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31
General Linux / What Is a Kernel Panic
« Last post by Vineesh K P on November 13, 2018, 06:19:13 am »
A Linux kernel panic is a computer error from which the Linux operating system (OS) cannot quickly or easily recover.

The kernel provides basic services for all other parts of the operating system. Kernel panics are generally caused by an element beyond the Linux kernel's control, including bad drivers, overtaxed memory and software bugs. The Linux platform is open-source, unlike Mac and Windows, so kernel development is open and collaborative.

Linux administrators can study the Linux kernel panic log to determine root causes, or dump the kernel contents with the crash utility for later analysis. Once the cause is determined, Linux kernel panics with commands can be resolved with programming that instructs the kernel how to debug the offending program, change a configuration or file path or make changes in the BIOS.
32
General Linux / What is the Difference between GRUB and GRUB2
« Last post by Vineesh K P on November 13, 2018, 05:59:13 am »
Hello Guys,

In this article, we will be comparing GRUB and GRUB2 boot loaders.

GRUB

The GRand Unified Bootloader is the software that is loaded by your computer after it turns on (after your computer's BIOS loading screens). GRUB then either automatically boots Ubuntu or gives you a list of installed Operating Systems and lets you choose one to boot. If you do not dual boot, you may not have seen this window.

GRUB 2

A complete rewrite of the original GRUB (legacy GRUB). On the surface, the majority of users won't notice any difference but the new version has fairly major structural changes and should be more reliable. The new version stores its configuration files differently, which means most online tutorials involving GRUB had to be rewritten. Other new features include the ability to boot LiveCD ISOs from the hard drive; support for other architectures such as PowerPC; theming and other graphical capabilities and scripting support.

BONUS!!!

BURG

As for BURG - the capitalization seems to depends on who you ask - it is a fork of GRUB. The main reason most users consider BURG is for the theming possibilities, replacing the two color boot screen above, with a colorful interface.
33
General Discussion / Why Use Incognito Mode When Browsing The Internet
« Last post by Vineesh K P on November 13, 2018, 01:43:34 am »
You might have noticed a mode in your browser called "Private Browsing" or "Incognito Mode". The name may vary depending on your browser of choice. But the features it offers remains the same.

When you open a browser window in private or incognito mode, the browser stops storing all the various stuff it usually stores about sites as you putter around the information superhighway. Typically, this stored stuff includes things like the site's URL, text you may have typed into the site's forms, and cookies from websites and all the pages you have visited will not be logged in History tab.

Here are some of the most common reasons people are using Incognito Browsing.

1. Signing into multiple email accounts at once
You could set up different browser "profiles" to switch between email accounts within one browser, but incognito mode is the quick and easy way of doing this on the fly — no setup required.


2. Watching weird videos

Again, though there is another way to pause videos getting added to your YouTube history (within YouTube settings themselves), the incognito mode is quick and easy.

3. Using computers that aren't yours

If you need to log into your email or your banking account or whatever on a computer away from home, just pop open incognito mode to provide a layer of protection against your passwords or user info being saved to that computer (not totally infallible, that computer could have keystroke logging software on it or something, but it helps).

4. Booking travel

If the airlines are going to play pricing games with us, then we're going to play games with them right back, dammit (though private browsing for a lower fare may or may not actually work).

5. To look like a fresh visitor

If you are tinkering with the code for a website, you may want to prevent your browser from saving ("caching") the site in order to force it to reload the potential changes each time. Also, since Google customizes search results, incognito mode can give you a clean slate of Google search results rather than ones affected by your past Googling.
34
Plesk / PHP-FPM does not work with 503 service unavailable
« Last post by mansoorm on November 09, 2018, 05:44:36 pm »
When the following error appears in the domain's error log /var/www/vhosts/system/example.com/logs/error_log:

[proxy:error] [pid 7314] (2)No such file or directory: AH02454: FCGI: attempt to connect to Unix domain socket /var/www/vhosts/system/example.com/php-fpm.sock (*) failed

Or

[proxy:error] [pid 15065:tid 139826443527936] (111)Connection refused: AH02454: FCGI: attempt to connect to Unix domain socket /data/vhosts/system/example.com/php-fpm.sock (*) failed
[proxy_fcgi:error] [pid 15065:tid 139826443527936] [client 203.0.113.2:50232] AH01079: failed to make connection to backend: httpd-UDS

The cause of the problem mentioned above is probably Pool configuration file is missing or corrupted.

