1 00:00:00,720 --> 00:00:01,740 In this lesson, 2 00:00:01,740 --> 00:00:03,719 we're going to dive deeper into the concepts 3 00:00:03,719 --> 00:00:04,980 of the Linux kernel 4 00:00:04,980 --> 00:00:07,440 by learning how to perform complex tasks 5 00:00:07,440 --> 00:00:09,660 by configuring kernel modules. 6 00:00:09,660 --> 00:00:11,880 Now, the Linux kernel is loaded into memory 7 00:00:11,880 --> 00:00:13,320 by the boot loader. 8 00:00:13,320 --> 00:00:14,310 The kernel modules 9 00:00:14,310 --> 00:00:17,130 are dynamically loaded and unloaded on demand, 10 00:00:17,130 --> 00:00:18,660 and they provide device drivers 11 00:00:18,660 --> 00:00:21,900 the ability to allow the kernel to access new hardware, 12 00:00:21,900 --> 00:00:23,850 support different file system types 13 00:00:23,850 --> 00:00:26,640 and generally extend the functionality of the kernel 14 00:00:26,640 --> 00:00:28,620 without the need to reboot the system, 15 00:00:28,620 --> 00:00:29,453 and this can lead to 16 00:00:29,453 --> 00:00:32,759 a lot of great flexibility during operations. 17 00:00:32,759 --> 00:00:36,480 Now, the /usr/lib/modules directory 18 00:00:36,480 --> 00:00:38,940 contains the modules of different kernel versions, 19 00:00:38,940 --> 00:00:41,040 that are going to be installed on the system. 20 00:00:41,040 --> 00:00:42,060 This holds a directory 21 00:00:42,060 --> 00:00:44,400 named after the kernel's version number. 22 00:00:44,400 --> 00:00:45,810 Inside this directory, 23 00:00:45,810 --> 00:00:48,630 modules are stored across various sub-directories 24 00:00:48,630 --> 00:00:51,000 based on the categories they belong to. 25 00:00:51,000 --> 00:00:53,220 For example, a Bluetooth driver 26 00:00:53,220 --> 00:00:57,140 might be stored in /usr/lib/modules 27 00:00:57,140 --> 00:01:02,140 /version number/kernel/drivers/bluetooth. 28 00:01:02,970 --> 00:01:07,970 Inside the /usr/lib/modules version number/kernel directory, 29 00:01:08,880 --> 00:01:10,590 there's going to be several subdirectories 30 00:01:10,590 --> 00:01:12,330 for each of the different devices, 31 00:01:12,330 --> 00:01:14,760 as well as some for the different architectures 32 00:01:14,760 --> 00:01:16,380 inside of these modules 33 00:01:16,380 --> 00:01:18,900 for different specific architecture types 34 00:01:18,900 --> 00:01:22,020 or crypto, which contains modules for encryption 35 00:01:22,020 --> 00:01:23,730 and other cryptographic functions. 36 00:01:23,730 --> 00:01:25,080 There's one called drivers, 37 00:01:25,080 --> 00:01:27,960 which contains modules for various types of hardware. 38 00:01:27,960 --> 00:01:31,410 fs contains modules for various types of file systems 39 00:01:31,410 --> 00:01:33,810 and net, which is a directory that contains modules 40 00:01:33,810 --> 00:01:35,070 for networking components, 41 00:01:35,070 --> 00:01:37,830 such as your firewalls and your protocols. 42 00:01:37,830 --> 00:01:39,360 This Linux system comes with 43 00:01:39,360 --> 00:01:41,130 a number of different commands as well 44 00:01:41,130 --> 00:01:43,230 to handle these kernel modules. 45 00:01:43,230 --> 00:01:44,730 This includes listing the modules 46 00:01:44,730 --> 00:01:46,650 currently loaded into the Linux kernel, 47 00:01:46,650 --> 00:01:48,420 displaying module information, 48 00:01:48,420 --> 00:01:49,770 as well as loading and unloading 49 00:01:49,770 --> 00:01:51,630 these different kernel modules. 50 00:01:51,630 --> 00:01:53,490 We're going to talk a little bit about these commands 51 00:01:53,490 --> 00:01:56,280 in a little bit more depth as we go through this lesson. 52 00:01:56,280 --> 00:01:59,580 Now, the first one I want to talk about is lsmod. 