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Domain No. 1 - Essential Commands

1. Logging in and out of the system

Hello students, so now we're going to log in to each of our previously installed operating systems. Currently, we're at the Ubuntu server command line, and our user in this machine was curly and the password, and we're logged in right now. In Linux, there are two kinds of users: regular users like the one we just created, and of course, on that one machine, there could be hundreds of users, and there's going to be a super user. A root user and that is if you're coming from Windowsbackground that is similar to an administrator on a Windows machinewhich have all the powers to make and break things basicallycan change things you can write to files that other peoplecannot that the regular users cannot so it's a good practiceto always log into a Linux machine using a non rootaccount only switch to root account when you really have tochange something or if there's a file that you cannot seebecause it requires root permission to even look at and we'regoing to discuss those in detail later on so if Iwant to exit out of here I can just simply typeexit and I'm back at the prompt log out logout willalso get me logged out of the system and back tothe prompt again now we're going to look at Susan Linuxand since my machine right now is showing unlocked I justhave to type in the password and I'm back in backin the GUI and there are two ways you can lockyour machine so if you're living suppose if you're in awork environment it's always always always a good idea to lockyour screen don't just assume that eventually it's going to lockitself out but because during that time if somebody really wantedto disrupt stuff they can come and do it and you'llbe blamed for it because it's your machine so always agood idea. Good security practise to lock your screen and if you're completelyleaving the system you can leave and you'll get these options so spend reboot shutdown and log out so you can logout and you can back up the prompt and here fromhere you can type in the password again and you're loggedback in now we are at our central machine and Larryis our user on that just logged in although I kindof briefly went over all of this during our installation processas well but since this is part of your domain andcompetencies so I wanted to make sure that I do showit to you again just so you know in each ofthese operating system how does the login and logout process work? So on a centralised machine, you see this little power button here. You just click on that, and from here, you just click on the user, and you have the logout option here, and then it will prompt you. You're going to be locked out in 60 secondsand you can do it earlier and it shouldbring you back to the login prompt. Here we go. So this is how you log in and log out of all these three flavours of Linux that we have discussed so far.

2. Getting to know Linux CLI

Students, hello and welcome back! Now in order to just get our feet wet, what I'm going to do in this lecture is log into the CLI and just show you some very basic commands. So that way you'll get some idea, and you'll start feeling comfortable around the Linux interface if you're completely new to it. So we are in a windowing environment right now. I'm going to open a terminal, and this is CentOS, by the way, or Red Hat, whatever you want to call it. And currently we are at the prompt, and just the fact that we are at the dollar sign prompt tells you that it's a non-root user who's logged in right now. So, let's say I want to know who I logged in as and I've switched back and forth from root to another user, then back to another user, and back to myself. And I kind of lost thought, losttrack of who I'm logged in as. The command is very simple. It's an English word. Who am I all together without any spaces. and it tells me I'm logged in as Larry Okay, suppose I lost track of exactly where I'm located in the directory tree, exactly where I'm located.I'll do a present working directory, PWD. It tells me I'm located in my home directory, which is homelarry. I'd like to see a list of the files that I own. Currently, I might not own any files at all. So what I'm going to do is I'm going tocreate some file, a very quick way to create somefiles which are empty, which have nothing in them, islike file one, file two, file three. I also do an LS. And you see, there are three files that I just created that are right here. Okay? So I just created three files. And when I did an LS, I found out that I had some basic information that was already there. And if I do it LSA, which is called a long listing, And I look down here, and there are some files that begin with a dash, which are file permissions that we'll discuss later. But the ones that start with the letter D are directories. And also on my screen, they are shown as blue. They are colored. So these are directories. The ones I just created are files. So for directories, you have to go to CD and change the directory. And suppose I want to go to desktop, and my current working directory is now home. Larry, desktop with a capital D Linux is case sensitive.Always double-check whether you're supposed to use uppercase or lowercase because it can make a difference. If you do all lower case on desktop, it will show you an error. Let me do it, and I'm going to do desktop. It says no such file. And if you're a new Linux user, you can say no, it's not true. It's there; the file is there; I've just seen it. But the reason it's not letting you in is because there is no such thing as all lowercase desktop in your directory. You have to do CD, capital D, and then the rest of the world, and now it will let you in, and you've got nothing in there right now, so it doesn't show any files. Dot dotit will move you up one step if you do a CD. So you're back in your home directory, and I have created three files, but now I don't want them. So I'm going to do file one, remove RMis for removing file two, remove file two, remove file three, and let's do an LS. Now all my files are gone; they've been removed. So here's another crucial piece of information if you want to know what my host name is. Currently I don't have a host name assigned to this machine, so it's showing "local host" local domain," so I haven't signed a domain yet and I haven't assigned a host name yet to this machine. I can also find out what the date is today, which shows the date the date came in. And suppose I want to change the password for Larry; since I'm logged in as Larry, that's the only password I can change right now. I cannot change passwords for other people or for root. I can only change a password for myself. When you do a PA SSWD, or lower case, it will ask you what your current password is. Suppose I purposely enter the wrong password. It gives me this error, this very weird error. This is basically saying you have entered the wrong password. But this is sent to us way oftelling you that you got a wrong password. But this is how you change the password, "passwd," and another command is the last user who logged in to this machine. This is the last user, since Larry is the only user on it so far. So he's the last user as well. And suppose I want to find out what version of operating system is running, and it says Linux, but that's not good enough. I want to get more information. So I provide UNI assistance and provide you with additional options for using your name. So I want to type in your name, and that gives you a lot more information. It tells me what the operating system is, what the domain name is, what the host name is, the actual architecture of my Linux operating system, the date it was installed, or the date it was available, or the date it was created. All of that information is available. So these are some of the commands I wanted you to get a feel for in Linux right now. So this is it. We're going to get into more detail and more complex stuff in the upcoming lectures.

