1 00:00:00,005 --> 00:00:02,002 - [Instructor] What is this Linux Kernel thing? 2 00:00:02,002 --> 00:00:04,002 Well, let's talk about it. 3 00:00:04,002 --> 00:00:06,009 The Kernel is a program, compiled program. 4 00:00:06,009 --> 00:00:08,005 The Kernel program has a name. 5 00:00:08,005 --> 00:00:09,009 That file has a name. 6 00:00:09,009 --> 00:00:15,002 The name is something like vmlinuz-. 7 00:00:15,002 --> 00:00:18,003 That program needs to be loaded into memory and run, 8 00:00:18,003 --> 00:00:21,001 and that operation is done by a boot loader. 9 00:00:21,001 --> 00:00:24,003 With Linux, we often have a boot loader called GRUB. 10 00:00:24,003 --> 00:00:27,002 So GRUB reads the kernel, file from disc, 11 00:00:27,002 --> 00:00:30,004 puts it in memory, and transfers control to it. 12 00:00:30,004 --> 00:00:33,001 The Kernel program, like other programs, 13 00:00:33,001 --> 00:00:36,000 actually has some command line parameters that you can set, 14 00:00:36,000 --> 00:00:37,007 and GRUB is responsible 15 00:00:37,007 --> 00:00:41,001 for passing those parameters to the Kernel. 16 00:00:41,001 --> 00:00:43,002 The Linux Kernel also has an API. 17 00:00:43,002 --> 00:00:45,003 It provides a programming interface. 18 00:00:45,003 --> 00:00:47,006 The functions that we can call from user space 19 00:00:47,006 --> 00:00:51,004 into the Kernel, we call system calls, 20 00:00:51,004 --> 00:00:53,004 but the Linux Kernel also provides 21 00:00:53,004 --> 00:00:56,001 virtual file systems, proc and sys, 22 00:00:56,001 --> 00:00:58,009 and the lesser known debugfs, for example. 23 00:00:58,009 --> 00:01:01,003 And through those virtual file systems, 24 00:01:01,003 --> 00:01:03,006 we can interact directly with the Kernel, 25 00:01:03,006 --> 00:01:05,004 getting information from the Kernel 26 00:01:05,004 --> 00:01:08,000 and changing things in the Kernel. 27 00:01:08,000 --> 00:01:10,007 And our system has device files. 28 00:01:10,007 --> 00:01:12,006 We interact with device drivers 29 00:01:12,006 --> 00:01:16,005 by doing operations on those device files. 30 00:01:16,005 --> 00:01:19,000 Those operations are standard system calls 31 00:01:19,000 --> 00:01:22,000 like read and write and open. 32 00:01:22,000 --> 00:01:23,006 The Kernel is a gatekeeper. 33 00:01:23,006 --> 00:01:25,006 The Kernel enforces privileges. 34 00:01:25,006 --> 00:01:29,002 In Linux, we call those privileges capabilities, 35 00:01:29,002 --> 00:01:31,002 and the Linux Kernel source code, 36 00:01:31,002 --> 00:01:34,002 it refers to the capabilities of a process 37 00:01:34,002 --> 00:01:36,009 to see if it's allowed to perform some sort 38 00:01:36,009 --> 00:01:39,003 of privilege operation. 39 00:01:39,003 --> 00:01:43,000 Linux Kernel also implements a number of security policies, 40 00:01:43,000 --> 00:01:46,008 the underlying mechanisms used by SE Linux 41 00:01:46,008 --> 00:01:48,009 and App Armor, for example. 42 00:01:48,009 --> 00:01:51,006 And finally, the Kernel provides controlled access 43 00:01:51,006 --> 00:01:54,002 to hardware and other resources. 44 00:01:54,002 --> 00:01:56,001 It wouldn't be safe to allow processes 45 00:01:56,001 --> 00:02:01,003 to willy-nilly access the disc at will, for example, no. 46 00:02:01,003 --> 00:02:03,007 The Kernel has to provide controlled access 47 00:02:03,007 --> 00:02:05,008 to make sure that things are done 48 00:02:05,008 --> 00:02:09,004 in an orderly and safe manner. 49 00:02:09,004 --> 00:02:11,001 The Kernel is modular. 50 00:02:11,001 --> 00:02:17,001 The Kernel itself, that vmlinuz file is relatively small. 51 00:02:17,001 --> 00:02:19,007 The Kernel image is sufficient to boot to user space 52 00:02:19,007 --> 00:02:22,002 to begin running the first process. 53 00:02:22,002 --> 00:02:24,001 Once we have that process 54 00:02:24,001 --> 00:02:25,008 and the ones that started, 55 00:02:25,008 --> 00:02:28,008 we can load additional functionality into the Kernel 56 00:02:28,008 --> 00:02:31,007 through the loadable Kernel module mechanism. 57 00:02:31,007 --> 00:02:34,001 The loadable module mechanism means 58 00:02:34,001 --> 00:02:36,009 we can just load the drivers that we need. 59 00:02:36,009 --> 00:02:38,001 We don't need to load drivers 60 00:02:38,001 --> 00:02:40,005 for hardware that's not present. 61 00:02:40,005 --> 00:02:43,003 We can also load additional sorts of functionality 62 00:02:43,003 --> 00:02:47,006 that's not drivers, but, say, for security or other things. 63 00:02:47,006 --> 00:02:51,000 We'll be looking at all of those in some detail.