1 00:00:00,000 --> 00:00:17,760 Hey guys and welcome back. So in this nugget right here, what we're going to be talking 2 00:00:17,760 --> 00:00:23,760 about is the startup configurations for our system. And what we are really going to be 3 00:00:23,760 --> 00:00:32,480 focusing on is something called Sys-V in NIT. Now here is the deal. When you start on your 4 00:00:32,480 --> 00:00:38,640 computer, certain services are going to have to be started. Maybe you want to have particular 5 00:00:38,640 --> 00:00:43,359 web servers running, maybe an NGINX server, maybe you want to have access to a graphical 6 00:00:43,359 --> 00:00:49,520 user interface to manage your system. All of these processes have to be controlled. And the 7 00:00:49,520 --> 00:00:56,640 original way to control such processes was using Sys-V in NIT. Now one of the main features that 8 00:00:56,640 --> 00:01:03,680 we have to understand with respect to Sys-V in NIT is the concept of run levels. So let's actually 9 00:01:03,680 --> 00:01:11,520 discuss the process in action then. So when a Sys-V in NIT system happens to boot up, the very 10 00:01:11,599 --> 00:01:19,759 first i.e. the number one process started by the kernel is something called NIT. This will always be 11 00:01:19,759 --> 00:01:27,439 the very first process started by Sys-V in NIT. Now this process itself in NIT, this is used to start 12 00:01:27,439 --> 00:01:34,079 all other processes. It's going to initialize all the other processes so to speak. Now what processes 13 00:01:34,079 --> 00:01:40,479 are going to be started is going to be determined by this run level concept we're talking about here. 14 00:01:40,480 --> 00:01:44,880 Or rather we're going to talk about should I say that we're just going to dig into. So what exactly 15 00:01:44,880 --> 00:01:52,079 do I mean when I talk about a run level? Well really a run level is just like a category. And 16 00:01:52,079 --> 00:01:58,400 this category is going to have particular services associated with it. So let's maybe just say you 17 00:01:58,400 --> 00:02:04,400 want to have a graphical user interface so that not everything is just managed via the CLI. You 18 00:02:04,400 --> 00:02:09,520 want to be able to click and you want to be able to drag and drop. Well the ability to have such a 19 00:02:09,520 --> 00:02:15,600 graphical user interface like I say will be defined within a particular run level and we'll get to 20 00:02:15,600 --> 00:02:21,280 see what those run levels are very very shortly. What is also important to note is that you yourself 21 00:02:21,280 --> 00:02:26,719 can actually define what services and features are available in each run level. So if you want to be 22 00:02:26,719 --> 00:02:33,040 able to control and do some type of modification that absolutely is possible for you as a system 23 00:02:33,120 --> 00:02:40,000 administrator. Now we do have three different sets of run levels that we have to be aware of. 24 00:02:40,000 --> 00:02:47,519 The very first one is called the Linux standard base. Okay now the second one is just called the 25 00:02:47,519 --> 00:02:55,120 red hat set and the third one is called the Debian set. Now quite honestly the standard set this is 26 00:02:55,120 --> 00:03:01,120 not really used quite so much but it's good for historical purposes. It lets you know why run levels 27 00:03:01,120 --> 00:03:05,840 were developed in the first place. It gives you a sense of what they began with when they were 28 00:03:05,840 --> 00:03:11,200 developing this concept. But the reality is we have two different modes of thought. If you happen to 29 00:03:11,200 --> 00:03:17,120 have a Debian based system it makes sense that we're going to be using a Debian set and if you have a 30 00:03:17,120 --> 00:03:24,719 red hat based system such as maybe say Rocky Linux or CentOS then you would follow the red hat set. 31 00:03:24,719 --> 00:03:31,040 Now these actual run levels are pretty similar across these different definitions but there are 32 00:03:31,120 --> 00:03:38,560 some slight variations. Let's actually talk about the run levels with respect to each different set. 33 00:03:38,560 --> 00:03:45,439 So the very first run level we want to talk about is run level zero. Now within the Linux 34 00:03:45,439 --> 00:03:53,599 standard base as well as the red hat set and the Debian set the definition of run level zero is 35 00:03:53,599 --> 00:04:00,159 exactly the same across all three. We have no variation at all. Ultimately whether we're using 36 00:04:00,240 --> 00:04:07,680 red hat or Debian or anything else if we use run level zero this is going to halt the system and 37 00:04:07,680 --> 00:04:14,319 when I say to halt the system that just means to shut down the system. So run level zero across 38 00:04:14,319 --> 00:04:20,959 all definitions going to do the same thing shut down the system. Now similarly with respect to 39 00:04:20,959 --> 00:04:28,319 the next run level which is run level one this is also the same across all definitions in the 40 00:04:28,879 --> 00:04:35,519 Linux standard base and the red hat set and the Debian set. No matter what we're using this is going 41 00:04:35,519 --> 00:04:42,959 to invoke what is called single user mode. So