1
00:00:00,910 --> 00:00:05,560
In this section we're going to continue looking at the darker run command or some slight variations

2
00:00:05,560 --> 00:00:06,250
of it.

3
00:00:06,430 --> 00:00:10,300
Now before I show you the next kind of variations command that we're going to look at I want to give

4
00:00:10,300 --> 00:00:11,730
you one quick reminder.

5
00:00:11,800 --> 00:00:16,900
Remember any time that we execute Docker run with an image we not only get that file system snapshot

6
00:00:17,050 --> 00:00:23,430
but we also get this default command that is supposed to be executed after the container is created.

7
00:00:23,500 --> 00:00:28,390
So the variation on Docker run that we're gonna look at is going to give you a way to override this

8
00:00:28,390 --> 00:00:34,690
default startup command here's how we do it will execute Docker run the image name just like we did

9
00:00:34,690 --> 00:00:40,840
before and then after that we'll supply a alternate command to be executed inside the container after

10
00:00:40,840 --> 00:00:41,950
it starts up.

11
00:00:41,950 --> 00:00:43,240
This is an override.

12
00:00:43,300 --> 00:00:47,940
So whatever default command is included inside of the image is not going to be executed.

13
00:00:47,950 --> 00:00:50,520
Let's try this out right now and just see how it works.

14
00:00:50,560 --> 00:00:50,800
All right.

15
00:00:50,830 --> 00:00:57,530
So I'm going to find my terminal and I'm going to execute Docker run and I'm going to specify my image.

16
00:00:57,550 --> 00:01:00,150
We're going to use a different image than what we used before.

17
00:01:00,220 --> 00:01:02,230
We're going to use an image called Busy Box.

18
00:01:02,230 --> 00:01:08,080
And I'll tell you why in just a moment after that we'll list out the alternate command to execute inside

19
00:01:08,080 --> 00:01:10,180
the container after it is created.

20
00:01:10,180 --> 00:01:16,690
And so I'm going to say that I want to run a command echo Hi there so this right here is the override.

21
00:01:16,690 --> 00:01:19,720
This is a command they'll be executed inside that container.

22
00:01:19,720 --> 00:01:21,480
The Echo command is going to print out.

23
00:01:21,490 --> 00:01:22,000
Hi.

24
00:01:22,060 --> 00:01:22,990
Inside my terminal.

25
00:01:23,170 --> 00:01:27,330
So if this works the way we would expect I'll see the text high there appear.

26
00:01:27,380 --> 00:01:28,110
So going to run that.

27
00:01:28,120 --> 00:01:33,490
And sure enough yep we see that we can change the text provided here to the Echo command as much as

28
00:01:33,490 --> 00:01:34,180
we please.

29
00:01:34,180 --> 00:01:40,630
So I could say by there or I could say how are you.

30
00:01:40,630 --> 00:01:43,280
You get the idea now.

31
00:01:43,290 --> 00:01:46,060
I want to show you a small variation on that command.

32
00:01:46,150 --> 00:01:50,050
And this is going to start to make things a little bit more interesting than just kind of echoing Tex

33
00:01:50,050 --> 00:01:51,450
back over to you.

34
00:01:51,520 --> 00:01:57,250
I want you to run Docker run busy box and then the override command that we're going to use this time

35
00:01:57,280 --> 00:02:02,830
is going to be less if you never used Alice before it's going to print out all the files and folders

36
00:02:02,980 --> 00:02:05,060
inside of a given directory.

37
00:02:05,140 --> 00:02:11,860
So let's try running this and see what happens so according to our docker container when we print out

38
00:02:11,920 --> 00:02:18,520
our files and folders we have been at sea Dev home proc Root says temp user ID var.

39
00:02:18,520 --> 00:02:20,550
These are all folders right here.

40
00:02:20,650 --> 00:02:25,810
And if you are on say a Windows machine right here these folders might look very strange to you and

41
00:02:25,810 --> 00:02:27,620
very unfamiliar.

