[docker] How to clear the logs properly for a Docker container?

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

Is there an elegant way to clear these logs?

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.

Use:

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

You may need sudo

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

ref. Jeff S. How to clear the logs properly for a Docker container?

Reference: Truncating a file while it's being used (Linux)

Here is a cross platform solution to clearing docker container logs:

docker run --rm -v /var/lib/docker:/var/lib/docker alpine sh -c "echo '' > $(docker inspect --format='{{.LogPath}}' CONTAINER_NAME)"

Paste this into your terminal and change CONTAINER_NAME to desired container name or id.

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

I needed something I could run as one command, instead of having to write docker ps and copying over each Container ID and running the command multiple times. I've adapted BMitch's answer and thought I'd share in case someone else may find this useful.

Mixing xargs seems to pull off what I need here:

docker ps --format='{{.ID}}' | \
  xargs -I {} sh -c 'echo > $(docker inspect --format="{{.LogPath}}" {})'

This grabs each Container ID listed by docker ps (will erase your logs for any container on that list!), pipes it into xargs and then echoes a blank string to replace the log path of the container.

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

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)

Docker4Mac, a 2018 solution:

LOGPATH=$(docker inspect --format='{{.LogPath}}' <container_name_or_id>)
docker run -it --rm --privileged --pid=host alpine:latest nsenter -t 1 -m -u -n -i -- truncate -s0 $LOGPATH

The first line gets the log file path, similar to the accepted answer.

The second line uses nsenter that allows you to run commands in the xhyve VM that servers as the host for all the docker containers under Docker4Mac. The command we run is the familiar truncate -s0 $LOGPATH from non-Mac answers.

If you're using docker-compose, the first line becomes:

local LOGPATH=$(docker inspect --format='{{.LogPath}}' $(docker-compose ps -q <service>))

and <service> is the service name from your docker-compose.yml file.

Thanks to https://github.com/justincormack/nsenter1 for the nsenter trick.

On my Ubuntu servers even as sudo I would get Cannot open ‘/var/lib/docker/containers/*/*-json.log’ for writing: No such file or directory

But combing the docker inspect and truncate answers worked :

sudo truncate -s 0 `docker inspect --format='{{.LogPath}}' <container>`

Docker for Mac users, here is the solution:

• 1. Find log file path by:

     $ docker inspect | grep log

• 2. SSH into the docker machine( suppose the name is default, if not, run docker-machine ls to find out):

     $ docker-machine ssh default

• 3. Change to root user(reference):

     $ sudo -i

• 4. Delete the log file content:

     $ echo "" > log_file_path_from_step1

sudo find /var/lib/docker/containers/ -type f -name "*.log" -delete

You can set up logrotate to clear the logs periodically.

Example file in /etc/logrotate.d/docker-logs

/var/lib/docker/containers/*/*.log {
 rotate 7
 daily
 compress
 size=50M
 missingok
 delaycompress
 copytruncate
}

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)

As a root user, try to run the following:

>  /var/lib/docker/containers/*/*-json.log

or

cat /dev/null > /var/lib/docker/containers/*/*-json.log

or

echo "" > /var/lib/docker/containers/*/*-json.log

To remove/clear docker container logs we can use below command

$(docker inspect container_id|grep "LogPath"|cut -d """ -f4) or $(docker inspect container_name|grep "LogPath"|cut -d """ -f4)

On Docker for Windows and Mac, and probably others too, it is possible to use the tail option. For example:

docker logs -f --tail 100

This way, only the last 100 lines are shown, and you don't have first to scroll through 1M lines...

(And thus, deleting the log is probably unnecessary)