How To Change Fitbit Time With Change In Time Zone

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Reason: This article mostly documents systemd timedatectl; explain bones commands like date and hwclock showtime (Discuss in Talk:System fourth dimension)

In an operating system, the fourth dimension (clock) is adamant past three parts: time value, whether it is local time or UTC or something else, fourth dimension zone, and Daylight Saving Time (DST) if applicable. This article explains what they are and how to read/set them. Two clocks are present on systems: a hardware clock and a system clock which are also detailed in this commodity.

Standard beliefs of nigh operating systems is:

Fix the system clock from the hardware clock on boot.
Continue authentic time of the system clock, run into #Fourth dimension synchronization.
Set the hardware clock from the system clock on shutdown.

Hardware clock

The hardware clock (a.k.a. the Real Time Clock (RTC) or CMOS clock) stores the values of: Year, Month, Day, Hour, Minute, and Seconds. Only 2016, or later, UEFI firmware has the ability to store the timezone, and whether DST is used.

Read hardware clock

# hwclock --evidence

Fix hardware clock from system clock

The following sets the hardware clock from the system clock. Additionally it updates /etc/adjtime or creates information technology if non present. Encounter hwclock(8) § The Adjtime File for more data on this file as well equally the #Time skew section.

# hwclock --systohc

Arrangement clock

The system clock (a.k.a. the software clock) keeps track of: time, time zone, and DST if applicable. It is calculated by the Linux kernel as the number of seconds since midnight January 1st 1970, UTC. The initial value of the system clock is calculated from the hardware clock, dependent on the contents of /etc/adjtime. After kicking-up has completed, the organisation clock runs independently of the hardware clock. The Linux kernel keeps track of the system clock past counting timer interrupts.

Read clock

To cheque the current system clock time (presented both in local fourth dimension and UTC) as well every bit the RTC (hardware clock):

$ timedatectl

Set system clock

To prepare the local time of the organization clock directly:

# timedatectl set-time "yyyy-MM-dd hh:mm:ss"

For example:

# timedatectl set-time "2014-05-26 11:xiii:54"

sets the fourth dimension to May 26th, year 2014, 11:13 and 54 seconds.

Time standard

There are 2 fourth dimension standards: localtime and Coordinated Universal Time (UTC). The localtime standard is dependent on the current time zone, while UTC is the global time standard and is contained of time zone values. Though conceptually different, UTC is besides known every bit GMT (Greenwich Mean Fourth dimension).

The standard used by the hardware clock (CMOS clock, the BIOS time) is gear up by the operating arrangement. By default, Windows uses localtime, macOS uses UTC, other UNIX and UNIX-like systems vary. An OS that uses the UTC standard volition generally consider the hardware clock equally UTC and make an adjustment to it to fix the OS time at kick according to the time zone.

If multiple operating systems are installed on a machine, they will all derive the electric current time from the same hardware clock: it is recommended to adopt a unique standard for the hardware clock to avoid conflicts beyond systems and set it to UTC. Otherwise, if the hardware clock is set to localtime, more than one operating system may conform it afterwards a DST change for example, thus resulting in an over-correction; bug may besides ascend when traveling between different time zones and using one of the operating systems to reset the organisation/hardware clock.

The hardware clock tin can be queried and fix with the timedatectl command. You can encounter the current hardware clock time standard of the Arch system using:

$ timedatectl | grep local

RTC in local TZ: no

To change the hardware clock time standard to localtime, use:

# timedatectl set-local-rtc          1

To revert to the hardware clock being in UTC, blazon:

# timedatectl set-local-rtc          0

These generate /etc/adjtime automatically and update the RTC accordingly; no further configuration is required.

During kernel startup, at the point when the RTC driver is loaded, the arrangement clock may exist gear up from the hardware clock. Whether this occurs depends on the hardware platform, the version of the kernel and kernel build options. If this does occur, at this point in the kicking sequence, the hardware clock time is causeless to be UTC and the value of /sys/class/rtc/rtcN/hctosys (North=0,1,ii,..) will be prepare to 1.

After, the system clock is set again from the hardware clock by systemd, dependent on values in /etc/adjtime. Hence, having the hardware clock using localtime may cause some unexpected beliefs during the kick sequence; e.g system time going backwards, which is always a bad idea (there is a lot more to it). To avoid it systemd will only synchronize back, if the hardware clock is set to UTC and keep the kernel uninformed most the local timezone. Equally a consequence timestamps on a FAT filesystem touched by the Linux system will be in UTC.

Note:

The use of timedatectl requires an active D-Bus. Therefore, information technology may not be possible to employ this command under a chroot (such every bit during installation). In these cases, yous tin can revert back to the hwclock control, or use systemd-nspawn instead of chroot.
If /etc/adjtime is not present, systemd assumes the hardware clock is set to UTC.

