How to clear the logs properly for a Docker container?

Question

I use docker logs [container-name] to see the logs of a specific container.

Is there an elegant way to clear these logs?

Answer 1

I do prefer this one (from solutions above):

truncate -s 0 /var/lib/docker/containers/*/*-json.log

However I'm running several systems (Ubuntu 18.x Bionic for example), where this path does not work as expected. Docker is installed through Snap, so the path to containers is more like:

truncate -s 0 /var/snap/docker/common/var-lib-docker/containers/*/*-json.log

Answer 2

First the bad answer. From this question there's a one-liner that you can run:

echo "" > $(docker inspect --format='{{.LogPath}}' <container_name_or_id>)

instead of echo, there's the simpler:

: > $(docker inspect --format='{{.LogPath}}' <container_name_or_id>)

or there's the truncate command:

truncate -s 0 $(docker inspect --format='{{.LogPath}}' <container_name_or_id>)

---

I'm not a big fan of either of those since they modify Docker's files directly. The external log deletion could happen while docker is writing json formatted data to the file, resulting in a partial line, and breaking the ability to read any logs from the docker logs cli. For an example of that happening, see this comment on duketwo's answer

Instead, you can have Docker automatically rotate the logs for you. This is done with additional flags to dockerd if you are using the default JSON logging driver:

dockerd ... --log-opt max-size=10m --log-opt max-file=3

You can also set this as part of your daemon.json file instead of modifying your startup scripts:

{
  "log-driver": "json-file",
  "log-opts": {"max-size": "10m", "max-file": "3"}
}

These options need to be configured with root access. Make sure to run a systemctl reload docker after changing this file to have the settings applied. This setting will then be the default for any newly created containers. Note, existing containers need to be deleted and recreated to receive the new log limits.

---

Similar log options can be passed to individual containers to override these defaults, allowing you to save more or fewer logs on individual containers. From docker run this looks like:

docker run --log-driver json-file --log-opt max-size=10m --log-opt max-file=3 ...

or in a compose file:

version: '3.7'
services:
  app:
    image: ...
    logging:
      options:
        max-size: "10m"
        max-file: "3"

---

For additional space savings, you can switch from the json log driver to the "local" log driver. It takes the same max-size and max-file options, but instead of storing in json it uses a binary syntax that is faster and smaller. This allows you to store more logs in the same sized file. The daemon.json entry for that looks like:

{
  "log-driver": "local",
  "log-opts": {"max-size": "10m", "max-file": "3"}
}

The downside of the local driver is external log parsers/forwarders that depended on direct access to the json logs will no longer work. So if you use a tool like filebeat to send to Elastic, or Splunk's universal forwarder, I'd avoid the "local" driver.

I've got a bit more on this in my Tips and Tricks presentation.

Answer 3

sudo sh -c "truncate -s 0 /var/lib/docker/containers/*/*-json.log"

Answer 4

Not sure if this is helpful for you, but removing the container always helps.

So, if you use docker-compose for your setup, you can simply use docker-compose down && docker-compose up instead of docker-compose restart. With a proper setup (make sure to use volume mounts for persistent data), you don't lose any data this way.

Sure, this is more than the OP requested. But there are various situations where the other answers cannot help (if using a remote docker server or working on a Windows machine, accessing the underlying filesystem is proprietary and difficult)

Answer 5

You can also supply the log-opts parameters on the docker run command line, like this:

docker run --log-opt max-size=10m --log-opt max-file=5 my-app:latest

or in a docker-compose.yml like this

my-app:
image: my-app:latest
logging:
    driver: "json-file"
    options:
        max-file: "5"
        max-size: 10m

Credits: https://medium.com/@Quigley_Ja/rotating-docker-logs-keeping-your-overlay-folder-small-40cfa2155412 (James Quigley)

Answer 6

You can't do this directly through a Docker command.

You can either limit the log's size, or use a script to delete logs related to a container. You can find scripts examples here (read from the bottom): Feature: Ability to clear log history #1083

Check out the logging section of the docker-compose file reference, where you can specify options (such as log rotation and log size limit) for some logging drivers.