i want to select all multi user meshes in a scene to make unique (to apply scale).how to do that?
Select all (A) -> Make Single User (U) -> Object & Data
Select one, shift+L -> object data selects all objects that uses same data so you can link them back if you want to.
If the objects are the same, not using different modifiers for example, could switch to using instancing with face duplication by selecting them and object menu -> make dupli-face, then make the dupli-object single user and apply scale.
thanks MartinZ and JA12.select all and then shift+L is useful to isolate instances.