1 00:00:00,005 --> 00:00:04,006 - [Instructor] Building a kernel is a pretty big deal, 2 00:00:04,006 --> 00:00:07,005 pretty powerful thing to do. 3 00:00:07,005 --> 00:00:09,003 Lots involved. 4 00:00:09,003 --> 00:00:11,007 The build uses a lot of utilities, 5 00:00:11,007 --> 00:00:15,007 so you might need to install quite a few packages. 6 00:00:15,007 --> 00:00:18,004 If you look under the documentation directory, 7 00:00:18,004 --> 00:00:20,009 there's an admin guide 8 00:00:20,009 --> 00:00:25,006 and there's a quickly build trimmed Linux text file there. 9 00:00:25,006 --> 00:00:29,009 And if you look in there, you'll see this sudo apt thing 10 00:00:29,009 --> 00:00:33,002 that it recommends for Ubuntu, for example, 11 00:00:33,002 --> 00:00:35,004 and there's others for other distros and so forth. 12 00:00:35,004 --> 00:00:37,007 So you can look in there to get an idea 13 00:00:37,007 --> 00:00:40,002 of what you need to install. 14 00:00:40,002 --> 00:00:42,007 So typically when you build a kernel, you want 15 00:00:42,007 --> 00:00:46,000 to build a bootable image 16 00:00:46,000 --> 00:00:51,006 for X86, 64, your usual desktops and servers. 17 00:00:51,006 --> 00:00:55,007 Then you want a bzimage, that's a compressed, 18 00:00:55,007 --> 00:00:59,006 stripped kernel file in the appropriate format 19 00:00:59,006 --> 00:01:02,007 for grub to understand, for example. 20 00:01:02,007 --> 00:01:04,005 But there's other images 21 00:01:04,005 --> 00:01:07,006 for other targets like maybe uImage. 22 00:01:07,006 --> 00:01:14,000 There's also just kind of the raw kernel binary vmlinux. 23 00:01:14,000 --> 00:01:16,007 When you make bzimage, it has to make a vmlinux 24 00:01:16,007 --> 00:01:19,000 and then it strips it and compresses it 25 00:01:19,000 --> 00:01:22,002 and adds some header stuff and then you get a bzimage. 26 00:01:22,002 --> 00:01:27,006 So vmlinux will be a byproduct of making bzimage. 27 00:01:27,006 --> 00:01:31,005 The make command supports a minus J for jobs option 28 00:01:31,005 --> 00:01:32,009 where you can give it a number 29 00:01:32,009 --> 00:01:35,008 and that's how many compiles at a time it's going to try 30 00:01:35,008 --> 00:01:37,004 to do in parallel. 31 00:01:37,004 --> 00:01:40,008 So if you have a machine with eight cores, 32 00:01:40,008 --> 00:01:42,000 you can say J eight 33 00:01:42,000 --> 00:01:46,000 and they'll try to be doing eight at a time, For example. 34 00:01:46,000 --> 00:01:50,000 The other common thing you'd probably do is make modules. 35 00:01:50,000 --> 00:01:54,005 When you say make all, it'll typically make bzimage 36 00:01:54,005 --> 00:01:56,009 and make modules, both of them. 37 00:01:56,009 --> 00:02:00,001 So this builds all the .kos for all the things 38 00:02:00,001 --> 00:02:03,006 that you configured your kernel to have as modules. 39 00:02:03,006 --> 00:02:06,002 That might be more than a thousand. 40 00:02:06,002 --> 00:02:08,006 All kinds of modules you'll probably never, ever use. 41 00:02:08,006 --> 00:02:10,006 I mean, how many different ethernet devices 42 00:02:10,006 --> 00:02:12,003 do you have on your system? 43 00:02:12,003 --> 00:02:14,000 So you don't need all the ethernet drivers, 44 00:02:14,000 --> 00:02:16,004 but they're going to get built 45 00:02:16,004 --> 00:02:17,007 and they'll probably get installed 46 00:02:17,007 --> 00:02:22,001 and they'll just sit there, but that makes it flexible. 47 00:02:22,001 --> 00:02:24,005 So building all these modules, that's a lot of code. 48 00:02:24,005 --> 00:02:28,009 This step typically takes quite a while. 