102.2: Install a boot manager

1. GRUB Legacy

We briefly touched on it. In the lesson on startup, there are different Linux bootloaders. The best known is Grub Legacy, which is basically Grub One. Then there is Grab Two and Lillo. First let's take a look at the Grub Legacy boot loader. I've prepared a small diagram here. What is that supposed to mean? After a system starts, the BIOS checks whether the hardware is working correctly. If this is the case, the BIOS also checks whether a bootloader is present. The Grub Legacy bootloader is located in the first 512 bytes of the hard disk, that is to say, in the master boot record.

There is also an image with the name "boot IMG." This step is also known as stage one of the boot process. The boot IMG file searches for another image file. This is called core IMG. This is stage one of five. The only job of boot IMG is to find and load the core IMG file. Incidentally, the core IMD file is no longer in the master boot record but in free space on the boot partition. The task of core IMG is only to find the boot partition of the system itself. With Grub's legacy This is always Boot Grub. That would be stage two. In Grub there is either a thegroup.com file or a menu LST file. Both files have almost the same content, just different names. Grub.com is more likely to be found on Redhead-based systems. Menu LST is more like Deion based systems. These two files are both Grub configuration files.

These files contain information about which hard drive is being used, where the kernel is located, where the in it ID is located, how long the timeout should be if you can choose between several operating systems, and so on. In a moment, we will look at a small example in a moment. Another important file is the device map file. This contains further information on where the kernel and the entire operating system can be found. So you have all the files that you need to boot the system. Let's take a look at the Grub conf file. Unfortunately, I do not currently have a system at hand using the Grub Legacy, which is why I looked for an example from the Internet. This file has been shortened a little. Usually we still see a lot of comments and so on, but they have been removed here. In the first line, we have the value default equals zero. The zero stands for the first image or for the first kernel shown here. In this example, only one kernel is shown here. At this stage, if two kernels were installed, the second kernel would follow.

The zero refers to the first kernel. "Default equals one" would refer to the second kernel. Timeout equals ten means that if you have a choice between two operating systems or between two kernels, then the user has 10 seconds to make their decision. The splash image entry is there so that you can save a graphic file. So that you can add the boot logo. A hidden menu means that the selection menu for which the timeout would apply is hidden and is not displayed. Below that, we can choose a title. Below that, you will find an indication of where the root system can be found. In this case, at the very beginning of the first hard drive. Below that, we find the kernel information and some other options. The Quiet option means, for example, that we cannot see on the screen what happens when booting. But if we want to see this,we simply remove the Quiet option. Finally, the init road is listed here in the last line. We don't need to know more about this file. It was probably too detailed for the LPIC One exam anyway. So let me switch to the terminal. Now there is a separate command to install Grub legacy.

This command is a pseudo-Grub install. It is important that we specify the partition on which our boot directory is located. This is usually located on Dev SDA One, but I think in my system it is Devasta Five. But this is not important because we will not perform a Grub installation here. And this is also not required for the Epic One exam. All you should know is what the command is from then on. Of course, you wouldn't do this in an already running system, but if you were using a live CD and the original bootloader no longer worked, you could reinstall group legacy.

But we cannot perform this now because, as I said, you do not do this on a live system. And by the way, my Ubuntu is an actual Ubuntu system where Grub Two is installed. So please only remember this command here. The Grub command, with no options, opens a Grub shell. So a shell is only available for Grub. There are various commands that can be used here. With help, you can display the corresponding commands. With Quid, you would leave the Grub shell again. Unfortunately, I can't run it here because I installed two things and the command doesn't work here. So this is an additional indication that we have not installed Grub like Bye.

2. GRUB 2

Grub Two is the successor to Grub Legacy and a complete redesign of the bootloader. So, the two no longer have that much in common. Before we talk about Grub Two, we need to briefly talk about GPT and how it differs from MBR. The master boot record supports a maximum of 26 partitions, provided that the logical partitions are added to the primary partitions. A petition can have a maximum size of two terabytes with GPT, which is the abbreviation for Guid partition table. The system can use up to 128 petitions and each partition can theoretically be one sat byte in size, which corresponds to about 900 million terabytes. If I didn't make a mistake in my calculation, GPT needs UEFI to start. We have already spoken briefly about the UEFI topic. So what does this graph say here? Like the BIOS before, the weefy performs various hardware tests and then also looks in the first 512 bytes of the hard drive to see whether it can find a bootloader or part of the bootloader.

There is also group two, with the boot EMG, and here it is stage one of the boot process, the so-called Gpth. hater simply tells the system that GPT is being used. This has nothing to do with the actual boot process, but should be mentioned anyway. The so-called petition entry area is not really part of the boot process either, but it is still important because it provides information about where and which petitions are located, which IDs they're using, and so on. As with Grub's legacy. Next we have the core EMG file too. It is stage 1.5. In Grub 2, the core EMG looks for a boot AVpartition, the so-called AV system partition, or ESP for short. I briefly mentioned this topic before. The ESP file must be VFAT or FET 32, as the WeFi image files can only be read in these formats. There are further images in the ESP partition, but they are not important for the Epic One check. It is more important that this is followed by stage two. And in this case, this is not boot Grub but group boot Grub Two. But this is not the case in every Linux distribution. In Ubuntu, the path would still be bootGrub for Red Hat Systems boot Grub Two.

