file access modify creation time will always be in UTC format.

In which time offset is +hours or -hours from Longitude: 0° (Prime Meridian)

Prime meridian (Greenbich) GPS: 0° 00′ 05.3101″ W

Other names: Z / Zulu Time Zone

Time Zone: UTC

date -u; # output UTC time

At sea: Longitudes between 7.5° West and 7.5° East

US-President Obama in the National Counterterrorism Center in McLean in 2015. In the top left corner you can see Zulu-time.

changing timezones

you could set

timedatectl list-timezones; # list all available timezones: (works Centos7, Debian8, Suse12)

suse12:~ # timedatectl; # print currently used timezone
 Local time: Wed 2017-06-07 11:32:35 CEST
 Universal time: Wed 2017-06-07 09:32:35 UTC
 RTC time: Tue 2017-06-06 18:33:12
 Time zone: Europe/Berlin (CEST, +0200)
 Network time on: no
 NTP synchronized: no
 RTC in local TZ: no

# permanently change timezone to America/Chicago (works Centos7, Debian8, Suse12)

timedatectl set-timezone America/Chicago

# alternatively interactive mode

tzselect

# debian only alternative:

dpkg-reconfigure tzdata

changing time zones manually

the file /etc/localtime contains the currently used timezone.

on debian this file is an copy of a file from /usr/share/zoneinfo/

on most distroy this is a softlink to a file below /usr/share/zoneinfo/

unfortunately hwlock can not work with softlinks?

etc_localtime.man.txt

root@Debian8:~# file /etc/localtime
 /etc/localtime: timezone data, version 2, 8 gmt time flags, 8 std time flags, no leap seconds, 144 transition times, 8 abbreviation chars

[root@CentOS7 ~]# file /etc/localtime
 /etc/localtime: symbolic link to `../usr/share/zoneinfo/Europe/Berlin'

suse12:~ # file /etc/localtime
 /etc/localtime: symbolic link to `../usr/share/zoneinfo/Europe/Berlin'

# so to manually change your timezone to "Chicago" you would

unlink /etc/localtime;

ln -sv /usr/share/zoneinfo/America/Chicago /etc/localtime;

per user time-zone settings

you could specify a different time-zone for every user via the TZ environment variable

# in user's .bashrc you would put

export TZ=:/usr/share/zoneinfo/America/Dominica

network time

the time of your server/pc can be synced with time-servers that read time from an attached atomic-clock.

having wrong date and time set may result in all sorts of errors – including browsers not accepting SSL certificates. (because they are not YET valid or have expired)

timedatectl; # will tell you if your clock was synced with an time server and if ntp service is working

root@debian8:~# apt get install ntp; # ntp service needs to be installed first

root@CentOS7 user]# yum install ntp; # ntp service needs to be installed first

ntpd -q -g; # sync local time with timeserver - works on debian8 and centos7
 ntpd: time slew +0.005187s

suse12:# rcntpd addserver de.pool.ntp.org; # add server as time-server

suse12:# ntpd -q -g; # takes very long... kind of stuck somewhere?
 7 Jun 11:50:09 ntpd[2153]: ntpd 4.2.8p8@1.3265-o Mon Jun 6 08:13:03 UTC 2016 (1): Starting
 7 Jun 11:50:09 ntpd[2153]: Command line: ntpd -q -g
 7 Jun 11:50:09 ntpd[2153]: proto: precision = 0.200 usec (-22)
 authreadkeys: full access list <NULL>
 7 Jun 11:50:09 ntpd[2153]: switching logging to file /var/log/ntp
 7 Jun 11:50:09 ntpd[2153]: Listen and drop on 0 v6wildcard [::]:123
 7 Jun 11:50:09 ntpd[2153]: Listen and drop on 1 v4wildcard 0.0.0.0:123
 7 Jun 11:50:09 ntpd[2153]: Listen normally on 2 lo 127.0.0.1:123
 7 Jun 11:50:09 ntpd[2153]: Listen normally on 3 eth0 172.20.0.25:123
 7 Jun 11:50:09 ntpd[2153]: Listen normally on 4 lo [::1]:123
 7 Jun 11:50:09 ntpd[2153]: Listen normally on 5 eth0 [fe80::215:5dff:fe00:709%2]:123
 7 Jun 11:50:09 ntpd[2153]: Listening on routing socket on fd #22 for interface updates

/etc/timezone

timezone.man.txt

root@debian8:~# cat /etc/timezone
 Europe/Berlin

root@Debian8:~# date
 Wed Jun 7 10:30:48 CEST (Central European Summer Time) 2017

suse12:# cat /etc/sysconfig/clock; # this seems to be a SUSE only file, neither Debian8 nor Centos7 have it
 TIMEZONE="Europe/Berlin"
 DEFAULT_TIMEZONE="US/Eastern"

timezone info files

seems to be binary files of some sort that define a timezone

root@Debian8:~# file /usr/share/zoneinfo/America/Dominica
 /usr/share/zoneinfo/America/Dominica: symbolic link to Marigot

root@Debian8:~# file /usr/share/zoneinfo/America/Marigot
 /usr/share/zoneinfo/America/Marigot: timezone data, version 2, 2 gmt time flags, 2 std time flags, no leap seconds, 1 transition time, 2 abbreviation chars

suse12:~ # file /usr/share/zoneinfo/America/Dominica
 /usr/share/zoneinfo/America/Dominica: timezone data, version 2, 2 gmt time flags, 2 std time flags, no leap seconds, 2 transition times, 2 abbreviation chars