Resolution

Regenerate the configuration:

Log into Plesk.
Go to Plesk > Domains > example.com > PHP Settings and click OK:


If multiple domains are affected:

   1. Connect to the server via SSH;
   2. Execute the following command to update settings on all domains:

    # /usr/local/psa/bin/php_settings -u

35
General Linux / Configure MySQL thread_cache_size
« Last post by arunlalpr on November 08, 2018, 09:17:21 am »

Configure MySQL thread_cache_size

This parameter sets the amount of thread for cache purposes. If client disconnects, his thread are kept in the cache. If the requests are less than the  thread_cache_size then threads that stored in cache will serve the requests.


To find the thread cache hit rate,

Kindly access Mysql and enter the following commands.

mysql> show status like 'Threads_created';
mysql> show status like 'Connections';




Now use the following formula to calculate the thread cache hit rate percentage:

100 - ((Threads_created / Connections) * 100)


In this case it is --->>> 100 - ((26/4304) * 100 ) = 99.39


The most useful thing  is that the thread_cache_size can be dynamically changed without having to restart the MySQL service.


36
General Discussion / Advantages of Anaconda Over Standard Python For Data Science
« Last post by Vineesh K P on November 05, 2018, 07:09:14 am »
Hello,

In this topic, we will be looking at the advantages of Anaconda Python over the Standard Python.

  • Common Machine Learning/Data Science libraries come preinstalled with it.
  • It gives high-performance computing with Anaconda Accelerate and several other components
  • Removes bottlenecks involved in installing the right packages while taking into considerations their compatibility with various other packages as might be encountered while using pip.
  • It has a dedicated package manager called conda
  • There is no risk of messing up required system libraries
37
General Discussion / How to Find SSH Port From WHM Interface
« Last post by Vineesh K P on November 03, 2018, 11:59:45 pm »
Hello All,

In this article, we will talk about how to find SSH port (or any other listening port) within the WHM interface.

  • Go to Plugins Section
  • Click on ConfigServer Security & Firewall
  • Under Server Information section, you can find View Listening Ports tab.

There you have it.
38
General Discussion / Amazon VPC for Use with an Amazon RDS DB Instance
« Last post by Vineesh K P on November 03, 2018, 06:09:06 pm »
Hello All,

In this article, we will be looking on how to set up Amazon VPC for using with an Amazon RDS DB instance.

It is a common scenario that an Amazon RDS DB instance in an Amazon VPC, that shares data with a web server that is running in the same VPC. In this tutorial you create the VPC for this scenario.

The diagram given below shows this scenario.

Because your Amazon RDS DB instance only needs to be available to your web server, and not to the public Internet, you create a VPC with both public and private subnets. The web server is hosted in the public subnet, so that it can reach the public Internet. The Amazon RDS DB instance is hosted in a private subnet. The web server is able to connect to the Amazon RDS DB instance because it is hosted within the same VPC, but the Amazon RDS DB instance is not available to the public Internet, providing greater security.

Step One - Create a VPC with Private and Public Subnets

Use the following procedure to create a VPC with both public and private subnets.

To create a VPC and subnets

  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • In the top-right corner of the AWS Management Console, choose the region to create your VPC in. This example uses the US West (Oregon) region.
  • In the upper-left corner, choose VPC Dashboard. To begin creating a VPC, choose Start VPC Wizard.
  • On the Step 1: Select a VPC Configuration page, choose VPC with Public and Private Subnets, and then choose Select.c
  • On the Step 2: VPC with Public and Private Subnets page, set these values:
Code: [Select]
IPv4 CIDR block: 10.0.0.0/16
IPv6 CIDR block: No IPv6 CIDR Block
VPC name: tutorial-vpc
Public subnet's IPv4 CIDR: 10.0.0.0/24
Availability Zone: us-west-2a
Public subnet name: Tutorial public
Private subnet's IPv4 CIDR: 10.0.1.0/24
Availability Zone: us-west-2a
Private subnet name: Tutorial Private 1
Instance type: t2.small
Important : If you do not see the Instance type box in the console, click Use a NAT instance instead. This link is on the right.
Key pair name: No key pair
Service endpoints: Skip this field.
Enable DNS hostnames: Yes
Hardware tenancy: Default

When you're finished, choose Create VPC.