53 00:01:59,580 --> 00:02:01,890 The lsmod command is used to display 54 00:02:01,890 --> 00:02:04,950 the currently loaded kernel modules, their sizes, 55 00:02:04,950 --> 00:02:07,980 their usage details and their dependent modules. 56 00:02:07,980 --> 00:02:11,430 The modinfo command is going to be used to display information 57 00:02:11,430 --> 00:02:13,410 about a particular kernel module, 58 00:02:13,410 --> 00:02:16,140 such as the file name of the module, the license, 59 00:02:16,140 --> 00:02:18,330 the description, the author's name, 60 00:02:18,330 --> 00:02:21,060 the module version number, the dependent modules 61 00:02:21,060 --> 00:02:23,160 and other parameters or attributes. 62 00:02:23,160 --> 00:02:25,140 To run this command simply type in 63 00:02:25,140 --> 00:02:28,590 modinfo, options and the module name. 64 00:02:28,590 --> 00:02:30,390 Another command that's important to know 65 00:02:30,390 --> 00:02:33,780 is insmod, which is used to install a module 66 00:02:33,780 --> 00:02:35,850 into the currently running kernel. 67 00:02:35,850 --> 00:02:38,460 This command inserts only the specified module 68 00:02:38,460 --> 00:02:41,490 and does not insert any dependent modules though. 69 00:02:41,490 --> 00:02:45,750 To use this type in insmod and the module name. 70 00:02:45,750 --> 00:02:48,630 The rmmod command is going to be used to remove a module 71 00:02:48,630 --> 00:02:50,490 from the currently running kernel. 72 00:02:50,490 --> 00:02:54,900 To run this command type rmmod and the module name. 73 00:02:54,900 --> 00:02:58,080 Another command we want to talk about is modprobe. 74 00:02:58,080 --> 00:03:01,140 modprobe is a command that's used to add or remove modules 75 00:03:01,140 --> 00:03:02,430 from the kernel. 76 00:03:02,430 --> 00:03:05,640 This command is capable of loading all the dependent modules 77 00:03:05,640 --> 00:03:08,100 before inserting the specified module though, 78 00:03:08,100 --> 00:03:09,990 making it easier to use. 79 00:03:09,990 --> 00:03:14,990 Therefore, we prefer to use this instead of insmod or rmmod. 80 00:03:15,210 --> 00:03:17,400 To add modules using the modprobe, 81 00:03:17,400 --> 00:03:20,790 simply type in the -a option and specify the modules 82 00:03:20,790 --> 00:03:21,900 you want to add. 83 00:03:21,900 --> 00:03:23,670 If you want to unload a module 84 00:03:23,670 --> 00:03:25,440 you're going to use the -r option 85 00:03:25,440 --> 00:03:27,750 to remove the specified modules. 86 00:03:27,750 --> 00:03:30,090 To run this, type in modprobe, 87 00:03:30,090 --> 00:03:32,610 the options and the module name. 88 00:03:32,610 --> 00:03:35,520 In addition to options for adding and removing modules, 89 00:03:35,520 --> 00:03:39,390 the modprobe command also has more options that you can use. 90 00:03:39,390 --> 00:03:42,180 You can use -f if you want to force the module 91 00:03:42,180 --> 00:03:44,100 to be inserted or removed. 92 00:03:44,100 --> 00:03:47,340 You can use -n if you need to conduct a dry run 93 00:03:47,340 --> 00:03:49,230 by making sure you look at the output results 94 00:03:49,230 --> 00:03:51,840 without actually executing operations. 95 00:03:51,840 --> 00:03:54,540 You can also use -s if you want to print errors 96 00:03:54,540 --> 00:03:57,600 to the system log rather than to the standard error. 97 00:03:57,600 --> 00:03:58,950 And you can use -v 98 00:03:58,950 --> 00:04:02,130 if you want to enable verbose mode for troubleshooting. 99 00:04:02,130 --> 00:04:03,270 In order for modprobe 100 00:04:03,270 --> 00:04:05,550 to accurately install dependent modules 101 00:04:05,550 --> 00:04:08,040 it reads the module's .dep file 102 00:04:08,040 --> 00:04:11,190 to identify how modules are linked to one another. 