1 00:00:00,000 --> 00:00:14,560 Hey guys and welcome back. 2 00:00:14,560 --> 00:00:18,440 So what I want to talk to you about in this nugget right here is a little bit of a change 3 00:00:18,440 --> 00:00:19,440 of pace. 4 00:00:19,440 --> 00:00:22,480 We're going to talk about the swap on command. 5 00:00:22,480 --> 00:00:28,240 Now when we're talking about swap space, what we mean is that when our RAM is being 6 00:00:28,239 --> 00:00:34,719 taxed a little bit too hard, i.e. we run out of RAM as opposed to just crashing the system, 7 00:00:34,719 --> 00:00:39,519 what the system is going to seek to do is going to seek to use this swap space. 8 00:00:39,519 --> 00:00:43,519 This is going to act as virtual memory, so to speak. 9 00:00:43,519 --> 00:00:48,599 And the way this is going to happen is it's actually going to use the hard disk. 10 00:00:48,599 --> 00:00:52,200 So really, this is not something we want to happen. 11 00:00:52,200 --> 00:00:54,679 This is more of a safety net. 12 00:00:54,679 --> 00:00:59,560 And because we are using the hard disk as opposed to the actual RAM, this is going to 13 00:00:59,560 --> 00:01:01,679 be very slow in comparison. 14 00:01:01,679 --> 00:01:07,599 So the performance will take a big hit, but it is a cheap and very useful solution. 15 00:01:07,599 --> 00:01:11,480 So before we get going, I shall just issue the free command. 16 00:01:11,480 --> 00:01:16,640 We can actually see here that we have our actual memory, which is our RAM. 17 00:01:16,640 --> 00:01:19,760 And below we actually have our swap space. 18 00:01:19,760 --> 00:01:26,520 This is how much of the disk we have allocated that can be used for this purpose of swapping. 19 00:01:26,520 --> 00:01:32,840 Now one thing to note here is with this concept of swapping, we can have a swap partition, 20 00:01:32,840 --> 00:01:38,400 which is a dedicated portion on the disk, which is used for this swapping action. 21 00:01:38,400 --> 00:01:43,920 But we can actually just create a swap file, so both solutions do work. 22 00:01:43,920 --> 00:01:49,719 So like I say, if I issue the swap on command, we can actually see we actually do have a 23 00:01:49,719 --> 00:01:50,719 swap file. 24 00:01:50,719 --> 00:01:51,719 It is a file. 25 00:01:51,719 --> 00:01:53,219 It's not a partition. 26 00:01:53,219 --> 00:01:58,560 We can see the size of the swap and we can see none of it happens to be used. 27 00:01:58,560 --> 00:02:03,719 This is a good sign for us because we don't want our swap file to be used because what 28 00:02:03,719 --> 00:02:09,199 it means, well, it means that our memory is running out and it's not a good thing. 29 00:02:09,199 --> 00:02:16,679 Now with the swap on command, we can actually create or remove a particular swap partition. 30 00:02:16,679 --> 00:02:20,799 Now as it transpires right now, I do not have a swap partition. 31 00:02:20,799 --> 00:02:26,799 Now if I actually wanted to create a swap partition, I could use a swap on command by saying swap 32 00:02:26,799 --> 00:02:32,639 on and then providing the actual device I want to make a swap partition, say for example, 33 00:02:32,639 --> 00:02:36,079 SDC2 or whatever it may be. 34 00:02:36,080 --> 00:02:42,400 Or if I wanted to remove a partition, I could say swap off and then specify the partition 35 00:02:42,400 --> 00:02:43,880 that could remove it. 36 00:02:43,880 --> 00:02:46,560 So I can do the same thing with respect to the swap file. 37 00:02:46,560 --> 00:02:49,920 I can say swap off and then give the name of the swap file. 38 00:02:49,920 --> 00:02:53,760 Oh, and of course, need that super user privilege. 39 00:02:53,760 --> 00:02:58,400 I can now say swap on and I no longer have that swap file. 40 00:02:58,400 --> 00:03:03,960 You see that now if I want to return that swap file, I just say swap on and again, just 41 00:03:04,040 --> 00:03:04,960 say swap file. 42 00:03:04,960 --> 00:03:08,400 And I don't know why I keep forgetting the super user. 43 00:03:08,400 --> 00:03:09,879 So there we go. 44 00:03:09,879 --> 00:03:13,480 Try again, swap on and it is back once again. 