Are file permissions in files on external devices silly?

Martin Pitt martin.pitt at
Fri Nov 21 18:33:02 UTC 2008

Jesse Ruffin [2008-11-21 11:46 -0500]:
> The real answer is to use mount options.


> ADFS, AFFS, FAT (and variants), HFS, HPFS, ISO9660, and UDF all
> support the 'gid' option. Combine that with the 'users' option

You mean the "uid" option, like the vfat and ntfs file systems have.

> As for doing this automatically, it could be included in the fstab
> for fixed devices, such as floppy drives and CD/DVD drives.
> Removable devices are a little harder

No, actually not. The hard part are drives in /etc/fstab, since we
cannot automatically change them during upgrades. However, that
shouldn't be a concern because hardly any removable USB device is in
fstab, except for CD-ROMs for historical reasons (which expose this
very problem with UDF).

For removable drives, once the kernel supports uid=/gid= options for
hfs+ (Mac) and ext3 (other Linuxes), they can be trivially applied
automatically in hal if a device is detected as removable. The hard
part is to get kernel support for it.

> Doing this by default seems safe to me, but it would need more
> thought and consensus before change.

I mostly agree. I know systems which use USB hard drives as their main
storage, where enforcing file system permissions is absolutely
required. However, on such configurations, these drives are in fstab
(for / or /home, etc.) and thus won't have the uid=/gid= options

I don't think any user will expect enforced file permissions on an
automount in /media/.


Martin Pitt                        |
Ubuntu Developer (  | Debian Developer  (
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