WP_Upgrader::maintenance_mode( bool $enable = false )

1003	public function maintenance_mode( $enable = false ) {1004		global $wp_filesystem;1005 1006		if ( ! $wp_filesystem ) {1007			require_once ABSPATH . 'wp-admin/includes/file.php';1008			WP_Filesystem();1009		}1010 1011		$file = $wp_filesystem->abspath() . '.maintenance';1012		if ( $enable ) {1013			if ( ! wp_doing_cron() ) {1014				$this->skin->feedback( 'maintenance_start' );1015			}1016			// Create maintenance file to signal that we are upgrading.1017			$maintenance_string = '<?php $upgrading = ' . time() . '; ?>';1018			$wp_filesystem->delete( $file );1019			$wp_filesystem->put_contents( $file, $maintenance_string, FS_CHMOD_FILE );1020		} elseif ( ! $enable && $wp_filesystem->exists( $file ) ) {1021			if ( ! wp_doing_cron() ) {1022				$this->skin->feedback( 'maintenance_end' );1023			}1024			$wp_filesystem->delete( $file );1025		}1026	}