WEBVTT 00:00.960 --> 00:02.550 -: In this section, we're going to continue looking 00:02.550 --> 00:06.450 at the docker run command or some slight variations of it. 00:06.450 --> 00:08.940 Now, before I show you the next kind of variations command 00:08.940 --> 00:09.810 that we're gonna look at, 00:09.810 --> 00:11.790 I wanna give you one quick reminder. 00:11.790 --> 00:15.060 Remember, any time that we execute docker run with an image, 00:15.060 --> 00:17.100 we not only get that file system snapshot, 00:17.100 --> 00:19.230 but we also get this default command 00:19.230 --> 00:20.820 that is supposed to be executed 00:20.820 --> 00:22.623 after the container is created. 00:23.550 --> 00:25.950 So, the variation on docker run that we're gonna look at 00:25.950 --> 00:28.260 is gonna give you a way to override 00:28.260 --> 00:29.853 this default startup command. 00:30.780 --> 00:31.800 Here's how we do it. 00:31.800 --> 00:34.200 We'll execute docker run, the image name, 00:34.200 --> 00:35.430 just like we did before, 00:35.430 --> 00:38.370 and then after that we'll supply a alternate command 00:38.370 --> 00:41.970 to be executed inside the container after it starts up. 00:41.970 --> 00:43.320 This is an override. 00:43.320 --> 00:46.110 So, whatever default command is included inside of the image 00:46.110 --> 00:47.970 is not going to be executed. 00:47.970 --> 00:50.550 Let's try this out right now and just see how it works. 00:50.550 --> 00:52.740 All right, so I'm going to find my terminal 00:52.740 --> 00:55.380 and I'm gonna execute docker run, 00:55.380 --> 00:57.600 and now I'm going to specify my image. 00:57.600 --> 01:00.240 We're gonna use a different image than what we used before. 01:00.240 --> 01:02.280 We're gonna use an image called busybox, 01:02.280 --> 01:04.530 and I'll tell you why in just a moment. 01:04.530 --> 01:07.080 After that, we'll list out the alternate command 01:07.080 --> 01:10.200 to execute inside the container after it is created. 01:10.200 --> 01:12.480 And so, I'm gonna say that I want to run a command, 01:12.480 --> 01:14.013 echo hi there. 01:15.000 --> 01:16.740 So, this right here is the override. 01:16.740 --> 01:19.740 This is a command that we executed inside that container. 01:19.740 --> 01:21.457 The echo command is going to print out 01:21.457 --> 01:23.220 "hi there" inside my terminal. 01:23.220 --> 01:25.290 So, if this works the way we would expect 01:25.290 --> 01:27.420 I'll see the text "hi there" appear. 01:27.420 --> 01:30.540 So, I'm gonna run that and sure enough, yep, we see that. 01:30.540 --> 01:32.070 We can change the text provided here 01:32.070 --> 01:34.230 to the echo command as much as we please. 01:34.230 --> 01:39.230 So I could say, "bye there," or I could say, "how are you?" 01:40.650 --> 01:41.583 You get the idea. 01:42.830 --> 01:46.170 Now, I wanna show you a small variation on that command, 01:46.170 --> 01:47.820 and this is going to start to make things 01:47.820 --> 01:48.810 a little bit more interesting 01:48.810 --> 01:51.540 than just kind of echoing text back over to you. 01:51.540 --> 01:54.840 I want you to run docker run, busybox, 01:54.840 --> 01:57.330 and then the override command that we're gonna use this time 01:57.330 --> 01:59.190 is going to be ls. 01:59.190 --> 02:00.570 If you've never used ls before, 02:00.570 --> 02:03.000 it's gonna print out all the files and folders 02:03.000 --> 02:05.160 inside of a given directory. 02:05.160 --> 02:07.560 So, let's try running this and see what happens. 02:08.820 --> 02:11.190 So, according to our docker container, 02:11.190 --> 02:13.260 when we print out our files and folders, 02:13.260 --> 02:16.380 we have bin at C, dev, home, proc, root, 02:16.380 --> 02:18.570 system, user and var. 02:18.570 --> 02:20.640 These are all folders right here. 02:20.640 --> 02:23.580 And, if you are on, say, a Windows machine right here, 02:23.580 --> 02:25.680 these folders might look very strange to you 02:25.680 --> 02:27.660 and very unfamiliar. 