9/11/2023 0 Comments Docker entrypoint![]() ![]() When we ran an ubuntu container earlier using “docker run ubuntu”, docker created a container from the ubuntu image and launched a bash program. On startup, CMD will run bash as a default command, but bash is not a continuous process like a web server or database server, it is simply a shell that listens for inputs from the terminal when it doesn’t find any terminal, it exits. Now let’s have a look at our “ubuntu” container Dockerfile that exited a few seconds ago. This instruction defines the process that will run when a container will start. If we look clearly at the above Dockerfile we can see an instruction called CMD. So who defines what process will run within a container? Let’s look at the Dockerfile of a popular docker image nginx. The CMD InstructionĪs we have discussed above that “as soon as a process inside a container stops or crashes, the container stops”. So, as soon as a process inside a container stops or crashes, the container also stops and exits. A container exists as long as some task or process is running or alive in it. An instance to host a web server, an application server, a database or simply to carry out any type of computation. ![]() The container exited because unlike virtual machines containers are not meant to host an operating system! They are meant to run a specific task or a process. ![]() If we run a docker ps -a to list all the stopped containers, now it shows us that our newly created container has exited and is in a stopped state. Now, if we run docker ps to list the running containers, it shows an empty list. When we run a docker run ubuntu command, it will run an instance of an ubuntu image and will exit immediately. Let’s suppose we were to run a docker container from an ubuntu image. We will also get to know how we can use CMD and ENTRYPOINT instructions effectively. We will discuss the usage of the CMD and ENTRYPOINT instructions in Dockerfile. In this blog, we will discuss a topic that constantly confuses the beginners. ![]()
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