Linux localtime File: How to Configure System Timezone

The localtime file in Linux is used to define the timezone, and thus adjust the system clock to local time.

On Red Hat-based systems (Red Hat, CentOS, Fedora, etc), to change a timezone, you must remove the existing /etc/localtime symbolic link and create a new one with the desired timezone zone file:

# rm -f /etc/localtime# ln -s /usr/share/zoneinfo/America/Sao_Paulo /etc/localtime

Or more simply, use the ln command's "-sf" option which removes the previous symbolic link before creating the new one:

# ln -sf /usr/shave/zoneinfo/America/Sao_Paulo /etc/localtime

In this example, the São Paulo timezone will be used by the system.

Once the zone is changed, the clock adjusts automatically to the new time.

/etc/timezone

On Debian-based distributions (Debian, Linux Mint, Ubuntu, etc), the timezone configuration is controlled through the /etc/timezone file, which contains the information about what the timezone is. See the example:

$ cat /etc/timezone America/Los_Angeles

The text to be placed in the /etc/timezone file must match the zone name contained in the /usr/share/zoneinfo/ directory:

# echo "America/Sao_Paulo" > /etc/timezone

After changing the contents of the /etc/timezone file, it is necessary to reconfigure the tzdata package:

# dpkg-reconfigure -f noninteractive tzdata

TZ Variable

The TZ variable can also be used to set the timezone for the logged-in user and works on any Linux.

If this variable is not set, the information from /etc/localtime or /etc/timezone will be used.

This variable is useful for configuring timezone information per user. The system can have one timezone, and each logged-in user can have their own zone. This can be useful in a server environment with users spread across different timezones.

See the example:

$ TZ='America/Miami'; export TZ

$ dateSat 19 Oct 2019 02:37:07 PM America

$ TZ='America/Sao_Paulo'; export TZ

$ dateSat 19 Oct 2019 11:38:01 AM -03

Like any environment variable, for it to work for programs executed in the shell, it must be exported with the "export" command.

Additionally, for the timezone configuration through the TZ variable to be permanent, it must be configured in one of the user's initialization files, preferably in the ~/.profile file.

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