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LPI Linux LPIC-1 101 and CompTIA Linux+

Change Runlevels and Reboot or Shutdown the System

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LPIC1 & CompTIA Linux+ Intro

Hardware Settings

Boot the System

Change Runlevels and Reboot or Shutdown the System

00:00:00 - Okay, welcome to Section 101.3 about runlevels
00:00:05 - and rebooting. What we're going to talk about in this nugget, we're going to talk
00:00:08 - about when the computer boots up, there are several different
00:00:11 - runlevels. So we're going to go through the runlevels,
00:00:15 - inittab which is, determines what runlevel a computer runs
00:00:19 - at, and then startup processes which take place in the
00:00:22 - init.d folder, how to switch between runlevels, and then
00:00:27 - rebooting and shutting down some of the ways that we have to,
00:00:31 - that we have to do that, also some messages that we can send
00:00:34 - to people. And then I want to briefly touch on upstart which
00:00:38 - is basically replacing a whole bunch of the stuff that we need
00:00:41 - to learn for the LPIC certification. So let's get started.
00:00:46 - We're going to start talking about what runlevels actually
00:00:49 - are. Alright, so a good way to think about runlevels is to think
00:00:54 - about them as like modes that the Linux computer runs in. Now,
00:00:57 - some of these are extremely standardized. For example, the
00:01:01 - runlevel 0, again these are computers so zero is a number,
00:01:05 - runlevel 0 is the halt level, meaning the, the stop or,
00:01:10 - or, you know, just halt the system. And this is one of
00:01:13 - the ones that is standard across all Linux distributions.
00:01:17 - The next runlevel is runlevel 1. Now, this is called single
00:01:21 - user mode. Some of the, sometimes distributions like currently
00:01:24 - Ubuntu, for example, calls this recovery mode, and the reason
00:01:28 - it's called recovery mode is because
00:01:31 - this is where you don't usually need any password to log in
00:01:35 - as the root user. So if your system is completely messed up
00:01:39 - and you have physical access to the machine, you can get into runlevel 1.
00:01:42 - Again, we're going to see how to do that in a little
00:01:45 - bit. This is another one of those runlevels, runlevel 1,
00:01:48 - single user mode or recovery mode is standard across all
00:01:51 - distributions. So it's important to know that. Then we get into
00:01:54 - some that aren't standard. Now, 1 or 0 through 6 are the
00:01:58 - runlevels that are available to Linux systems. But different
00:02:01 - distributions use some of them differently. For example, runlevel 2
00:02:04 - in a Debian-based distribution like Ubuntu,
00:02:09 - this is the default runlevel. This is the runlevel that everything
00:02:12 - runs in whether you're running X Windows or just running in
00:02:15 - the terminal mode, everything runs in runlevel 2. So this is
00:02:18 - like a Debian-based operating system's normal mode or default
00:02:23 - mode. So that's, again, if you're using a Debian or Ubuntu system.
00:02:27 - Now, runlevel 3, if you have a Red Hat system or a SUSE Linux
00:02:31 - system, this is a runlevel that they use for text mode. So
00:02:37 - if you want the computer to fully boot up and be usable but
00:02:39 - you don't want to load a graphical user environment or X Windows,
00:02:43 - that's where runlevel 3 comes. So like a lot of
00:02:47 - servers, Red Hat servers or SUSE servers, are running at runlevel 3
00:02:51 - because they don't use a graphical user environment.
00:02:54 - Runlevel 4, again, this is available and you can customize
00:02:57 - this if you want, any of them, apart from 0, 1 and we're going
00:03:00 - to talk about 6 later on. But 1 through 5 are customizable.
00:03:04 - This is just the default, but 4, 4 is kind of special because you
00:03:08 - can make your own runlevel. If, if there's something you specifically
00:03:11 - want, say, you want certain programs to load, you want certain
00:03:15 - services to load in a certain configuration, you can customize
00:03:19 - runlevel 4 and you can call it whatever you want, wild card.
00:03:22 - It's, it's not one that's used by default in any major distributions.
00:03:27 - Then we have runlevel 5 which, again, this is just a
00:03:30 - Red Hat SUSE thing. This is their GUI mode. So if you have Red Hat
