The DEBIAN_FRONTEND variable is used to specify the frontend interface that should be used by the apt-get package manager when installing, upgrading, or removing packages on Ubuntu or Debian systems.
apt-get is a command-line tool for managing packages on Ubuntu and Debian systems. It has a number of options that allow you to specify how packages should be installed, upgraded, or removed.
The DEBIAN_FRONTEND variable is used to specify the frontend interface that should be used when running apt-get. There are several possible values for this variable:
noninteractive: This value specifies that apt-get should run non-interactively, without displaying any interactive prompts or dialogs. This can be useful when running apt-get in automated scripts or in environments where interaction is not possible.
readline: This value specifies that apt-get should use the readline library to provide command-line editing and history features.
text: This value specifies that apt-get should use a text-based interface, displaying messages and prompts in the terminal window.
teletype: This value specifies that apt-get should use a teletype interface, displaying messages and prompts on the console and ignoring any terminal-specific escape sequences.
By default, the DEBIAN_FRONTEND variable is set to text, which means that apt-get will use a text-based interface when running.
To set the DEBIAN_FRONTEND variable, you can use the export command in your terminal, like this:
export DEBIAN_FRONTEND=noninteractive
This will set the DEBIAN_FRONTEND variable to noninteractive, which means that apt-get will run non-interactively until the variable is unset or changed to a different value.
You can unset the DEBIAN_FRONTEND variable by running the following command:
unset DEBIAN_FRONTEND
This will reset the DEBIAN_FRONTEND variable to its default value of text.
Keep in mind that the DEBIAN_FRONTEND variable is specific to Ubuntu and Debian systems, and may not be available on other Linux distributions. Consult the documentation for your Linux distribution for more information about available frontend interfaces and how to set them.