Local File logging driver

Estimated reading time: 2 minutes

The local logging driver captures output from container’s stdout/stderr and writes them to an internal storage that is optimized for performance and disk use.

By default, the local driver preserves 100MB of log messages per container and uses automatic compression to reduce the size on disk. The 100MB default value is based on a 20M default size for each file and a default count of 5 for the number of such files (to account for log rotation).

Note: the local logging driver currently uses file-based storage. The file-format and storage mechanism are designed to be exclusively accessed by the Docker daemon, and should not be used by external tools as the implementation may change in future releases.

Usage

To use the local driver as the default logging driver, set the log-driver and log-opt keys to appropriate values in the daemon.json file, which is located in /etc/docker/ on Linux hosts or C:\ProgramData\docker\config\daemon.json on Windows Server. For more about configuring Docker using daemon.json, see daemon.json.

The following example sets the log driver to local and sets the max-size option.

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

Restart Docker for the changes to take effect for newly created containers. Existing containers do not use the new logging configuration.

You can set the logging driver for a specific container by using the --log-driver flag to docker container create or docker run:

$ docker run \
      --log-driver local --log-opt max-size=10m \
      alpine echo hello world

Options

The local logging driver supports the following logging options:

Option Description Example value
max-size The maximum size of the log before it is rolled. A positive integer plus a modifier representing the unit of measure (k, m, or g). Defaults to 20m. --log-opt max-size=10m
max-file The maximum number of log files that can be present. If rolling the logs creates excess files, the oldest file is removed. A positive integer. Defaults to 5. --log-opt max-file=3
compress Toggle compression of rotated log files. Enabled by default. --log-opt compress=false

Examples

This example starts an alpine container which can have a maximum of 3 log files no larger than 10 megabytes each.

$ docker run -it --log-driver local --log-opt max-size=10m --log-opt max-file=3 alpine ash
local, docker, logging, driver