[SOLVED] Why can't I give write permissions to a mount point

SteveMann · 08-25-2022, 01:54 PM

I have a mount point that I want anyone who mounts the device to be able to create or write files.

Code:

drwxr-xr-x   6 root root 4096 Aug 25 13:35 ./
drwxr-xr-x  24 root root 4096 Aug 12 06:55 ../
drwxrwxr-x+  3 root root 4096 Apr 13  2020 d/
drwxr-xr-x   2 root root 4096 Jul  2  2020 temp/
drwxr-xr-x   2 root root    0 Aug 24 18:34 x/
drwxr-xr-x   2 root root 4096 Apr 11  2020 z/

If I use

Code:

sudo chmod +777 /mnt/x

Nothing changes.

This is an Ubuntu desktop system and I am the only user.

Ideas?

michaelk · 08-25-2022, 01:58 PM

It depends on the filesystem whether it is native i.e. ext, xfs etc. local, remote and if it is ntfs maybe on kernel version.

SteveMann · 08-25-2022, 02:13 PM

The shared drive is on Ubuntu 18 and shared by Samba. The mounting system is on Ubuntu 20

This is how I am sharing the device:

Quote:

[share]
comment = Steve's Public folder
path = /home/steve/share
create mask=0777
directory mask=2777
read only = no
browsable = yes
guest ok = yes
force group = steve
force user = steve
ntlm auth = true
writeable = yes
public = yes

sundialsvcs · 08-25-2022, 02:58 PM

"Local permissions on the mount-point directory" mean nothing: that directory is merely a dummy placeholder. You have to establish permission using the facilities of "whatever has been mounted at that location." Since this is a Microsoft/SMB mount point accessed through Samba, permissions are established on the Microsoft server-side and you should start your explorations with those logs. Samba maps your Linux user-identity to something that the server will recognize, and the server determines what you can do. I recommend that you proceed by reading a lot about Samba and how it relates to Microsoft's somewhat-byzantine security protocol.

As a categorical statement: any remote filesystem that you mount "is the property of" the remote side and operates according to its rules. "Your identity," as seen by the remote side, is what determines the permissions that it will or will not grant. And there are many ways which can be used to establish that identity-mapping, depending on the exact situation.

michaelk · 08-25-2022, 03:43 PM

As posted CIFS/SMB permissions do not map to linux permissions which is why chmod does not do anything.
Because CIFS/SMB mounts are generally single-user, and the same credentials are used no matter what user accesses the mount, newly created files and directories will generally be given ownership corresponding to whatever credentials were used to mount the share which is root. By creating a special group and adding all those users to that group you can mount the share with the gid=XXX to allow anyone in the group to read/write.

https://linux.die.net/man/8/mount.cifs

Usually if someone mounts the share in their file browser it will be automatically mounted as that user. However, it isn't available to the command line without running additional commands.

SteveMann · 08-25-2022, 04:33 PM

Let me back up two steps...
I have a drive on an Ubuntu system that I want anyone on the local network to be able to mount with RWX permissions.

Is samba and mount cifs the wrong approach?

SteveMann · 08-25-2022, 04:33 PM

Quote:

Originally Posted by sundialsvcs

I recommend that you proceed by reading a lot about Samba and how it relates to Microsoft's somewhat-byzantine security protocol.

The more I read, the less I know.

michaelk · 08-25-2022, 05:11 PM

On the Ubuntu 18 PC in the file browser you should be able to right click on a directory and select "local network share", click on the read/write and guest access boxes. Click create share.

On the Ubuntu 20 PC you can access the share from the file browser just by entering smb://server_name/share_name

In addition:
https://wiki.samba.org/index.php/Set...ndalone_Server

chrism01 · 08-26-2022, 01:37 AM

You haven't actually said what OS the other (remote) users are on.
If it's some sort of *nix, then nfs is more usual, but for MSWin clients, then yes, Samba is 'normal'.

yancek · 08-26-2022, 05:01 AM

Quote:

Is samba and mount cifs the wrong approach?

Yes. Your posts above indicating you have a server setup on 18.04 with a client on 20.04 so use the Ubuntu documentation at the link below to set it up. It is not dsifficult.

https://ubuntu.com/server/docs/service-nfs

SteveMann · 08-26-2022, 09:47 AM

Quote:

Originally Posted by chrism01

You haven't actually said what OS the other (remote) users are on.
If it's some sort of *nix, then nfs is more usual, but for MSWin clients, then yes, Samba is 'normal'.

I had been using the samba share mounted on PCs (and mapped to drive Z) for a couple of years. Permissions only became a problem when I tried to mount the drive on another Ubuntu system so that I could pipe data to the shared drive.

So, I think my original question is wrong. I assumed that it was simply a permissions problem.

SteveMann · 08-26-2022, 09:50 AM

[QUOTE=yancek;6376207]Yes. Your posts above indicating you have a server setup on 18.04 with a client on 20.04 so use the Ubuntu documentation at the link below to set it up. It is not dsifficult.

I had been using the samba share mounted on PCs (and mapped to drive Z) for a couple of years. Permissions only became a problem when I tried to mount the drive on another Ubuntu system so that I could pipe data to the shared drive.

So, I think my original question is wrong. I assumed that it was simply a permissions problem.

Hmm, I could try sharing the folder with nfs for the Ubuntu computers... Thanks for the tip.

michaelk · 08-26-2022, 10:06 AM

nfs has its own idiosyncrasies. Another suggestion might be to use sshfs which is a fuse filesystem for sftp. Using automount or autofs would only mount the share when accessed.