3. Changing host and domain name

Hello users. So this is not something I was planning on doing, but since it came up in the last lecture, I did not assign a host name or domain name to my server. So I'm going to show you the commands to do it. although it's far advanced right now for you guys because we're just starting off. So don't worry about remembering any of this. I just want you to sort of remember the process that you go through in order to change the host name. Okay? So far, I've changed it to my server, and I'm going to change it to Set OS dash LS LFCs; sorry for the pause. LFCs, so let's do that. So first I'm going to become Super User Su. Or Su is actually the switch user that asks you for the password. I'm going to enter the super user password. And now you see a hash sign or a pound sign, and that means I am root. See, when I type in "Who am I?" it says root. So now I have the power to change stuff. So first thing I'm going to do is I'm goingto use an editor called VI Editor and I'm goingto go into this file etc network, and I havechanged the host name to this, my server. But I don't want this. I want to change it. To change anything, you have to type I to get into insert mode. So LFCs are sorry. Centaus o LFCs are And test.com. This is my fully qualified domain name. That's what it's domain name.And Wqbang is what you type in to get out of the VI Editor after saving it. If you just do a "queue bang," that's going to let you quit without saving anything. So, if you made any changes that you don't want to save, you believe you made a mistake. The easy way to get out of it is to go to get out.Okay, the next file that I'm going to go into is the VI ATC host file. And as you can see, I have an IP address, which is not really a working IP address right now. I just put it in there just to show you. This is the format, and I want to change it here as well. So I'm going to delete it. You delete it with a small "x." If I just keep typing X, he's going to keep deleting the characters. And then we'll type it, insert it, change it to Santosh.LFCs.test.com, and then space the host name. Actually, I had two tabs in there. In order to have hostname that far, ifI want to, I can bring it closer. It doesn't really matter. White space is white space. In Linux, it could be one space or five spaces. So that tells the system that this is the host name. Again, the escape key And that WQ bang, which I've now saved. But in order for it to take effect. There are two things you can do. You can either reboot the machine and then the system will recognise during the reboot that there's been a change of the host name, or you can do it while the system is running. So another so the way to do that is etc niddnetwork restart and you got an okay, that's been restarted. And so far as you can see, it's showing my server as the name of the server. But we have changed it already. So I'm going to exit out of it. And there's one more step to this, which is a hostname. Santos LFCs Chess.com is my host name. If I do a host name at this point, it's not showing the new host name, but if you look at my prompt, it still says my server. So in order to change that, I have to run this command. And don't worry about these commands. I don't want you to be overwhelmed about this because we're going to go over each of these later don't waI've logged back in after exiting out completely, and now you can see that I'm showing the new hostname. And if I type the hostname command at this point, this is the new host name with the domain name as ame. And if I Okay, so sorry, this was a segue that was kind of not intended initially, but I just thought it would be a good idea for us to do it because I didn't do it initially. And once we actually get to this topic, then it will make more sense to you. You.

