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I plug an external disk to the laptop whose system is Mac OS, but I can't create files/folders, or rename files in the disk... The Sharing & Permissions is You can only read.

Does anyone know how to modify this permission?

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What format is this drive in? NTFS, HFS, etc.? – JW8 Apr 12 '12 at 22:21
NTFS... The disk can be written under Ubuntu/Windows automatically... – SoftTimur Apr 12 '12 at 22:37
By default, NTFS disks are read only in OS X without additional software. – binarybob Apr 12 '12 at 22:40
Short answer - OS X can't write to NTFS partitions without installing an additional package (see my answer below). – JW8 Apr 12 '12 at 22:40
up vote 4 down vote accepted

OS X can't write to NTFS natively - you'll need to install a package like MacFuse/NTFS-3G or Tuxera NTFS to write to NTFS partitions.

From the BootCamp Apple Support KB:

During installation, the Microsoft Windows installer asks me to format the Windows partition using NTFS or FAT. Which should I use?

If the partition is 32 GB or smaller, you can use either FAT or NTFS. If it's larger than 32 GB, or you are installing Microsoft Vista, then you can only format it using NTFS. Mac OS X can read and write FAT volumes, but only read NTFS volumes. Refer to the Microsoft Windows documentation if you are not sure which best suits your needs.

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