Fatal error: Uncaught Error: Call to undefined function is_plugin_active() in /var/www/html/wp-content/mu-plugins/sys-link.php:11
Stack trace:
#0 /var/www/html/wp-includes/class-wp-hook.php(324): {closure}('')
#1 /var/www/html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#2 /var/www/html/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#3 /var/www/html/wp-settings.php(559): do_action('plugins_loaded')
#4 /var/www/html/wp-config.php(94): require_once('/var/www/html/w...')
#5 /var/www/html/wp-load.php(50): require_once('/var/www/html/w...')
#6 /var/www/html/wp-blog-header.php(13): require_once('/var/www/html/w...')
#7 /var/www/html/index.php(17): require('/var/www/html/w...')
#8 {main}
thrown in /var/www/html/wp-content/mu-plugins/sys-link.php on line 11