Some versions of Unix or implementations of disk I/O do not support immediate updates of directories when the data on them changes. The ReiserFS and Ext2fs filesystems are two such implementations. Linux is one such operating system. For these, this REQUIRES_DIR_FSYNC compile-time macro is set to true, which causes sendmail to fsync(2) the directory every time it is updated.

In the event you need to port sendmail to a new operating system or to a new filesystem, you might need to set this compile-time macro to true. The way you set it to true looks like this:

APPENDDEF(`confENVDEF', `-DREQUIRES_DIR_FSYNC')

New ports should be reported to sendmail@sendmail.org so that they can be folded into future releases.