103 00:04:11,190 --> 00:04:13,560 The depmod command is going to be used 104 00:04:13,560 --> 00:04:15,600 to update the database of dependencies, 105 00:04:15,600 --> 00:04:18,750 so the modprobe can actually function properly. 106 00:04:18,750 --> 00:04:21,720 The depmod or dependent modules command 107 00:04:21,720 --> 00:04:26,610 will search the contents of /lib/modules for each module. 108 00:04:26,610 --> 00:04:28,860 Any module can export a symbol 109 00:04:28,860 --> 00:04:31,800 indicating they can provide a service to other modules. 110 00:04:31,800 --> 00:04:36,090 Then the depmod tool can build the module's .dep file 111 00:04:36,090 --> 00:04:38,550 by aggregating all the instances of symbols 112 00:04:38,550 --> 00:04:40,740 that are being exported and used. 113 00:04:40,740 --> 00:04:45,540 To run the command, simply type in depmod with the options. 114 00:04:45,540 --> 00:04:48,720 The modprobe command can also add or remove modules. 115 00:04:48,720 --> 00:04:50,790 And because the modules have dependencies, 116 00:04:50,790 --> 00:04:52,830 we need a way of specifying what options 117 00:04:52,830 --> 00:04:54,930 are to be used with these modules. 118 00:04:54,930 --> 00:04:58,020 All the .conf files or config files 119 00:04:58,020 --> 00:05:03,020 are going to be located inside the /etc/modprobe.d directory. 120 00:05:03,930 --> 00:05:06,120 This is a directory extension that specifies 121 00:05:06,120 --> 00:05:09,210 the options required for the various modules. 122 00:05:09,210 --> 00:05:11,160 You can also use the alias command, 123 00:05:11,160 --> 00:05:14,640 which is alias the alternative name and the module name 124 00:05:14,640 --> 00:05:16,590 and it will specify an alternative name 125 00:05:16,590 --> 00:05:18,660 for a module with a long name. 126 00:05:18,660 --> 00:05:20,908 For example, if I had something that had a really long name 127 00:05:20,908 --> 00:05:23,640 and I just wanted to call it, Jason, I could do that. 128 00:05:23,640 --> 00:05:25,620 We can also use the blacklist command 129 00:05:25,620 --> 00:05:28,500 which is used by typing blacklist and the module name 130 00:05:28,500 --> 00:05:30,690 to ignore any internal aliases, 131 00:05:30,690 --> 00:05:33,660 which occurs when a module defines its own aliases. 132 00:05:33,660 --> 00:05:35,280 And if we want to use the install 133 00:05:35,280 --> 00:05:37,710 we can do install module name and command 134 00:05:37,710 --> 00:05:39,480 to run the specified command 135 00:05:39,480 --> 00:05:42,390 without inserting the module into the kernel. 136 00:05:42,390 --> 00:05:45,600 In addition to loading modules into the kernel at runtime 137 00:05:45,600 --> 00:05:47,850 you can also change some of the kernel's parameters 138 00:05:47,850 --> 00:05:49,260 while it's running. 139 00:05:49,260 --> 00:05:52,110 You can use these parameters to improve system performance 140 00:05:52,110 --> 00:05:55,260 hardening your security, configure networking limitations, 141 00:05:55,260 --> 00:05:58,080 change virtual memory settings and much more. 142 00:05:58,080 --> 00:06:02,400 To do this you're going to go into the /proc/sys directory. 143 00:06:02,400 --> 00:06:04,500 This directory lists all the parameters 144 00:06:04,500 --> 00:06:06,840 that you can configure on your system. 145 00:06:06,840 --> 00:06:09,180 Like the directories containing kernel modules, 146 00:06:09,180 --> 00:06:13,350 this /proc/sys directory is divided into several categories, 147 00:06:13,350 --> 00:06:15,450 including crypto which includes parameters 148 00:06:15,450 --> 00:06:18,510 related to encryption and other cryptographic services. 