1
00:00:06,900 --> 00:00:09,900
- In this video, I'll tell
you about kernel modules.

2
00:00:09,900 --> 00:00:12,570
A kernel module is an
object file containing code

3
00:00:12,570 --> 00:00:14,970
that extends the Linux kernel.

4
00:00:14,970 --> 00:00:17,610
An object file is what you
get when you compile a file

5
00:00:17,610 --> 00:00:20,340
that is written in the
C programming language.

6
00:00:20,340 --> 00:00:22,440
And for every single piece of hardware,

7
00:00:22,440 --> 00:00:25,113
you need a kernel module
in order to use it.

8
00:00:26,070 --> 00:00:29,100
Kernel modules are obtained
from the initramfs,

9
00:00:29,100 --> 00:00:31,320
which is created upon system installation

10
00:00:31,320 --> 00:00:33,390
to match all hardware that is found

11
00:00:33,390 --> 00:00:35,013
while your system was installed.

12
00:00:36,450 --> 00:00:37,890
There is systemd-udevd,

13
00:00:37,890 --> 00:00:40,170
which is used as a plug-and-play manager

14
00:00:40,170 --> 00:00:43,350
to load kernel files
dynamically when needed.

15
00:00:43,350 --> 00:00:44,700
And alternatively,

16
00:00:44,700 --> 00:00:47,193
kernel files can be
loaded manually, as well.

17
00:00:49,320 --> 00:00:51,390
So how do we manage kernel modules?

18
00:00:51,390 --> 00:00:53,790
Well, there's a couple
of commands involved

19
00:00:53,790 --> 00:00:57,720
like lsmod, which shows all
modules currently loaded.

20
00:00:57,720 --> 00:01:01,140
And modprobe, which is used to
manually load a kernel file,

21
00:01:01,140 --> 00:01:02,913
including its dependencies.

22
00:01:03,750 --> 00:01:05,310
There is modprobe -r,

23
00:01:05,310 --> 00:01:08,370
which is used to manually
unload a kernel file.

24
00:01:08,370 --> 00:01:09,480
And modinfo,

25
00:01:09,480 --> 00:01:12,960
which provides information
about kernel modules.

26
00:01:12,960 --> 00:01:16,500
And then there is depmod,
which generates the modules.dep

27
00:01:16,500 --> 00:01:18,393
kernel module dependency file.

28
00:01:19,560 --> 00:01:22,770
Kernel module parameters
are listed by modinfo.

29
00:01:22,770 --> 00:01:25,200
And they can be specified in include files

30
00:01:25,200 --> 00:01:26,970
in /etc/modprobe.d/,

31
00:01:26,970 --> 00:01:30,423
which allows you to change
default kernel module parameters.

32
00:01:31,320 --> 00:01:33,300
All right. So let me demonstrate

33
00:01:33,300 --> 00:01:36,000
how you can manage kernel modules.

34
00:01:36,000 --> 00:01:37,860
I composed a small demo.

35
00:01:37,860 --> 00:01:41,220
Most important steps are on the slides.

36
00:01:41,220 --> 00:01:45,000
Feel free to post the
video and try for yourself.

37
00:01:45,000 --> 00:01:47,493
And then, you can watch
what I've been doing.

38
00:01:48,690 --> 00:01:50,103
So let's go for it.

39
00:01:53,550 --> 00:01:55,380
So first, lsmod.

40
00:01:55,380 --> 00:01:57,210
The lsmod command to show
when all the kernel modules

41
00:01:57,210 --> 00:01:59,490
that are currently loaded.

42
00:01:59,490 --> 00:02:04,020
I wanna know if we have cdrom available.

43
00:02:04,020 --> 00:02:05,610
And there we can see that right now,

44
00:02:05,610 --> 00:02:08,373
we do have cdrom, which is loaded.

45
00:02:09,210 --> 00:02:12,933
So I want to unload modprobe -r cdrom.

46
00:02:13,770 --> 00:02:15,300
And uh oh. What do we get?

47
00:02:15,300 --> 00:02:17,523
We get module cdrom is in use.

48
00:02:18,420 --> 00:02:20,730
Before continuing, it's a good idea

49
00:02:20,730 --> 00:02:22,863
to verify that you have nothing mounted.

50
00:02:24,930 --> 00:02:28,140
The findmnt command is a
convenient way to figure out

51
00:02:28,140 --> 00:02:31,500
if anything related to your
cdrom is currently mounted.

52
00:02:31,500 --> 00:02:36,500
Look at the second column and
look for either sr0 or cdrom.

53
00:02:36,540 --> 00:02:38,070
And if you can find it in here,

54
00:02:38,070 --> 00:02:40,470
you mount it before continuing.

55
00:02:40,470 --> 00:02:44,190
If you don't find it, as
is the case right here,

56
00:02:44,190 --> 00:02:46,140
we need to make sure that we get rid of

57
00:02:46,140 --> 00:02:48,330
this module cdrom is in use.

58
00:02:48,330 --> 00:02:49,560
Now, why do we get this?

59
00:02:49,560 --> 00:02:52,560
Well, we get it because we have isofs.

60
00:02:52,560 --> 00:02:55,890
Isofs is currently using the cdrom module.

61
00:02:55,890 --> 00:03:00,090
And that means that we can't
unload it at this moment.

62
00:03:00,090 --> 00:03:02,730
You may see, depending who
your current configuration,

63
00:03:02,730 --> 00:03:05,970
other modules, as well, like sr_mod.

64
00:03:05,970 --> 00:03:07,650
And if you see them, well,

65
00:03:07,650 --> 00:03:09,930
you need to unload these dependencies.

66
00:03:09,930 --> 00:03:14,930
So modprobe -r isofs.

67
00:03:16,650 --> 00:03:20,190
And then, we can try the
modprobe -r cdrom again.

68
00:03:20,190 --> 00:03:22,503
And as you can see, now it is working.

69
00:03:23,370 --> 00:03:24,990
Now, I would like to show you

70
00:03:24,990 --> 00:03:28,620
modprobe on isofs, at this moment.

71
00:03:28,620 --> 00:03:31,410
Because what is modprobe isofs doing?

72
00:03:31,410 --> 00:03:34,263
Well, this module has a dependency.

73
00:03:35,790 --> 00:03:37,950
And as a result, right now,

74
00:03:37,950 --> 00:03:40,350
we can see that cdrom is available again.

75
00:03:40,350 --> 00:03:41,730
We just unloaded it.

76
00:03:41,730 --> 00:03:44,670
We did not load it again,
but we loaded isofs.

77
00:03:44,670 --> 00:03:46,860
And because we loaded isofs,

78
00:03:46,860 --> 00:03:49,230
isofs has triggered the dependency,

79
00:03:49,230 --> 00:03:52,710
and for that reason, cdrom is now here.

80
00:03:52,710 --> 00:03:55,440
And that brings us back
to our starting point

81
00:03:55,440 --> 00:03:57,720
modprobe -r cdrom.

82
00:03:57,720 --> 00:04:00,840
It's not going to work,
but at least you know why.

83
00:04:00,840 --> 00:04:02,820
And this concludes the small demo

84
00:04:02,820 --> 00:04:04,683
about managing kernel modules.