github.com/fcwu/docker@v1.4.2-0.20150115145920-2a69ca89f0df/docs/sources/userguide/dockerizing.md (about) 1 page_title: Dockerizing Applications: A "Hello world" 2 page_description: A simple "Hello world" exercise that introduced you to Docker. 3 page_keywords: docker guide, docker, docker platform, virtualization framework, how to, dockerize, dockerizing apps, dockerizing applications, container, containers 4 5 # Dockerizing Applications: A "Hello world" 6 7 *So what's this Docker thing all about?* 8 9 Docker allows you to run applications inside containers. Running an 10 application inside a container takes a single command: `docker run`. 11 12 ## Hello world 13 14 Let's try it now. 15 16 $ sudo docker run ubuntu:14.04 /bin/echo 'Hello world' 17 Hello world 18 19 And you just launched your first container! 20 21 So what just happened? Let's step through what the `docker run` command 22 did. 23 24 First we specified the `docker` binary and the command we wanted to 25 execute, `run`. The `docker run` combination *runs* containers. 26 27 Next we specified an image: `ubuntu:14.04`. This is the source of the container 28 we ran. Docker calls this an image. In this case we used an Ubuntu 14.04 29 operating system image. 30 31 When you specify an image, Docker looks first for the image on your 32 Docker host. If it can't find it then it downloads the image from the public 33 image registry: [Docker Hub](https://hub.docker.com). 34 35 Next we told Docker what command to run inside our new container: 36 37 /bin/echo 'Hello world' 38 39 When our container was launched Docker created a new Ubuntu 14.04 40 environment and then executed the `/bin/echo` command inside it. We saw 41 the result on the command line: 42 43 Hello world 44 45 So what happened to our container after that? Well Docker containers 46 only run as long as the command you specify is active. Here, as soon as 47 `Hello world` was echoed, the container stopped. 48 49 ## An Interactive Container 50 51 Let's try the `docker run` command again, this time specifying a new 52 command to run in our container. 53 54 $ sudo docker run -t -i ubuntu:14.04 /bin/bash 55 root@af8bae53bdd3:/# 56 57 Here we've again specified the `docker run` command and launched an 58 `ubuntu:14.04` image. But we've also passed in two flags: `-t` and `-i`. 59 The `-t` flag assigns a pseudo-tty or terminal inside our new container 60 and the `-i` flag allows us to make an interactive connection by 61 grabbing the standard in (`STDIN`) of the container. 62 63 We've also specified a new command for our container to run: 64 `/bin/bash`. This will launch a Bash shell inside our container. 65 66 So now when our container is launched we can see that we've got a 67 command prompt inside it: 68 69 root@af8bae53bdd3:/# 70 71 Let's try running some commands inside our container: 72 73 root@af8bae53bdd3:/# pwd 74 / 75 root@af8bae53bdd3:/# ls 76 bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var 77 78 You can see we've run the `pwd` to show our current directory and can 79 see we're in the `/` root directory. We've also done a directory listing 80 of the root directory which shows us what looks like a typical Linux 81 file system. 82 83 You can play around inside this container and when you're done you can 84 use the `exit` command or enter Ctrl-D to finish. 85 86 root@af8bae53bdd3:/# exit 87 88 As with our previous container, once the Bash shell process has 89 finished, the container is stopped. 90 91 ## A Daemonized Hello world 92 93 Now a container that runs a command and then exits has some uses but 94 it's not overly helpful. Let's create a container that runs as a daemon, 95 like most of the applications we're probably going to run with Docker. 96 97 Again we can do this with the `docker run` command: 98 99 $ sudo docker run -d ubuntu:14.04 /bin/sh -c "while true; do echo hello world; sleep 1; done" 100 1e5535038e285177d5214659a068137486f96ee5c2e85a4ac52dc83f2ebe4147 101 102 Wait what? Where's our "Hello world" Let's look at what we've run here. 103 It should look pretty familiar. We ran `docker run` but this time we 104 specified a flag: `-d`. The `-d` flag tells Docker to run the container 105 and put it in the background, to daemonize it. 106 107 We also specified the same image: `ubuntu:14.04`. 108 109 Finally, we specified a command to run: 110 111 /bin/sh -c "while true; do echo hello world; sleep 1; done" 112 113 This is the (hello) world's silliest daemon: a shell script that echoes 114 `hello world` forever. 115 116 So why aren't we seeing any `hello world`'s? Instead Docker has returned 117 a really long string: 118 119 1e5535038e285177d5214659a068137486f96ee5c2e85a4ac52dc83f2ebe4147 120 121 This really long string is called a *container ID*. It uniquely 122 identifies a container so we can work with it. 123 124 > **Note:** 125 > The container ID is a bit long and unwieldy and a bit later 126 > on we'll see a shorter ID and some ways to name our containers to make 127 > working with them easier. 128 129 We can use this container ID to see what's happening with our `hello world` daemon. 130 131 Firstly let's make sure our container is running. We can 132 do that with the `docker ps` command. The `docker ps` command queries 133 the Docker daemon for information about all the containers it knows 134 about. 135 136 $ sudo docker ps 137 CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 138 1e5535038e28 ubuntu:14.04 /bin/sh -c 'while tr 2 minutes ago Up 1 minute insane_babbage 139 140 Here we can see our daemonized container. The `docker ps` has returned some useful 141 information about it, starting with a shorter variant of its container ID: 142 `1e5535038e28`. 143 144 We can also see the image we used to build it, `ubuntu:14.04`, the command it 145 is running, its status and an automatically assigned name, 146 `insane_babbage`. 147 148 > **Note:** 149 > Docker automatically names any containers you start, a 150 > little later on we'll see how you can specify your own names. 151 152 Okay, so we now know it's running. But is it doing what we asked it to do? To see this 153 we're going to look inside the container using the `docker logs` 154 command. Let's use the container name Docker assigned. 155 156 $ sudo docker logs insane_babbage 157 hello world 158 hello world 159 hello world 160 . . . 161 162 The `docker logs` command looks inside the container and returns its standard 163 output: in this case the output of our command `hello world`. 164 165 Awesome! Our daemon is working and we've just created our first 166 Dockerized application! 167 168 Now we've established we can create our own containers let's tidy up 169 after ourselves and stop our daemonized container. To do this we use the 170 `docker stop` command. 171 172 $ sudo docker stop insane_babbage 173 insane_babbage 174 175 The `docker stop` command tells Docker to politely stop the running 176 container. If it succeeds it will return the name of the container it 177 has just stopped. 178 179 Let's check it worked with the `docker ps` command. 180 181 $ sudo docker ps 182 CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 183 184 Excellent. Our container has been stopped. 185 186 # Next steps 187 188 Now we've seen how simple it is to get started with Docker let's learn how to 189 do some more advanced tasks. 190 191 Go to [Working With Containers](/userguide/usingdocker). 192