4. Using the find command to search and locate files

Hello students and welcome! In this lecture we're going to talk about the Linux find command, which is one of the most important and widely used commands in Linux systems. Find commands are used to search and locate lists of files and directories based on conditions that you specify. for files that match the arguments. Find can be used in a variety of conditions. You can find files by permissions, by users, by groups, by file type, by date, by size, and you can use other criteria as well. So we are logged into our Linux machine now, and we're going to use some examples. So one of the things that you can do—I haven't discussed it yet—is There's a thing; there's a help feature in Linux on all standard Linux machines called manual pages, or man pages. So if you ever need to look up information that you're not sure about, you can type man and then the command that you're looking for, like in my case, I want to look up "find," and it'll give you pages after pages of results depending on how intense that command is and how much detail it needs. but got quite a bit of detail on the syntax and the use of the fine command. So going into the details of this right now will probably be too much; it will be overkill because right now we're just going on fine command. Just type Q to get out of it. But I wanted to show that feature of Linux: anytime you have any confusion, instead of going to Google, you can just type in man for that command. So we'll start off with a very simple example. The reason I'm logged in as root is that when you're writing a find command, if you're logged in as a non-root user and you're searching through your entire system, then there will be a lot of file systems and a lot of directories that a non-root user would not have access to. They can't even see what's in there. So you're going to get a lot of permission denied ifyou were to run the fine command as a regular user. So that's why it's a good idea to run a command as a root user. So that way, it will go through each and every directory and subdirectory and get you the output that you're looking for. So suppose I'm in the root directory right now when you have the backslash; that's also called the root directory. So I'm in the root directory right now. Let's see what I have in here. Okay, these are like the general files. There are a couple of files that I have created. So what I'm going to do is create a file, and I'll call it the TouchTest TXT Perfect File. Okay, I just created that. Now I'm going to find it and see if my system can find it. Find. This is the syntax that means you start from the current directory, where I am right now in the present working directory. Then you type in name of thefile that's to follow test TXT. Now since I only have one file, that should give methe output of that one file that I just created. Well, I created one before, which is under Larry. So the test TXT is on both of them. Okay, so that's how simple it is. You need to remember the syntax of it, and if you forget, just look up the main pages. So in this case, we use the dot to tell the system to start finding things from our current directory. But what if I want to specify a particular directory? Okay, so now what I've done is I went tohome that is still owned by Ruth and I createda file there which is called Test two TXT. Okay? So I'm going to use the same fine command this time, but instead of using the dot, I'm specifying the actual directory, which is the flashhome name of the file, and I'm going to call it Test Two TXT to see if our system will find it. And yes, he did find it, and it gives you the exact path of where that file is located. So right now I'm using very simple examples. Whatever I'm trying to find, it gets found right away, and there's only one instance of it. However. If you're on a server that has been up for a while doing a lot of stuff, Then you're going to have several instances of that file, probably at different locations, and your system is going to take a while to by taking a while.I mean, it could take probably 30 seconds or a minute, depending on how much stuff you have or how much the system has to go through in order to get you the right file that you're looking for. But right now it's very quick for us because it's a test machine and I don't have too much installed on it right now. Okay, one more example before we wrap up the finding discussion: we want to find all the empty files. Okay, so I am trying to remember how to find out where we are currently. In the command line, type "present working directory," or "PWD." So I'm in slash TMP right now. I'm in the root directory, and the subdirectory is TMP. And anything that you don't want to keep in Linux for a long time, just make it a habit of putting it in TMP so that you can remember to remove it when you're done with it. So what I've done, I've used the touch command and thenI've created empty one and empty two and empty three. Okay, this is how I did it. So now I'm going to have my find command go and search all these empty files to see if it can actually find it. So I'm going to type in the path first. So find in slash temp. I am telling my system specifically go to slash temp. Don't worry about looking anywhere else because the file and the file type are empty. Let's see if we can find it. It found all three files that I have. Because when you create a file with a touch command, it is empty. because the touch command is used just for testing purposes if you have write access to a certain directory. Because if you don't have right access, you're goingto get a message denied that you don't haveright permission to write anything in this directory. It won't let you create a file even by touching it. So that's what touch is used for. And that's why these files are empty. They have nothing in them. Unless you use the VI editor to go into the file and actually write something in there and then save it, you'll have something in it. Okay, this is our discussion about the find command.