00:03:34 - or SUSE, generally your, your computer usually runs
00:03:37 - in either runlevel 3 or runlevel 5. Runlevel 5 is
00:03:41 - the one that loads X Windows. Generally, runlevel 5
00:03:44 - will have a graphical login screen. We're going to you see that in a
00:03:47 - minute. So that's the, that's how they default to a GUI mode
00:03:52 - using runlevel 5. And then last but not least, this
00:03:55 - is another special one, runlevel 6, which is the reboot
00:03:59 - runlevel, which if you reboot your system, it goes into
00:04:02 - runlevel 6, and that's what happens, it reboots. So again,
00:04:06 - these are the runlevels defined. This is where they're normally
00:04:09 - used. And again now, if it's a little confusing, Debian and
00:04:13 - Ubuntu only using runlevel 2, what they do is they
00:04:17 - allow you the option in runlevel 2 to start the graphical
00:04:20 - user interface or not. They just didn't make it a whole new
00:04:23 - runlevel. So it's, it's key to know that Red Hat and SUSE
00:04:28 - use runlevel 3 or 5, Debian and Ubuntu, those
00:04:31 - types of distributions generally just use number 2, but
00:04:35 - 0, 1, and 6 are all pre-defined. These are Linux standard
00:04:39 - runlevels for halt single user mode and the reboot mode, alright.
00:04:44 - So let's move on and, and look at some of the, how this
00:04:48 - works in an actual running system.
00:04:52 - Okay, you can see that I've booted up my system here. Now, this is running
00:04:55 - CentOS which is basically Red Hat, CentOs version 5.4.
00:04:59 - And since it booted up and gave me this text-based login
00:05:03 - screen, you can safely assume that it's probably set at runlevel 3.
00:05:08 - Let's check that out right now.
00:05:11 - The login is root and where the default runlevel information is stored
00:05:16 - is in the etc directory and the file, vi is the editor that
00:05:20 - I am going to choose to use here, but it's in a file called
00:05:23 - inittab.
00:05:25 - So let's look inside here. Now, oh, you know what, this is actually
00:05:28 - just what I described to you in the last, in a couple slides
00:05:31 - ago. Maybe I should have just brought you in here instead of written
00:05:34 - all that out. But anyway, that describes the runlevels in a
00:05:38 - Red Hat system. So
00:05:41 - you'll notice here it says, multiuser mode, without NFS.
00:05:45 - So Red Hat uses runlevel 2 as a multiuser system
00:05:52 - but without loading NFS, and that's the way that they've
00:05:55 - chosen to use runlevel 2. What this shows right here,
00:05:59 - the initdefault, it shows the init runlevel is at 3
00:06:04 - which is what we guessed. So we can pat ourselves in the back because
00:06:07 - we guessed correctly. This text-based login means that we're at
00:06:10 - runlevel 3. Now, this file shows a bunch of other things
00:06:14 - as well. For example, it talks about what to do when it
00:06:17 - boots up into certain runlevels to go to that
00:06:22 - rc.d directory and run the, the
00:06:24 - boot up files. We're going to talk about that in a minute. It says,
00:06:27 - here it, it says what to do if you do ctrlaltdel.
00:06:31 - Now, what it actually does on the system if you type ctrlaltdel,
00:06:33 - it runs the sbin/shutdown command
00:06:38 - with these flags. Now, pay attention to this because we're going
00:06:41 - to look at how to shut down and reboot systems in just a little
00:06:44 - bit. But anyway, that's something to look at. And then down here,
00:06:48 - the same kind of thing. This is actually neat. If there's a UPS
00:06:51 - that sends a signal to the, to the computer that it's lost power,
00:06:55 - of course a UPS will keep it running, but this is going to
00:06:58 - do something that's going to say, power failure, system shutting
00:07:00 - down and it's going to do that in two minutes. So it's going to
00:07:04 - give a two-minute warning to the people logged in. Again, that warning
00:07:08 - is something you really need to know how to give for
00:07:11 - the LPIC certification. Now, this is neat too. You can shut,
00:07:14 - you, you can cancel a shutdown process. Say, the power kicks
00:07:17 - back on, then if you do the shutdown -c with this, it will
00:07:20 - actually stop that shutdown process. So like if you're a Star Trek
00:07:24 - fan and the auto-destruct sequence has started, you can stop the auto-shutdown
00:07:28 - sequence after it's already begun even if you're not Captain
