Strange file permissions on FAT32 under Ubuntu

Question

On my machine (Lenovo ThinkPad w510, Ubuntu 10.10) I have (at least) two logical partitions:

• an ext4 partition to which Ubuntu is installed;
• a FAT32 partition (the bigger one) on which I store all my working data.

For some strange reason, the default file permissions on these partitions differ.

For example, when I download rebar from its git repository, there is different behaviour after I do git clone https://github.com/RJ/erlang_rebar_example_project.git:

• on ext4 partition I just do cd rebar && make and it works;
• on FAT32 I can not do make, because all the files inside the cloned rebar folder have the following permission: -rw-r--r--. If I do sudo chmod 777 -R rebar the file permissions don't change.

What is wrong here?

Answer 1

-rw-r--r-- isn't the real set of attributes. FAT32 only has RHSA, Read-Hidden-System-Archive. Ubuntu maps those to "similar" Unix attributes depending on mount options. You can explicitly set this mask with the umask= mount option. (There's also a dmask for directories only and fmask for files only).