1 00:00:00,000 --> 00:00:12,360 Okay, so this is top, the performance dashboard for Linux. When I tell people about top, there's 2 00:00:12,360 --> 00:00:17,120 always people asking me, Hey, standard, have you heard of H top? Yes, of course, I've heard 3 00:00:17,120 --> 00:00:23,320 of H top. And there are other top like utilities as well. The reason I'm showing you top and 4 00:00:23,320 --> 00:00:28,480 nothing else is simple to explain. Top will always be present on your system. Because 5 00:00:28,480 --> 00:00:35,240 top is a standard Linux utility. H top is a fancy version of top, it's showing you colors, 6 00:00:35,240 --> 00:00:40,360 it's showing you much more details. But it also has a much larger system overhead. And 7 00:00:40,360 --> 00:00:46,160 for that reason, you won't find H top by default installed on most systems. You can see it 8 00:00:46,160 --> 00:00:53,360 right here in bold typeface. Top is using a CPU percentage of about 0.3%. I have seen 9 00:00:53,360 --> 00:00:59,880 H top systems that are using about 4% just for H top. And let's face it, you are using 10 00:00:59,880 --> 00:01:04,279 utilities like this. If you have an issue with your performance, then you don't want 11 00:01:04,279 --> 00:01:10,959 to earn a utility. That's a performance hit itself. Also notice that in many cases, it 12 00:01:10,959 --> 00:01:16,400 will not be allowed to install different utilities anyway. Imagine that you're a consultant and 13 00:01:16,400 --> 00:01:21,040 you want to help a customer with their performance problems. And then you are going to tell them, 14 00:01:21,080 --> 00:01:27,360 hey, can you install H top for me? Most likely they are going to tell you no, because installing 15 00:01:27,400 --> 00:01:34,400 unauthorized software is not something that is easily done in many Linux installations. Now 16 00:01:34,400 --> 00:01:40,440 the top interface right here is a little bit boring. I'm using Q to quit. And I'm going to 17 00:01:40,480 --> 00:01:49,800 give us some action using DDIF is dev 0, OF is dev null. And I'm making it background job. And 18 00:01:49,800 --> 00:01:54,680 then I'm running top again, so that at least we have one process that is creating some 19 00:01:54,680 --> 00:02:00,879 action. First thing I would look at in the top interface is the load average. Load average is 20 00:02:00,879 --> 00:02:08,119 giving the total amount of runnable processes over the last 1, 5 and 15 minutes. A runnable 21 00:02:08,119 --> 00:02:14,279 process is a process that is currently active, but also a process that wants to be served. So 22 00:02:14,279 --> 00:02:19,960 if you see six runnable processes, it doesn't mean that these are always active at the same 23 00:02:19,960 --> 00:02:26,360 time, because that is determined by the number of CPUs that you have. One CPU can only have one 24 00:02:26,360 --> 00:02:34,279 process active at any moment in time. So on a four CPU system, if you have a load average of six, 25 00:02:34,360 --> 00:02:39,279 that indicates that you have more processes than your system can handle. And you need to further 26 00:02:39,279 --> 00:02:45,279 investigate what is going on. So for the proper identification of what is going on, it's important 27 00:02:45,279 --> 00:02:51,639 that you know how many CPUs you have. Now here, you can almost guess, look, we have the DD process 28 00:02:51,639 --> 00:03:00,360 causing 100%. And we have my system, the CPUs line, and the parameter I'm looking at is ID for 29 00:03:00,360 --> 00:03:07,479 the idle loop. Idle loop is the amount of time my CPU is doing nothing. So for 50% of its time, my 30 00:03:07,479 --> 00:03:14,520 CPU is doing nothing. That means that this must be a two CPU system. You want to know it for sure, 31 00:03:14,559 --> 00:03:20,240 just press one from the top interface. And there you can see that yes, indeed, this is a two CPU 32 00:03:20,240 --> 00:03:28,520 system. Now CPUs is the next item that I'm interested in. You can see my active CPU is busy 33 00:03:28,520 --> 00:03:36,199 in user and in system space. User and system space are the areas of your operating system, where 34 00:03:36,199 --> 00:03:44,800 system space relates to kernel work, and user space relates to user processes. So here, the