00:07:32 - Picard. Anyway, this starts up the login screens like we, we logged in,
00:07:37 - you know, you saw that login prompt and password prompt at first. Those are programs
00:07:41 - that have to run. And then we mentioned runlevel 5 is a
00:07:45 - GUI environment. So this runs xdm which is the X display
00:07:50 - manager only during runlevel 5. So it's saying if it's
00:07:54 - runlevel 5, then you want to run this preferred desktop manager.
00:07:58 - Now, again, if you're, if you're an X Windows geek here, xdm
00:08:02 - is very rarely used the program itself, but an X display
00:08:06 - manager, either GDM or KDM for Gnome or KDE is generally what
00:08:11 - it's gonna start, and this preferred desktop manager program is
00:08:14 - going to read your configuration files and determine what graphical
00:08:18 - user login to start. But that's a little bit beyond the scope
00:08:22 - of this. Basically, the inittab shows the init process how
00:08:27 - to start. And remember the init process, that's the very first process
00:08:30 - that boots or that, that runs on a system and spawns everything
00:08:33 - else. So this is kind of like the configuration file for init.
00:08:36 - And now what we're going to do is look at what, how init
00:08:41 - starts these things like, here, let me scroll back up here. See all
00:08:44 - these etc/rc.d folders? These are folders that
00:08:49 - are talking, that are referencing startup scripts, and we're
00:08:53 - going to look at that next. But let's look over what we just
00:08:55 - talked about in inittab so you kind of get exactly what it
00:08:59 - is. It is just a configuration file.
00:09:03 - Okay, so init, it tell, or inittab, this file, tells init what to
00:09:07 - do. It sets the default runlevel and it's required knowledge for
00:09:12 - LPIC. And I wanted to bring this slide up just to focus on the
00:09:14 - inittab a little bit more. It's required that you understand
00:09:17 - and can configure inittab file, but the whole idea of
00:09:21 - that is being phased out or phased out with the upstart program
00:09:26 - and that could, way to configure stuff. Right now the upstart program
00:09:28 - which is in Ubuntu, it does, it's backwards compatible. So if
00:09:33 - you put things in a file called etc/inittab,
00:09:36 - it will honor them. But even that eventually will most likely
00:09:39 - go away. You still need to understand this because right now in Red Hat,
00:09:42 - in the Red Hat Enterprise Linux and, and those types
00:09:46 - of things, it, it's still, that's the way you configure
00:09:49 - things. But if you have, for example, on your computer Ubuntu
00:09:52 - installed then you say, oh, I'm going to check out my inittab file, it actually
00:09:56 - won't be there. There's no inittab file at all, but you still need to
00:09:59 - understand and, and know how to use it, alright. So what does inittab
00:10:03 - do? It, it tells init what to do next, alright. It's the configuration file.
00:10:06 - So let's look at some of those ways that you can configure
00:10:09 - startup scripts, alright.
00:10:14 - Okay, inside the et cetera directory again or etc, this is where most
00:10:18 - of our configuration things are, there's a folder called
00:10:21 - init.d.
00:10:23 - And inside here you're going to see all of these different files.
00:10:27 - Now, these are scripts like command line scripts that were put
00:10:31 - here by different applications. Now, you can add some yourself,
00:10:33 - but these are mainly just scripts. Well, I'll look at one really
00:10:36 - quick.
00:10:38 - For example, if we look at the NFS script, okay, it's this
00:10:43 - long script that does a whole bunch of stuff, okay.
00:10:46 - This is the, it starts up the NFS, the network file sharing
00:10:50 - server. So all of these are programs like that that start
00:10:53 - things or also stop things. For example, if you want to
00:10:56 - stop something, you use these programs too. It's just kind of like the,
00:10:59 - the switch to turn things on and off. For example, let's shut
00:11:03 - something off. Let's do, let's, something that's not going to hurt us
00:11:06 - here. I hate for it to just shut off something that's going to hurt. So we're going to
00:11:10 - do sendmail, okay, sendmail.
00:11:14 - We're going to send it the stop command. Now, I did the dot