45 00:03:13,480 --> 00:03:18,280 Now what I could do is if I wanted to create my own swap file, so what I'll do is I'll 46 00:03:18,280 --> 00:03:23,600 just say swap off swap file and I'll just remove this swap file. 47 00:03:23,600 --> 00:03:25,159 So it's fully gone. 48 00:03:25,159 --> 00:03:29,080 If I wanted to create my own, I could use the command DD. 49 00:03:29,360 --> 00:03:36,360 So I'll say pseudo DD and I'll make the input file equal to something called dev zero. 50 00:03:36,360 --> 00:03:41,960 This is just going to create a file full of zeros and I'll make the output file equal 51 00:03:41,960 --> 00:03:43,680 to swap file. 52 00:03:43,680 --> 00:03:49,520 I'll say the bite size is equal to one meg and I'll make the count 128. 53 00:03:49,520 --> 00:03:52,960 So we'll have 128 units of one meg. 54 00:03:52,960 --> 00:03:54,840 That's going to be the size of the swap file. 55 00:03:54,920 --> 00:03:58,080 If I hit enter, we have now generated this file. 56 00:03:58,080 --> 00:04:05,039 So if I do an LS dash L or rather LS dash L on swap file, we can actually see the size 57 00:04:05,039 --> 00:04:06,719 of the file we have created. 58 00:04:06,719 --> 00:04:12,840 Now, if we want to make this a swap file, what we should do is we should change the permissions 59 00:04:12,840 --> 00:04:20,240 or make this 600 so that only the root user can actually access and modify this file. 60 00:04:20,240 --> 00:04:24,319 The reason being is that this file is going to contain RAM information. 61 00:04:24,319 --> 00:04:26,040 So that could be potentially sensitive. 62 00:04:26,040 --> 00:04:29,639 You don't want regular users to be able to access this file. 63 00:04:29,639 --> 00:04:31,439 So I'll change the permissions. 64 00:04:31,439 --> 00:04:36,319 If I add a whip, notice that the permissions have changed from here. 65 00:04:36,319 --> 00:04:39,839 We only have read writes, nothing for the other group. 66 00:04:39,839 --> 00:04:45,360 And what I now want to do is I want to actually denote that this file is going to be a swap 67 00:04:45,360 --> 00:04:46,360 file. 68 00:04:46,360 --> 00:04:51,800 Now, the way I can do this is I can say pseudo MK swap and then specify the swap file I'm 69 00:04:51,800 --> 00:04:52,800 targeting. 70 00:04:52,800 --> 00:04:54,400 I'm setting up some swap space. 71 00:04:54,400 --> 00:04:58,759 And now what I want to do is I actually want to enable it as a swap on because right now, 72 00:04:58,759 --> 00:05:01,160 if I just say swap on, we don't have anything. 73 00:05:01,160 --> 00:05:05,400 I will say pseudo swap on and then give the name of the swap file. 74 00:05:05,400 --> 00:05:06,400 There we go. 75 00:05:06,400 --> 00:05:12,720 If I now say swap on, we have now generated this swap file of 128 meg. 76 00:05:12,720 --> 00:05:18,199 If our system happens to be taxed, we can now use this space as a little backup. 77 00:05:18,199 --> 00:05:22,000 So really, as we can see here, the swap on command and the swap off command. 78 00:05:22,199 --> 00:05:23,800 In fact, let me just briefly show you. 79 00:05:23,800 --> 00:05:28,199 I can just turn this off once again, swap off for the swap file and swap on. 80 00:05:28,199 --> 00:05:30,600 It's no longer there and put it back. 81 00:05:30,600 --> 00:05:33,399 These commands are very, very useful. 82 00:05:33,399 --> 00:05:39,899 They allow you to control either swap files or if we happen to have a swap partition, 83 00:05:39,899 --> 00:05:42,199 we can do the very same thing. 84 00:05:42,199 --> 00:05:46,500 So really, I just wanted to highlight this at the end of this skill for the purposes 85 00:05:46,500 --> 00:05:47,500 of the examination. 86 00:05:47,500 --> 00:05:49,399 Really do focus on these commands. 87 00:05:49,399 --> 00:05:53,199 I recommend you read the man pages and lab this up. 88 00:05:53,199 --> 00:05:53,699 Okay, doc. 89 00:05:53,699 --> 00:05:57,299 So I hope this has been informative for you and I'd like to thank you for viewing.