UseDNS no

3. Restart SSHd service

   How to restart SSH service

If not specified, S3 buckets are by default private. This is to ensure objects in these buckets which are not meant for public consumption are not accessible to everyone.

The following are steps in creating a private S3 bucket.

1. On S3 main screen, click on the Create Bucket button.
   
2. Choose a unique name for your bucket and choose the region that you want your S3 bucket to be hosted. Click Create.
   

   The name must be unique regardless of regions. You’ll get an error when trying to use bucket name already being used anywhere within S3

3. Once created, you can see the details of your bucket by clicking on the Properties tab.
   
4. Load the bucket that you’ve just created by clicking on the name.
   
5. Upload a file to your S3 bucket to test by clicking on Upload from the Actions select button.
   
6. Click on the Add Files button.
   
7. Select the files that you want to upload.
   
8. Click on the Start Upload button to start uploading the files you’ve just selected.
   
9. Select the object from the list on the left, and click on the Properties tab. Then click on the hyperlink of the file in Link.
   
10. You should get this permission error when accessing the object.
    

Vim has the ability to display line numbers on the left side of the text, but normally is not enabled by default.

You can set Vim to display line number by following any of the following methods;

Git is a by far the most widely used distributed version control system while being free and open source.

Despite the popularity, it’s not installed by default in Ubuntu. You can install the program by following these steps;

1. Update apt‘s package list

   $ sudo apt -y update

2. Install git-core package

   $ sudo apt -y install git-core

3. Test by running git from the command line

   $ git
   usage: git [--version] [--help] [-C <path>] [-c name=value]
              [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
              [-p | --paginate | --no-pager] [--no-replace-objects] [--bare]
              [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
              <command> [<args>]
   
   These are common Git commands used in various situations:
   
   start a working area (see also: git help tutorial)
      clone      Clone a repository into a new directory
      init       Create an empty Git repository or reinitialize an existing one
   ------ snipped ------

You can change the port that your SSH server runs other than the default 22 by specifying the desired port number in your SSH server configuration file.

Set the Port option in /etc/ssh/sshd_config to your desired port as in the following example;

Port 22

You can use any number between 1 to 65535 as long as it’s not used by other programs.

Be sure to reboot your SSH server afterwards.

SSH clients will automatically be disconnected from the server and prompt the below message after being idle or inactive for a while.

Read from remote host oseems.com: Connection reset by peer
Connection to oseems.com closed.

This is due to the SSH servers’ configuration (often by default) to avoid hanging sessions and free up resources.

If you have administrative access to the SSH servers, you can configure it so that it will not easily disconnect idle sessions. This could be achieved by setting the parameters for TCPKeepAlive, ClientAliveInterval, and ClientAliveCountMax as per the following;

TCPKeepAlive no 
ClientAliveInterval 30
ClientAliveCountMax 240

What it basically means is that the server will not send the TCP alive packet to check if the client’s connection is working, yet will still send the encrypted alive message every 30 seconds. It will only disconnect after at least 2 hours of inactivity.

The following is the full explanation for the options;

 TCPKeepAlive
         Specifies whether the system should send TCP keepalive messages to the other side.  If they are sent, death of the
         connection or crash of one of the machines will be properly noticed.  However, this means that connections will die
         if the route is down temporarily, and some people find it annoying.  On the other hand, if TCP keepalives are not
         sent, sessions may hang indefinitely on the server, leaving “ghost” users and consuming server resources.

         The default is “yes” (to send TCP keepalive messages), and the server will notice if the network goes down or the
         client host crashes.  This avoids infinitely hanging sessions.

         To disable TCP keepalive messages, the value should be set to “no”.

         This option was formerly called KeepAlive.

 ClientAliveCountMax
         Sets the number of client alive messages (see below) which may be sent without sshd(8) receiving any messages back
         from the client.  If this threshold is reached while client alive messages are being sent, sshd will disconnect the
         client, terminating the session.  It is important to note that the use of client alive messages is very different
         from TCPKeepAlive (below).  The client alive messages are sent through the encrypted channel and therefore will not
         be spoofable.  The TCP keepalive option enabled by TCPKeepAlive is spoofable.  The client alive mechanism is valu‐
         able when the client or server depend on knowing when a connection has become inactive.

         The default value is 3.  If ClientAliveInterval (see below) is set to 15, and ClientAliveCountMax is left at the
         default, unresponsive SSH clients will be disconnected after approximately 45 seconds.  This option applies to pro‐
         tocol version 2 only.

 ClientAliveInterval
         Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will send a
         message through the encrypted channel to request a response from the client.  The default is 0, indicating that
         these messages will not be sent to the client.  This option applies to protocol version 2 only.

If you don’t have administrative access to the server, you can configure your SSH client to send the alive message to the server instead to achieve the same result. The key here is the ServerAliveInterval option for the SSH client.

You can do this by updating /etc/ssh/ssh_config (applying the setting to every user in the system) or in ~/.ssh/config (single user). Set the following option to have the client send the alive packet every 30 seconds to the server;

ServerAliveInterval 30

The other alternative is to manually set the ServerAliveInterval option every time you’re connecting to a server by using the -o ServerAliveInterval=<time-in-second> prefix as the following example;

$ ssh -o ServerAliveInterval=30 [email protected]

SSH in most system by default allow public key login. You can disable it with these simple steps if you somehow need to;

1. Set PubkeyAuthentication to no in /etc/ssh/sshd_config

   PubkeyAuthentication no

2. Reload or restart SSH

   How to restart SSH service

You will get the below error when logging in to phpMyAdmin without password even if your actual MySQL account itself is passwordless. This is because phpMyAdmin is normally configured to disable passwordless login due to security reasons.

To enable passwordless MySQL login in phpMyAdmin, you’ll need to set AllowNoPassword option in phpMyAdmin‘s configuration to TRUE.

To enable the option, uncomment or add the following line;

$cfg['Servers'][$i]['AllowNoPassword'] = TRUE;

Depending on distributions, there could be multiple occurrences of that particular line. Ubuntu for example has the following 2 lines;

if (!empty($dbname)) {
    // other configuration options
    $cfg['Servers'][$i]['AllowNoPassword'] = TRUE;
    // it should be placed before the following line
    $i++;
}

// other configuration options
$cfg['Servers'][$i]['AllowNoPassword'] = TRUE;

To use Google‘s G Suite for email while your DNS is managed by your cPanel‘s account, you’ll have to configure the MX entry for your domain from within cPanel to point to Google‘s mail servers.

This can be done with these simple steps;

1. From within your cPanel’s main interface, look for Email section and click on MX Entry
   
2. Select the domain that you wish to edit from the list
   
3. Set to Automatically Detect Configuration in the Email Routing menu
   
4. Delete existing MX records
   
5. Start adding MX records for Google mail server
   
6. Continue doing so for all the following mail servers
   

   Priority	Destination
   1	ASPMX.L.GOOGLE.COM
   5	ALT1.ASPMX.L.GOOGLE.COM
   5	ALT2.ASPMX.L.GOOGLE.COM
   10	ASPMX2.GOOGLEMAIL.COM
   10	ASPMX3.GOOGLEMAIL.COM