Hi friends, welcome to the Learning Series of Red Hat system administration or rH 133. I'm Hutchison foster your course instructor. And here in system administration, we are going to cover a huge range of topics. System Administration is a vital section component, which you would need to be prepared of for pursuing printed certifications. Or if you are simply learning this red hat code for administering your system. If you want to be a master of Red Hat, you must go through this process.

So what are the topics that we are going to learn here within System Administration. So, we will start with our system initialization, which deals with the boot process, the bootloader and everything that exists between when you start using Start by pressing the power button till an authentication screen appears on your screen on your desktop, where you will write your username and password all the process behind that then we will learn about our RPM Red Hat package management then we will learn about kernel services Linux is actually a kernel and red hat is an operating system. So, to properly use the power of open source, we have to be aware of kernel services not just aware, but master will be exploring the corner services and trying to control it and learn about everything. Then we will learn about system services that are in user domain, not the system domain, the control domain.

Then we will learn about user administration where the user information the country Preparations and other things we will be dealing in. Then we will learn about our file system management. In advanced level two File System Management allows us to manage the file according to us all the files and folders that are part everything. Then we will learn about network configuration, where we will learn be learning about the network systems. If you want to configure the land or basic configuration with a server. Then we will be learning about virtualization which is a trending topic these days.

Virtualization is being used along with the cloud in Linux, to empower present scenario servers and everything. All applications these days are powered with cloud on cloud run in background with Linux operating system, either powered by virtualization containerization the Docker and Zen are very popular. So Zen is a virtualization tool which is being used with Red Hat. And obviously Red Hat is an important component of ami, Amazon Linux, which is the default operating system for when you consider the EC two or other services on AWS. So, we will learning about them. Then we will learn about troubleshooting at last about system administration all we have learned So without wasting any time, let us start with our system initialization.

So, go the boot sequence is the thing which is appearing on your when you start your system, press the Power button. The system begins to boot what is good For those who don't know, there is a piece of code actually a first line of code that is being executed when current begin to flow in your motherboard circuit. And the first code that is being executed is the boot code. The bootloader which is located in the primary section primary partition of the hardest and it is being loaded in the cache. So, the boot process is start which consists of a bootloader after the bootloader is being loaded, the kernel is being initialized the main kernel thread which is starts the parent of all process on your system that is in it or initial I in it which is very interesting and enters the desired run level. Run level as you could also understand by safe mode, the example of safe mode if you have been using Windows operating system over a time, you might have seen safe mode in XP and seven.

The Safe Mode is nothing other than run level. But here is a difference in red, we have multiple multi level run level. So there are seven or eight various levels which we can define and execute. So here are the three commands or files that is being executed behind the scene from bootloader kernel initialization and initialization of the parent process in it all are loaded from ATC location and RC dot d the D stands for daemon it loads the system in it process has been called then other domain demons and local demons is being loaded. The bootloader consists of two stages. First stage second stage, the first stage is a small.

It consists of a less number of files, which resides in MBR or boot sector. boot sector is the key sector of your hard disk of your storage device. Then, comes the second stage where the partition is being loaded, which is being loaded from the boot partition, which you create during the installation of your operating system. If you're dealing with hacking, ethical hacking or other parts of things you have been aware about boot sector viruses, boot sector virus The most horrible virus if there is an boot sector virus, you could not kill it. The concept is very simple. The software which you use to find and remove viruses is called anti virus which starts after the bootloader is when they started and system process has been initialized.

When the virus starts before the antivirus itself, you could not help it, nothing can stop it. So, to secure boot sector is very important. If you are dealing with server when you are going to be a Server Administration at certain organization, you must be aware of the threats that could that may someday attack on your system and you have to prevent those attacks. So be aware about boot sector virus then The minimum a specification for lame x is a data mined, the labels are being used the kernel location where the kernel is their kernel files are located, the operating system root filesystem route is being loaded first, then you will be asked the user which user want to access. If you provide root or non root user, it will go to that user's account you will be logged in with that account. Then the location of initial ram disk has been loaded that is in it rd, which is again a demand then minimum a specification for other OMS that is a boot device or level could be.

Then there comes the grand unified bootloader or grub, which is located in the file called grub dot configure or Gru b dot c. To grow up is a commodity grub is a bootloader. The default bullshitter for Red Hat, which is a very powerful, which can load multiple operating system at the same time. Try to remember the days when you want to install Windows and Linux simultaneously on a system, you have to first Install GRUB or Linux at the first, then you would install the windows in other partition. So the grub would be the parent process parent or bootloader, which could start Windows or Linux at the same time. You can switch that around so that it unifies all kinds of bootloader at the same place. It is very powerful and red hat is being configured with Chrome.

You can configure in the graph with this file. You can also go with command line interface that is available at boot ROM. You can boot from a which can boot from the partition to 82 or 83 or various other partitions. The bootloader file could be located in a harness, SSD pendrive compact this and various other devices storage devices. So be aware about bootloader it supports a mt five password protection which is an encryption. The configuration file is being located in the boot directory and within grub.

The changes to this file could take effect immediately after you write the changes. So harbor precautions over there. If MBR on the location, Dave has the SDA is corrupted, you can reinstall the first stage bootloader with the command has been grub install Dave SDA the bootloader. The copy of a bootloader is located here in as when we can start a boot process with grub. The process is start with the image selection image of the OS. We select a space followed by up down arrows on the board a splash screen.