00:11:17 - and then forward slash to say that it's in this directory. We're going to talk
00:11:20 - about path and stuff later, but just know that if
00:11:23 - in a file like this you're going to have to do./sendmail
00:11:25 - to say the files right in here. Let me say stop and then it's
00:11:29 - going to stop the sendmail process. That told us what it was doing.
00:11:33 - If we want to start it,
00:11:35 - sendmail start.
00:11:37 - And most of them have commands like this.
00:11:41 - If we just say that, I will give us our different options. So we could
00:11:44 - restart. We can do a conditional restart. Just get the status so sendmail status.
00:11:49 - Oh, good. It's running. It tells us it's running. So this is where
00:11:52 - all the commands for different server processes live, okay. This is how you start up
00:11:56 - and stop things. But you'll notice that these aren't, these aren't
00:12:00 - separated by runlevels, okay. Now, the different runlevels,
00:12:03 - let's look back here and what I'm going to do is ls -l, and I'm just
00:12:09 - going to look for rc., grep for rc., just so that
00:12:14 - that's all we see. Alright, so what we have here, you'll see that
00:12:19 - there's these files. There's rc, there's rc0, rc1, rc2
00:12:23 - and these probably are going to look a little bit familiar, right?
00:12:26 - Now, the rc, the number, and then the.d means
00:12:30 - the different commands at that runlevel. Now, there's also
00:12:34 - rc.local which runs at every runlevel and
00:12:38 - like rc.sysinit. And these, these are things that run
00:12:41 - no matter what. But we're talking about the different runlevels
00:12:44 - have different options and different, different things that start up.
00:12:46 - So let's look into, let's see, we're running in runlevel 3,
00:12:49 - right? So let's go into the rc3.d folder.
00:12:54 - And now, if you're expecting to see a bunch of different scripts,
00:12:56 - well, they look a little bit funny. First of all, they're blue.
00:12:59 - Well, why are they blue? Well, let's look at it, ls -l.
00:13:02 - We'll see that these are symbolic links and it points
00:13:06 - to.., previous directory, init.d, that folder we
00:13:10 - we're in last time, and then one of those files. See how it shows
00:13:13 - one of those files that we're looking at before? And you'll
00:13:17 - notice that they're not named exactly the same either. They
00:13:20 - start with either a k or an s, a capital K or a capital S, and then
00:13:24 - a number and then the name of that, that startup and shutdown
00:13:29 - script. So why, what's with the K's and the S's? Well, it's not
00:13:32 - too difficult to understand it. The K means you kill the process
00:13:36 - or shut it down and the S means you start it up.
00:13:40 - You may be thinking, okay, if I boot into runlevel 3, why would
00:13:43 - I be killing off processes like, like NFS, right? NFS
00:13:47 - isn't, isn't going to be running. Why would I, why would I need to shut that off?
00:13:50 - Well, the reason is we can switch between runlevels while
00:13:55 - the computer is running. So you may want to kill a bunch of processes
00:13:59 - and start up a bunch of different ones. So every runlevel
00:14:02 - has these things that it stops and these things that it starts
00:14:05 - and they're going to be a little bit different in every
00:14:08 - runlevel. So let's look, cd../rc4.d.
00:14:15 - Okay, there's a bunch of stuff in here, but it's a slightly
00:14:19 - different list, alright. You'll see, for example, there's no, oh, I'm trying
00:14:24 - to look at one that's not here. Okay, up in the top you saw there's
00:14:27 - that first boot, S99, first boot, and there's not that one
00:14:33 - in this rc4.d, right? So first boot is a process
00:14:37 - that they don't start. Well, that's interesting. A lot of
00:14:42 - these processes are going to be similar across different runlevels
00:14:45 - because you're going to want all of them to be working like networking,
00:14:49 - you want networking to work in pretty much every runlevel
00:14:52 - except like that runlevel 1, that single user mode, that's
00:14:55 - not going have, let's look, here. Let's go back there and look.
00:14:58 - runlevel. So let's look, cd../rc4.d.
00:15:02 - Let's look. See here, almost every single process is killed. See, because
00:15:07 - it has that K under it. So the only thing that started is
00:15:11 - the vm2 monitor which is
00:15:14 - a virtual machine or,
