Docker image usage


When running a container, if the image used does not exist locally, docker will automatically download it from the docker image warehouse. The default is to download from the Docker Hub public image source.

Let’s learn:

  • 1. Manage and use local Docker host images

  • 2. Create images

List the image list

We can use docker images to list the images on the local host. 

php@php:~$ docker images           
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              14.04               90d5884b1ee0        5 days ago          188 MB
php                 5.6                 f40e9e0f10c8        9 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        4 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
training/webapp     latest              6fae60ef3446        11 months ago       348.8 MB

Description of each option:

  • REPOSTITORY: Indicates the warehouse source of the image

  • TAG: Mirror tag

  • ##IMAGE ID:Mirror ID

  • ##CREATED:

    Mirror creation time

  • SIZE:

    Mirror size

    • The same warehouse source can have multiple TAGs, representing this There are different versions of the warehouse source. For example, in the ubuntu warehouse source, there are many different versions such as 15.10, 14.04, etc. We use REPOSTITORY:TAG to define different images.

So, if we want to use the ubuntu system image of version 15.10 to run the container, the command is as follows: 

php@php:~$ docker run -t -i ubuntu:15.10 /bin/bash 
root@d77ccb2e5cca:/#

If we want to use the ubuntu system image of version 14.04 to run the container, the command As follows: 

php@php:~$ docker run -t -i ubuntu:14.04 /bin/bash 
root@39e968165990:/#

If you do not specify a version label for an image, for example, if you only use ubuntu, docker will use the ubuntu:latest image by default.

Get a new image

When we use a non-existent image on the local host, Docker will automatically download the image. If we want to download this image in advance, we can use the docker pull command to download it. 

Cphp@php:~$ docker pull ubuntu:13.10
13.10: Pulling from library/ubuntu
6599cadaf950: Pull complete 
23eda618d451: Pull complete 
f0be3084efe9: Pull complete 
52de432f084b: Pull complete 
a3ed95caeb02: Pull complete 
Digest: sha256:15b79a6654811c8d992ebacdfbd5152fcf3d165e374e264076aa435214a947a3
Status: Downloaded newer image for ubuntu:13.10

After the download is completed, we can directly use this image to run the container.

Find the image
We can search for the image from the Docker Hub website. The Docker Hub URL is:

https://hub.docker.com/

We also You can use the docker search command to search for images. For example, we need an httpd mirror as our web service. We can search httpd through the docker search command to find the image that suits us. 
php@php:~$  docker search httpd

docker35.png

NAME:

The name of the image warehouse source

DESCRIPTION:

The description of the image

OFFICIAL:

Whether docker is officially released

Drag the image

We decided to use the official version of httpd image in the picture above, use the command docker pull to Download the image. 

php@php:~$ docker pull httpd
Using default tag: latest
latest: Pulling from library/httpd
8b87079b7a06: Pulling fs layer 
a3ed95caeb02: Download complete 
0d62ec9c6a76: Download complete 
a329d50397b9: Download complete 
ea7c1f032b5c: Waiting 
be44112b72c7: Waiting

After the download is completed, we can use this image. 

php@php:~$ docker run httpd

Create an image

When the image we download from the docker image warehouse cannot meet our needs, we can change the image in the following two ways.

    1. Update the image from the already created container and submit the image

  • 2. Use the Dockerfile command to create a new image

Update the image

Before updating the image, we need to use the image to create A container. 
php@php:~$ docker run -t -i ubuntu:15.10 /bin/bash
root@e218edb10161:/#
uses the apt-get update command within the running container to update.

After completing the operation, enter the exit command to exit the container.

