Introduction

When I logged into a Ubuntu server, the system interface and messages are shown all shown in Chinese. I want them to be displayed in English. After some searching, I found out that we can change the locale settings. The definition of locale is:

In computing, a locale is a set of parameters that defines the user’s language, region and any special variant preferences that the user wants to see in their user interface

Set up locale for normal Linux system

In Linux systems, there are several environment variables related to the locale settings, such as LANG, LC_COLLATE, LC_TIME, LC_ALL etc. A valid locale is like en_US.UTF-8. You can check this documentation on how locale is formed.

To see your default settings, use the locale command without any option. The output looks like:

LANG=en_US.UTF-8
LANGUAGE=zh_CN:zh
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=

These settings are often pre-set by the system root. On CentOS, the system-wide default locale settings are stored in /ect/locale.conf. On Ubuntu, the system locale settings are store in /etc/default/locale.

Among the locale env variables, LC_xxx variables except LC_ALL are ordinary environment variables which can be set individually.

Special variables are LANG, LANGUAGE and LC_ALL. Their priority are listed here:

  1. LANGUAGE
  2. LC_ALL
  3. LC_xxx, according to selected locale category: LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, LC_MESSAGES, …
  4. LANG

LANG is special variable which will set the LC_* variable if it is not set. LC_ALL will set all other LC_XXX variables to the same value. Usually, you do not need to set up LC_ALL in your bash_profile. LANGUAGE is a variable used for message handling, which has a higher priority than LC_ALL, LC_xxx and LANG for messages (see the link here). To verify this, suppose that we have the following settings inside .bash_profile:

export LANG=en_US.utf8
export LANGUAGE=zh_CN.utf8

After sourcing the file, you will find that the messages given for command output will be in Chinese (i.e., LANG is overridden.)

Set up locale for docker container

Ubuntu docker

I try to build a Ubuntu container. I want to set my locale to en_US.UTF-8 inside the container by simply adding the following ENV instruction:

ENV LC_ALL=en_US.UTF-8

When I run the built image, I get the following warning:

bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

The locale command inside container gives the following message:

locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
LANG=
LANGUAGE=
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-8

It seems that the locale file en_US.UTF-8 does not exist inside container. After some searching, I found the correct way to set up locales inside the Ubuntu container. First, we need to install the locales package which provides the locale-gen command:

RUN apt-get update && apt-get install -y locales

After installing the locales packages, a file named local.gen will be created under /etc. According to the documentation of locale-gen:

locale-gen is a program that reads the file /etc/locale.gen and invokes localedef for the chosen localisation profiles. Run locale-gen after you have modified the /etc/locale.gen file.

We should uncomment the line # en_US.UTF-8 UTF-8 in locale.gen and run locale-gen command to generate the needed locale file. After that we can set related settings to en_US.UTF-8:

RUN sed -i -e 's/# en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen && \
    locale-gen
ENV LC_ALL en_US.UTF-8

We can also directly generate the locale file by appending the locale as the argument to locale-gen:

RUN locale-gen en_US.UTF-8

Putting this all together, we may use the following instructions inside Dockerfile:

RUN apt-get update && apt-get install -y locales && locale-gen en_US.UTF-8

CentOS docker

If you tried to build an image based on a CentOS image. You need to use localedef to generate locale files instead of locale-gen:

# -i: specify the locale definition file
# -f: specify the character set
RUN localedef -i en_US -f UTF-8 en_US.UTF-8

Other settings are similar to that of Ubuntu.

References