There is a hair line crack in the ceiling of my bedroom,how to repair?

Do you know if your ceiling is plaster (older homes) or sheetrock/drywall? If your ceiling is white, then a little spackle pressed in with a putty knife will do the trick. Smooth it with a tiny bit of water on your finger before it dries. If color is different, then you will need to paint over the spackle. Homes settle over time and cracks appear-if they're not growing quickly or getting wider, or if two cracks aren't meeting (like one up a wall and another across a ceiling), they're quite normal.

You might also check and see what caused the crack? Do you have any leaks in your roof? Or recent earthquake?

Yes, you can get tubs of it in various sizes at a hardware store, and a putty knife that will fit inside the tub. For deep cracks, you will need to halfway fill the crack, let it dry and then fill it the rest of the way. When the crack is filled, smooth it with the putty knife or your finger dipped in water and let dry. A small amount of sanding will bring it to its final smoothness. Excuse my late reply-I didn't see that you had answered!

Yes, spackle is the stuff, usually sold in tubs of different sizes. While at the hardware store, also get a putty knife that will fit into the tub. Press the spackle into the crack. If the crack is deep, fill it about halfway, let it dry and the top off with more spackle. Use the putty knife to smooth off even with the ceiling if it's a smooth ceiling. If the ceiling is texture, use your finger to work it in smoothly, then lightly wet your finger tip and smooth it out. When it's dry, you can sand it with a fine sandpaper but it shouldn't be necessary. Spackle is white, so there's no need to paint, but it does dry matte, so if your ceiling is shiny, you'll have to touch it up with some paint. Since spackle only fills a crack and doesn't really attach two surfaces together again, there may be returning cracks over the years, but hopefully with these recent cracks, the ceiling has eased itself for a while. If you do get more cracks right after doing this or the crack reopens more than a few inches, then I'd call a structural contractor or engineer to make sure it's not a problem with soil or foundation, etc. But for ordinary cracks, this should solve things for a long time. Keep the spackle tightly closed and it should stay good for a long time!

It could have been caused by just the house shifting or settling, plaster would most likely be your best route