The container with ID e218edb10161 at this time is a container that has been changed according to our needs. We can submit the container copy through the command docker commit. 

php@php:~$ docker commit -m="has update" -a="php" e218edb10161 php/ubuntu:v2
sha256:70bf1840fd7c0d2d8ef0a42a817eb29f854c1af8f7c59fc03ac7bdee9545aff8

Description of each parameter:

  • -m:Submitted description information

  • -a:Specify the image author

  • ##e218edb10161:Container ID

  • php/ubuntu :v2:Specify the target image name to be created

We can use the

docker images command to view our new imagephp/ubuntu: v2: 

php@php:~$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
php/ubuntu       v2                  70bf1840fd7c        15 seconds ago      158.5 MB
ubuntu              14.04               90d5884b1ee0        5 days ago          188 MB
php                 5.6                 f40e9e0f10c8        9 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        4 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
training/webapp     latest              6fae60ef3446        12 months ago       348.8 MB

Use our new image

php/ubuntu to start a container 

php@php:~$ docker run -t -i php/ubuntu:v2 /bin/bash                            
root@1a9fbdeb5da3:/#

Build the image

We use Command

docker build to create a new image from scratch. To do this, we need to create a Dockerfile that contains a set of instructions to tell Docker how to build our image. 

php@php:~$ cat Dockerfile 
FROM    centos:6.7
MAINTAINER      Fisher "fisher@sudops.com"

RUN     /bin/echo 'root:123456' |chpasswd
RUN     useradd php
RUN     /bin/echo 'php:123456' |chpasswd
RUN     /bin/echo -e "LANG=\"en_US.UTF-8\"" > /etc/default/local
EXPOSE  22
EXPOSE  80
CMD     /usr/sbin/sshd -D

Each command will create a new layer on the image, and the prefix of each command must be uppercase.

The first FROM specifies which image source to use

The RUN command tells docker to execute the command in the image and install what. . .

Then, we use the Dockerfile file to build an image through the docker build command. 

php@php:~$ docker build -t php/centos:6.7 .
Sending build context to Docker daemon 17.92 kB
Step 1 : FROM centos:6.7
 ---> d95b5ca17cc3
Step 2 : MAINTAINER Fisher "fisher@sudops.com"
 ---> Using cache
 ---> 0c92299c6f03
Step 3 : RUN /bin/echo 'root:123456' |chpasswd
 ---> Using cache
 ---> 0397ce2fbd0a
Step 4 : RUN useradd php
......

Parameter description:

  • -t: Specify the target image name to be created

  • .: The directory where the Dockerfile file is located, you can specify the absolute path of the Dockerfile

Use docker images to check that the created image already exists in the list, the image ID is 860c279d2fec

php@php:~$ docker images 
REPOSITORY          TAG                 IMAGE ID            CREATED              SIZE
php/centos       6.7                 860c279d2fec        About a minute ago   190.6 MB
php/ubuntu       v2                  70bf1840fd7c        17 hours ago         158.5 MB
ubuntu              14.04               90d5884b1ee0        6 days ago           188 MB
php                 5.6                 f40e9e0f10c8        10 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago          182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago          324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago          194.4 MB
ubuntu              15.10               4e3b13c8a266        5 weeks ago          136.3 MB
hello-world         latest              690ed74de00f        6 months ago         960 B
centos              6.7                 d95b5ca17cc3        6 months ago         190.6 MB
training/webapp     latest              6fae60ef3446        12 months ago        348.8 MB

We can use the new image to create the container

php@php:~$ docker run -t -i php/centos:6.7  /bin/bash
[root@41c28d18b5fb /]# id php
uid=500(php) gid=500(php) groups=500(php)

From the above we can see that the new image already contains the user php we created

Set the image label

We can use the docker tag command to add a new tag to the image. 

php@php:~$ docker tag 860c279d2fec php/centos:dev

docker tag Image ID, here is 860c279d2fec, user name, image source name (repository name) and new tag name (tag).

Using the docker images command, you can see that the image with the ID 860c279d2fec has one more label. 

php@php:~$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
php/centos       6.7                 860c279d2fec        5 hours ago         190.6 MB
php/centos       dev                 860c279d2fec        5 hours ago         190.6 MB
php/ubuntu       v2                  70bf1840fd7c        22 hours ago        158.5 MB
ubuntu              14.04               90d5884b1ee0        6 days ago          188 MB
php                 5.6                 f40e9e0f10c8        10 days ago         444.8 MB
nginx               latest              6f8d099c3adc        13 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        5 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
centos              6.7                 d95b5ca17cc3        6 months ago        190.6 MB
training/webapp     latest              6fae60ef3446        12 months ago       348.8 MB

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