add_action( 'pre_get_posts', 'sk_show_all_entries' );
/**
* Shows all posts on archives.
*
* @author Bill Erickson
* @link http://www.billerickson.net/customize-the-wordpress-query/
* @param object $query data.
*
*/
function sk_show_all_entries( $query ) {
if ( $query->is_main_query() && ! is_admin() && is_archive() ) {
$query->set( 'posts_per_page', '-1' );
}
}