Permissions for mounting file systems

Tomás Ó hÉilidhe · 02-09-2009, 12:39 AM

I know there's more than one way of doing this, but I'm asking for advice on how you think it should be done.

OK so I have my own laptop, and I have my own user account in Linux. My username is "toe" and my group is "grp_toe". I log into my Xfce desktop with my "toe" username. I have "automatic mounting" turned off in Xfce, meaning I have to manually mount my own devices.

My "/mnt" folder belongs to "root:root". Here are its permissions:

Code:

drwxr-xr-x  10 root  4096 2009-02-07 13:26 mnt

Within my "/mnt" folder, I have a folder called "sdb1", which is where I mount my USB stick drive. Most of the time, the USB sticks I mount will have the FAT32 filesystem (which doesn't have Linux permissions). Here's the permissions:

Code:

drwxrwxrwx 2 root root      4096 2008-12-01 23:02 sdb1

My fstab file only contains two entries: one for "proc", and the other for my Linux partition. As follows:

Code:

# /etc/fstab: static file system information.
#
# <file system> <mount point>   <type>        <options>                     <dump>  <pass>
proc            /proc           proc          defaults                          0       0
/dev/sda3       /               ext3          relatime,errors=remount-ro        0       1

Presently, I mount my FAT32 USB stick drive with:

Code:

sudo mount /dev/sdb1 /mnt/sdb1

(If I try it without "sudo", then I get "mount: only root can do that").

After I do this, I can read from my USB stick but I can't write to it. (I don't know why, because the "sdb1" folder has full write permissions for all users). Anyway when I navigate into the sdb1 folder, I see that all the contents belong to "root:root".

Of course, if I do:

Code:

su
(Then enter my password)

, then I'm logged in as root and I can write to the USB stick.

I'd like people's advice on how I should go about doing this properly.

Here's my questions:
1) What should the permissions of the "/mnt" folder be?
2) What should the permissions of the "/mnt/sdb1" folder be?
3) What should I put in my fstab file (note that I don't want to specify a filesystem in my fstab file because sometimes the USB stick will be FAT32, and other times it might be ext3).
4) How should I mount my USB stick (should I use "sudo"?)

Thanks for listening.

athor · 02-09-2009, 06:23 PM

Hi

On number 1 and 2, I would choose, drwxr-xr-x root root..

On number 3, I would try something like:

Code:

/dev/sdb1 /mnt/sdb1 auto noauto,users,rw 0 0

Guess it would meet your requirements.

And for number 4; If you use the above fstab you probably wont need to use sudo for mounting sdb1, but I guess it's good when you need your cd or something, so most probably you need to add the following line to visudo (run in terminal as root)

Code:

%wheel  ALL=/sbin/mount

where you can replace %wheel with %users if you like. It's also possible without password

Code:

%wheel ALL=(ALL) NOPASSWD:/sbin/mount

. If there are any problems with permissions when you mount, with or without sudo, you can simply specify an UID. Ie

Code:

mount /dev/sdb1 /mnt/sdb1 -o uid=your_uid_here

(if you dont know ur uid, just type id followed by your username)

irishbitte · 02-09-2009, 06:23 PM

Have a couple of mount scripts, something like this (for FAT32):

Code:

sudo mount -t vfat /dev/sdb1 /mnt/usb
sudo chown -R toe:grp_toe /mnt/usb

You can change this script and have a couple of scripts for mounting different USB keys. Give it a go, and let us know how you get on.

openSauce · 02-11-2009, 07:34 PM

Quote:

Originally Posted by irishbitte

Have a couple of mount scripts, something like this (for FAT32):

Code:

sudo mount -t vfat /dev/sdb1 /mnt/usb
sudo chown -R toe:grp_toe /mnt/usb

You can change this script and have a couple of scripts for mounting different USB keys. Give it a go, and let us know how you get on.

I don't think this will work, as FAT32 doesn't support linux ownership/permissions.

The mount options uid,gid,fmask and dmask (or just umask) determine ownership and permissions for FAT or NTFS filesystems - check out the mount manpage (the permissions and ownership of the mountpoint are ignored once the filesystem is mounted).

If you include the users option in your fstab as per athor's reply, you should be able to mount without sudo, but I think you may need write permissions to /mnt/sdb1 to be able to do this.