Many developers working in international teams or handling cross-timezone projects require consistent date formatting. The ISO 8601 standard (YYYY-MM-DD HH:MM:SS) provides this consistency while being:

• Sortable by alphabetical order
• Unambiguous across regions
• Compatible with most databases
• Human-readable

The most reliable method to enforce ISO format globally is through locale settings. Edit the locale configuration file:

sudo nano /etc/default/locale

Add or modify these variables:

LC_TIME=en_DK.UTF-8
LC_ALL=en_US.UTF-8
LANG=en_US.UTF-8

The en_DK locale specifically uses ISO date formats while maintaining English language output.

For temporary changes or containerized environments, set these variables in your .bashrc or shell profile:

export LC_TIME=en_DK.UTF-8
export TIME_STYLE=+"%Y-%m-%d %H:%M:%S"

Verify the changes with these commands:

date
# Should output: 2023-11-15 14:30:22

ls -l --time-style=+"%Y-%m-%d %H:%M:%S"
# Shows files with ISO timestamps

Some applications may need additional configuration:

For PostgreSQL:

ALTER DATABASE your_db SET datestyle TO 'ISO, YMD';

For Python scripts:

import locale
locale.setlocale(locale.LC_TIME, 'en_DK.UTF-8')

On older systems without en_DK locale, create a custom locale:

sudo localedef -i en_US -f UTF-8 en_US.UTF-8_ISO

Then modify the date format in /usr/share/i18n/locales/en_US before compiling.

• If changes don't apply: sudo locale-gen and reboot
• Missing locales: sudo apt-get install locales-all
• Docker containers: Set ENV variables in Dockerfile

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Many Linux applications inherit their datetime formatting from system locale settings rather than implementing custom formats. The ISO 8601 standard (YYYY-MM-DD HH:MM:SS) offers several advantages:

• Lexicographical order matches chronological order
• Unambiguous across international regions
• Widely supported in programming languages

1. Modifying locale configuration files

Edit /etc/locale.conf (systemd systems) or /etc/default/locale (Debian/Ubuntu):

LC_TIME="en_US.UTF-8"
TIME_STYLE="+%Y-%m-%d %H:%M:%S"

2. Environment Variable Overrides

Add these to /etc/environment or shell rc files:

export LC_TIME=en_DK.UTF-8
export TIME_STYLE=iso

For GNU coreutils (ls, date commands)

alias date='date "+%Y-%m-%d %H:%M:%S"'
alias ls='ls --time-style="+%Y-%m-%d %H:%M:%S"'

PHP Configuration

date_default_timezone_set('UTC');
ini_set('date.format', 'Y-m-d H:i:s');

Python Standardization

import datetime
datetime.datetime.now().isoformat(sep=' ', timespec='seconds')

After making changes, verify with:

date
ls -l --time-style=+"%Y-%m-%d %H:%M:%S"

For systemd services, check with:

systemctl show-environment | grep LC_TIME

Older systems may require additional steps:

sudo locale-gen en_DK.UTF-8
sudo update-locale LC_TIME=en_DK.UTF-8

The DK locale uses ISO formatting by default, making it a good fallback when custom formats aren't respected.