Dtyjlui

I have two SSD's with an ext4 filesystem on them. When I mount sda1 onto /mnt/old-samsung-830 it changes the owner and group of the /mnt/old-samsung-830 directory from root:root to jim:jim. However, if I umount sda1, and mount sdb1 onto the same directory, the owner and group remains as root. I cannot explain this behavior & want someone to explain why/how this is happening. Here is the example:

### **Note the two disks are unmounted** ###

$ lsblk

NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT

sda                   8:0    0 223.6G  0 disk  

└─sda1                8:1    0 223.6G  0 part  

sdb                   8:16   0 238.5G  0 disk  

└─sdb1                8:17   0 238.5G  0 part  



### **Note the permissions of the old-samsung-830 directory ** ###

[jim@computer mnt]$ ls -al

total 16

drwxr-xr-x  4 root root 4096 Feb  2 19:14 .

drwxr-xr-x 17 root root 4096 Feb  2 13:03 ..

drwxr-xr-x  2 root root 4096 Feb  2 19:14 old-samsung-830

drwxr-xr-x  2 root root 4096 Feb  2 18:59 storage



### **Time to mount sda1.  Notice the owner and group has changed to jim** ###

[jim@computer mnt]$ sudo mount /dev/sda1 old-samsung-830

[jim@computer mnt]$ ls -al

total 16

drwxr-xr-x  4 root  root  4096 Feb  2 19:14 .

drwxr-xr-x 17 root  root  4096 Feb  2 13:03 ..

drwxr-xr-x 17 jim jim 4096 Feb  2 19:00 old-samsung-830

drwxr-xr-x  2 root  root  4096 Feb  2 18:59 storage



### **Time to unmount this, and try the other drive in the same directory** ###

[jim@computer mnt]$ sudo umount /dev/sda1 

[jim@computer mnt]$ sudo mount /dev/sdb1 old-samsung-830

[jim@computer mnt]$ ls -al

total 16

drwxr-xr-x  4 root root 4096 Feb  2 19:14 .

drwxr-xr-x 17 root root 4096 Feb  2 13:03 ..

drwxr-xr-x  3 root root 4096 Feb  2 19:16 old-samsung-830

drwxr-xr-x  2 root root 4096 Feb  2 18:59 storage

[jim@computer mnt]$ 

This is a very fresh Ubuntu install, and I have only got basic stuff (i.e. no fancy fstab or facl's) working on the PC. I just want someone to explain how it's possible that when sda1 is mounted, it changes the permissions of the folder to jim:jim, but then when sdb1 is mounted on the same directory, it stays as root. How is this possible?

I ultimately would love all my drives to mount and use jim:jim (just like when sda1 was mounted). But I don't understand how or why it works.

It does not change the permissions of the subdirectory.

When you mount a filesystem onto a mountpoint, the original mountpoint becomes inaccessible and its name refers to the mounted filesystem. So, after

sudo mount /dev/sda1 old-samsung-830

the name ./old-samsung-830 no longer refers to your subdirectory, but to the mounted filesystem.

In your case, it looks that one of the filesystems is owned by jim:jim and the other by root:root. That's perfectly natural. If you don't like it, you can always sudo chown -R on the mounted filesystem.

(Pet peeve: Folders are the pretty pictures displayed in a GUI. The structures in the filesystem are directories. While most folders do indeed correspond to directories, this is not always the case; the GUI can, and does, create and manage folders which do not correspond to filesystem directories.)