Linux System Administration: Adding Recovery Mode To Grub Menu

 On normal startup of the Linux system you probably see this menu every time you boot up

In this post we are going to add a recovery mode for each of these choices.

Here are the steps to create recovery mode options in the GRUB menu:

1. Log into the system normally

2. Open a terminal session, switch to root privilege or root user

3. Type vi /etc/default/grub to edit the grub file

4. Once you are in the grub file find the line that says GRUB_DISABLE_RECOVERY="true" and change it to GRUB_DISABLE_RECOVERY="false" then press esc then type :wq!

5.  When you get your command prompt back type grub2-mkconfig -o /boot/grub2/grub.cfg to regenerate the grub file

6. When you reboot the system you will see that for each choice on the menu there's an equivalent recovery mode option, you can press esc to stop the menu countdown

Linux Administration: Reset Lost Root Password

 There are times when you need to change the root password, it could be that you are trying to prevent a malicious former employee or that you yourself have forgotten the password.  Well you don't have to rebuild the system.  That would be an option and a costly one at that.  What you could do instead is to reset the root password on the existing install.

Here are the steps to reset the root password on your Linux system:

1. Boot up your Linux system normally when you get the boot menu press esc to stop the countdown, then press e to edit the boot file.

2. Go to the line where you see rhgb and quiet then remove the options from the line

3. Replace the options with rd.break and enforcing=0 the option tells Linux to break at the ram disk break point in the boot process and the if you are using SELinux to enforce it, be mindful that the \ is not part of the command, it's a line break symbol in the boot configuartion file.

Linux Virtualization: Add Guest Addition To CentOS 8 Stream For Fullscreen Mode

 I've done a post on this before, but it was for an older version of Linux CentOS it no longer works for CentOS 8 Stream.  So instead of updating the existing post, I am doing another post so it won't confuse you.  The older post is for older version of CentOS and this one is for CentOS 8

The first thing you noticed after your install of CentOS on VirtualBox is that it's pretty small even if you put it in Fullscreen mode, it doesn't not fill the whole screen at all, as a matter of fact the size stayed the same.

In this post we are going to install the Guest Addition tool in VirtualBox to make the VM fullscreen truly fullscreen. 

Here are the steps to make the VM fullscreen:

1. Log into your system as root

2. Run dnf update -y, if you have no internet access type dhclient -v to get access

3. Next we want to install Red Hat's repository of tools with this command dnf install epel-release

4. Once the update is finished run the command dnf install gcc make perl kernel-devel kernel-headers bzip2 dkms -y to install headers and build tools

9. Type in the root password and click on "Authenticate"

10. If you don't see your VM going fullscreen, then try reboot

11. Once rebooted click on "View", then "Full-screen Mode" to use your VM in fullscreen mode

Linux Storage Management: Create Logical Volume Management (LVM) On Install

LVM in Linux allows multiple disks to be combined into one called logical volumes via software.  In this post we are going to create LVMs for a brand new system.  There are two scenarios, the first is LVM on a new system and the second scenario is to create LVM on an existing system.

JavaScript Array Methods: some() Method

The some() array works similar to the every() method, it also returns true or false when the condition is met.  some() needs to match just one element in the array that meets the condition to return true.  So lets run the same code that we ran for the every() method.  We will test to see if the array is greater than 50 for the first condition, and then we will test to see if the array is greater than 70 for the second condition.  For the every() method the first condition returns true, while the second condition returns false.  Let's see what happens with the some() method.

    <script>
        var oilPrices = [70.15, 69.50, 71.23, 74.32, 76.99];

        var greaterThanFifty = oilPrices.some(function (value) { return value > 50; });

        var greaterThanSeventy = oilPrices.some(function (value) { return value > 70 });

        console.log("greaterThanFifty: " + greaterThanFifty);
        console.log("greaterThanSeventy: " + greaterThanSeventy);
    </script>

JavaScript Classes : Inheritance

If you come from C# or Java, JavaScript inheritance is a little different than what you are used to.  In JavaScript you don't inherit from a class, but you inherit the classes' prototype object.  In our previous post we created an Account class.  In this post we are going to inherit from the account class.  First let's recreate the Account class with the code below.

    <script>
    <script>
        function Account(balance, type) {
            this.balance = balance;
            this.type = type;
        }

        Account.prototype.deposit = function (d) {

            this.balance = this.balance + d;
            return this.balance;
        }

        Account.prototype.withdrawal = function (w) {
            this.balance = this.balance - w;
            return this.balance;
        }

    </script>

JavaScript Array Deep Dive: Reading and Assigning Values To Array

In the previous post we created arrays of different types, in this post we are going to read the values from our arrays.

Let's work with the following arrays

1. var numbers = [1,2,3,4];
2. var stringArray = new Array("USA", "Canada","China");
3. var objectArray = [{firstName: "Jane", lastName:"Johnson", weight:"115lbs"},{firstName: "Jack", lastName:"Johnson", weight:"200lbs"}];

Let's start with getting a value from an array:

To get the second value of an array you would write the following code by using the :

console.log(numbers[1]);
console.log(stringArray[1]);
console.log(objectArray[1]);

JavaScript Array Deep Dive: Creating Arrays

Arrays in JavaScripts are a collection of values stored in what are called elements.  Each element is represented by a numeric index that is zero based, meaning the first element of an array starts at index zero.  JavaScript arrays are dynamic and can contain many types of objects including functions.  The useful thing about arrays is that they are a specialized object that contains a variety of built-in methods that are useful in the manipulation of the array.

First let's create an empty array, there are several ways to do this:

1. var empty = [ ];
2. var empty = new Array();
3. var empty = new Array(0);

JavaScript Array Methods: Array.isArray() Method

The Array.isArray() method is a useful method to determine object is of type array.  Let's demonstrate with some code.

    <script>
        var oilPrices = [70.15, 69.50, 71.23, 74.32, 69.50, 76.99];
        var iamObject = new Object();

        console.log(Array.isArray(oilPrices));
        console.log(Array.isArray(iamObject));
    </script>

The code above tests to see if the oilPrices array is of type array which it is, and then it tests to see iamObject is an array.  The console.log out put should return true, and the second console.log should return false.

JavaScript Functions : Argument Lists Object

In JavaScript when you define a function you get a built-in Arguments object, this object is an array-like object that puts the arguments/parameters of the your function in an object which can be accessed via indexes much like an array.

This can be useful if you have a function that takes multiple parameters, but you don't know how parameters there will be.  Let's modify our addNumbers function so that it can add more than two numbers using the Arguments object.

    <script>
        function addNumbers() {
            var sum = 0;

            for (var i = 0; i < arguments.length; i++)
                sum += arguments[i];

            return sum;
        }

        console.log("The sum of the numbers are " + addNumbers(1, 2, 3, 4, 5, 6, 7, 8, 9, 10));
    </script>