Configurando a Data e Hora

Os sistemas operacionais modernos distinguem entre os dois tipos de relógios a seguir:

  • A real-time clock (RTC), comumente referido como hardware clock, (normalmente um circuito integrado na placa do sistema) que é completamente independente do estado atual do sistema operacional e funciona mesmo quando o computador é desligado .

  • A system clock, também conhecido como software clock, que é mantido pelo kernel e seu valor inicial é baseado no relógio em tempo real. Depois que o sistema é inicializado e o relógio do sistema é inicializado, o relógio do sistema é completamente independente do relógio em tempo real.

A hora do sistema é sempre mantida em Coordinated Universal Time (UTC) e convertida nos aplicativos para a hora local conforme necessário. Local time é a hora real em seu fuso horário atual, levando em consideração o daylight saving time (DST). O relógio em tempo real pode usar o UTC ou a hora local. UTC é recomendado.

Fedora 31 oferece três ferramentas de linha de comando que podem ser usadas para configurar e exibir informações sobre a data e hora do sistema: o utilitário timedatectl, que é novo em Fedora 31 e faz parte do `systemd`pass:attribute []; o tradicional comando date; e o utilitário hwclock para acessar o relógio do hardware.

Usando o Comando timedatectl

O utilitário timedatectl é distribuído como parte do sistema systemd e gerenciador de serviços e permite que você reveja e altere a configuração do relógio do sistema. Você pode usar esta ferramenta para alterar a data e a hora atuais, definir o fuso horário ou ativar a sincronização automática do relógio do sistema com um servidor remoto.

Para obter informações sobre como exibir a data e hora atuais em um formato personalizado, consulte também Configuring_the_Date_and_Time.adoc#sect-Configuring_the_Date_and_Time-date.

Exibindo a Data e Hora Atuais

Para exibir a data e hora atuais junto com informações detalhadas sobre a configuração do relógio do sistema e do hardware, execute o comando timedatectl sem opções de linha de comando adicionais:

timedatectl

Isso exibe a hora local e universal, o fuso horário atualmente usado, o status da configuração do Protocolo de Tempo de Rede (NTP) e informações adicionais relacionadas ao DST.

Example 1. Exibindo a Data e Hora Atuais

A seguir está um exemplo de saída do comando timedatectl em um sistema que não usa NTP para sincronizar o relógio do sistema com um servidor remoto:

~]$ timedatectl
      Local time: Mon 2013-09-16 19:30:24 CEST
  Universal time: Mon 2013-09-16 17:30:24 UTC
        Timezone: Europe/Prague (CEST, +0200)
     NTP enabled: no
NTP synchronized: no
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  Sun 2013-03-31 01:59:59 CET
                  Sun 2013-03-31 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  Sun 2013-10-27 02:59:59 CEST
                  Sun 2013-10-27 02:00:00 CET

Mudando a Hora Atual

Para alterar a hora atual, digite o seguinte em um prompt de shell como root:

timedatectl set-time HH:MM:SS

Substitua HH por uma hora, MM por um minuto e SS por um segundo, todos digitados na forma de dois dígitos.

Este comando atualiza a hora do sistema e o relógio do hardware. O resultado é semelhante ao uso dos comandos date --set e hwclock --systohc.

O comando falhará se um serviço NTP estiver habilitado. Veja Configuring_the_Date_and_Time.adoc#sect-Configuring_the_Date_and_Time-timedatectl-NTP para desativar temporariamente o serviço.

Example 2. Mudando a Hora Atual

Para alterar o horário atual para 23h26, execute o seguinte comando como root:

~]# timedatectl set-time 23:26:00

Por padrão, o sistema está configurado para usar UTC. Para configurar seu sistema para manter o relógio na hora local, execute o comando timedatectl com a opção set-local-rtc como`root`:

timedatectl set-local-rtc boolean

Para configurar seu sistema para manter o relógio na hora local, substitua boolean with yes (ou, alternativamente,` y`, true,` t` ou 1). Para configurar o sistema para usar UTC, substitua boolean with no (ou, alternativamente,` n`, false,` f` ou 0). A opção padrão é no.

Mudando a Data Atual

Para alterar a data atual, digite o seguinte em um prompt de shell como root:

timedatectl set-time YYYY-MM-DD

Substitua YYYY por um ano de quatro dígitos, MM por um mês de dois dígitos e DD por um dia do mês de dois dígitos.

Observe que alterar a data sem especificar a hora atual resulta na configuração da hora para 00:00:00.

Example 3. Mudando a Data Atual

Para alterar a data atual para 2 de junho de 2013 e manter a hora atual (23h26), execute o seguinte comando como root:

~]# timedatectl set-time "2013-06-02 23:26:00"

Mudança do Fuso Horário

Para listar todos os fusos horários disponíveis, digite o seguinte em um prompt de shell:

timedatectl list-timezones

Para alterar o fuso horário usado atualmente, digite como root:

timedatectl set-timezone time_zone

Replace time_zone with any of the values listed by the timedatectl list-timezones command.

