To build your own custom docker image, you need to pull a base image first. Lets start with Ubuntu. You can find more about Ubuntu image at

https://hub.docker.com/_/ubuntu/

Lets pull Ubuntu 16.04 image

docker pull ubuntu:16.04

root@boby:~# docker pull ubuntu:16.04
16.04: Pulling from library/ubuntu
d54efb8db41d: Pull complete 
f8b845f45a87: Pull complete 
e8db7bf7c39f: Pull complete 
9654c40e9079: Pull complete 
6d9ef359eaaa: Pull complete 
Digest: sha256:dd7808d8792c9841d0b460122f1acf0a2dd1f56404f8d1e56298048885e45535
Status: Downloaded newer image for ubuntu:16.04
root@boby:~# 

Now Ubuntu image is available on your docker installation. Lets verify it with command

docker images

Example

root@boby:~# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              16.04               0ef2e08ed3fa        4 weeks ago         130 MB
root@boby:~# 

Run container with terminal

To install software and create your own image, you need to start it with

docker run -ti ubuntu /bin/bash

Example

root@boby:~# docker run -ti ubuntu /bin/bash
Unable to find image 'ubuntu:latest' locally
latest: Pulling from library/ubuntu
Digest: sha256:dd7808d8792c9841d0b460122f1acf0a2dd1f56404f8d1e56298048885e45535
Status: Downloaded newer image for ubuntu:latest
root@e0039fd6fc1e:/# 

Now you are inside the container, lets install some software.

apt update && apt -y upgrade
apt -y install nginx

You have nginx installed, exit the container

exit

This will stop running container.

root@boby:~# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
root@boby:~# 

To see the container, run

docker ps -a

Example

root@boby:~# docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                      PORTS               NAMES
e0039fd6fc1e        ubuntu              "/bin/bash"         4 minutes ago       Exited (0) 57 seconds ago                       pensive_kalam
root@boby:~# 

Now lets commit the container as our own for later use

docker commit -m "my nginx install" e0039fd6fc1e hostonnet/nginx:1

Example

root@boby:~# docker commit -m "my nginx install" e0039fd6fc1e hostonnet/nginx:1
sha256:98a9ccdf456ba6d08c9dc3ac63079c6896298c37c5b5fe07de6f6c47506d4168
root@boby:~# 

To see the available images, run

docker images

You can see the new image now listed

root@boby:~# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
hostonnet/nginx     1                   98a9ccdf456b        36 seconds ago      254 MB
ubuntu              16.04               0ef2e08ed3fa        4 weeks ago         130 MB
ubuntu              latest              0ef2e08ed3fa        4 weeks ago         130 MB
root@boby:~# 

Lets run our newly created image.

root@boby:~# docker run -ti hostonnet/nginx:1 /bin/bash
root@2af374559746:/# service nginx status
 * nginx is not running
root@2af374559746:/# 

As you can see, this image have nginx already installed. Lets install PHP with apt install php, then exit the container.

Commit the new container with

root@boby:~# docker commit -m "installed php" 3199ecaef06a hostonnet/nginx:2.0
sha256:57f7c9cea522d278b126fa5d3e79c3016e48ffe389efd9fc11641a1d89d28de7
root@boby:~# 

Run the container, verify php is available

root@boby:~# docker run -ti hostonnet/nginx:2.0 /bin/bash
root@b0d9d40a9818:/# php -v
PHP 7.0.15-0ubuntu0.16.04.4 (cli) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.15-0ubuntu0.16.04.4, Copyright (c) 1999-2017, by Zend Technologies
root@b0d9d40a9818:/# exit
root@boby:~#