Container

In order to remove all docker network interfaces (including all the bridge interfaces), run

docker network rm $(docker network ls -q)

in your favourite shell.

This will attempt to remove some pre-defined networks that can’t be removed and hence show you these error messages:

Error response from daemon: bridge is a pre-defined network and cannot be removed
Error response from daemon: host is a pre-defined network and cannot be removed
Error response from daemon: none is a pre-defined network and cannot be removed

You can safely ignore those error messages.

Problem:

You want to start docker container but you see an error message like this:

docker: invalid reference format.

Solution:

Docker is telling you that the syntax of the docker image name (& version) is wrong. Note that this is not the same as docker not being able to find the image in the registry. Docker will not even be able to lookup the image in the registry if you see an invalid reference format error!

Common causes include:

• You used a colon at the end of the image name, e.g. ubuntu: – omit the colon ; using just ubuntu will refer to ubuntu:latest
• You used a dash at the end of the image name, e.g. ubuntu- – omit the dash ; using just ubuntu will refer to ubuntu:latest
• You used variables like ubuntu:$VERSION but $VERSION is not set. Ensure you have set $VERSION to an appropriate (non-empty) value like latest or 18.04!
• You used multiple colons like ubuntu:18.04:2 or ubuntu:ubuntu:18.04. Use only a single colon in the image name!
• You mixed up the order of command line arguments, so another argument is being interpreted as the image name. Check the syntax of your docker command, e.g. docker run and compare some examples with your command.

If you want to interactively edit a file in a docker container, you might want to install an editor like GNU nano (for example to debug your config files) in your Docker container that allows you direct access to the container’s file system.

docker exec -it [container name or ID] bash -c 'apt-get -y update && apt -y install nano'

This will work for most debian/Ubuntu-based containers ; for other containers you might need to use a package manager other than apt

Now you can use docker exec -it to interactively edit a config file, e.g.:

docker exec -it [container name or ID] nano /etc/host.conf

docker exec runs a program in a container that’s already running. For example, you can use it to create a backup in a container that currently runs your database server.

docker run starts a new container and runs a command in it. For example, your can use it to run a specific script in a container.

Note: This will only remove docker images without a tag, but not all images not associated to a running or stopped container. See our post on How to automatically cleanup (prune) docker images daily in case this is not the desired behaviour.

docker image prune provides an easy way to remove “unused” (i.e. untagged) docker images from a system and hence fixes or significantly delays docker eating up all your disk space on.

I created a systemd-timer based daily prune routine using TechOverflow’s Simple systemd timer generator.

Quick install using

wget -qO- https://techoverflow.net/scripts/install-cleanup-docker.sh | sudo bash

This is the script which automatically creates & installs both systemd config files.

#!/bin/sh
# This script installs automated docker cleanup via "docker image prune"
# onto systemd-based systems.
# It requires that docker is installed properly

cat >/etc/systemd/system/PruneDocker.service <<EOF
[Unit]
Description=PruneDocker

[Service]
Type=oneshot
ExecStart=/usr/bin/docker image prune -f
WorkingDirectory=/tmp
EOF

cat >/etc/systemd/system/PruneDocker.timer <<EOF
[Unit]
Description=PruneDocker

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target
EOF

# Enable and start service
systemctl enable PruneDocker.timer && sudo systemctl start PruneDocker.timer

To view logs, use

journalctl -xfu PruneDocker.service

To view the status, use

sudo systemctl status PruneDocker.timer

To immediately cleanup your docker images, use

sudo systemctl start PruneDocker.service

Use

docker image prune -f

to remove all unused/old (“dangling”) docker images. -f will skip the confirmation prompt.

This command will remove all images that a) don’t have a tag themselves and b) no image with a tag depends on the image.

Example output:

Deleted Images:
deleted: sha256:b6e0e69c6ba1e811063921d18b52627a9fb905e0bdfd80e226e86958831df636
[...]
deleted: sha256:6a40d04ddf00ad0f1806df7b2d4a2d44a6d8031cab5c369a4bf3d1694d5c48b4

Total reclaimed space: 985.3MB

Problem:

When running docker-compose start, you see an error message like this:

Starting mongodb     ... error
Starting myapp       ... error

ERROR: No containers to start

Solution:

In order to start your containers, use docker-compose up, instead of docker-compose start!

Start all services

docker-compose up -d

Stop all services

docker-compose down

docker-compose restart

docker-compose pull
docker-compose restart

View logs

docker-compose logs

To view and follow use

docker-compose logs -f

Start a specific service (and all the services it depends on)

docker-compose start myservice

Show info about which container images are being used

docker-compose images

Run this command in your shell:

docker rm $(docker ps -a -q)