Write denied on exfat usb hdd mounted locallly

[Kobold]

I don’t understand whats going on here, i’m using several exfat partition’s on my USB HDD’s also and never had the slightest access problem.

It was always running flawless like a native ext4 partition. The only difference is, that i use Veracrypt to mount it.

I never used all this complicated mount commands or was in need to load additional exfat packages and have 99 more problems.

Since when there is write access denied? Maybe this device has some serious issues…

[linux-aarhus]

@Kobold

I don’t understand whats going on here, i’m using several exfat partition’s on my USB HDD’s also and never had the slightest access problem.

I never had any issues either - but there is a clear difference betwen

• kernel exFAT programs
• userspace exFAT programs

Plasma’s kio and the generic gvfs handles access to devices flawless on systems with kernel exFAT programs.

The issue appears when you use the mount command to mount in a specified folder.

Because you can only use mount as superuser the mount is inheriting root permissions - which makes the device read-write for root only.

Manjaro default to use kernel exFAT programs so a mounting a exFAT device in a specific folder makes root the owner and denies write to all other users even when mounting in a user’s home.

Replacing the kernel exFAT programs with the userspace exFAT programs makes the mount writeable for world - just as one would expect.

I have seen several comments lately where members have trouble understanding why they cannot access their NFTS and exFAT devices the same way they are used to.

I have been slightly confused myself over these topics - but from the investigation I conducted for this topic - I am fairly certain it is related to improvements in security for filesystems not native to Linux.

E.g. to avoid malicious change to the systems efi partition

• FAT32
• mounted at /boot/efi

This is achieved by applying mount options umask=0077 in /etc/fstab making it inaccessible to everyone but root.

[andrewysk]

@davidmiller

• Mount the drive with write permissions using sudo mount -t exfat /dev/sdX1 /mnt/your_folder -o rw.
• Check ownership and permissions with ls -l /mnt/your_folder and adjust if needed using sudo chown -R $USER:$USER /mnt/your_folder.

Did the mount according to ur command above.

sudo chown -R $USER:$USER ~/mount-6TB

ls -ld mount-6TB                                      
drwxr-xr-x 974 root root 1048576 Jul  4 22:56 mount-6TB

whoami                                                     
manjaro

@linux-aarhus

• 0022 equals 0755
• 0000 equals 0777

How do you get the fmask and dmask value ? i can’t seems to find way to calculate the value that i want.
i want
file permission: owner (rwx), group (r-x), other (—)
folder permission: owner (rwx), group (r-x), other (—)
How to calc ?
Thanks.

@linux-aarhus

fmask and dmask options for the kernel to able to deviate from the default - which is 0022 otherwise known as 0755 or u+rwx,g+rx,o+rx.

Btw, your cmd with fmask and dmask did the trick.
I now realized the issue with write denied is due to exfat does not have permission metadata… hence when i mount it as normal fs, it will causes the exfat fs being mounted under root owner… hence it made it to be owner of the exfat to be root… hence when i am in manjaro user acc, i can’t write to the fs.

I can access it with

[andrewysk]

@linux-aarhus

e device to readily writeable on need to insure the ntfs-3g userspace is available (default installed)

Denied because exfat has not permission metadata. hence when sudo mount, it mount as root…
the way to overcome mount as root is :

sudo mount -t exfat -o sync,rw,uid=$UID,gid=$GID,fmask=0002,dmask=0002,iocharset=utf8 /dev/disk/by-partuuid/e5608bd6-3920-4b72-972d-6c29f1d0305e mount-6TB 

the uid and gid value is the key here.

[andrewysk]

@andrewysk

Did the mount according to ur command above.

sudo chown -R $USER:$USER ~/mount-6TB

chown is futile against FAT fs, due to it does not consist of permission metadata.

[Nachlese]

@andrewysk

file permission: owner (rwx), group (r-x), other (—)
folder permission: owner (rwx), group (r-x), other (—)
How to calc ?

there are rwx permissions for owner, group and others

r (read) counts 4
w (write) counts 2
x (execute) counts 1

file permission: owner (rwx), group (r-x), other (—)

corresponds to 750

[andrewysk]

hmm… u made a mistake somewhere… fmask is opposite of chmod

i tried ur fmask=0750… the outcome is
0750 u(---),g(-w-),o(rwx)

i tried on errors until i got this:
0117 u(rw-),g(rw-),o(---)
001 001 111
1 1 7
can u go through that again and teach me how to calculate… i used to learn binary … but i have since return everything to my teacher…
sort of understand… but don’tknow how to calculate… especially when this is “mask” (sort of opposite)

[andrewysk]

This mount along took me days to get it understood… and it is base on fat only. my brain is rusty.
still got manjaro to fix… hopefully won’t take 1 month to learn how to fix… sigh.!