Step Two - Create Additional Subnets

You must have either two private subnets or two public subnets available to create an Amazon RDS DB subnet group for an RDS DB instance to use in a VPC. Because the RDS DB instance for this tutorial is private, add a second private subnet to the VPC.

To create an additional subnet

  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • To add the second private subnet to your VPC, choose VPC Dashboard, choose Subnets, and then choose Create Subnet.
  • On the Create Subnet page, set these values:
    Name tag: Tutorial private 2

    VPC: Choose the VPC that you created in the previous step, for example: vpc-identifier (10.0.0.0/16) | tutorial-vpc

    Availability Zone: us-west-2b

    Note : Choose an Availability Zone that is different from the one that you chose for the first private subnet.

    IPv4 CIDR block: 10.0.2.0/24
  • When you're finished, choose Yes, Create.
  • To ensure that the second private subnet that you created uses the same route table as the first private subnet, choose VPC Dashboard, choose Subnets, and then choose the first private subnet that you created for the VPC, Tutorial private 1.
  • Below the list of subnets, choose the Route Table tab, and note the value for Route Table—for example: rtb-98b613fd.
  • In the list of subnets, deselect the first private subnet.
  • In the list of subnets, choose the second private subnet Tutorial private 2, and choose the Route Table tab.
  • If the current route table is not the same as the route table for the first private subnet, choose Edit. For Change to, choose the route table that you noted earlier—for example: rtb-98b613fd.
  • To save your selection, choose Save.

Step Three - Create a VPC Security Group for a Public Web Server

Next you create a security group for public access. To connect to public instances in your VPC, you add inbound rules to your VPC security group that allow traffic to connect from the internet.

To create a VPC security group

  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • Choose VPC Dashboard, choose Security Groups, and then choose Create Security Group.
  • On the Create Security Group page, set these values:
    Name tag: tutorial-securitygroup

    Group name: tutorial-securitygroup

    Description: Tutorial Security Group

    VPC: Choose the VPC that you created earlier, for example: vpc-identifier (10.0.0.0/16) | tutorial-vpc
  • To create the security group, choose Yes, Create.

To add inbound rules to the security group

  • Determine the IP address that you will use to connect to instances in your VPC. To determine your public IP address, you can use the service at https://checkip.amazonaws.com. An example of an IP address is 203.0.113.25/32.

    If you are connecting through an Internet service provider (ISP) or from behind your firewall without a static IP address, you need to find out the range of IP addresses used by client computers.

    Warning : If you use 0.0.0.0/0, you enable all IP addresses to access your public instances. This approach is acceptable for a short time in a test environment, but it's unsafe for production environments. In production, you'll authorize only a specific IP address or range of addresses to access your instances.
  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • Choose VPC Dashboard, choose Security Groups, and then choose the tutorial-securitygroup security group that you created in the previous procedure.
  • Choose the Inbound Rules tab, and then choose Edit.
  • Set the following values for your new inbound rule to allow Secure Shell (SSH) access to your EC2 instance. If you do this, you can connect to your EC2 instance to install the web server and other utilities, and to upload content for your web server.

    Type: SSH (22)

    Source: The IP address or range from Step 1, for example: 203.0.113.25/32.
  • Choose Add another rule.
  • Set the following values for your new inbound rule to allow HTTP access to your web server.

    Type: HTTP (80)

    Source: 0.0.0.0/0.
  • To save your settings, choose Save.

Step Four - Create a VPC Security Group for a Private Amazon RDS DB Instance

To keep your Amazon RDS DB instance private, create a second security group for private access. To connect to private instances in your VPC, you add inbound rules to your VPC security group that allow traffic from your web server only.