5. Archiving and Compressing files in Linux

Hello and welcome. In this lecture, we're going to talk about Linux archiving and compression tools. As a result, File Archiving Tool consolidates a collection of files into a single standalone file that can be backed up to multiple media files. It can be transferred across a network or sent via email. Tar is the most widely used archiving utility in Linux. When an archiving utility is used along with the compression tool, it reduces the amount of disc space needed to store the same files and information. So basically, if you have, say, three files that take up like 50 megs, they're big files. And if you tar them and combine all three of them together, then it will take a lot less space than 50 minutes. And once you send them wherever you want to send them via email or via whatever means, then you untar them, and you'll have the original three files back with whatever size they had. So Tar bundles a group of files together into a single archive. It's commonly called a tar file or tarball. The name originally stood for tape archiver. But we must note that we can use this tool to archive data to any kind of writable media, not only to tape. Tar is normally used with a compression tool such as gzip, bzip2, or xz to produce a compressed Torball. Now we're going to use some examples in which we're going to use all three compression tools, which are the dot GZ, dot BZ 2, and dot XZ. And we're going to see examples of all three of them. So I have five files here, from file one to file five, just by using touch. And now I am going to archive all five of them by using the three compression methods. So the first one is going to be TAR CZF. And I'll tell you what that means in a minute. When using numbers one through five, my files dot tar and dot GZ file. Okay, so in the CZF, you are creating a Tar archive. That's what the C is for. Z is to process archives through g zip.So zip—that's where the Z comes from, and F is for file. And if you want to look up more information onTar, you can of course do the main tar. It'll give you all the details about the syntax and all the options available. Okay, so this is going to tar all of our five files into one tarball. Okay, done. Let's see if it's created. Yeah, the red one right here is the file. Okay, now let's use the other compression method, which is BZ 2. So now we've got to do tar cjfmifiles and tar BZ two.Again, file one through s and tar In this case, C again is to create a Tar archive. The small J is to process the archive through B ZIP 2. Okay, and let's see if that's created. and our second file is created as well. And now we're going to use the last compression method, which is Tar C, capital J F, myfile, tar XZ, files one through five. Then here we go. Get all three bundles, or Tarballs, created here, and you can use a command, which is LS LH, and then grab for Tar. It'll give you the exact size of the tar balls. So you can compare this to the original size of your file to see if it's less or not. It should be. Now, I want to look at the contents of one of my tar files. So I'll run tartvfmyfiles, targz, and it will show me that I have files one through five in my Tarbaux. These are the contents of mine. Now, the next step is going to be that we're going to run the compression again, which will be like Gzip Dmifiles tar GZ. The second one will be XZ Dmifiles Tar. On the last one, there were no files; it's just a file. So instead of doing files, we'll just do files. Okay, so we got the three archives created and now we have actually shipped our tarball, and now we want to extract it to get the original files back. So in order to do that, we have to run the Tar X VF. Okay, now we're going to untar the file. So the command for that is to start with Tar. Again. Xxvf: x is for extraction, v is for verbose, and F is for file. And I'm going to use one example out of the three. And there we go. All of our five files are extracted. Again, suppose you're at a new location this time. All of this was our discussion of how you archive a file and compress a file. All this is a very broad subject, and we can go into further detail about it. But as far as the exam point of view is concerned, I think this much information should be sufficient. And you can look at the manned pages just to look at some other options that are available in the TAR utilities.

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