00:15:16 - let's look and see what that is,
00:15:19 - vi S02 l.
00:15:22 - Alright, so this one is,
00:15:26 - oh, the event manager. Yes, so the kernel event manager runs.
00:15:29 - That makes sense. Even in single user mode, we're going to want
00:15:32 - that, but everything else is mostly stopped, okay, because we're
00:15:37 - in just recovery mode. If something is going wrong, we don't
00:15:40 - want all those different processes to be running. So that's
00:15:43 - how these different things work. Now, you can manually create
00:15:46 - things, for example, oh, if we're going to totally mess up our
00:15:49 - system, we're going to do a symbolic link to
00:15:54 - ../init.d/nfs and we're going to link it
00:16:00 - to start, okay, and we're going to do it in what order?
00:16:06 - 88 just because, nfs, okay. So now, what does that done? Let's do an ls.
00:16:11 - And now we see, right over there you'll see S88nfs
00:16:16 - at the, almost to the very end. So it is going to
00:16:19 - start nfs in single user mode. Now, the network isn't running
00:16:22 - so it's going to hang and it's not going to work. It's not something
00:16:25 - I would suggest doing, but that's how you would do it, alright.
00:16:28 - And you'll notice the, the things are all in numerical order. Well, that's
00:16:31 - because that's the order it does things in. You know, some things
00:16:34 - like nfs, for example, you want nfs to start after networking
00:16:38 - starts. So you would put the number of nfs higher than the number
00:16:42 - for networking. So networking starts before. Does it make sense?
00:16:45 - The same thing going backwards. If you're going to kill a process,
00:16:49 - that depends on networking, you want to stop the process before
00:16:52 - you stop networking because, obviously, if you stop networking
00:16:56 - first, it's going to complain. For example, if you look up,
00:17:00 - here I'll show you, if you look right up here, kill 90 network,
00:17:05 - see, that happened towards the end of the killing process as
00:17:09 - you see. It stopped all these things that depend on networking. All
00:17:12 - of these processes, most of them depending on networking,
00:17:15 - stopped before networking because if you just kill networking,
00:17:18 - well, all these are going to hang and bad things are going to happen.
00:17:21 - So you have to know that there's two things. There's the K or the S
00:17:24 - for kill or start, and then there's a numerical order it processes
00:17:28 - all of these different scripts. Now, I don't want to have my
00:17:32 - system completely messed up. So I am going to
00:17:36 - erase that nfs thing that I just entered there. Yes, I want to remove that symbolic link.
00:17:39 - But again, these aren't actual files. These are just links back
00:17:43 - to that init.d folder where all those scripts are. And
00:17:46 - if it's a K in the beginning, it stops it. And if it's an S at the
00:17:49 - beginning, it starts it. So now you are a pro on the
00:17:54 - rc number.d folders, alright. So let's look at what we've
00:17:59 - learned so far, and we'll move on to rebooting the system and notifying
00:18:03 - users because that will be terribly, terribly important if
00:18:07 - you are going to do some maintenance on your server.
00:18:10 - Okay, so init.d, these are the startup,
00:18:15 - startup and shutdown.
00:18:22 - These are the scripts that run, okay, and that's where they're stored.
00:18:24 - Now, usually, packages will put things in your, you don't have to write
00:18:27 - these scripts or even place them. But these are where they're
00:18:30 - located. And then down here, etc/rc and then
00:18:34 - this is the number. I just put that X there to,
00:18:38 - to show whatever runlevel folder you're talking about.
00:18:40 - So rc, the number for other runlevel that you're currently
00:18:43 - at or switching to,.d, and inside are symbolic links,
00:18:48 - but you got to spell symbolic right,
00:18:52 - symbol,
00:18:57 - We'll pretend that I spelled that right right at the beginning. I didn't
00:19:00 - have to pause the thing and spell it out. Put symbolic links back
00:19:05 - to these. So again, these are symbolic links to this folder,
00:19:11 - the scripts that live inside that folder. The K at the beginning
00:19:16 - is whether it's killed or started or kill or start,
00:19:22 - the number, usually a two-digit number,