So what is image selection? The same process suppose I know our desktop or laptop, we have two operating system actually the operating system is called as image a Windows image and one rendered image windows seven And redhead take it as that when the grub bootloader is being initialized is started and it will show you the options either you want to load redhead or Windows you could select anyone from them because you have provided the image for those operating systems. You can select by up and down arrow. If there is a single image provided, it will not ask you, it will you can similarly, simply go with your default image. We can also pass arguments which can allow which allows us to change an existing stanza in Mino editing mode. We can issue boot commands interactively on graph command line, which is specifically a threat.

If you are trying to help hack the grand unified bootloader there is a threat out there, you have to can, you can switch off various modes of the kernel, which won't allow anyone to pass arguments when the graph is being loaded. Be aware of that. Then there comes a kernel initialization, which happens after you selected the image. The kernel boot time functions is started with a device detection, the detection of all the devices device driver initialization, the initial drivers are being initialized, the USB driver, the sound driver, other drivers as well. Then the mount root within it mounts the root filesystem in read only mode, the root file system the file system of your system we A root user is being loaded at first, but it will be only displayed you could not write it or edit it then loads the initial process which is called in it or parent of all process.

You have been typing a command called I nit init zero, which can shut down your system, it will shut down your system. So we can pass the value zero to the init process and it will kill the init process. When we kill the parent process all the child process or everything that exists on your radar system would automatically be killed and the system shuts down. Similarly, if we want to restart our system, we will write in it six which will show the status code of six to the init process and your system resets starts. So, this is a clarification of the init process. The init initialization is being read from the configuration file which is which is again located in etc.

And in a tap directory what does it actually do it initialize the run level, the default run level of your system. System ID, which is being followed by system initialization scripts that are being executed to load the kernel and everything else. The role level is specific a script directories are being located it past a certain key sequences. It defines the UPS power fail the story scripts is pawn gateways on virtual consoles. The Void consoles that you see there are seven virtual consoles, six command line consoles or Virtual Console, then the graphical console, then it initializes x in the run level five initially in level five. So here comes a run level, where any process defines run level.

There are seven run levels from zero to six. Then as an emergency run level, as could be considered as safe mode, zero to six are different run levels and emergency run level. Run level is selected by either the default in the EDC directory with init tab at boot passing bootloader loading with an argument from the bootloader you can define the level by pressing the status code When the bootloader the grub is being loaded or you can provide it from command line in it neural level, you can create a new run level loader and they will change run level. And by default, a normal run level five is being loaded to show current and previous run levels data was executed, you can go to S bin and run level. Then there comes another important file that is RC dot system in it the system initialization proc file which is a daemon again import it does pull up perform important tasks for activating YouTube and SC Linux, the security and as Linux which is a security feature which is securing the kernel and system utilities.

It says the kernel parameters in system controller configure in the ATC directory. It says the system clock, The clock the date, time, and everything is determined with this process. It loads the key maps or key steps. It enables swap partition, the partition which is being loaded. It says the host host name. It loads the root filesystem.

Check and remounted. It activates the rate partition and LVM devices, low virtual machine low level virtual machines It enables disk quotas the quota or quota assigned to different partitions or this it checks and Mark Other file systems where if you place a pendrive that is another file system not native to your system, it could be mounted and being checked by this process. It cleans up the stale locks and P ID files. Name comes system, we run labels. Labels define which services to start Each level has a corresponding directory, the same directory etc RC dot d RC x dot d, where x is our level 0123456 s and so on the system we in it a script resides in the init path in a dot d daemon the symbolic link in the run level directory Call the init dot d the daemon is scripts, the init script with a start or stop argument.

So it will determine which level to load. These files are vital if you want to configure the system you have to configure after the system is being loaded, you can configure it for all the next times or other times. When the system boots up, you can deter my visual level to load what to configure and go through these files. Then there is another file that is called RC dot local which is being executed after Darren no specific scripts are being loaded. It is a common place for custom modification. In most cases, it is recommended that you create a system we in it a script in this file.

Init dot d the daemon file for any parent process is used under the service you are restarting is very important. And it doesn't guarantee existing script can be used as a starting point for this local script. So this is a process of loading the bootloader image, run level init process the kernel, the local file. You can control various services and process with utilities. There are different utilities to control default services startup and to control services manually. If you want to control the default services at a startup, when the system is being restarted, you can go through system config services.

Si es we check configuration. The system config service is a graphical utility that requires an X interface, which is an X Window interface actually x windows a genome or KD, the graphical mode or the GI interface in Linux, the NT si s we is based on utility usable in virtual consoles or the command line mode. Then we can go with our check config which is fast versatile command line utility that works well and is usable with a script and kick start initializations. We can manually control various services and utilities with service command which immediately it starts or stops I standalone service. We can use the check Failure to immediately start or stop exci and at the demo, managed services. So this was just a brief introduction about system initialization.

We have learned everything from the power on button, what are the process that exists? Go through this thing in detail. Take the various files, explore the files that we have learned about here and try to read those files. You actually don't need to configure it, if you're not an advanced user, or administration basically must have an idea of what is going on behind the system. Because attackers can attack at any level, and you have to be cautious about everything. You can do a routine checkup of these things.

If you are Being aware of the process, if something is not going correctly, you can always check it if you know what are the sequence, correct sequence. So keep learning keep moving ahead. We will be learning more in the coming videos.