Example 4. Mudança do Fuso Horário

To identify which time zone is closest to your present location, use the timedatectl command with the list-timezones command line option. For example, to list all available time zones in Europe, type:

~]# timedatectl list-timezones | grep Europe
Europe/Amsterdam
Europe/Andorra
Europe/Athens
Europe/Belgrade
Europe/Berlin
Europe/Bratislava
…

To change the time zone to Europe/Prague, type as root:

~]# timedatectl set-timezone Europe/Prague

Synchronizing the System Clock with a Remote Server

As opposed to the manual adjustments described in the previous sections, the timedatectl command also allows you to enable automatic synchronization of your system clock with a group of remote servers using the NTP protocol. Enabling NTP enables the chronyd or ntpd service, depending on which of them is installed.

The NTP service can be enabled and disabled using a command as follows:

timedatectl set-ntp boolean

To enable your system to synchronize the system clock with a remote NTP server, replace boolean with yes (the default option). To disable this feature, replace boolean with no.

Example 5. Synchronizing the System Clock with a Remote Server

To enable automatic synchronization of the system clock with a remote server, type:

~]# timedatectl set-ntp yes

The command will fail if an NTP service is not installed. See Installing chrony for more information.

Using the date Command

The date utility is available on all Linux systems and allows you to display and configure the current date and time. It is frequently used in scripts to display detailed information about the system clock in a custom format.

For information on how to change the time zone or enable automatic synchronization of the system clock with a remote server, see Configuring_the_Date_and_Time.adoc#sect-Configuring_the_Date_and_Time-timedatectl.

Exibindo a Data e Hora Atuais

To display the current date and time, run the date command with no additional command line options:

date

This displays the day of the week followed by the current date, local time, abbreviated time zone, and year.

By default, the date command displays the local time. To display the time in UTC, run the command with the --utc or -u command line option:

date --utc

You can also customize the format of the displayed information by providing the +"format" option on the command line:

date +"format"

Replace format with one or more supported control sequences as illustrated in Configuring_the_Date_and_Time.adoc#exam-Configuring_the_Date_and_Time-date-Display. See Configuring_the_Date_and_Time.adoc#tabl-Configuring_the_Date_and_Time-date-Format for a list of the most frequently used formatting options, or the date(1) manual page for a complete list of these options.

Table 1. Commonly Used Control Sequences
Control Sequence Description

%H

The hour in the HH format (for example, 17).

%M

The minute in the MM format (for example, 30).

%S

The second in the SS format (for example, 24).

%d

The day of the month in the DD format (for example, 16).

%m

The month in the MM format (for example, 09).

%Y

The year in the YYYY format (for example, 2013).

%Z

The time zone abbreviation (for example, CEST).

%F

The full date in the YYYY-MM-DD format (for example, 2013-09-16). This option is equal to %Y-%m-%d.

%T

The full time in the HH:MM:SS format (for example, 17:30:24). This option is equal to %H:%M:%S
Example 6. Exibindo a Data e Hora Atuais

To display the current date and local time, type the following at a shell prompt:

~]$ date
Mon Sep 16 17:30:24 CEST 2013

To display the current date and time in UTC, type the following at a shell prompt:

~]$ date --utc
Mon Sep 16 15:30:34 UTC 2013

To customize the output of the date command, type:

~]$ date +"%Y-%m-%d %H:%M"
2013-09-16 17:30

Mudando a Hora Atual

To change the current time, run the date command with the --set or -s option as root:

date --set HH:MM:SS

Substitua HH por uma hora, MM por um minuto e SS por um segundo, todos digitados na forma de dois dígitos.

By default, the date command sets the system clock to the local time. To set the system clock in UTC, run the command with the --utc or -u command line option:

date --set HH:MM:SS --utc
Example 7. Mudando a Hora Atual

Para alterar o horário atual para 23h26, execute o seguinte comando como root:

~]# date --set 23:26:00

Mudando a Data Atual

To change the current date, run the date command with the --set or -s option as root:

date --set YYYY-MM-DD

Substitua YYYY por um ano de quatro dígitos, MM por um mês de dois dígitos e DD por um dia do mês de dois dígitos.

Observe que alterar a data sem especificar a hora atual resulta na configuração da hora para 00:00:00.

Example 8. Mudando a Data Atual

Para alterar a data atual para 2 de junho de 2013 e manter a hora atual (23h26), execute o seguinte comando como root:

~]# date --set 2013-06-02 23:26:00

Using the hwclock Command

hwclock is a utility for accessing the hardware clock, also referred to as the Real Time Clock (RTC). The hardware clock is independent of the operating system you use and works even when the machine is shut down. This utility is used for displaying the time from the hardware clock. hwclock also contains facilities for compensating for systematic drift in the hardware clock.

