FAT filesystems really don't have permissions. The way that linux handles this is that when you mount a FAT drive, all the files are given the _same_ file permissions at mount time. Furthermore, once mounted, these permissions can't be modified. The default permissions that mount will use for FAT partitions is "rwxr-xr-x". To change this, you can add an option "umask=" in the fstab file. For example, on my computer, I use: /dev/hda1 /mnt/c vfat defaults,umask=0000 0 0 The argument to umask is and octal number. To understand what this number means, you have to understand how file permissions actually work in unix. The way file permissions are stored on the disk is as a 9-bit binary number. The best way to show this is with examples. File permission are commonly represented in three ways: rwxr-xr-x - human readable 111101101 - binary number 7 5 5 - 3 octal numbers The last one is the most important. If you read the manpage for chmod, you will notice that you can specify the desired permissions using and octal number. Examples: gsteele@atlas:~$ chmod 0755 foo gsteele@atlas:~$ ls -l foo -rwxr-xr-x 1 gsteele gsteele 1123166 Mar 27 11:42 foo* gsteele@atlas:~$ chmod 0766 foo gsteele@atlas:~$ ls -l foo -rwxrw-rw- 1 gsteele gsteele 1123166 Mar 27 11:42 foo* gsteele@atlas:~$ chmod 0777 foo gsteele@atlas:~$ ls -l foo -rwxrwxrwx 1 gsteele gsteele 1123166 Mar 27 11:42 foo* (Note: the first number is related to "special file permissions". You should always leave this number as 0. You can read about these here: http://www.lns.cornell.edu/public/COMP/info/fileutils/fileutils_3.html#SEC4) Now, umask is like the binary NOT of the file permissions you want. For example: rwxr-xr-x - desired file permissions 111101101 - binary file permissions 000010010 - umask 0 2 2 - octal umask So, for example, in my fstab file, I use umask=0000, so that the permissions on my dos drive are rwxrwxrwx. If you wanted the permissions on the dos drive to be rwxrwxr-x, you would set umask=0002.
Extracted from http://electron.mit.edu/~gsteele/linuxfaq/index.html#2