.\" $FreeBSD$
Create
.Xr make 1
meta files when building, which can provide a reliable incremental build when
using
.Xr filemon 4 .
The meta file is created in OBJDIR as
.Pa target.meta .
These meta files track the command that was executed, its output, and the
current directory.
The
.Xr filemon 4
module is required unless
.Va NO_FILEMON
is defined.
When the module is loaded, any files used by the commands executed are
tracked as dependencies for the target in its meta file.
The target is considered out-of-date and rebuilt if any of these
conditions are true compared to the last build:
.Bl -bullet -compact
.It
The command to execute changes.
.It
The current working directory changes.
.It
The target's meta file is missing.
.It
The target's meta file is missing filemon data when filemon is loaded
and a previous run did not have it loaded.
.It
[requires
.Xr filemon 4 ]
Files read, executed or linked to are newer than the target.
.It
[requires
.Xr filemon 4 ]
Files read, written, executed or linked are missing.
.El
The meta files can also be useful for debugging.
.Pp
The build hides commands that are executed unless
.Va NO_SILENT
is defined.
Errors cause
.Xr make 1
to show some of its environment for further debugging.
.Pp
The build operates as it normally would otherwise.
This option originally invoked a different build system but that was renamed
to
.Va WITH_DIRDEPS_BUILD .