149 00:06:18,510 --> 00:06:20,640 debug, which includes parameters related to 150 00:06:20,640 --> 00:06:22,080 debugging the kernel, 151 00:06:22,080 --> 00:06:24,090 dev, which includes parameters related to 152 00:06:24,090 --> 00:06:25,890 specific hardware devices, 153 00:06:25,890 --> 00:06:29,460 fs, which includes parameters related to file system data, 154 00:06:29,460 --> 00:06:31,380 kernel, which includes parameters related to 155 00:06:31,380 --> 00:06:33,210 miscellaneous kernel functions, 156 00:06:33,210 --> 00:06:34,770 net, which includes parameters 157 00:06:34,770 --> 00:06:36,660 related to networking functions, 158 00:06:36,660 --> 00:06:38,700 user, which includes parameters related to 159 00:06:38,700 --> 00:06:40,290 user space limitations, 160 00:06:40,290 --> 00:06:42,660 and vm, which includes parameters related to 161 00:06:42,660 --> 00:06:44,880 virtual memory management. 162 00:06:44,880 --> 00:06:47,340 Another command that's really powerful in Linux 163 00:06:47,340 --> 00:06:49,230 is the sysctl command. 164 00:06:49,230 --> 00:06:52,800 This is spelled S-Y-S-C-T-L. 165 00:06:52,800 --> 00:06:54,540 This is a powerful Linux command, 166 00:06:54,540 --> 00:06:57,030 which acts as an interface to dynamically change 167 00:06:57,030 --> 00:06:58,590 the kernel parameters. 168 00:06:58,590 --> 00:07:00,060 With the help of this command 169 00:07:00,060 --> 00:07:01,740 you can modify the kernel parameters 170 00:07:01,740 --> 00:07:05,640 without recompiling the kernel or rebooting your machine. 171 00:07:05,640 --> 00:07:07,680 The parameters available for modification 172 00:07:07,680 --> 00:07:11,760 can all be found under the /proc/sys directory. 173 00:07:11,760 --> 00:07:13,680 You can also view a parameter value 174 00:07:13,680 --> 00:07:16,500 by displaying the content of the appropriate file. 175 00:07:16,500 --> 00:07:19,680 It has various options, including things like -a 176 00:07:19,680 --> 00:07:21,570 which is used to display all the parameters 177 00:07:21,570 --> 00:07:23,140 and their current values, 178 00:07:23,140 --> 00:07:25,830 w parameter equals value, 179 00:07:25,830 --> 00:07:28,350 which is going to be used to set a parameter value 180 00:07:28,350 --> 00:07:30,000 inside of the kernel. 181 00:07:30,000 --> 00:07:33,120 You also can use option -p and a file name 182 00:07:33,120 --> 00:07:36,360 to load the sysctl settings from a specified file 183 00:07:36,360 --> 00:07:40,410 or the /etc/sysctl.conf file, 184 00:07:40,410 --> 00:07:42,720 if no file name is being provided. 185 00:07:42,720 --> 00:07:45,900 If you use -e, you can use this to ignore errors 186 00:07:45,900 --> 00:07:47,580 about unknown keys. 187 00:07:47,580 --> 00:07:50,280 If you use the option -r with a pattern 188 00:07:50,280 --> 00:07:52,680 you can use this to apply a command to a parameter 189 00:07:52,680 --> 00:07:54,300 that matches a given pattern, 190 00:07:54,300 --> 00:07:56,940 if you're using an extended regular expression. 191 00:07:56,940 --> 00:07:58,680 To run the sysctl command, 192 00:07:58,680 --> 00:08:02,100 you're going to type S-Y-S-C-T-L and the options 193 00:08:02,100 --> 00:08:03,660 on the command line. 194 00:08:03,660 --> 00:08:07,440 The /etc/sysctl.conf file 195 00:08:07,440 --> 00:08:09,240 is going to enable configuration changes 196 00:08:09,240 --> 00:08:11,130 to your running Linux kernel. 197 00:08:11,130 --> 00:08:13,560 These changes can include all sorts of improvements 198 00:08:13,560 --> 00:08:15,750 to your networking, security configurations 199 00:08:15,750 --> 00:08:17,640 or logging of information. 200 00:08:17,640 --> 00:08:18,660 So as you can see, 201 00:08:18,660 --> 00:08:21,000 it's really important to understand these modules 202 00:08:21,000 --> 00:08:22,260 and how to modify them, 203 00:08:22,260 --> 00:08:25,260 because they bring a lot of capability to your Linux system.