usage 35 00:03:44,800 --> 00:03:50,919 is mainly happening in kernel space. That is surprising in most cases, because in most cases, 36 00:03:50,919 --> 00:03:56,720 you will see a higher level of activity in user space. And if you see a high level of activity in 37 00:03:56,720 --> 00:04:03,479 kernel space, that indicates that you have very busy drivers. Now knowing what is going on in my 38 00:04:03,479 --> 00:04:10,119 command, the DD, IF and OF is, I know that I'm going from one driver to another driver. So that does 39 00:04:10,119 --> 00:04:17,559 make sense. The other parameter I'm interested in is ID. ID is the idle loop, the percentage of time 40 00:04:17,559 --> 00:04:23,040 that your system is doing nothing. And I want the idle loop to be as high as possible. The other 41 00:04:23,040 --> 00:04:29,279 parameters are not so interesting. In the past, when disks were still slow, instead of all being SSD, 42 00:04:30,079 --> 00:04:37,920 you would be interested in WA. WA is waiting for IO. And waiting for IO is what you get if your 43 00:04:37,920 --> 00:04:43,600 system is waiting for your disk to process the files. But nowadays, disks are fast enough, and 44 00:04:43,600 --> 00:04:50,000 for that reason, you don't see waiting for IO anymore. Now we have the memory usage. And in the 45 00:04:50,000 --> 00:04:56,160 memory usage, we have this line indicating that we have about four gigabytes in total, of which three 46 00:04:56,160 --> 00:05:04,799 gigabytes is free, and only 530 megabytes is used. And we also have 554 in buffers and cache. 47 00:05:05,839 --> 00:05:11,440 Buffers and cache is an area that your Linux system is using to speed up a little bit. And by keeping 48 00:05:11,440 --> 00:05:16,720 more files in buffers and cache, the next time you read the same file, you can serve it from the cache, 49 00:05:16,720 --> 00:05:23,040 and that will make your system faster. In the end, buffers and cache is not required, and that is why 50 00:05:23,040 --> 00:05:29,600 available memory is showing even more than what you see in free. And that is because your operating 51 00:05:29,600 --> 00:05:35,519 system is considering everything in cache, and it knows if the data in cache is actively being 52 00:05:35,519 --> 00:05:41,920 used or not. And if it's not actively being used, the Linux kernel knows that it can be dropped if 53 00:05:41,920 --> 00:05:48,720 more memory is needed. And in the last column, we can see the actual activity. By default, it's 54 00:05:48,720 --> 00:05:55,279 sort on CPU usage. You can also sort it on other things, and the easy way to do so is by using 55 00:05:55,279 --> 00:06:00,640 greater than or smaller than. Greater than is bringing you to the right, so right now I'm 56 00:06:00,640 --> 00:06:08,559 sorting on memory usage, and smaller than is bringing you to the left. So if I do that a couple of times 57 00:06:08,559 --> 00:06:15,839 right now, it is sorting on virtual memory usage. The virtual memory is not memory that is really in 58 00:06:15,839 --> 00:06:21,600 use. If you want to check memory that is really in use, go for a resident memory. So I'm using my 59 00:06:21,600 --> 00:06:29,279 uppercase arrow to the right once more. Now top is awesome, because apart from this overview, 60 00:06:29,279 --> 00:06:35,040 you can reanalyze and kill processes, and you can also reorganize the top interface. 61 00:06:36,160 --> 00:06:42,720 If you press F, then you get all the fields that you could be seeing in top. And if there is anything 62 00:06:42,720 --> 00:06:48,799 that you would like to see, you just use your arrow key to go over the option that you want to see. 63 00:06:48,799 --> 00:06:55,440 Here I see last used CPU. Well, that's what I want to see, so I'm using spacebar to select it, Q to 64 00:06:55,440 --> 00:07:01,839 get back to top, and look at that. We now have an additional column for the last CPU. And if you want 65 00:07:01,839 --> 00:07:09,839 to write your modifications to a persistent configuration file, use uppercase W. Uppercase W 66 00:07:09,920 --> 00:07:14,399 will write a file with the name toprc to make your setting persistent. 67 00:07:14,399 --> 00:07:19,920 So when I quit and I start top again, I can see my CPU column is listed again.