Linux/Time

Time Zones
See current timezone setting: sudo zdump /etc/localtime  # /etc/localtime  Wed Mar 14 09:46:46 2012 MDT strings /etc/localtime     # MST7MDT,M3.2.0,M11.1.0  (and other garbage)

Set timezone for all users: mv /etc/localtime /etc/localtime.original ln -sfn /usr/share/zoneinfo/America/Denver /etc/localtime
 * 1) cp /usr/share/zoneinfo/America/Boise /etc/localtime

Set time zone for current user: export TZ=America/Denver

In Linux, most timezone information is controlled by GLIBC, which relies on the file /etc/localtime. Different distributions do different things with this file; some have it as a symbolic link to the proper timezone definition file (usually in /usr/share/zoneinfo), but most have it as an actual, explicit file.

Verifying the Timezone File

zdump is a small program that is part of GLIBC. It dumps the information about a given timezone file. If you want to verify what the Daylight Savings times are for a given year with a given file, you can do something like this:

$ zdump -v /etc/localtime | grep 2007

The -v tells zdump to display timezone information for all transitions rather than just the current date.

date: date Sun May 2 15:49:55 MDT 2010

Time Zone: ENVIRONMENT TZ Specifies the timezone, unless overridden by command line parameters. If neither is specified, the setting from /etc/localtime is used.

Time zones are kept here: /usr/share/zoneinfo/

NTP
See NTP

File Time
Files have access, modify and change times.


 * access time (atime): time the file was last accessed
 * modify time (mtime): file modification times
 * change time (ctime): status change times

$ stat test/ File: `test/' Size: 4096           Blocks: 8          IO Block: 4096   directory Device: 900h/2304d     Inode: 20987905    Links: 2 Access: (0700/drwx--) Uid: ( 1068/ kenneth)   Gid: ( 1068/ kenneth) Access: 2010-09-20 11:30:01.000000000 -0600 Modify: 2010-09-20 11:14:45.000000000 -0600 Change: 2010-09-20 11:14:45.000000000 -0600

List file times: $ ls -lt $ ls -ltr # reverse

Modifiers: -t mtime - modification time -u atime - access time -c ctime - change time

America Time Zones
Etc/UTC
 * 1) cat /etc/timezone

Universal UTC Zulu Etc/UTC

US/Central America/Chicago

US/Eastern America/New_York

US/Hawaii Pacific/Honolulu

US/Mountain America/Denver

US/Pacific America/Los_Angeles

https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

Sat 16 Feb 15:46:56 UTC 2019
 * 1) date

Sat 16 Feb 08:47:01 MST 2019
 * 1) TZ=America/Denver date

keywords
Linux date time timezone