00:19:29 - and then the actual name
00:19:34 - of the script. So we have K01 name of the script, S01
00:19:40 - name the script and it's either kill or start the process depending
00:19:45 - on what you want it to do. And now what we're going to do is
00:19:50 - talk about switching in between. Now, again, when you switch
00:19:53 - between runlevels, that's where the kill and the start things
00:19:57 - really matter, okay, because again when you just boot a system
00:20:00 - into the default runlevel, there's not going to be any programs
00:20:03 - that are there for it to kill off, right, because it's just starting.
00:20:07 - But when you switch between runlevels, it's going to kill
00:20:10 - off the processes that shouldn't be running in the runlevel
00:20:12 - you're switching to. So that's where the, the K and S really
00:20:16 - matter or really make the most sense is when you're switching
00:20:18 - between runlevels and not just starting up, okay. And I still
00:20:21 - spelled symbolic wrong. Can you believe that? Symbolic links. Boy, I'm having a rough time
00:20:26 - today. Anyway, symbolic links are the named these, pointing back
00:20:32 - to the scripts that reside inside init.d, alright. So let's
00:20:36 - look at how to start up and shut down the computer properly
00:20:40 - with notifying people because that's one of the keys in the
00:20:43 - LPIC certification. You need to know not only how to restart
00:20:47 - and shut down, but you need to know how to notify users, how you're,
00:20:50 - how you're going to do that, alright.
00:20:53 - Okay, we're back here at the command line. What I want to do
00:20:55 - is look at the manual page for the shutdown command, alright.
00:20:59 - Inside here you're going to see that shutdown actually does
00:21:02 - quite a few things, alright. One of the nice things it will
00:21:05 - let you do is it will let you just warn about it and not
00:21:09 - actually do it. For example, this
00:21:11 - -k, it's not really shut down. It just sends a warning
00:21:15 - user to everybody. So if you're planning on shutting down in the
00:21:17 - future but you don't know what time, you just want to send a warning
00:21:20 - out to people, you can do that. You can have it reboot instead
00:21:22 - of just shutting down which is great if you're not near the
00:21:25 - server because if it's just shutdown, you have to go press the power button. That
00:21:28 - can be a real pain in the butt. If you can do some other
00:21:33 - things like, here, let's scroll down a little bit more. There's some other
00:21:37 - things here. You can cancel an already running shutdown. We learned
00:21:40 - about that in the inittab file. Remember, if the power comes back
00:21:43 - on, we can tell it, okay, I don't really want to shut down. Never mind.
00:21:47 - But the one thing is the time. You have to tell it when to shut
00:21:50 - down and that accepts a couple different types of inputs.
00:21:55 - It can be a specific time like 12:05 we're going
00:22:00 - to do it or it can be like how many minutes from now or you
00:22:04 - can actually use the word now if you want which stands for
00:22:07 - +0 minutes, meaning in zero minutes or right now
00:22:10 - I want you to shut down. So let's look at a, at a few examples of
00:22:13 - what that looks like in action, okay. Let's clear this. We're going to do
00:22:17 - shutdown -k. We're going to do it, let's say, now, alright.
00:22:23 - Again, k doesn't really shut down, but we're going to send
00:22:27 - this message,
00:22:29 - oh, my goodness, there's a monster, okay.
00:22:35 - So everybody got this message that says, oh, my goodness,
00:22:38 - there's a monster. The system is going to shut down to maintenance
00:22:41 - mode now. But of course, since we said -k, it was canceled, right?
00:22:45 - So alright, let's do it, instead of now, let's send a different message.
00:22:48 - Let's say, shut down, we're not going do -k. We're going
00:22:54 - to do, well, let's say, +3 minutes, alright. So it's going
00:23:00 - to shut down in three minutes, and we're going to send the message,
00:23:03 - I have to install Halo. I just got the CD, alright.
00:23:12 - So everybody that's logged in on the terminal, this will pop up.
00:23:16 - So this broadcast message isn't just for me, right? It's not
00:23:19 - just for me. It's everybody got that message.
00:23:23 - Shutdown was canceled, alright. So what if we wanted to let