02:27.660 --> 02:30.300 So, in fact, these are folders that are being printed out 02:30.300 --> 02:34.290 that are not belonging to you on your computer. 02:34.290 --> 02:38.160 These are folders that exist solely inside that container. 02:38.160 --> 02:40.230 I wanna remind you about exactly what happens 02:40.230 --> 02:42.600 when we create a container out of an image. 02:42.600 --> 02:44.850 So, over here we've got the busybox image, 02:44.850 --> 02:48.600 it has some default file system snapshot 02:48.600 --> 02:50.910 and some presumably default command. 02:50.910 --> 02:53.250 You know, who knows what it is off top of my head 02:53.250 --> 02:56.520 but it definitely has this default file system snapshot. 02:56.520 --> 02:59.190 The busybox image has default folders 02:59.190 --> 03:02.010 of bin, dev, at C, home, proc, root, and so on. 03:02.010 --> 03:04.380 All the ones that you see listed right here. 03:04.380 --> 03:07.680 So, when we create a new container out of that image, 03:07.680 --> 03:10.443 we take this file system snapshot, 03:11.670 --> 03:14.430 we stick it in as the folder for that container, 03:14.430 --> 03:17.730 and then the command that we execute is ls. 03:17.730 --> 03:19.740 So we list out all the files and folders 03:19.740 --> 03:21.060 inside of our hard drive, 03:21.060 --> 03:24.990 which then prints out bin, dev, at C home, proc and route. 03:24.990 --> 03:26.610 So, that's pretty much it. 03:26.610 --> 03:28.230 Now, one thing you might be a little bit curious about 03:28.230 --> 03:30.840 is why we chose to use the busybox image here 03:30.840 --> 03:34.350 as opposed to the hello world one that we were using before. 03:34.350 --> 03:36.357 Well, let's go back over to our terminal really quickly 03:36.357 --> 03:39.810 and we're gonna try running hello world with the ls command. 03:39.810 --> 03:42.780 So I'll do a docker run, hello dash world, 03:42.780 --> 03:44.313 and I'll do ls right here. 03:45.150 --> 03:46.050 And you're gonna very quickly 03:46.050 --> 03:48.420 see that we get a kind of nasty error message. 03:48.420 --> 03:51.645 Well, let's try doing the echo command and see what happens. 03:51.645 --> 03:55.500 I'll do docker run, hello world, echo hi there, 03:55.500 --> 03:58.230 and we get a very similar error message here as well. 03:58.230 --> 03:59.670 So, what's going on? 03:59.670 --> 04:01.560 Well, here's the issue. 04:01.560 --> 04:05.160 When we run the alternate commands or those alternate echo 04:05.160 --> 04:07.170 and ls commands with busybox, 04:07.170 --> 04:08.400 those commands work 04:08.400 --> 04:12.930 because ls and echo are two programs that exist 04:12.930 --> 04:16.620 inside of the busybox file system image. 04:16.620 --> 04:19.470 Somewhere inside of this folder system right here 04:19.470 --> 04:23.040 is a ls command or an actual ls executable 04:23.040 --> 04:25.710 and a echo executable as well. 04:25.710 --> 04:28.440 And so we can safely execute those commands with busybox 04:28.440 --> 04:29.700 because those are programs 04:29.700 --> 04:32.490 that exist inside this file system. 04:32.490 --> 04:36.060 However, with our hello world program over here, 04:36.060 --> 04:38.991 the only thing that exists inside this file system snapshot 04:38.991 --> 04:43.260 is a single program, like one single file 04:43.260 --> 04:45.360 and all that thing does is echo out 04:45.360 --> 04:47.250 or kind of print out that singular message 04:47.250 --> 04:49.380 that we saw when we ran that container. 04:49.380 --> 04:52.200 So, these startup commands that we are executing 04:52.200 --> 04:54.570 are being based upon the file system 04:54.570 --> 04:55.650 included with the image. 04:55.650 --> 04:58.200 And if we try to execute a command inside the container 04:58.200 --> 05:01.920 that uses a program that is not contained 05:01.920 --> 05:05.340 within this file system, we're going to see that air. 05:05.340 --> 05:08.700 Okay, so a little bit more on docker run command. 05:08.700 --> 05:10.020 Let's take another quick break right now 05:10.020 --> 05:11.673 and continue in the next section.