[root@CentOS7 ~]# file /usr/share/zoneinfo/America/Dominica
 /usr/share/zoneinfo/America/Dominica: timezone data, version 2, 2 gmt time flags, 2 std time flags, no leap seconds, 1 transition time, 2 abbreviation chars

temporary timezone changes

works on Debian8 and CentOS7 as well.

suse12:# export TZ=:/usr/share/zoneinfo/America/Dominica
 suse12:# date
 Mi 7. Jun 04:34:22 AST (Atlantic Standard Time) 2017

locale

locale basically defines country-wise-settings in terms of charset, currency and formatting (e.g. 1,000,00 USD vs 1000€)

locale.man.txt

locale -a; # show all available (installed) locale-definition files (does not display all locales in Debian8?)

locale -m; # display all available charsets

dpkg-reconfigure locales; # Debian8 only - change locale

this way you can change language of the entire system:

example output: locale_m_debian8_available_charsets.txt

root@Debian8:~# locale -a| grep en_US
 en_US.utf8

[root@CentOS7 ~]# locale -a| grep en_US
 en_US
 en_US.iso88591
 en_US.iso885915
 en_US.utf8

suse12:~ # locale -a| grep en_US
 en_US
 en_US.iso885915
 en_US.utf8

the files are located under:

root@Debian8:~# /usr/share/i18n/locales/

[root@CentOS7 ~]# /usr/share/i18n/locales/

[root@CentOS7 ~]# file /usr/share/i18n/locales/wo_SN
 /usr/share/i18n/locales/wo_SN: ISO-8859 text

wo_SN.txt (source „The Debian Project“ -> so Suse12 and CentOS use some Debian files 😉

suse12:~ # /usr/share/i18n/locales/

root@Debian8:~# 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=

suse12:~ # locale
 LANG=de_DE.UTF-8
 LC_CTYPE="de_DE.UTF-8"
 LC_NUMERIC="de_DE.UTF-8"
 LC_TIME="de_DE.UTF-8"
 LC_COLLATE="de_DE.UTF-8"
 LC_MONETARY="de_DE.UTF-8"
 LC_MESSAGES="de_DE.UTF-8"
 LC_PAPER="de_DE.UTF-8"
 LC_NAME="de_DE.UTF-8"
 LC_ADDRESS="de_DE.UTF-8"
 LC_TELEPHONE="de_DE.UTF-8"
 LC_MEASUREMENT="de_DE.UTF-8"
 LC_IDENTIFICATION="de_DE.UTF-8"
 LC_ALL=

[root@CentOS7 ~]# locale
 LANG=de_DE.UTF-8
 LC_CTYPE="de_DE.UTF-8"
 LC_NUMERIC="de_DE.UTF-8"
 LC_TIME="de_DE.UTF-8"
 LC_COLLATE="de_DE.UTF-8"
 LC_MONETARY="de_DE.UTF-8"
 LC_MESSAGES="de_DE.UTF-8"
 LC_PAPER="de_DE.UTF-8"
 LC_NAME="de_DE.UTF-8"
 LC_ADDRESS="de_DE.UTF-8"
 LC_TELEPHONE="de_DE.UTF-8"
 LC_MEASUREMENT="de_DE.UTF-8"
 LC_IDENTIFICATION="de_DE.UTF-8"
 LC_ALL=

lang

there are environment variables that define the currently used language.

„$LC_ALL environment variable will overrides all other ($LC_LANG, $LANG) localisation settings (except $LANGUAGE under some circumstances)“. (src)

currently used OS set-language. can also affect sorting of directories.

root@Debian8:~# echo $LANG
 en_US.UTF-8

[root@CentOS7 ~]# echo $LANG
 de_DE.UTF-8

suse12:~ # echo $LANG
 de_DE.UTF-8

suse12:/home/user/test # export LANG=de_DE.UTF-8
 suse12:/home/user/test # ll
 insgesamt 0
 -rw-r--r-- 1 root root 0 7. Jun 11:10 apple
 -rw-r--r-- 1 root root 0 7. Jun 11:10 Apple
 -rw-r--r-- 1 root root 0 7. Jun 11:10 banana
 -rw-r--r-- 1 root root 0 7. Jun 11:10 Banana
 suse12:/home/user/test # export LANG=POSIX
 suse12:/home/user/test # ll
 total 0
 -rw-r--r-- 1 root root 0 Jun 7 11:10 Apple
 -rw-r--r-- 1 root root 0 Jun 7 11:10 Banana
 -rw-r--r-- 1 root root 0 Jun 7 11:10 apple
 -rw-r--r-- 1 root root 0 Jun 7 11:10 banana

manpages

tzselect.debian8.man.txt

tzselect.suse12.man.txt

„It comes handy when you want to know what time it is in other countries, or if you just wonder what timezones exist.“

Links:

http://dwaves.de/2017/06/20/linux-debian8-change-language-of-entire-system/

http://dwaves.de/2017/06/12/iconv-allows-file-conversion-between-charsets-encodings-utf-8-t-iso-8859-1/

http://dwaves.de/2015/04/07/linux-set-timezone-and-sync-time-and-date-with-internet-timeserver-configure-ntp/

https://www.cyberciti.biz/faq/centos-linux-6-7-changing-timezone-command-line/

http://dwaves.de/2015/04/07/linux-debian-set-timezone-and-sync-time-and-date-with-internet-timeserver-configure-ntp/

http://www.leapsecond.com/java/gpsclock.htm

https://www.timeanddate.com/worldclock/timezone/zulu

RFCs:

ntp protocol – https://tools.ietf.org/html/rfc1305

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