The hardware clock stores the values of: year, month, day, hour, minute, and second. It is not able to store the time standard, local time or Coordinated Universal Time (UTC), nor set the Daylight Saving Time (DST).

The hwclock utility saves its settings in the /etc/adjtime file, which is created with the first change you make, for example, when you set the time manually or synchronize the hardware clock with the system time.

In Fedora 6, the hwclock command was run automatically on every system shutdown or reboot, but it is not in Fedora 31. When the system clock is synchronized by the Network Time Protocol (NTP) or Precision Time Protocol (PTP), the kernel automatically synchronizes the hardware clock to the system clock every 11 minutes.

For details about NTP, see Configuring NTP Using the chrony Suite and Configuring NTP Using ntpd. For information about PTP, see Configuring PTP Using ptp4l. For information about setting the hardware clock after executing ntpdate, see Configuring the Hardware Clock Update.

Exibindo a Data e Hora Atuais

Running hwclock with no command line options as the root user returns the date and time in local time to standard output.

hwclock

Note that using the --utc or --localtime options with the hwclock command does not mean you are displaying the hardware clock time in UTC or local time. These options are used for setting the hardware clock to keep time in either of them. The time is always displayed in local time. Additionally, using the hwclock --utc or hwclock --local commands does not change the record in the /etc/adjtime file. This command can be useful when you know that the setting saved in /etc/adjtime is incorrect but you do not want to change the setting. On the other hand, you may receive misleading information if you use the command an incorrect way. See the hwclock(8) manual page for more details.

Example 9. Exibindo a Data e Hora Atuais

To display the current date and the current local time from the hardware clock, run as root:

~]# hwclock
Tue 15 Apr 2014 04:23:46 PM CEST     -0.329272 seconds

CEST is a time zone abbreviation and stands for Central European Summer Time.

For information on how to change the time zone, see Configuring_the_Date_and_Time.adoc#sect-Configuring_the_Date_and_Time-timedatectl-Time_Zone.

Setting the Date and Time

Besides displaying the date and time, you can manually set the hardware clock to a specific time.

When you need to change the hardware clock date and time, you can do so by appending the --set and --date options along with your specification:

hwclock --set --date "dd mmm yyyy HH:MM"

Replace dd with a day (a two-digit number), mmm with a month (a three-letter abbreviation), yyyy with a year (a four-digit number), HH with an hour (a two-digit number), MM with a minute (a two-digit number).

At the same time, you can also set the hardware clock to keep the time in either UTC or local time by adding the --utc or --localtime options, respectively. In this case, UTC or LOCAL is recorded in the /etc/adjtime file.

Example 10. Setting the Hardware Clock to a Specific Date and Time

If you want to set the date and time to a specific value, for example, to "21:17, October 21, 2014", and keep the hardware clock in UTC, run the command as root in the following format:

~]# hwclock --set --date "21 Oct 2014 21:17" --utc

Synchronizing the Date and Time

You can synchronize the hardware clock and the current system time in both directions.

  • Either you can set the hardware clock to the current system time by using this command:

    hwclock --systohc

    Note that if you use NTP, the hardware clock is automatically synchronized to the system clock every 11 minutes, and this command is useful only at boot time to get a reasonable initial system time.

  • Or, you can set the system time from the hardware clock by using the following command:

    hwclock --hctosys

When you synchronize the hardware clock and the system time, you can also specify whether you want to keep the hardware clock in local time or UTC by adding the --utc or --localtime option. Similarly to using --set, UTC or LOCAL is recorded in the /etc/adjtime file.

The hwclock --systohc --utc command is functionally similar to timedatectl set-local-rtc false and the hwclock --systohc --local command is an alternative to timedatectl set-local-rtc true.

Example 11. Synchronizing the Hardware Clock with System Time

To set the hardware clock to the current system time and keep the hardware clock in local time, run the following command as root:

~]# hwclock --systohc --localtime

To avoid problems with time zone and DST switching, it is recommended to keep the hardware clock in UTC. The shown Configuring_the_Date_and_Time.adoc#exam4-sect4-synchornizing-systohc-hwclock is useful, for example, in case of a multi boot with a Windows system, which assumes the hardware clock runs in local time by default, and all other systems need to accommodate to it by using local time as well. It may also be needed with a virtual machine; if the virtual hardware clock provided by the host is running in local time, the guest system needs to be configured to use local time, too.

Additional Resources

For more information on how to configure the date and time in Fedora 31, see the resources listed below.

Installed Documentation

  • timedatectl(1) — The manual page for the timedatectl command line utility documents how to use this tool to query and change the system clock and its settings.

  • date(1) — The manual page for the date command provides a complete list of supported command line options.

  • hwclock(8) — The manual page for the hwclock command provides a complete list of supported command line options.

See Also