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73 lines
3.4 KiB
Markdown
73 lines
3.4 KiB
Markdown
---
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draft: false
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title: "How to find that one volume you're pretty sure you didn't lose"
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date: "2024-06-25"
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series: []
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author: "Nick Dumas"
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cover: ""
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tags: ["bash", "docker"]
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summary: "Docker volumes can be opaque, so I wrote a small bash script to help you troubleshoot."
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showFullContent: false
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---
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## What I expect you to know
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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.
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## The Problem
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Over the lifetime of a Docker host machine, it's like that orphaned volumes ( and other detritus ) will accumulate over time. You might also find yourself fumbling a configuration and orphaning a volume yourself.
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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.
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## Make a list
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Luckily, we have tools at our disposal to handle this. My thought process almost always starts with "Can I turn a list of the things I care about into a newline separated list?" If I can do that, I can start automating my troubleshooting.
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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:
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```
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docker volume ls
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DRIVER VOLUME NAME
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local d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2
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local grafana-storage
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local plausible_db-data
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local plausible_event-data
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```
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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`. Generally, Docker uses Go's `text/template` library to back this feature, and more specifically, individual flags (usually) [document](https://docs.docker.com/reference/cli/docker/volume/ls/#format) the template verbs available. Here, we want `Name`.
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```
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docker volume ls --format "{{.Name}}"
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d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2
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grafana-storage
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plausible_db-data
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plausible_event-data
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```
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And now we have a newline separated list of volume names.
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## Process of elimination
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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/`.
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```
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#! /bin/bash
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# Newline separated list of volume names
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volumes=$(docker volume ls --format="{{.Name}}")
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for volume in $volumes; do
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# Help the user keep track of which volume they're exploring
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echo "Mounting $volume in a temporary image."
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docker run --rm -v $volume:/test/ -it alpine /bin/sh
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done
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```
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Running this script should do something like this:
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```
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./cycle-volumes.sh
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Mounting d35fce052fbce42b94b2f9b2957be0f77090fa006b1a192030eff07db3675af2 in a temporary image.
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/ # ls /test/
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clickhouse-server.err.log clickhouse-server.log.1.gz clickhouse-server.log.4.gz clickhouse-server.log.7.gz
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clickhouse-server.log clickhouse-server.log.2.gz clickhouse-server.log.5.gz clickhouse-server.log.8.gz
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clickhouse-server.log.0.gz clickhouse-server.log.3.gz clickhouse-server.log.6.gz
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/ #
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Mounting grafana-storage in a temporary image.
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/ # ls /test
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alerting csv file-collections grafana.db plugins png
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/ # exit
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Mounting plausible_db-data in a temporary image.
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/ # exit
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Mounting plausible_event-data in a temporary image.
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/ # exit
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```
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You can use bash to explore the volume and identify its contents, make note of which ones are which, and proceed accordingly. |