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Linux Timezone Management

1. Understanding /usr/share/zoneinfo​

The /usr/share/zoneinfo directory, also known as the "tz database" or "tzdata", is a crucial component of Linux systems that contains timezone information files.

Structure​

/usr/share/zoneinfo/
├── Africa/
├── America/
├── Asia/
├── Europe/
└── ...

Purpose​

  • Contains timezone rules and data files
  • Manages daylight saving transitions
  • Stores historical timezone changes
  • Provides UTC offset information

2. Using tzselect - Interactive Timezone Selector​

Starting tzselect​

/usr/bin/tzselect

Interactive Process​

  1. Select continent/region:
1) Africa
2) Americas
3) Antarctica
4) Asia
...
  1. Select country:
# For Asia/Jerusalem:
4) Asia
5) Israel
  1. Confirm selection:
The following information has been given = Israel
Therefore TZ='Asia/Jerusalem' will be used.
Selected time is now:   Fri Jun 27 09:41:46 IDT 2025.
Universal Time is now:  Fri Jun 27 06:41:46 UTC 2025.

3. User-Specific Timezone Configuration (.profile)​

Editing .profile​

nano ~/.profile

Add Timezone Configuration​

# Add to ~/.profile
TZ='Asia/Jerusalem'; export TZ

.profile TZ Characteristics​

  • User-specific environment setting
  • Does not affect system-wide timezone
  • Applied only to user's shell sessions
  • Changes are temporary
  • Requires shell restart or source command

Apply Changes​

source ~/.profile

4. System-Wide Timezone Configuration (timedatectl)​

Understanding timedatectl Output​

timedatectl
Local time: Fri 2025-06-27 09:59:57 IDT
Universal time: Fri 2025-06-27 06:59:57 UTC
RTC time: Fri 2025-06-27 06:59:58
Time zone: Asia/Jerusalem (IDT, +0300)
System clock synchronized: yes
NTP service: active
RTC in local TZ: no

Components Explained​

  • Local time: Current time in selected timezone
  • Universal time: UTC time
  • RTC time: Hardware clock time
  • Time zone: Current system timezone
  • NTP service: Network Time Protocol status

Setting System Timezone​

sudo timedatectl set-timezone Asia/Jerusalem

Method 2: Manual Configuration​

# Update localtime symlink
sudo ln -sf /usr/share/zoneinfo/Asia/Jerusalem /etc/localtime
# Update timezone file
echo "Asia/Jerusalem" | sudo tee /etc/timezone

Verify Changes​

# Check current settings
timedatectl

# Verify timezone file
cat /etc/timezone

# Check localtime symlink
ls -l /etc/localtime

Best Practices​

  1. System-wide Changes

    • Use timedatectl for permanent system changes
    • Affects all users and services
    • Persists across reboots

  2. User-specific Changes

    • Use .profile for personal timezone preferences
    • Only affects user sessions
    • Useful for development environments

  3. Docker Containers

    • Use timezone volume mounts
    • Set TZ environment variable
    volumes:
      - /usr/share/zoneinfo/Asia/Jerusalem:/etc/timezone:ro
      - /usr/share/zoneinfo/Asia/Jerusalem:/etc/localtime:ro
    environment:
      - TZ=Asia/Jerusalem

  4. Troubleshooting

    • Check file permissions
    • Verify timezone file exists
    • Ensure NTP service is running
    • Check for error messages in system logs