1 00:00:00,000 --> 00:00:11,440 In the end, working with devices on Linux is all about working with kernel modules. 2 00:00:11,440 --> 00:00:16,120 Because for every device that you are using, a kernel module is required. 3 00:00:16,120 --> 00:00:21,959 Kernel modules are loaded first through init-ramfs or init-rd while you are booting. 4 00:00:21,959 --> 00:00:27,100 Init-ramfs or init-rd are system specific and they are automatically generated at the 5 00:00:27,100 --> 00:00:31,900 end of the installation to make sure that you have all the configuration that you need 6 00:00:31,900 --> 00:00:32,900 inside. 7 00:00:32,900 --> 00:00:38,740 Where init-ramfs is what you will find on Red Hat oriented Linux and init-rd is the 8 00:00:38,740 --> 00:00:40,939 equivalent on Ubuntu. 9 00:00:40,939 --> 00:00:44,099 You can find the result in the slash boot directory. 10 00:00:44,099 --> 00:00:49,419 If ever you need to manually trigger the generation of an init-ramfs, you use DRAKUT. 11 00:00:49,419 --> 00:00:51,820 That's a Red Hat utility. 12 00:00:51,820 --> 00:00:54,340 Now the big question is, why would you want to do that? 13 00:00:54,340 --> 00:00:59,900 Well, you might want to do that if you have just installed this fancy new GPU card in 14 00:00:59,900 --> 00:01:02,660 your system, for instance. 15 00:01:02,660 --> 00:01:07,459 Then your init-ramfs won't know about it and you need to regenerate it. 16 00:01:07,459 --> 00:01:11,019 Use DRAKUT or DRAKUT-F to force it. 17 00:01:11,019 --> 00:01:16,779 To do the equivalent on Ubuntu, you use mkinitramfs. 18 00:01:16,779 --> 00:01:23,139 Now when you are booting, systemd starts systemd-udevd to manage on-demand loading of kernel modules. 19 00:01:23,139 --> 00:01:28,419 So when you plug in a USB thumb drive that contains a VFAT file system which hasn't been 20 00:01:28,419 --> 00:01:35,180 mounted yet, well, systemd-udevd makes sure that the VFAT kernel module will be loaded. 21 00:01:35,180 --> 00:01:41,180 And manual loading can be done as well using modprobe and the deprecated intmod command. 22 00:01:41,180 --> 00:01:47,019 But you will notice that the automatic procedure is so good that you rarely will use modprobe 23 00:01:47,019 --> 00:01:50,099 to manually load kernel modules. 24 00:01:50,139 --> 00:01:53,339 Nevertheless, let's discuss how it works. 25 00:01:53,339 --> 00:01:59,300 So if you want to see if manual loading is necessary, first you need to find out if your 26 00:01:59,300 --> 00:02:01,860 device already has a kernel module. 27 00:02:01,860 --> 00:02:06,260 lspci-k is an awesome command to find out. 28 00:02:06,260 --> 00:02:09,259 Next you can get kernel module parameters. 29 00:02:09,259 --> 00:02:12,460 Use modinfo on the kernel module that you want to use. 30 00:02:12,460 --> 00:02:19,740 And then modprobe can be used to manually load the modules, including all of their dependencies. 31 00:02:19,740 --> 00:02:22,460 To do the opposite, use modprobe-r. 32 00:02:22,460 --> 00:02:26,619 That will remove manually loaded kernel modules. 33 00:02:26,619 --> 00:02:30,779 And these kernel module dependencies, well, there is depmod. 34 00:02:30,779 --> 00:02:37,220 And depmod is a process that runs to automatically generate kernel module dependencies. 35 00:02:37,220 --> 00:02:41,339 Normally you don't have to worry about depmod, but if ever you are loading a kernel module 36 00:02:41,339 --> 00:02:46,100 and you feel you are missing a dependency, it doesn't hurt to run the depmod utility 37 00:02:46,100 --> 00:02:48,259 manually. 38 00:02:48,259 --> 00:02:56,899 In old Linux releases, insmod and rmmod were used, but these really are deprecated nowadays. 39 00:02:56,899 --> 00:03:00,619 Final thing you need to know about kernel modules is that they can come with kernel 40 00:03:00,619 --> 00:03:01,619 module parameters. 41 00:03:01,619 --> 00:03:06,619 Modinfo is what you use to find available parameters. 42 00:03:06,619 --> 00:03:15,139 And you can specify the parameters in etcmodprobe.conf and or in drop-in files in etcmodprobe.d. 43 00:03:15,139 --> 00:03:19,740 And alternatively, you can use a parameter name followed by its value as an argument 44 00:03:19,740 --> 00:03:23,779 while manually loading the parameter. 45 00:03:23,779 --> 00:03:27,020 Now messages about loading parameters are not consistent. 46 00:03:27,020 --> 00:03:32,139 And as a result, it can be hard to find out if your kernel module has correctly identified 47 00:03:32,139 --> 00:03:33,139 the parameter. 48 00:03:33,139 --> 00:03:38,399 But you can give it a try using dmessage or files in sysmodules. 