This parameter controls whether Samba honors a request from an SMB client to ensure any outstanding operating system buffer contents held in memory are safely written onto stable storage on disk. If set to yes, which is the default, then Windows applications can force the smbd server to synchronize unwritten data onto the disk. If set to no then smbd will ignore client requests to synchronize unwritten data onto stable storage on disk. In Samba 4.7.0, the default for this parameter changed from no to yes to better match the expectations of SMB2/3 clients and improve application safety when running against smbd. The flush request from SMB2/3 clients is handled asynchronously inside smbd, so leaving the parameter as the default value of yes does not block the processing of other requests to the smbd process. Legacy Windows applications (such as the Windows 98 explorer shell) seemed to confuse writing buffer contents to the operating system with synchronously writing outstanding data onto stable storage on disk. Changing this parameter to no means that smbd 8 will ignore the Windows applications request to synchronize unwritten data onto disk. Only consider changing this if smbd is serving obsolete SMB1 Windows clients prior to Windows XP (Windows 98 and below). There should be no need to change this setting for normal operations. sync always yes