makefs.8: Clarify that makefs-generated zpools always have the same GUID

PR:		282832
MFC after:	1 week

usr.sbin/makefs/makefs.8

@@ -507,6 +507,21 @@ The root dataset is always created implicitly and contains the entire input
 directory tree unless additional datasets are specified using the options
 described below.
 .Pp
+To keep images reproducible, the pool GUID and other random identifiers will
+always be the same across runs of
+.Nm .
+This means that when a pool is first imported, its GUID should be reset
+using
+.Xr zpool-reguid 8
+to avoid conflicting with other pools also generated by
+.Nm ;
+otherwise, it will not be possible to import other pools.
+This can be configured from
+.Pa /etc/rc.conf
+using the
+.Va zpool_reguid
+variable.
+.Pp
 The arguments consist of a keyword, an equal sign
 .Pq Ql = ,
 and a value.
@@ -584,11 +599,13 @@ The following properties may be set for a dataset:
 .El
 .Sh SEE ALSO
 .Xr mtree 5 ,
+.Xr rc.conf 5 ,
 .Xr zfsconcepts 7 ,
 .Xr zfsprops 7 ,
 .Xr zpoolprops 7 ,
 .Xr mtree 8 ,
-.Xr newfs 8
+.Xr newfs 8 ,
+.Xr zpool-reguid 8
 .Sh HISTORY
 The
 .Nm