So I will switch to my terminal and we'll take a look at the directory for City Boot Grub. There are, for example, the Grub INF file and the Grub CFG file, which are now important. We take a look at the Grub CFG and it looks completely different from the Grubcon file from Grub legacy. If you could still make various changes directly in the file in the old Grub dot conf, this is not recommended for the new Grub dot CFG. This is also at the top of the command mentioned. Do not edit this file. In general, you shouldn't change anything manually within Grub. Let me leave. There we are. If we now want to change something, we would do it in another file which can be found in the Etsy default Grub. Yeah, this file looks a lot more similar to the old Grub configuration from Grub legacy. We have the default system that should be started again.

We have a timeout value, we have a hidden style, and so on and so on. We could now make the desired changes and save them. And to make these changes effective, we need to run the Grub mkconfig command. Let's take a look at the main page config to generate a Grub configuration file. We can just do that. Even if we haven't made any changes to the file, it should work anyway. So we are typing Zoodograb mkconfig. By the way, on Redhead Systems, the command is called Grub Two mkconfig. Perfect. Okay, We noticed that the system has written a new Grub CFG file. We find this in Grub, as shown at the beginning. For this reason, you should not make any manual changes to the file. because such a file can be created automatically even without programming knowledge. Instead of Grub mkconfig, you can also use the Update Grub command. This can only be found on Debian-based systems. Let's take a quick look at the main page. Update grub, update grab two times for Grab.Mkconfig. That was it for Grab two. We don't need to know anything else for the Epic One exam here either. We do not have to install or completely configure Grub to.We only need to know where Grub is stored, what the corresponding configuration files are, and how these configuration files can be used.

102.3: Manage shared libraries

1. Shared Libraries

This lesson is about what are known as "shared libraries." What are shared libraries anyway? Shared libraries are files that provide functionality that other programmes can use. If there are shared libraries that provide specific functions, a programmer does not have to reprogram everything from scratch for each program, but simply uses this specific library for this specific function in the next few videos. When it comes to package management, you will find that when installing a program, Linux often tells you that the files AB are required to be able to install the program. Often, this is a library that we then have to install. Additionally, if another programme that we want to install also needs this library, it does not have to be reinstalled and the programme does not have to take it with it because it is already installed. Shared libraries have the file extension.so, which stands for Shared Object. From the lesson about the Linux directories, you already know where these shared files can be found because they were mainly in the lib directory. We look at this directory again.

We have various subdirectories in which the libraries can be found everywhere. But we already see some libraries directly in the lib directory. As I said, they have the ending, so for sharedobjects, the version numbers of the library are partly located after the ending, but that's quite normal. Otherwise, we still have the directory user lip, and the shared libraries are also located here in userlip, and we also have the directory user local. And in my case, there is only one one-sho no Chevrolet library here in this directory. Let's look at the first command we will need to use when dealing with libraries. That would be the command LDD man LDD printshared object dependencies With LDD, you can see which libraries an already installed programme is using. The entire path to the binary file of the programme must always be specified with the command SO. If we, for example, enter LDD in it to show us which libraries are linked or used with the init command, then we get no results. So we always have to use the entire path.

And it should be, in this case, Led Asben in it. And as a result, we can see which libraries are used and where they are stored. We see the paths here, in this case, lip, lip, and so on. And if you take a closer look at this, you will find that this library, Linux vdso, is used by both programs, demessage and init, so here and here. And that is, of course, the main advantage of these libraries, that they are used by different programmes and are not installed 27 times on the server in different directories but only once. Let's look at the LD config command configure dynamic linker LD configured configuration runtime bindings led config generates the necessary links and cache for the most recently discovered shared libraries in the directory specified on the command line, and so on. Maybe that doesn't tell us much at first. It means that the LD programme creates the necessary links and the library cache.

This is, for example, necessary if we have installed new libraries ourselves, and these may be in other directories. For example, we will install a third party software in opt and there will also be a lib directory in the application directory in which the libraries are then located. These libraries would then have to be made known throughout the system using LD config. LD config must be executed with root rights. Ultimately, we don't see if and what happens, because everything happens in the background. However, as long as no error message appears,we can assume that everything is correct. Let's look at a file. That would be the file that the command accesses. That would be the file etsyldsonf. This file is very small and says nothing else than that. All files with the extension conf are in the directory etsyld, so conf d should be used. We might take a look at the directory etsy sol d, so we only have two files here. Let's see what they say. Cat lip sync, for example. And this file simply specifies a path, in this case, user local lib, so a path that could contain libraries.

Let's look at the other file cat so on. Here too, there are only a few paths in which libraries could be present. This means that if we now install a programme and want to make the libraries known globally, we either add the appropriate path in one of the theconf files, or we just create a new separate confile that we place here in this directory. after changing the file or after creating a new file. We have to run LD config once, and the library would then also be available globally for other programmes to make such a directory known. You can also use the variable LD library path. Let's take a look at what value this variable has. We do that with the echo command echo, and we see that this variable is empty. We can fill it with an appropriate path. We are using export, for example, and we have now assigned the path up lipped to the variable. Let's see if it works. We echo the dollar leery path and we see that the path is now stored in this variable. If we fill this variable with a path, Linux knows that this variable contains paths to libraries. because this variable is only available for this purpose. We will not go into the fundamental topic of variables at this point, because this is a topic for a separate later lesson. But since the LD library path was explicitly mentioned in the goals of LPI, we had to briefly discuss it.

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