00:23:28 - that run in the background so in that three minutes I could do a couple
00:23:31 - really, really cool things? You know, for example, let's just
00:23:34 - hold on to my command prompt, I had to hit Control-C and then it canceled
00:23:39 - the shutdown. So let's say we want to do that. We'll add the
00:23:42 - ampersand because the ampersand will put it in the background, alright.
00:23:45 - Let's look at that message. It will still be running, but I'll have
00:23:48 - my command prompt back, alright. So see there? Now, I have my command
00:23:52 - prompt, but it just said, in three minutes it's going to shut down and you
00:23:56 - better believe in three minutes this computer is going to shut down. But
00:23:59 - then I discover, oh, you know what,
00:24:02 - I don't want to shut down to install Halo.
00:24:04 - shutdown -c for cancel and then we'll tell people why
00:24:08 - we're canceling too. We're going to say, it turns out Halo doesn't
00:24:13 - run under Linux.
00:24:19 - Shutdown canceled. So everybody got this broadcast message
00:24:22 - that it turns out Halo doesn't run under Linux. Shutdown canceled, alright.
00:24:26 - And then the shell told us that that shutdown +3, it's
00:24:31 - done, it finished, alright. So that's how you can warn everybody
00:24:34 - of an imminent shutdown and that's how you can actually shut down
00:24:38 - the system. Now, we have one more thing that we need to learn
00:24:41 - before we move on to the next nugget, and that is about
00:24:46 - init and telinit. Now, we're talking about switching between runlevels.
00:24:49 - Well, right now we're in runlevel 3 because that's the
00:24:52 - default that we've booted into. But if we want to change, we can do one
00:24:56 - of two things. We can tell the init command. Now, remember, init
00:25:00 - is the process that runs every other command, right. So we can
00:25:03 - tell init to go into runlevel, let's say runlevel 1.
00:25:09 - Well, we can tell it to do that. That's not really the proper
00:25:12 - way to do it. The best way to do it is use a command called
00:25:16 - telinit
00:25:18 - and then the runlevel you want it to switch to. So we do that
00:25:21 - and it's going to switch to runlevel 1. You see how it's stopping
00:25:24 - all those processes. Now, if you remember, a few minutes ago, you
00:25:28 - can guess all of those processes that it's stopping were the
00:25:31 - ones that had the K in front of it. And then it starts up,
00:25:36 - let's see, okay, and then it started up like one, yeah, going into single user
00:25:40 - mode. It didn't do much because, remember, a single user mode
00:25:43 - had barely anything running. And thankfully, I erased that NFS
00:25:47 - command that put in there because otherwise it would be hanging
00:25:49 - saying, I don't have any network connection. So right now we are
00:25:52 - in user or single user mode in runlevel 1, and let's say we
00:25:57 - want to switch back to runlevel 3. Again, remember I said init
00:26:01 - or telinit is you can do that, and we're going to see in Linux that init works
00:26:06 - the same way as if I were to type telinit, alright. Now, it's
00:26:10 - taking a little bit longer because it has to do more stuff to
00:26:13 - switch into mode or level 3 because there's all these
00:26:17 - things to start up. Now, it's going to start all those things up.
00:26:21 - And then I want to show you the difference. See, now one of the
00:26:23 - things it started up was that login command. Remember, runlevel 1
00:26:26 - doesn't have a login. It just logs you right in as the root user.
00:26:30 - So if you forget your root password, you want to go into single user
00:26:33 - mode so you can fix that. But we have to log back in, alright.
00:26:38 - And now what I want to show you, ls -l /sbin,
00:26:43 - this is the directory that init is stored in. I want
00:26:47 - to grep init. So it just shows us the things with the word
00:26:50 - init in it. Now, if you see the one on the bottom there, the telinit
00:26:53 - command is just a symbolic link pointing to the init command.
00:26:57 - So really in this Linux system it doesn't matter if you use
00:27:01 - telinit in the runlevel or init in the runlevel.
00:27:04 - But the, the proper or the, the more correct way to do it, the preferred
00:27:10 - way to do it is to use telinit because there are some systems
00:27:13 - like Unix that won't work if you telinit directly