UTC in Microsoft Windows

To dual kicking with Windows it is recommended to configure Windows to use UTC, rather than Linux to use localtime. (Windows by default uses localtime [1].)

It can be done by a simple registry fix: Open regedit and add a DWORD value with hexadecimal value i to the registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Command\TimeZoneInformation\RealTimeIsUniversal

Yous can do this from an Administrator Command Prompt running:

reg add together "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation" /five RealTimeIsUniversal /d 1 /t REG_DWORD /f

Alternatively, create a *.reg file (on the desktop) with the post-obit content and double-click it to import information technology into registry:

Windows Registry Editor Version five.00  [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation] "RealTimeIsUniversal"=dword:00000001

Should Windows ask to update the clock due to DST changes, let it. It will go out the clock in UTC as expected, only correcting the displayed time.

The #Hardware clock and #System clock fourth dimension may need to exist updated after setting this value.

If you are having issues with the starting time of the time, endeavour reinstalling tzdata and then setting your time zone over again:

# timedatectl fix-timezone America/Los_Angeles

Historical notes

For really old Windows, the above method fails, due to Windows bugs. More precisely,

For 64-scrap versions of Windows 7 and older builds of Windows 10, there was a bug that fabricated information technology necessary to have a QWORD value with hexadecimal value of i instead of a DWORD value. This bug has been fixed in newer builds and now just DWORD works.
Before Vista SP2, at that place is a bug that resets the clock to localtime later resuming from the suspend/hibernation state.
For XP and older, there is a bug related to the daylight saving time. See [ii] for details.
For fifty-fifty older versions of Windows, yous might want to read https://world wide web.cl.cam.ac.u.k./~mgk25/mswish/ut-rtc.html - the functionality was not even documented nor officially supported then.

For these operating systems, it is recommended to utilise localtime.

UTC in Ubuntu

Ubuntu and its derivatives have the hardware clock set to be interpreted every bit in "localtime" if Windows was detected on whatever disk during Ubuntu installation. This is plainly done deliberately to allow new Linux users to try out Ubuntu on their Windows computers without editing the registry.

For changing this behavior, see above.

Time zone

To check the current zone defined for the organization:

$ timedatectl condition

To list available zones:

$ timedatectl list-timezones

To set up your time zone:

# timedatectl ready-timezone          Zone/SubZone

Example:

# timedatectl set-timezone Canada/Eastern

This volition create an /etc/localtime symlink that points to a zoneinfo file nether /usr/share/zoneinfo/. In instance y'all choose to create the link manually (for example during chroot where timedatectl will not work), keep in mind that it must be a symbolic link, as specified in localtime(5) § DESCRIPTION:

# ln -sf /usr/share/zoneinfo/Zone/SubZone          /etc/localtime

Tip: The fourth dimension zone can also be selected interactively with tzselect.

See timedatectl(1) and localtime(5) for details.

Setting based on geolocation

Note: Some desktop environments have back up for automated fourth dimension zone selection (east.thou. come across GNOME#Date & time).

To set the timezone automatically based on the IP address location, one tin can utilise a geolocation API to call up the timezone, for example curl https://ipapi.co/timezone, and pass the output to timedatectl prepare-timezone for automatic setting. Some geo-IP APIs that provide gratis or partly complimentary services are listed beneath:

Abstract IP geolocation API
FreegeoIP
IP-api
IPAPI
Ipdata
Ipstack
TimezoneApi

Update timezone every time NetworkManager connects to a network

Create a NetworkManager dispatcher script:

/etc/NetworkManager/dispatcher.d/09-timezone

#!/bin/sh instance "$2" in     up)         timedatectl set-timezone "$(gyre --fail https://ipapi.co/timezone)"     ;; esac

Alternatively, the tool tzupdate ^AUR automatically sets the timezone based on the geolocation of the IP accost. This comparing of the most popular IP geolocation apis may exist helpful in deciding which API to utilize in production.

Fourth dimension skew

Every clock has a value that differs from real time (the best representation of which existence International Diminutive Time); no clock is perfect. A quartz-based electronic clock keeps imperfect fourth dimension, but maintains a consistent inaccuracy. This base 'inaccuracy' is known as 'fourth dimension skew' or 'time drift'.

When the hardware clock is ready with hwclock, a new drift value is calculated in seconds per twenty-four hours. The drift value is calculated by using the difference betwixt the new value set and the hardware clock value but before the set, taking into account the value of the previous drift value and the last fourth dimension the hardware clock was set. The new drift value and the time when the clock was fix is written to the file /etc/adjtime overwriting the previous values. The hardware clock can therefore be adjusted for drift when the command hwclock --accommodate is run; this also occurs on shutdown but only if the hwclock daemon is enabled, hence for Arch systems which employ systemd, this does non happen.

