In this post, I’ve decided to share with you some useful commands and tools I frequently use when working with awesome Docker technology. There is no particular order or “ ” for every I will simply present the use case and how the specific command or tool are helping me with my work. coolness level “hack.” Cleaning Up After working with for some time, you start accumulating development junk: unused volumes, networks, exited containers and unused images. Docker One command to “Rule Them All” $ docker system prune is a very useful command (also works for and sub-commands), but it is only available for . So if you’re using older Docker versions, the following commands can help you to replace the command. prune volume network Docker 1.13 prune Remove dangling volumes volumes are volumes not in use by any container. To remove them, combine two commands: first, list volume IDs for volumes and then remove them. dangling dangling $ docker volume rm $(docker volume ls -q -f “dangling=true”) Remove exited containers The same principle works here too. First, list the containers (only IDs) you want to remove (with filter) and then remove them (consider to force remove). rm -f $ docker rm $(docker ps -q -f “status=exited”) Remove dangling images images are untagged images, that are the leaves of the images tree (not intermediary layers). dangling docker rmi $(docker images -q -f “dangling=true”) Autoremove interactive containers When you run a new interactive container and want to avoid typing command after it exits, use option. Then when you exit from the created container, it will be automatically destroyed. rm --rm $ docker run -it --rm alpine sh Inspect Docker Resources — is a lightweight and flexible command-line processor. It is like for JSON data. You can use it to slice and filter, and map and transform structured data with the same ease that , , and friends let you play with text. jq jq JSON sed sed awk grep and commands can produce output in format. Combine these commands with processor. [docker info](https://docs.docker.com/engine/reference/commandline/info/) [docker inspect](https://docs.docker.com/engine/reference/commandline/inspect/) JSON jq Pretty JSON and jq processing # show whole Docker info$ docker info --format “{{json .}}” | jq . # show Plugins only$ docker info --format “{{json .Plugins}}” | jq . # list IP addresses for all containers connected to ‘bridge’ network $ docker network inspect bridge -f ‘{{json .Containers}}’ \| jq ‘.[] \| {cont: .Name, ip: .IPv4Address}’ Watching Containers Lifecycle Sometimes you want to see containers being activated and exited when you run certain docker commands or try different restart policies. The command combined with can be pretty useful here. I found that the command (even with option) is not useful for this because it doesn’t allow you to see the same information as you can with the command. [watch](http://man7.org/linux/man-pages/man1/watch.1.html) [docker ps](https://docs.docker.com/engine/reference/commandline/ps/) docker stats --format docker ps Display a table with ‘ID Image Status’ for active containers and refresh it every 2 seconds $ watch -n 2 ‘docker ps --format \“table {{.ID}}\t {{.Image}}\t {{.Status}}”’ Enter into Host/Container Namespace Sometimes you want to connect to the Docker host. The command is the default option, but this option may not be available, due to security settings, firewall rules or other undocumented issues (just try googling “how to into Docker for Mac VM” to see what I mean). ssh ssh , by Jérôme Petazzoni, is a small and very useful for this use cases. The command allows you to into ame paces. I like to use the minimalistic ( ) Docker image. [nsenter](https://github.com/jpetazzo/nsenter) tool nsenter enter n s 580 kB walkerlee/nsenter Enter into Docker Host You can use to enter into Docker host namespaces. --pid=host # get a shell into Docker host$ docker run --rm -it --privileged --pid=host \walkerlee/nsenter -t 1 -m -u -i -n sh Enter into ANY Container It’s also possible to enter into any container with and . But in most cases, it’s better to use the standard command. The main difference is that doesn’t enter the , and therefore evades resource limitations (which can be useful for debugging). nsenter --pid=container:[id OR name] [docker exec](https://docs.docker.com/engine/reference/commandline/exec/) nsenter cgroups # get a shell into ‘redis’ container namespace$ docker run --rm -it --privileged --pid=container:redis \walkerlee/nsenter -t 1 -m -u -i -n sh Heredoc Docker Container Sometimes you want to get some tool as a Docker image, but you do not want to search for a suitable image or to create a new (no need to keep it for future use, for example). Sometimes storing Docker image definition in a file looks like an overkill – you need to decide how you edit, store and share this Dockerfile. Sometimes it’s better to have a single line command, that you can copy, share, embed into a shell script or create special command So, when you want to create a new ad-hoc container with a single command, try a approach. Dockerfile alias. Heredoc Create Alpine Based Container with ‘htop’ Tool $ docker build -t htop — << EOFFROM alpineRUN apk --no-cache add htopEOF Docker Command Completion The Docker CLI syntax is very rich and constantly growing: adding new commands and new options. It’s hard to remember every possible command and option, so having a nice command completion for a terminal is a . must have The command completion is a kind of terminal plugin, that lets you auto-complete or auto-suggest what to type in next by hitting the key. Docker command completion works for commands and options. The Docker team prepared command completion for the , and commands, for both and shell. tab docker docker-machine docker-compose Bash Zsh If you are using Mac and , then installing the Docker commands completion is pretty straight forward. Homebrew # Tap homebrew/completion to gain access to these$ brew tap homebrew/completions # Install completions for docker suite$ brew install docker-completion$ brew install docker-compose-completion$ brew install docker-machine-completion If you’re not using Mac, read the official Docker documentation for install instructions: , and . docker engine docker-compose docker-machine Start Containers Automatically When running a process inside a Docker container, a failure may occur due to multiple reasons. In some cases, you can fix it by re-running the failed container. If you are using a Docker orchestration engine, like Swarm or Kubernetes, the failed service will be restarted automatically. If not, then you might want to restart the container based on the of the container’s main process, or always restart (regardless the ). Docker 1.12 introduced the command: for this use case. exit code exit code docker run restart Restart Always Restart the container with a restart policy of so that if the container exits, Docker will restart it. redis always $ docker run --restart=always redis Restart Container on Failure Restart the container with a restart policy of and a maximum restart count of . redis on-failure 10 $ docker run --restart=on-failure:10 redis Network Tricks There are times when you might want to create a new container and connect it to an existing network stack. This might be the Docker host network or another container’s network. This is helpful when debugging and auditing network issues. The option allows you to do this. docker run --network/net Use the Docker host network stack $ docker run --net=host … The new container will attach to the same network interfaces as the Docker host. Use another container’s network stack $ docker run --net=container:<name|id> … The new container will attach to the same network interfaces as the other container. The target container can be specified by or . id name Attachable Overlay Network Using Docker Engine running in , you can create a multi-host network on a manager node. When you create a new , you can attach it to the previously created network. swarm mode overlay swarm service overlay Sometimes you need to attach a new Docker container (filled with different networking tools), to an existing network, in order to inspect the network configuration or debug network issues. You can use the command for this, eliminating the need to create a completely new “debug service”. overlay docker run Docker 1.13 brings a new option to the command: . The option enables manual container attachment. docker network create attachable attachable # create an attachable overlay network$ docker network create --driver overlay --attachable mynet # create net-tools container and attach it to mynet overlay network $ docker run -it --rm --net=mynet net-tools sh I hope you find this post useful. If you have more tricks on your own, please leave them in the comments box! Originally published at codefresh.io on January 5, 2017.