[andrewysk]

$udisksctl mount -b /dev/sdb1
This will be a short and sweet cmd to mount to it own /run/media folder with no permission issue. just can’t define where to mount…

[Nachlese]

@andrewysk

hmm… u made a mistake somewhere

you asked for how file permissions are calculated

touch testfile

chmod 750 testfile 
ls -al testfile 
-rwxr-x--- 1 jo jo 0 Jul  7 23:54 testfile

chmod 057 testfile 
ls -al testfile 
----r-xrwx 1 jo jo 0 Jul  7 23:54 testfile

@andrewysk

can u go through that again and teach me how to calculate

no - sorry

[andrewysk]

@andrewysk

How do you get the fmask and dmask value ? i can’t seems to find way to calculate the value that i want.
i want
file permission: owner (rwx), group (r-x), other (—)
folder permission: owner (rwx), group (r-x), other (—)
How to calc ?

sorry for the misunderstand. i was meant to say for fmask and dmask.

[Molski]

@andrewysk

How do you get the fmask and dmask value ? i can’t seems to find way to calculate the value that i want.
i want
file permission: owner (rwx), group (r-x), other (—)
folder permission: owner (rwx), group (r-x), other (—)
How to calc ?

For each permission, ower/group/other. It is just a 3-bit binary value. So from most to least significant bits (or flags in this context):

1. Read access
2. Write access
3. Executable (or directory listing access for directories)

So in binary, each digit is worth 4, 2, and 1 respectfully. You just add them up to get every combination of rwx or not. This is a number between 0 and 7.

When you put three in a row, you get the user/group/other permissions, as a 3 digit number (that are 0-7).

You can not use this octal format at all, if you want. It is just a quicker way if you’re used to it.

[linux-aarhus]

@andrewysk

when i mount it as normal ext4 fs, it will causes the exfat fs being mounted

I think you are confusing something here - exfat and ext4 is two different filesystems

• exfat is Windows filesystem created
• ext4 is the defacto Linux filesystem

@andrewysk

How do you get the fmask and dmask value

Simple

0777 == u+rwx,g+rwx,o+rwx
0000

so for any directory

0755 == u+rwx,g+rx,o+rx
0022

and for files

0644 == u+rw,g+r,o+r
0133

The best option for you is to use the userspace programs.

sudo pacman -Syu exfat-utils

This will give you want you need - a permissionless exfat mount

Permissions set only applies for the mountpoint - see the permissions like a sheeps pen

• read permissions lets you look at the sheeps
• write permissions lets you go through the gate
• once you are inside you can slaughter all sheeps

[andrewysk]

Got it. Thanks.

[andrewysk]

Is it valid if i enter mask with 3 digits only?
fmask=007 for files (rwx, r–, —)
mask=022 for folders (rwx, r-x, r-x)

is it valid if enter chmod permission in 4 digits ?
chmod 0740 for files (rwx, r–, —)
chmod 0755 for folders (rwx, r-x, r-x)

This will clear my doubts in my mind regarding fmask and chmod.
If mask can be enter 3 digits (instead of what i see all 4 digits), why do i bother to confuse myself with 4 digits when convert from chmod permission ?

thanks.

[linux-aarhus]

Please see → umask - ArchWiki

Use the userspace tools - then you don’t have to bother at all …

[Aragorn]

@andrewysk

i want
file permission: owner (rwx), group (r-x), other (—)
folder permission: owner (rwx), group (r-x), other (—)
How to calc ?

fmask and dmask are the bisected versions of the umask for files and directories respectively in the mount options for non-POSIX filesystems.

As for how to calculate the values, see the following two sections from my tutorial on POSIX permissions…

@Aragorn

For those of you who aren’t good with numbers, here’s a little table with the possible permissions values within a single triad. Note that some of these permissions below are nonsensical from the practical standpoint, but they are shown just for the sake of being able to understand how a permissions mask translates into an octal value.

PERMISSIONS           BINARY VALUE    OCTAL VALUE

    ---                  000              0
    --x                  001              1
    -w-                  010              2
    -wx                  011              3
    r--                  100              4
    r-x                  101              5
    rw-                  110              6
    rwx                  111              7

When it comes to file permissions, the most common way you’ll see these octal numbers being used is in reference to all three of the triads, i.e. user, group and others. A typical example for a system directory would be 755, which translates into drwxr-xr-x permissions. For non-executable files, a typical example would be 644, which translates to -rw-r--r--.

@Aragorn

UMASK

In UNIX systems, the command umask is used in combination with a three-digit octal number ─ one for each permissions triad ─ to determine the permissions that a new file or new directory must be created with, but in an inverse way, i.e. the octal number does not represent the permissions that the file or directory will be created with, but what octal value must be subtracted from 777 for directories and 666 for files. So a umask of 022 means that new directories will be created with a 755 (drwxr-xr-x) permissions mask, and new files with a 644 (-rw-r--r--) permissions mask.

Normally, the root account’s umask should always be 022 ─ notwithstanding the fact that the permissions on the root user’s home directory /root should always be set to 700 or 750 ─ and this is usually also the case for unprivileged user accounts, but personally, I prefer a umask of 077 for unprivileged user accounts, for reasons of privacy on systems with multiple unprivileged accounts.

The umask is commonly set in the shell’s configuration files ─ systemwide, this will be in /etc/login.defs, and individual users can set it in ~/.bashrc or ~/.zshrc, depending on what shell they use.