How to Set Timezone and Locale for Docker Image

When I deployed my java applications on the latest Wildfly Docker image I noticed a missing language support for German Umlaute and the timezone CET. So the question was: How can I change this general setting in a Docker container?

Verify Timezone and Language

To verify the timezone and language supported by your running docker container can verify the settings by executing the date and locale command:

$ docker exec <CONTAINER-ID> date
Fri Oct 23 15:21:54 UTC 2020

$ docker exec <CONTAINER-ID> locale
LANG=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

Replace <CONTAINER-ID> with the docker id of your running container.

In this example we can see that the container is supporting only the most basic setup. But there are ways to change these settings.

Changing Timezone and Locale by Environment Variables

I most cases you can adjust language and timezone with the standard Linux environment variables TZ, LANG, LANGUAGE and LC_ALL. See the following example:

docker run -e TZ="CET" \
   -e LANG="de_DE.UTF-8" \
   -e LANGUAGE="de_DE:de" \
   -e LC_ALL="en_US.UTF-8" \
   -it jboss/wildfly

In this example I run the official Wildfly container with timezone CET and locale de_DE. You can verify the settings again with the date and locale command.

In most cases it will be sufficient to just set the timezone and the en_US UTF-8 support:

docker run -e TZ="CET" \
   -e LANG="en_US.UTF-8" \
   -it jboss/wildfly

Changing Timezone and Language by Dockerfile

Another way is to change the Docker image during build time:

FROM jboss/wildfly:20.0.1.Final

# ### Locale support de_DE and timezone CET ###
USER root
RUN localedef -i de_DE -f UTF-8 de_DE.UTF-8
RUN echo "LANG=\"de_DE.UTF-8\"" > /etc/locale.conf
RUN ln -s -f /usr/share/zoneinfo/CET /etc/localtime
USER jboss
ENV LANG de_DE.UTF-8
ENV LANGUAGE de_DE.UTF-8
ENV LC_ALL de_DE.UTF-8
### Locale Support END ###

CMD ["/opt/jboss/wildfly/bin/standalone.sh", "-b", "0.0.0.0", "-bmanagement", "0.0.0.0"]

In this example I run the localdef and change the language in /etc/locale.conf/

This will build a complete new Image with standard Locale ‘de_DE’ and timzone CET.

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