What I expect you to know #
This article is only relevant if you know about and use Docker volumes and have some fluency in bash. I’ll explain the code as I go, if it helps.
The Problem #
Over the lifetime of a Docker host machine, it’s likely that orphaned volumes and other detritus will accumulate over time. You might find yourself fumbling a configuration and orphaning a volume yourself. However we got here, we have a bunch of volumes and we need to know if any of them are important. In a perfect world, they’ll have decent names.
We don’t live in a perfect world.
Make a list #
Luckily, we have tools at our disposal to handle this. My thought process almost always starts with “Can I make a newline separated list of the things I care about?” If I can do that, I can start automating my troubleshooting.
Let’s start with docker volume ls
. This is how we list volumes, but the default output isn’t quite what I’m looking for:
docker volume ls
DRIVER VOLUME NAME
local d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2
local grafana-storage
local plausible_db-data
local plausible_event-data
This is human readable, and we could even do some slicing with cut
or awk
, but Docker gives us a flag that will take us exactly where we need to go: --format
. Docker uses Go’s text/template
library to power this feature and individual flags (usually) document the template verbs available. Here, we want Name
.
docker volume ls --format "{{.Name}}"
d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2
grafana-storage
plausible_db-data
plausible_event-data
We now have a newline separated list of volume names.
Process of elimination #
The next part is fairly straightforward. We loop over this list and ask Docker to create a temporary container based on alpine, with a single volume mounted at /test/
.
#! /bin/bash
# Newline separated list of volume names
volumes=$(docker volume ls --format="{{.Name}}")
for volume in $volumes; do
# Help the user keep track of which volume they're exploring
echo "Mounting $volume in a temporary image."
docker run --rm -v $volume:/test/ -it alpine /bin/sh
done
Running this script should do something like this:
./cycle-volumes.sh
Mounting d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2 in a temporary image.
/ # ls /test/
clickhouse-server.err.log clickhouse-server.log.1.gz clickhouse-server.log.4.gz clickhouse-server.log.7.gz
clickhouse-server.log clickhouse-server.log.2.gz clickhouse-server.log.5.gz clickhouse-server.log.8.gz
clickhouse-server.log.0.gz clickhouse-server.log.3.gz clickhouse-server.log.6.gz
/ #
Mounting grafana-storage in a temporary image.
/ # ls /test
alerting csv file-collections grafana.db plugins png
/ # exit
Mounting plausible_db-data in a temporary image.
/ # exit
Mounting plausible_event-data in a temporary image.
/ # exit
You can use bash to explore the volume and identify its contents, make note of which ones are which, and proceed accordingly.