Source

File: wp-admin/includes/class-wp-filesystem-ftpext.php

public function chmod( $file, $mode = false, $recursive = false ) {
		if ( ! $mode ) {
			if ( $this->is_file( $file ) ) {
				$mode = FS_CHMOD_FILE;
			} elseif ( $this->is_dir( $file ) ) {
				$mode = FS_CHMOD_DIR;
			} else {
				return false;
			}
		}

		// chmod any sub-objects if recursive.
		if ( $recursive && $this->is_dir( $file ) ) {
			$filelist = $this->dirlist( $file );

			foreach ( (array) $filelist as $filename => $filemeta ) {
				$this->chmod( $file . '/' . $filename, $mode, $recursive );
			}
		}

		// chmod the file or directory.
		if ( ! function_exists( 'ftp_chmod' ) ) {
			return (bool) ftp_site( $this->link, sprintf( 'CHMOD %o %s', $mode, $file ) );
		}

		return (bool) ftp_chmod( $this->link, $mode, $file );
	}