To clear the Apache2 error log file, run the below command on terminal:
sudo bash -c 'echo > /var/log/apache2/error.log' 

The command sudo bash -c 'echo > /var/log/apache2/error.log' is used to clear the contents of the Apache2 error log file.

The sudo command is used to run the following command as the superuser (root). bash -c 'echo > /var/log/apache2/error.log' is using the bash shell to run the command echo > /var/log/apache2/error.log.

The echo command is used to output an empty string, and the output is being redirected to the file /var/log/apache2/error.log using > symbol. This truncates the file and clears any previous contents of the error.log file. It is typically used to clear out any old data that is no longer needed, to make the log file smaller and more manageable.