00:27:18 - to switch runlevels. It just doesn't accept user commands
00:27:21 - from even root. So telinit will be a different program
00:27:25 - on those systems that tell init what to do. So while, while
00:27:29 - running init and then the runlevel will work in a Linux system
00:27:32 - perfectly fine because it's just a symbolic link. Telinit
00:27:35 - is just a symbolic link to the init command. The proper way to do
00:27:39 - it is to use the telinit command so that no matter what
00:27:42 - kind of a Unix or Linux system you're on, you can, you know,
00:27:45 - you can be assured that it's going to work. So that's the difference
00:27:48 - between telinit and init, and right now you know more than
00:27:51 - probably 50% of the Linux admins out there. Nobody really, most
00:27:55 - people don't know why you use telinit or init. They just know that
00:27:57 - it's proper to use telinit. And now you know more than a lot of people.
00:28:01 - So anyway, that is basically all we have to learn about in
00:28:05 - this section. So let's look back over, make sure we cover anything,
00:28:08 - and then we can move on to the next section or the next nugget
00:28:12 - that we're going to go over.
00:28:14 - Alright, it looks like we did a good job here. We covered runlevels
00:28:19 - very thoroughly. We went over inittab and some of the things
00:28:22 - that you can edit in there, basically that it's the configuration
00:28:25 - file for the init process to say what to do when it boots
00:28:28 - up. We went over the init.d folder which contains all the
00:28:32 - scripts to start and stop the different services that are running
00:28:35 - on your Linux box. We learned not only how to use init and telinit
00:28:39 - but actually what the difference is between them and just
00:28:42 - know that telinit is the one that you want to use because that's
00:28:44 - the more proper way to do things. We learned how to reboot
00:28:48 - and shut down, and specifically with shutdown we learned how to
00:28:52 - send some broadcast messages. Now, one of the things that you may
00:28:56 - be wondering is what if people are logged in to the graphical
00:28:59 - user environment? Well, generally, there's only one user and
00:29:02 - a computer if they're logged in to the graphically user environment.
00:29:05 - So you don't have to worry too much because it's generally
00:29:08 - you, and if you're going to reboot your computer, you know it.
00:29:10 - But a lot of times on a server many people will be logged
00:29:14 - in in the console, you know, over the,
00:29:16 - over the text-based thing. So you want to be able to send that message
00:29:19 - to all the users saying, hey, save your stuff or, you know, just know
00:29:22 - it's going to reboot. So that's why it's important for us to know how to send those
00:29:25 - command line messages. And then we briefly talked about and
00:29:29 - briefly because really that's, it's not something you're going
00:29:31 - to be tested on at all but upstart is a new configuration system
00:29:35 - that's kind of going to replace inittab and that whole init
00:29:39 - process that it is now. But what we learned today about inittab
00:29:42 - is what you need to know for the test. Just don't be confused if
00:29:45 - some of those files are missing in the systems that you administer
00:29:49 - on a day-to-day basis, alright. So I hope that this has been informative
00:29:52 - for you, and I would like to thank you for viewing.

Design Hard Disk Layout

Install a Boot Manager

Manage Shared Libraries

Debian Package Management

RPM & YUM Package Management

Work on the Command Line

Process Text Streams Using Filters

Perform Basic File Management

Use Streams, Pipes, and Redirects

Create, Monitor, and Kill Processes

Process Priorities

Search Text Files with Regular Expressions

Perform Basic File Editing Operations Using vi

Create Partitions and Filesystems

Maintain the Integrity of Filesystems

Control Mounting and Unmounting of Filesystems

Manage Disk Quotas

Manage File Permissions and Ownership

Create and Change Hard and Symbolic Links

Find System Files and Place Files in the Correct Location

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Shawn Powers

Shawn Powers

CBT Nuggets Trainer

Certifications:
LPIC-1; CompTIA Linux+, A+; Cisco CCNA

Area Of Expertise:
Linux

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