42
00:02:27,670 --> 00:02:34,260
So in fact these are folders that are being printed out that are not belonging to you on your computer.

43
00:02:34,270 --> 00:02:38,140
These are folders that exist solely inside that container.

44
00:02:38,140 --> 00:02:42,070
I want to remind you about exactly what happens when we create a container out of an image.

45
00:02:42,580 --> 00:02:44,690
So over here we've got the busy box image.

46
00:02:44,830 --> 00:02:50,870
It has some default files system snapshot and some presumably default command.

47
00:02:50,880 --> 00:02:55,860
You know who knows what it is off top of my head but it definitely has this default file system snapshot

48
00:02:56,440 --> 00:03:02,770
that busy box image has default folders of bin Dev Etsy home proc route and so on all the ones you see

49
00:03:02,830 --> 00:03:04,340
listed right here.

50
00:03:04,360 --> 00:03:12,490
So when we create a new container out of that image we take this file system snapshot we stick it in

51
00:03:12,610 --> 00:03:17,590
as the folder for that container and then the command that we execute is less.

52
00:03:17,710 --> 00:03:22,880
So we list out all the files and folders inside of our hard drive which then prints out bin Dev at the

53
00:03:22,880 --> 00:03:26,560
home proc and root so that's pretty much it.

54
00:03:26,580 --> 00:03:30,990
Now one thing you might be all a bit curious about is why we chose to use the busy box image here as

55
00:03:30,990 --> 00:03:34,310
opposed to the hello world one that we were using before.

56
00:03:34,320 --> 00:03:36,570
Well let's go back over to our terminal really quickly.

57
00:03:36,600 --> 00:03:42,870
We're going to try running hello world with the LDS command so I'll do Docker run Hello dash world and

58
00:03:42,870 --> 00:03:48,370
I'll do El s right here and you're gonna very quickly see that we get a kind of nasty error message.

59
00:03:48,390 --> 00:03:51,700
Well let's try doing the echo command and see what happens.

60
00:03:51,930 --> 00:03:55,460
I'll do Docker run hello world echo Hi there.

61
00:03:55,470 --> 00:03:57,970
And we get a very similar error message here as well.

62
00:03:58,200 --> 00:03:59,640
So what's going on.

63
00:03:59,640 --> 00:04:00,570
Well here's the issue.

64
00:04:01,530 --> 00:04:07,830
When we run the alternate commands or those alternate echo and Ellis commands with busy box those commands

65
00:04:07,830 --> 00:04:17,250
work because Ellis and Echo are two programs that exist inside of the busy box file system image somewhere

66
00:04:17,340 --> 00:04:24,720
inside of this folder system right here is a Ellis command or an actual LDS executable and a echo executable

67
00:04:24,750 --> 00:04:25,680
as well.

68
00:04:25,770 --> 00:04:30,870
And so we can safely execute those commands with busy box because those are programs that exist inside

69
00:04:30,870 --> 00:04:32,400
this file system.

70
00:04:32,460 --> 00:04:39,090
However with our hello world program over here the only thing that exists inside this file system snapshot

71
00:04:39,300 --> 00:04:46,320
is a single program like one single file and all that thing does is echo out or kind of print out that

72
00:04:46,320 --> 00:04:49,350
singular message that we saw when we ran that container.

73
00:04:49,350 --> 00:04:55,110
So these startup commands that we are executing are being based upon the file system include with the

74
00:04:55,110 --> 00:04:55,560
image.

75
00:04:55,590 --> 00:05:01,320
And if we tried to execute a command inside the container that uses a program that doesn't or is not

76
00:05:01,410 --> 00:05:05,330
contained within this file system we're going to see that error.

77
00:05:05,370 --> 00:05:05,640
OK.

78
00:05:05,730 --> 00:05:08,670
So a little bit more on Docker on command.

79
00:05:08,670 --> 00:05:11,490
Let's take another quick break right now and continue in the next section.