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I have just demonstrated you how you are able to use variables when you need to insert, for example,

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path in the Docker run command.

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And notice that if you use variables then it is important in which folder you are located.

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If you use specifically variable because it will actually get path to current folder and place it inside

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of the Docker run command.

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Great.

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Now let me explain you actually what happens when you run container and how you are able to run container

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in background using dash option.

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Okay, let's get started with Hello world container and let's run it once again.

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Docker run.

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Hello world Enter.

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You will see this result in terminal but container exits and I have explained you before that basically

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container exits as soon as there are no processes running inside of the container.

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And in this example, there was process that has printed this text to this terminal and afterwards this

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process was terminated and Docker terminates container afterwards as well.

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Let's try to run another container, for example, Alpine.

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Let's clear our terminal and Docker run Alpine.

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Same happens here.

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Docker runs container.

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It creates process, but this process terminates and afterwards Docker terminates container as well.

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But which process actually starts in this specific container?

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Let me enter Docker history Alpine.

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And here at the top you will see command bin.

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In this case, I'll explain you what this command actually means a bit later.

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But now you should understand and remember that with this command you are able to find at the top specific

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command that is executed as soon as new container is created based on specific image.

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In this case, image name is Alpine.

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So if you create new container with Alpine image, it runs command bin.

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It is actually shell.

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But this process, this process has standard in and standard output and it weights that someone or some

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other process will connect to its standard in and standard output.

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And in such case, this process will be kept running and will accept some characters via standard input

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and may produce some output via standard output STD out.

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But if we simply run container in such way, we don't connect to standard input of this process.

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And that's why this process terminates automatically because there is no standard input connection or

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standard output connection.

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That's what happens under the hood.

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But you are able to connect to standard input of this process.

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If you'll add two flags, Dash I and Dash T, basically you could add only dash flag.

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Let me show you that Docker run dash I Alpine.

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And now I'm connected to standard in of this process bin.

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And if I'll enter, for example, LZ, I will see list of folders inside of the container.

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And if I'll go to another tab and enter Docker.

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PS I'll see list of containers that are currently up and running.

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And again I see here same command as I have shown you just in Docker history output.

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It is command that was automatically executed when container was created.

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And for this specific image alpine image, this command is been.

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But let me now try to exit from this connection to standard input of Shell inside of the container as

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usually let's try to use control C combination and you see it doesn't work.

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The reason for that is that we are connected now directly to specific process and it does not accept

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such termination commands.

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You are also able to try to stop container here using stop command like Docker stop and here maybe is

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or ID of the container or its name.

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For example this one let me copy name paste here, press enter and you will see that the docker is trying

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to stop container.

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Let's wait a bit.

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It actually sends sigterm signal to process.

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But in such case, C is running with process ID one and it doesn't accept any such kind of commands.

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And when Docker is not able to stop container during 10s, it will try to kill it.

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It is actually hard stop of the container and in such case we stop command.

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It will try to perform, let's say soft stop.

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So finally in such case in 10s Docker has stopped this container.

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And of course here in this step we have disconnected from standard input of the.

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Great.

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That's what happens when you try to connect to specific process that actually keeps container running.

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But as soon as process ends, container exits as well.

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Let's try something else.

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Let's clear terminal here and let's try to run Nginx server.

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Docker run Nginx.

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And here you see that we are actually connected to standard input of nginx process.

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We could verify that here.

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Let's go back to this step, clear it and Docker PS and we see that Nginx container is running and here

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you see basically command that was executed.

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And here is actually the name of process that is running inside of the container.

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This process name is Nginx.

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And actually here on this step, we are able to get output from this process.

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And actually in previous lectures we have seen that it produces some logs when clients connect to this

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container.

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Actually, let me show you that quickly.

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Let me terminate this container.

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Actually here I'm able to use control C and let's use port mapping.

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Docker run 80 here, we'll be 80 Nginx.

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Press enter.

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And let's now try to connect to port 80.

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80.

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And connection was successful and here Nginx has served default content.

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Let's go back to this output and here we see actually some text that was produced into standard output

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by nginx process inside of the container.

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Here is this process.

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Great, but how you are able actually to run container in background.

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You are able to use dash option and in such case those logs will be actually created and saved in background

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into log file and you will be able to observe them later on.

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But with option you will get back to terminal because container will be running in background.

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Let me show you that.

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Let me terminate this one clear terminal and here run same container but with option dash D without

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any arguments.

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And you'll simply see ID of the container that was just created.

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We could verify that here in this step Docker.

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PS You see here start characters of this ID and you see that now this container is still running because

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there is running process nginx process, but we have not connected to that process here.

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That's what actually this option does.

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With this option in place, container is started in background and you will get back to your terminal

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window, but container will be still kept running in background.

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Let me try now to connect to our web page here, Refresh page, go back here and of course, in this

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window will not see any logs because again, container is running in background, but you are able to

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read those logs using Docker logs command and use some characters from the ID of specific container

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that is up and running now.

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And I could use, for example, characters nine two that are starting characters of this ID here.

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And let's press enter and you see log that tells us that there was connection to web server and here

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is response code not modified.

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That's how you are able to get logs that were produced by specific process inside of the container.

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And again, this container enginex container is still up and running here because there is a single

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process inside of that container.

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Now you are able, if you want to stop this container using Docker stop command, let me clear terminal

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again Docker PS and get some characters from ID or use this name and use Docker stop command and type

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here for example, nine two and now you see that this container was stopped much faster than previous

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container because previously that container was not listening to any commands.

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And that's why finally in 10s process was killed automatically.

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In such case, this process enginex process listens to such commands and Docker was able to terminate

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this container in soft, let's say, manner.

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That's what option does, and that's how you're able to run such containers as, for example, Nginx

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in background.

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It will not interrupt your current terminal window and you will be able to perform any other actions,

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create other containers and so on.

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Great.

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That's all for this lecture.

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And in the next one let me demonstrate you how you are able to run multiple containers simultaneously

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using same image.

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Let's do that next.

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Bye bye.