Note: If the hwclock has been prepare again less than 24 hours later on a previous set, the drift is not recalculated every bit hwclock considers the elapsed fourth dimension period too short to accurately calculate the drift.

If the hardware clock keeps losing or gaining time in large increments, it is possible that an invalid drift has been recorded (but only applicative, if the hwclock daemon is running). This can happen if you take ready the hardware clock time incorrectly or your time standard is not synchronized with a Windows or macOS install. The drift value tin be removed by starting time removing the file /etc/adjtime, so setting the correct hardware clock and organisation clock fourth dimension. Yous should and then check if your time standard is right.

Annotation: If you wish to brand use of the drift value stored in /etc/adjtime fifty-fifty when using systemd, (e.m. you lot cannot or do non want to use NTP), you must call hwclock --adapt on a regular ground, possibly past creating a cron job.

The software clock is very accurate but like nearly clocks is not perfectly accurate and will drift besides. Though rarely, the system clock can lose accuracy if the kernel skips interrupts. There are some tools to ameliorate software clock accurateness:

See #Time synchronization.

Time synchronization

The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. The following are implementations of NTP available for Arch Linux:

Chrony — A customer and server that is roaming friendly and designed specifically for systems that are not online all the time.

https://chrony.tuxfamily.org/ || chrony

ConnMan — A lightweight network director with NTP support.

https://01.org/connman (waybackmachine) || connman

Network Time Protocol daemon — The reference implementation of the protocol, specially recommended to be used on time servers. It can also adjust the interrupt frequency and the number of ticks per 2nd to decrease arrangement clock migrate, and volition cause the hardware clock to be re-synchronised every eleven minutes.

https://world wide web.ntp.org/ || ntp

ntpclient — A simple command-line NTP client.

http://doolittle.icarus.com/ntpclient/ || ntpclient ^AUR

NTPsec — A fork of NTPd, focused on security.

https://ntpsec.org/ || ntpsec ^AUR

OpenNTPD — Part of the OpenBSD project and implements both a client and a server.

https://www.openntpd.org/ || openntpd

sntp — An SNTP client that comes with NTPd. It supersedes ntpdate and is recommended in non-server environments.

https://world wide web.ntp.org/ || ntp

systemd-timesyncd — A simple SNTP daemon that only implements a client side, focusing merely on querying time from one remote server. It should be more appropriate for almost installations.

https://www.freedesktop.org/wiki/Software/systemd/ || systemd

Per-user/session or temporary settings

For some use cases it may exist useful to alter the time settings without touching the global system values. For example to test applications relying on the fourth dimension during development or adjusting the organisation time zone when logging into a server remotely from another zone.

To brand an application "see" a unlike date/time than the system ane, you can apply the faketime(1) utility (from libfaketime).

If instead yous want an application to "see" a different fourth dimension zone than the organisation one, set the TZ environment variable, for example:

$ date && export TZ=":/usr/share/zoneinfo/Pacific/Fiji" && date

Tue Nov  one xiv:34:51 CET 2016 Midweek Nov  2 01:34:51 FJT 2016

This is dissimilar than just setting the time, as for instance it allows to exam the behavior of a program with positive or negative UTC offset values, or the effects of DST changes when developing on systems in a not-DST time zone.

Some other use example is having unlike time zones set for different users of the aforementioned arrangement: this tin can exist accomplished by setting the TZ variable in the shell's configuration file, come across Surround variables#Defining variables.

Tips and tricks

fake-hwclock

warning-fake-hwclock designed particularly for arrangement without battery backed up RTC, information technology includes a systemd service which on shutdown saves the electric current time and on startup restores the saved time, thus avoiding strange time travel errors.

Install faux-hwclock-git ^AUR, showtime/enable the service fake-hwclock.service.

Troubleshooting

Clock shows a value that is neither UTC nor local time

This might exist caused by a number of reasons. For instance, if your hardware clock is running on local fourth dimension, merely timedatectl is set to assume information technology is in UTC, the result would exist that your timezone's start to UTC effectively gets applied twice, resulting in wrong values for your local time and UTC.

To forcefulness your clock to the correct time, and to also write the correct UTC to your hardware clock, follow these steps:

Setup ntpd (enabling information technology as a service is not necessary).
Set your fourth dimension zone correctly.
Run ntpd -qg to manually synchronize your clock with the network, ignoring large deviations between local UTC and network UTC.
Run hwclock --systohc to write the current software UTC time to the hardware clock.