49 00:02:28,009 --> 00:02:29,009 Now if you want, 50 00:02:29,009 --> 00:02:31,005 after you've built your modules, 51 00:02:31,005 --> 00:02:35,001 you can install them into your system 52 00:02:35,001 --> 00:02:39,006 or copy this stuff over and install into another system. 53 00:02:39,006 --> 00:02:43,006 So the make modules install copies all the .kos 54 00:02:43,006 --> 00:02:48,004 and populates the lib module's kernel version directory, 55 00:02:48,004 --> 00:02:50,007 and it calls depmod 56 00:02:50,007 --> 00:02:54,006 to create the modules .dep file and so forth. 57 00:02:54,006 --> 00:02:56,009 Now, lib modules is typically not writeable 58 00:02:56,009 --> 00:02:58,008 by an ordinary user. 59 00:02:58,008 --> 00:03:01,007 So when you do a make modules install, 60 00:03:01,007 --> 00:03:05,001 you probably have to do a sudo, right? 61 00:03:05,001 --> 00:03:08,002 So targets with the word install in them 62 00:03:08,002 --> 00:03:09,009 like modules install, 63 00:03:09,009 --> 00:03:11,001 are installing in your system. 64 00:03:11,001 --> 00:03:14,000 And typically you need to run those with sudo. 65 00:03:14,000 --> 00:03:15,008 You need to be root. 66 00:03:15,008 --> 00:03:18,000 Similarly, there's a make install, 67 00:03:18,000 --> 00:03:22,006 which is for installing your kernel into /boot, 68 00:03:22,006 --> 00:03:27,008 and that should rename it vmlinuz, 69 00:03:27,008 --> 00:03:32,004 not be the image, vmlinuz-kernel version. 70 00:03:32,004 --> 00:03:35,004 And hopefully we will update your grub config 71 00:03:35,004 --> 00:03:37,005 and create an initramfs 72 00:03:37,005 --> 00:03:41,005 or initrdimage if you need that. 73 00:03:41,005 --> 00:03:44,000 Maybe not, it depends on the distro, 74 00:03:44,000 --> 00:03:46,009 but make install is at least an important 75 00:03:46,009 --> 00:03:49,009 step in getting that done. 76 00:03:49,009 --> 00:03:52,002 There's also clean targets. 77 00:03:52,002 --> 00:03:56,000 Make clean removes the stuff you built, 78 00:03:56,000 --> 00:03:58,004 the kernel file, the object files. 79 00:03:58,004 --> 00:04:00,003 So that's a pretty big deal. 80 00:04:00,003 --> 00:04:04,000 If you want to just clean part of the tree, 81 00:04:04,000 --> 00:04:07,008 you can use M=$PWD 82 00:04:07,008 --> 00:04:12,004 and minus C options to make to say where you want to clean 83 00:04:12,004 --> 00:04:16,001 or M equals a directory where you want to clean. 84 00:04:16,001 --> 00:04:18,002 Make clean does not remove your .config. 85 00:04:18,002 --> 00:04:22,003 So you don't lose all that work of configuring your kernel, 86 00:04:22,003 --> 00:04:24,003 but make mrproper does. 87 00:04:24,003 --> 00:04:28,001 Mrproper is a more thorough cleaning. 88 00:04:28,001 --> 00:04:32,001 Also because the lens kernel has been ported to a bunch 89 00:04:32,001 --> 00:04:35,001 of architectures, you can clearly cross compile it 90 00:04:35,001 --> 00:04:37,002 for other architectures. 91 00:04:37,002 --> 00:04:42,008 So typically that would involve installing a cross compiler, 92 00:04:42,008 --> 00:04:45,003 setting, an environment variable, cross compile 93 00:04:45,003 --> 00:04:48,002 to be the prefix for that cross compiler, 94 00:04:48,002 --> 00:04:49,008 make file will use that. 95 00:04:49,008 --> 00:04:51,007 And then you do a make, 96 00:04:51,007 --> 00:04:55,003 and there's that capital ARCH equals architecture space 97 00:04:55,003 --> 00:04:57,005 and the name of the image to make. 98 00:04:57,005 --> 00:05:02,000 For arm, it's often uImage, not bzimage, for example.