think about this we know that we can have the 42 00:04:42,959 --> 00:04:49,680 concept of multiple users on our system. Let's maybe say we had the user John and we had the user 43 00:04:49,680 --> 00:04:56,959 Simona and the user Trevor as well as the administrator called Roots. If we happen to specify 44 00:04:56,959 --> 00:05:04,560 that our system uses run level one we know this is going to be single user mode that means if 45 00:05:04,560 --> 00:05:10,719 John tried to log into the system he would not be able to. If Simona tried to log into the system 46 00:05:10,719 --> 00:05:16,319 she would not be able to and likewise Trevor would also be locked out. The only person the 47 00:05:16,319 --> 00:05:22,799 single user who can log into the system will be that Root administrator. So run level one no 48 00:05:22,800 --> 00:05:28,800 matter what your definition is going to lock down the system to only be accessed by the administrator. 49 00:05:28,800 --> 00:05:35,520 So this is really all about locking down the system and limiting access to only the person 50 00:05:35,520 --> 00:05:42,960 with the highest priorities available. Now the next run level we have is run level two. So we 51 00:05:42,960 --> 00:05:49,360 can see we're just incrementing these numbers zero one two and there is a little bit of a difference 52 00:05:49,360 --> 00:05:55,199 between the definitions right here. When we are talking about the Linux standard base what run 53 00:05:55,199 --> 00:06:01,280 level two gives us it gives us multi user mode so that would mean that John and Simona and Trevor 54 00:06:01,280 --> 00:06:07,840 could all log on to the system but there would be no networking okay. So this means if they want to 55 00:06:07,840 --> 00:06:13,439 log into their Gmail account there's going to be no network access they can just access the system 56 00:06:13,439 --> 00:06:18,800 without being able to connect to any other systems or computers. Also it's worth noting 57 00:06:18,800 --> 00:06:24,879 that run level two means that we do not get a graphical user interface so whilst we can grant 58 00:06:24,879 --> 00:06:31,040 multiple users access to the system all of those users must work directly from the command line. 59 00:06:31,040 --> 00:06:38,079 Now with respect to Red Hat based systems run level two very very similar it's going to be 60 00:06:38,159 --> 00:06:46,159 multi user modes but with no ability for network file sharing and similarly no ability for a 61 00:06:46,159 --> 00:06:51,439 graphical user interface so very very similar in that respect no network file sharing everything 62 00:06:51,439 --> 00:06:57,519 must be done via the CLI but multiple users can log on to the system so Trevor John and Simona 63 00:06:57,519 --> 00:07:02,479 are going to be able to access the system at run level two. Now the difference here and this one 64 00:07:02,480 --> 00:07:10,160 is quite a stark difference is that with the Debian sets at run level two we do get multi user 65 00:07:10,160 --> 00:07:17,920 modes however networking is not disabled we do have networking and we also have a graphical user 66 00:07:17,920 --> 00:07:26,960 interface and in fact for run levels two three four and five for Debian systems this definition 67 00:07:26,959 --> 00:07:33,599 is exactly the same so run level two run level three run level four and run level five for Debian 68 00:07:33,599 --> 00:07:40,479 based systems are all going to act in this manner multi user with network access with a graphical 69 00:07:40,479 --> 00:07:47,439 user interface so keep that in mind so now as we progress to run level three we already know what 70 00:07:47,439 --> 00:07:53,839 that is going to look like for Debian systems but what about with the Linux standard base well for 71 00:07:53,919 --> 00:07:59,519 Linux standard base as well as our red hat systems this is going to be the exact same definition 72 00:07:59,519 --> 00:08:05,279 we're going to get multi user modes and just like before we're not going to get a graphical user 73 00:08:05,279 --> 00:08:10,959 interface but we will have network access in fact let me just write that a little bit clearer 74 00:08:11,679 --> 00:08:18,719 so run level three LSB and red hat similar to the previous run level but this time we do have 75 00:08:18,720 --> 00:08:25,120 network access we can share files we can talk to different computers we can access the internet so 76 00:08:25,120 --> 00:08:32,879 on so forth now run level four with respect to run level four for the LSB this is actually not 77 00:08:32,879 --> 00:08:40,480 defined there is no run level four for the Linux standard base however run level four for red hat 78 00:08:40,480 --> 00:08:47,600 based systems is exactly the same as run level three so carbon copy right here and as we know 79 00:08:47,600 --> 00:08:53,279 with Debian based systems two three four and five are all exactly the same and this is the part which 80 00:08:53,279 --> 00:09:00,159 I find a little bit frustrating because ultimately I just feel this is unnecessarily confusing why 81 00:09:00,159 --> 00:09:05,840 have multiple run levels that do the exact same thing sometimes I feel they're just trying to make 82 00:09:05,840 --> 00:09:11,120 the exam a