Today I learned that the default locale for an Ubuntu image in a Docker container is not what I expected it to be. I was trying to view some Greek file names in a container and they did not appear correctly. I immediately knew there must be something off with locale of the container.
What is a locale? It’s how Linux systems determines which language and character set a user sees when they log into a terminal session. What is the default locale when pulling down a fresh Ubuntu 16.04 image?
root@4ff94ee1780d:/# locale
LANG=
LANGUAGE=
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=What??!! POSIX??!!! What’s the POSIX Locale? The POSIX locale is another name for the C locale (That’s ANSI C not the C Language) which is another name for “if you expect to see any Unicode characters, haha, the jokes on you” locale.
How to fix this? Basically you need to add the locale-gen program to your container, generate and set the locale to something more appropriate. This can be accomplished by adding the following to your Dockerfile:
FROM ubuntu:16.04
RUN apt-get clean && apt-get update
RUN apt-get install locales
RUN locale-gen en_US.UTF-8
ENV LANG en_US.UTF-8
ENV LANGUAGE en_US:en
ENV LC_ALL en_US.UTF-8 After rebuilding my docker image and running it, I “ssh” (start an interactive bash session) into the container to check.
root@15dc539c6e1c:/# locale
LANG=en_US.UTF-8
LANGUAGE=en_US:en
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=en_US.UTF-8Looks good. Finally, I check the previous Greek test files and see that the characters are properly rendered.