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69 lines
2.1 KiB
Markdown
69 lines
2.1 KiB
Markdown
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---
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title: "Auto Purge Old Docker Images"
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date: 2020-09-28T23:30:22-04:00
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draft: false
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tags: []
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---
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I use [Watchtower](https://github.com/containrrr/watchtower) to automatically update the docker images I use. After leaving it for several months, I've realized that I have been storing over 100GB of old docker images. I needed a way to automatically purge old images and [Systemd Timers](https://opensource.com/article/20/7/systemd-timers) is the solution.
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First it's useful to know the docker command that purges unused images that are older than 24 hours old.
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```bash
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docker image prune -fa --filter "until=24h"
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```
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Then we can create a oneshot service file that will describe its dependencies and descriptions for Systemd to manage. This file is `/etc/systemd/system/docker-purge.service`.
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```yml
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[Unit]
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Description=Purge Docker Images Older than 24 Hours
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Requires=docker.service
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Wants=docker-purge.timer
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[Service]
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Type=oneshot
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ExecStart=/usr/bin/docker image prune -fa --filter "until=24h"
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[Install]
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WantedBy=multi-user.target
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```
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Now we can create the systemd timer that will hook to this service. This is `/etc/systemd/system/docker-purge.timer`.
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```yaml
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[Unit]
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Description=Purge Docker Images Older than 24 Hours
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Requires=docker-purge.service
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[Timer]
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Unit=docker-purge.service
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OnCalendar=*-*-* 00:00:00
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AccuracySec=24h
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[Install]
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WantedBy=timers.target
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```
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This tells Systemd to run the service every day if enabled/started, though not necessarily at midnight. Systemd will schedule a time to run the service within the `AccuracySec` parameter. That is, it will schedule a time to run sometime everyday.
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Finally, let's enable and start the timer.
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```bash
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sudo systemctl enable docker-purge
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sudo systemctl start docker-purge
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```
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We can check the time that docker-purge is scheduled to run next by asking Systemd to list its timers.
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```bash
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systemctl list-timers
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```
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If you want to play around with the `OnCalendar` parameter. A useful command is
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```bash
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systmed-analyze calendar --iterations=$N "$TIME"
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```
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Where you replace `$N` with an integer, and `$TIME` with your sample time string.
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