little bit more difficult to remember stuff but like I say I can't control this this 83 00:09:11,200 --> 00:09:18,960 just as the way it is so again we move on on we go to run level five in the case of the Linux 84 00:09:18,960 --> 00:09:25,440 standard base this is going to be a multi user mode so we can have multiple users and we're going to 85 00:09:25,440 --> 00:09:31,600 get networking and we're going to get that graphical user interface and with red hat based systems 86 00:09:31,600 --> 00:09:36,639 same type of deal we're going to get multi user modes we're going to get our networking access 87 00:09:36,639 --> 00:09:43,039 and finally we're going to get our graphical user interface for red hat based systems and for Debian 88 00:09:43,039 --> 00:09:49,439 as we know two three four and five all exactly the same and now we come to the last run level this 89 00:09:49,439 --> 00:09:56,159 is run level six and you will be pleased to know that this is exactly the same across all definitions 90 00:09:56,159 --> 00:10:03,600 whether it's Linux standard base red hat or Debian run level six will always reboot the system so run 91 00:10:03,600 --> 00:10:09,440 level zero that will shut down the system run level six that will reboot the system and one two 92 00:10:09,440 --> 00:10:15,519 three four and five depending on the definition will give you some combination of a cli or a 93 00:10:15,519 --> 00:10:22,080 graphical user interface it will toggle single users and multi users and give different definitions 94 00:10:22,080 --> 00:10:28,320 depending on the network access available now one thing to note is that you actually can define 95 00:10:28,320 --> 00:10:35,040 additional run levels at run level seven eight and nine but there are no standards for these run 96 00:10:35,040 --> 00:10:41,280 levels so there are no defaults defined now just a word on the applicability of these run levels 97 00:10:41,280 --> 00:10:47,600 of course run level zero will be used if we want to shut down a system similarly run level six to 98 00:10:47,600 --> 00:10:54,320 reboot a system also very very useful let's talk about run level one now now run level one is kind 99 00:10:54,320 --> 00:10:59,840 of like safe mode on your system so to speak this is being kind of designed to fix really bad 100 00:10:59,840 --> 00:11:05,520 problems if you are troubleshooting some type of serious issue on your machine you want to boot 101 00:11:05,520 --> 00:11:12,000 up with minimal processes with only access to the root user so that you can fix these critical 102 00:11:12,000 --> 00:11:18,240 issues say for example you may have a particular virus running on your system which is running on 103 00:11:18,240 --> 00:11:24,320 a particular process you want to boot the system up with limited processes with only one user to 104 00:11:24,320 --> 00:11:30,639 go in and try to fix that problem this is where you would want to be using run level one now run 105 00:11:30,639 --> 00:11:37,840 level two on red hat systems this is not really used very often that is simply because networking 106 00:11:37,840 --> 00:11:43,919 is so well vital to the day-to-day operations of a system administrator so just disabling 107 00:11:44,000 --> 00:11:50,479 the networking not quite so common whereas on a debian based system we know run level two actually 108 00:11:50,479 --> 00:11:56,639 does allow us to get networking access so it would be much more common on that type of distribution 109 00:11:57,279 --> 00:12:04,240 now run level three at least in the red hat definition whereby we do not get a graphical 110 00:12:04,240 --> 00:12:10,319 user interface this is very common to run on servers now the reason why is because it's more 111 00:12:10,320 --> 00:12:16,480 lightweight so we don't need to have as much intensive processing power and also it reduces 112 00:12:16,480 --> 00:12:23,360 the attack surface simply put the more processes and more applications running on your system the 113 00:12:23,360 --> 00:12:30,400 more potential for an attacker to find a vulnerability in a particular application or a particular process 114 00:12:30,400 --> 00:12:36,800 and gain access to the system so to limit things servers are often run without the graphical user 115 00:12:36,799 --> 00:12:44,000 interface and for red hat based systems we know we can do this on run level three whereas run 116 00:12:44,000 --> 00:12:50,719 level five this does provide the graphical user interface this is a common run level for client 117 00:12:50,719 --> 00:12:56,959 desktop computers whereby the average user wants to have the ability to drag and drop and to access 118 00:12:56,959 --> 00:13:02,399 the system in a nice friendly manner with this graphical user interface run level five would be 119 00:13:02,399 --> 00:13:09,039 the run level for that scenario so that is us for our introduction into sysvianet and the run 120 00:13:09,039 --> 00:13:15,039 levels what I now want to talk to you about is some configuration files with respect to our run 121 00:13:15,039 --> 00:13:19,439 levels and well that's what we're talking about in the very next nuggets I hope this has been 122 00:13:19,439 --> 00:13:22,639 informative for you and I'd like to thank you for viewing