Docker Maintenance CheatSheet and Tips

Dec 21, 2023

Table of Contents

• Tips
• Disk Usage Check
• System Info
• Clear up the Clutter
• Volume Mount Point
• References

Related to: Docker

Tips §

• Check the size of the container folders. We should not have big containers since the images are responsible for having the OS and so on…
• If the folders are big, it’s probably the log file. We should limit it Docker Logging
• Run daily or weekly prune docker system prune -f. This should be in a cron job.
• Be careful with other types of logs, too - always set a max size and a max retention period.

Disk Usage Check §

The system df gives us the size of our Docker items separated by type.

df is a mention of the Linux df command

Think of disk free to remember it.

docker system df
TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          80        40        24.08GB   8.086GB (33%)
Containers      77        59        794.6MB   347.1kB (0%)
Local Volumes   36        36        75.07GB   0B (0%)
Build Cache     0         0         0B        0B

The -v or --verbose gives us a lot more detailed information.

docker system df -v
Images space usage:
 
REPOSITORY                                TAG                      IMAGE ID       CREATED         SIZE      SHARED SIZE   UNIQUE SIZE   CONTAINERS
mysql                                     8                        73246731c4b0   2 days ago      618.8MB   0B            618.8MB       1
fluentd                                   latest                   b0035f156c01   2 months ago    256.3MB   206.8MB       49.53MB       1
 
Containers space usage:
 
CONTAINER ID   IMAGE                                                  COMMAND                  LOCAL VOLUMES   SIZE      CREATED             STATUS                       NAMES
d04f1c9bbea1   mysql:8                                                "docker-entrypoint.s…"   1               6B        37 minutes ago      Up 37 minutes                mysql-server
e753f696afb5   saerp-fluentd:latest                                   "tini -- /bin/entryp…"   1               0B        12 hours ago        Up 12 hours                  fluentd_fluentd.1.tg7nel4rnjwwh7om39gqoibdq
 
Local Volumes space usage:
 
VOLUME NAME                                                        LINKS     SIZE
fluentd_kibanadata                                                 1         36B
mysql-data                                                         1         16.49GB
 
Build cache usage: 0B
 
CACHE ID   CACHE TYPE   SIZE      CREATED   LAST USED   USAGE     SHARED

Besides this, you can check the good old du -h --max-depth=1 | sort -h. Just keep in mind that it can be quite slow, depending on the number of folders and files.

System Info §

Use the following command to get the overall config status of your docker installation.

docker system info

A useful output is the Docker Root Dir, which shows where in your local system docker has its files.

As with most docker commands, we can get the JSON output using --format "{{ json . }}"

docker system info --format "{{ json . }}"

Clear up the Clutter §

Use the system prune command to clear the “unused” stuff in your docker installation.

This will remove unused images and build cache, networks, and containers.

docker system prune -f

-f or --force is added to avoid prompt for confirmation

The best approach is adding a cron job to run the command weekly or daily.

Volume Mount Point §

Getting the local folder where a docker volume is located is useful.

It’s the same result as the Docker Root Dir: on the previous command with the /volumes/volumeName added. But it’s good for a quick check.

docker volume ls 
docker volume inspect --format '{{ .Mountpoint }}' volumeName

References §

• docker system | Docker Docs

Backlinks

• Create a Cron to Run a Script in a Time Interval Linux Dec 21, 2023