To create a VPC security group

  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • Choose VPC Dashboard, choose Security Groups, and then choose Create Security Group.
  • On the Create Security Group page, set these values:

    Name tag: tutorial-db-securitygroup

    Group name: tutorial-db-securitygroup

    Description: Tutorial DB Instance Security Group

    VPC: Choose the VPC that you created earlier, for example: vpc-identifier (10.0.0.0/16) | tutorial-vpc
  • To create the security group, choose Yes, Create.

To add inbound rules to the security group

  • Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
  • Choose VPC Dashboard, choose Security Groups, and then choose the tutorial-db-securitygroup security group that you created in the previous procedure.
  • Choose the Inbound Rules tab, and then choose Edit.
  • Set the following values for your new inbound rule to allow MySQL traffic on port 3306 from your EC2 instance. If you do this, you can connect from your web server to your DB instance to store and retrieve data from your web application to your database.

    Type: MySQL/Aurora (3306)

    Source: The identifier of the tutorial-securitygroup security group that you created previously in this tutorial, for example: sg-9edd5cfb.
  • To save your settings, choose Save.

Step Five - Create a DB Subnet Group

A DB subnet group is a collection of subnets that you create in a VPC and that you then designate for your DB instances. A DB subnet group allows you to specify a particular VPC when creating DB instances.

To create a DB subnet group

  • Open the Amazon RDS console at https://console.aws.amazon.com/rds/.
  • In the navigation pane, choose Subnet groups.
  • Choose Create DB Subnet Group.
  • On the Create DB subnet group page, set these values in Subnet group details:

    Name: tutorial-db-subnet-group

    Description: Tutorial DB Subnet Group

    VPC: tutorial-vpc (vpc-identifier)
  • In the Add subnets section, click the Add all the subnets related to this VPC link.
  • Choose Create.

Your new DB subnet group appears in the DB subnet groups list on the RDS console. You can click the DB subnet group to see details, including all of the subnets associated with the group, in the details pane at the bottom of the window.
39
General Discussion / What is cpanelsolr and why needed it on cPanel servers
« Last post by joseletk on November 03, 2018, 04:19:07 am »
cpanelsolr was introduced in cPanel version 64. cpanelsolr uses Java to index email messages managed by dovecot. cPanel describe the service as;

Code: [Select]
Fast Email Searching (IMAP Full-Text Search)
Full-Text Search Indexing (powered by Solr) provides fast search capabilities for IMAP mailboxes. Users of iOS devices, Microsoft® Outlook™, SquirrelMail, Horde, Roundcube, and Mozilla™ Thunderbird will notice significantly improved search speed and convenience.
Unless you have high email usage this service is probably not needed and there have been reports this service consumes a lot of memory. On low memory systems, you would be advised to disable cpanelsolr.

How to disable cpanelsolr
---------------------------------
To disable cpanelsolr, we can use the service manager inside WHM to enable and disable services.

Follow the steps below to disable the cpanel-dovecot-solr service.

Code: [Select]
1) Login to WHM with the root user account
2) Select “Service Manager”
3) Once the page loads untick the two boxes next to the cpanel-dovecot-solr service.
4) Click save at the bottom of the page
This will now disable the cpanel-dovecot-solr service and you should notice your memory usage won’t be as high. It’s important to remember you should only disable this service if you are having problems with it or your system is running a low amount of memory.
=====================================================
40
General Discussion / Useful Screen Commands
« Last post by nidhinjo on November 01, 2018, 12:52:29 pm »
>> To install screen

Code: [Select]
#yum install screen
>> After installation if you see "/var/run/screen must have permissions 777" then change the permission to 777 

Code: [Select]
#chmod 777 /var/run/screen
>> To list screenname and state (attached or detached)

Code: [Select]
#screen -ls
After typing screen -ls it will show whether screen is "detached" or "attached" state

>> To reattach "detached" screen

Code: [Select]
#screen -r <screenname>
>> Leaving screen

Code: [Select]
press down ctrl + A together and type D   (ctrl A + D)

>> When u type screen -ls if the screen is attached, then do the below

Code: [Select]
#screen -D <screenname>     then

#screen -r <screenname>
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