If you haven’t installed Docker, please read Part 1 of this Docker series.
Managing container lifecycles is more involved than starting and stopping. In this second part of Docker Containers, we show how to administer images locally and on remote repositories. The syntax for maintaining images is the subcommand image. We will cover list/ls/inspect, pull and rm/prune in this article.
Working with Images
List Images
The first part of managing images is to know which images are being used, what their disk utilization is and the image version. Listing images is done in one of two ways: either long docker image list or more Linux/UNIX friendly docker image ls.
docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
python latest e285995a3494 10 days ago 921MB
postgres latest 75993dd36176 10 days ago 376MBInspecting images provides information such as environment variables, parent image, commands used during initialization, network information, volumes and much more. This data is vital when troubleshooting issues with container startup or creating new images. The following is only an excerpt – the actual command has about two pages of data.
docker inspect postgres
[
{
"RepoTags": [
"postgres:latest"
],
"Hostname": "81312c458473",
"ExposedPorts": {
"5432/tcp": {}
},
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/lib/postgresql/14/bin",
"PG_MAJOR=14",
"PG_VERSION=14.5-1.pgdg110+1",
"PGDATA=/var/lib/postgresql/data"
],
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"CMD [\"postgres\"]"
.......Search Repositories
Searching repositories can be accomplished by either going to Docker Hub, or searching by command line, docker search <string>, so you never have to leave the shell. Here’s an example:
docker search postgres
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
postgres The PostgreSQL object-relational database sy… 11486 [OK]
bitnami/postgresql Bitnami PostgreSQL Docker Image 154 [OK]
circleci/postgres The PostgreSQL object-relational database sy… 30
ubuntu/postgres PostgreSQL is an open source object-relation… 19
bitnami/postgresql-repmgr 18
rapidfort/postgresql RapidFort optimized, hardened image for Post… 15Pulling Images
In order to run containers, you will need to pull the image from a repository. This can be accomplished either by docker pull <image name> or docker run <image name> which will automatically pull the image if it doesn’t exist locally. By default, pull will get the latest version, Alternatively, you can specify a version by using a colon, :, after the image name like this: docker pull <image>:4.2.0
docker pull postgres
Using default tag: latest
latest: Pulling from library/postgres
31b3f1ad4ce1: Pull complete
1d3679a4a1a1: Pull complete
667bd4154fa2: Pull complete
87267fb600a9: Pull complete
Digest: sha256:b0ee049a2e347f5ec8c64ad225c7edbc88510a9e34450f23c4079a489ce16268
Status: Downloaded newer image for postgres:latest
docker.io/library/postgres:latestRemoving and Pruning Images
Unfortunately, Docker doesn’t automatically remove images, so disk utilization tends to grow fairly quickly if not managed. Docker has two commands to remove images, prune, rm and rmi. As part of normal maintenance, prune should run in cron every few weeks or once a month depending on how active the system is.
docker image prune – Deletes unused imagesdocker rm <container IDs> – Removes container IDs from the system.docker rmi <image ID> – Remov the image.
docker image prune
WARNING! This will remove all dangling images.
Are you sure you want to continue? [y/N] y
<none> <none> 48e3a3f31a48 10 months ago 999MB
<none> <none> 89108dc97df7 10 months ago 1.37GB
<none> <none> 26e43fa5dd7c 11 months ago 998MB
<none> <none> b98d351f790b 11 months ago 1.37GB
<none> <none> 334a4df3c05a 11 months ago 998MB
<none> <none> 17c5a57654e4 11 months ago 1.37GBPlease checkout the other container articles here.