49 00:03:38,399 --> 00:03:43,979 Let me show you, and let me show you specifically how we can use kernel module parameters. 50 00:03:43,979 --> 00:03:44,979 I'm using lsmod. 51 00:03:44,979 --> 00:03:51,300 lsmod is giving a list of all the kernel modules that are currently loaded. 52 00:03:51,300 --> 00:03:54,460 And I'm going for cdrom. 53 00:03:54,460 --> 00:03:57,380 That's a relatively innocent kernel module. 54 00:03:57,380 --> 00:04:02,059 We can see the cdrom as a kernel as a lot of dependencies, and we can see them right 55 00:04:02,059 --> 00:04:03,059 here, like srmod. 56 00:04:03,059 --> 00:04:09,300 srmod is a SCSI cdrom module, which is backing the cdrom module. 57 00:04:09,300 --> 00:04:13,419 Now if I want to know what is going on, I'm using modinfo. 58 00:04:13,860 --> 00:04:18,940 On cdrom, and modinfo is showing me a list of parameters. 59 00:04:18,940 --> 00:04:23,179 And I'm going for the parameter debug, which is a boolean. 60 00:04:23,179 --> 00:04:29,019 Debug is logging additional information if anything is happening to the dmessage output. 61 00:04:29,019 --> 00:04:34,660 So I want cdrom to be loaded with the parameter debug is 1. 62 00:04:34,660 --> 00:04:40,059 Boolean is an on-off value, so typically 0 and 1 would work. 63 00:04:40,059 --> 00:04:48,940 I'm going into etcmodprobe.d because etcmodprobe.d contains a couple of example files. 64 00:04:48,940 --> 00:04:52,899 And I do not want anything that is a blacklist. 65 00:04:52,899 --> 00:04:55,739 Oh, we only have blacklists? 66 00:04:55,739 --> 00:04:59,179 Blacklists are to prevent the loading of specific kernel modules. 67 00:04:59,179 --> 00:05:00,459 I don't want them. 68 00:05:00,459 --> 00:05:06,220 So I'm going to have a look at usrlibmodprobe.d. 69 00:05:06,220 --> 00:05:08,779 So remember, etc is for the customization. 70 00:05:08,779 --> 00:05:10,899 Usrlib is for the standard stuff. 71 00:05:10,899 --> 00:05:15,420 And maybe we have something in the standard configuration that I do like. 72 00:05:15,420 --> 00:05:19,179 And there I can see a potential candidate, this ALSA. 73 00:05:19,179 --> 00:05:23,059 This ALSA is for the ALSA sound module. 74 00:05:23,059 --> 00:05:26,660 And there we can see some options. 75 00:05:26,660 --> 00:05:29,820 Well, honestly, I also don't like it. 76 00:05:29,820 --> 00:05:31,339 Now what are we going to do? 77 00:05:31,339 --> 00:05:38,500 Well, man-kmodprobe, I want to know if there is any decent documentation about modprobe.conf. 78 00:05:38,500 --> 00:05:41,899 So man on modprobe.conf. 79 00:05:41,899 --> 00:05:47,140 Let's check it out to see if we have anything that we can do in here. 80 00:05:47,140 --> 00:05:49,579 So we have install. 81 00:05:49,579 --> 00:05:55,820 I don't care about install because install is for running a specific command. 82 00:05:55,820 --> 00:05:57,339 I care about options. 83 00:05:57,339 --> 00:05:58,459 This is the one I need. 84 00:05:58,459 --> 00:06:02,779 So we need options, CD-ROM debug is one, finally. 85 00:06:02,779 --> 00:06:10,140 So vim on etc modprobe.d CD-ROM.conf. 86 00:06:10,140 --> 00:06:16,140 And I'm going to put in options, CD-ROM debug is one. 87 00:06:16,140 --> 00:06:18,459 And that should be doing it. 88 00:06:18,459 --> 00:06:19,299 All right. 89 00:06:19,299 --> 00:06:22,940 Now I'm going to use modprobe-r CD-ROM. 90 00:06:22,940 --> 00:06:28,260 I'm trying to unload CD-ROM, but unfortunately, CD-ROM is in use. 91 00:06:28,859 --> 00:06:29,980 Okay. 92 00:06:29,980 --> 00:06:34,059 That means that it is automatically started and I'm going to reboot. 93 00:06:34,059 --> 00:06:40,779 And after the reboot, we are going to see if we can find anything about these options. 94 00:06:40,779 --> 00:06:45,059 So now we are back and I'm going to use dmessage, pipe less, 95 00:06:45,059 --> 00:06:47,260 because less allows me to search for it. 96 00:06:47,260 --> 00:06:49,459 And I'm searching for CD-ROM. 97 00:06:49,459 --> 00:06:54,779 And here we can see CD-ROM, that's not very much information. 98 00:06:54,779 --> 00:06:57,339 And N isn't giving me anything either. 99 00:06:57,339 --> 00:07:03,940 Now, as I mentioned before, it's not always easy to find information about parameters. 100 00:07:03,940 --> 00:07:08,500 The other choice that you've got is in the sysmodules file system. 101 00:07:08,500 --> 00:07:15,260 You go to CD-ROM and there you might have a subdirectory with the name parameters. 102 00:07:15,260 --> 00:07:20,179 I don't, so apparently this module doesn't clearly keep track of its parameters. 103 00:07:20,179 --> 00:07:21,980 Too bad, but that's the way it is.