Docker Image Usage
When running a container, if the image used does not exist locally, Docker will automatically download it from the Docker image repository, with the default being the Docker Hub public image source.
Let's learn:
- Managing and using local Docker host images
- Creating images
Listing Image List
We can use docker images to list the images on the local host.
tutorialpro@tutorialpro:~$ 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
Option descriptions:
- REPOSITORY: Indicates the image repository source
- TAG: Image tag
- IMAGE ID: Image ID
- CREATED: Image creation time
- SIZE: Image size
The same repository source can have multiple TAGs, representing different versions of the repository source. For example, in the ubuntu repository source, there are multiple versions like 15.10, 14.04, etc. We use REPOSITORY:TAG to define different images.
So, if we want to use the ubuntu system image version 15.10 to run a container, the command is as follows:
tutorialpro@tutorialpro:~$ docker run -t -i ubuntu:15.10 /bin/bash
root@d77ccb2e5cca:/#
Parameter explanations:
- -i: Interactive operation.
- -t: Terminal.
- ubuntu:15.10: This means using the ubuntu 15.10 image as the base to start the container.
- /bin/bash: The command following the image name is the command we want to execute, here we want an interactive shell, so we use /bin/bash.
If you want to use the ubuntu system image version 14.04 to run a container, the command is as follows:
tutorialpro@tutorialpro:~$ docker run -t -i ubuntu:14.04 /bin/bash
root@39e968165990:/#
If you do not specify a version tag for an image, such as just using ubuntu, Docker will default to using the ubuntu:latest image.
Getting a New Image
When we use an image that does not exist on the local host, Docker will automatically download that image. If we want to download the image in advance, we can use the docker pull command.
tutorialpro@tutorialpro:~$ 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 downloading, we can directly use this image to run a container.
Finding Images
We can search for images on the Docker Hub website. The Docker Hub URL is: **
We can also use the docker search command to search for images. For example, if we need an httpd image for our web service, we can search for httpd using the docker search command.
tutorialpro@tutorialpro:~$ docker search httpd
Click on the image to view it in full size:
NAME: Image repository source name DESCRIPTION: Image description OFFICIAL: Whether it is an official Docker release stars: Similar to stars in Github, it indicates likes or favorites. AUTOMATED: Automated build.
Pulling an Image
We decided to use the official httpd image from the above list, and we use the docker pull command to download the image.
tutorialpro@tutorialpro:~$ 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 downloading, we can use this image.
tutorialpro@tutorialpro:~$ docker run httpd
Deleting an Image
To delete an image, we use the docker rmi command, for example, to delete the hello-world image:
$ docker rmi hello-world
Creating an Image
When the image downloaded from the Docker image repository does not meet our needs, we can modify the image in two ways:
- Update the image from a created container and commit this image
- Create a new image using the Dockerfile instruction
Updating an Image
tutorialpro@tutorialpro:~$ docker run -t -i ubuntu:15.10 /bin/bash
root@e218edb10161:/#
Use the apt-get update command inside the running container to update.
After completing the operations, exit the container by typing exit.
The container with ID e218edb10161 is now modified according to our needs. We can commit the container副本 using the docker commit command.
tutorialpro@tutorialpro:~$ docker commit -m="has update" -a="tutorialpro" e218edb10161 tutorialpro/ubuntu:v2
sha256:70bf1840fd7c0d2d8ef0a42a817eb29f854c1af8f7c59fc03ac7bdee9545aff8
Parameter explanations:
- -m: Commit description message
- -a: Specify the image author
- e218edb10161: Container ID
- tutorialpro/ubuntu:v2: Specify the target image name to be created
We can use the docker images command to view our new image tutorialpro/ubuntu:v2:
tutorialpro@tutorialpro:~$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
tutorialpro/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 tutorialpro/ubuntu to start a container:
tutorialpro@tutorialpro:~$ docker run -t -i tutorialpro/ubuntu:v2 /bin/bash
root@1a9fbdeb5da3:/#
Building an Image
We use the docker build command to create a new image from scratch. To do this, we need to create a Dockerfile file that contains a set of instructions to tell Docker how to build our image.
tutorialpro@tutorialpro:~$ cat Dockerfile
FROM centos:6.7
MAINTAINER Fisher "[email protected]"
RUN /bin/echo 'root:123456' |chpasswd
RUN useradd tutorialpro
RUN /bin/echo 'tutorialpro:123456' |chpasswd
RUN /bin/echo -e "LANG=\"en_US.UTF-8\"" >/etc/default/local
EXPOSE 22
EXPOSE 80
CMD /usr/sbin/sshd -D
Each instruction creates a new layer on the image, and each instruction must be prefixed with a capital letter.
The first FROM specifies which base image to use.
The RUN instruction tells Docker to execute commands inside the image, such as installing software.
We then use the Dockerfile to build an image with the docker build command.
tutorialpro@tutorialpro:~$ docker build -t tutorialpro/centos:6.7 .
Sending build context to Docker daemon 17.92 kB
Step 1 : FROM centos:6.7
---> d95b5ca17cc3
Step 2 : MAINTAINER Fisher "[email protected]"
---> Using cache
---> 0c92299c6f03
Step 3 : RUN /bin/echo 'root:123456' |chpasswd
---> Using cache
---> 0397ce2fbd0a
Step 4 : RUN useradd tutorialpro
......
Parameter explanation:
- -t: Specifies the target image name.
- .: The directory where the Dockerfile is located, or the absolute path to the Dockerfile.
Using docker images to view the created image, which is now listed with the image ID 860c279d2fec.
tutorialpro@tutorialpro:~$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
tutorialpro/centos 6.7 860c279d2fec About a minute ago 190.6 MB
tutorialpro/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 a container.
tutorialpro@tutorialpro:~$ docker run -t -i tutorialpro/centos:6.7 /bin/bash
[root@41c28d18b5fb /]# id tutorialpro
uid=500(tutorialpro) gid=500(tutorialpro) groups=500(tutorialpro)
From the above, we see that the new image includes the user tutorialpro.
Setting Image Tags
We can use the docker tag command to add a new tag to the image.
tutorialpro@tutorialpro:~$ docker tag 860c279d2fec tutorialpro/centos:dev
The docker tag command uses the image ID (here, 860c279d2fec), the username, repository name, and the new tag.
Using docker images, we can see that the image with ID 860c279d2fec now has an additional tag.
tutorialpro@tutorialpro:~$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
tutorialpro/centos 6.7 860c279d2fec 5 hours ago 190.6 MB
tutorialpro/centos dev 860c279d2fec 5 hours ago 190.6 MB
tutorialpro/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