Root doesn‘t have the permission to change a directory owner - linux

Question

I can't change a directory's owner even if I'm root.
I want to build a NAS by using raspberry 3B+.
So I have created a user named dorm.
Then I changed sshd_file in order to restrict SFTP users(dorm) to
only visit his home directories
Now the user(dorm) doesn't have the write permission. So After I
google it,I should mkdir a 777 directory at /home/dorm/ .So I made it by root.
Then I wanna change its owner by chown -R dorm:dorm
/home/dorm/Documents. I failed.

Answer 1

Maybe its best to remove the user and try again, this is what I did to make it work.
log into newly setup raspberry pi as pi user, only default logins exist.
pi#raspberrypi:~ $ whoami
pi
pi#raspberrypi:~ $ lslogins -u
UID USER PROC PWD-LOCK PWD-DENY LAST-LOGIN GECOS
0 root 84 root
1000 pi 5 15:31 ,,,
add new user dorm
$ sudo adduser dorm
Adding user `dorm' ...
Adding new group `dorm' (1001) ...
Adding new user `dorm' (1001) with group `dorm' ...
Creating home directory `/home/dorm' ...
Copying files from `/etc/skel' ...
New password:
Retype new password:
passwd: password updated successfully
Changing the user information for dorm
Enter the new value, or press ENTER for the default
Full Name []:
Room Number []:
Work Phone []:
Home Phone []:
Other []:
Is the information correct? [Y/n] y
pi#raspberrypi:~ $ lslogins -u
UID USER PROC PWD-LOCK PWD-DENY LAST-LOGIN GECOS
0 root 87 root
1000 pi 5 15:31 ,,,
1001 dorm 0 ,,,
make a backup and edit your sshd_config file,
pi#raspberrypi:~ $ sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config-bak
pi#raspberrypi:~ $ sudo vim /etc/ssh/sshd_config
pi#raspberrypi:~ $ diff /etc/ssh/sshd_config /etc/ssh/sshd_config-bak
122,128d121
<
< Match User dorm
< X11Forwarding no
< AllowTcpForwarding no
< PermitTTY no
< ForceCommand internal-sftp
< ChrootDirectory /home/dorm
restart ssh service with sudo service sshd restart
change the ownership of the dorm home directory to root.
$ sudo chown root:root /home/dorm
$ sudo chmod 755 /home/dorm
from the dorm user's directory use sudo as the pi user to create the Documents folder and give ownership to the dorm user
pi#raspberrypi:/home/dorm $ ls
pi#raspberrypi:/home/dorm $ mkdir Documents
mkdir: cannot create directory ‘Documents’: Permission denied
pi#raspberrypi:/home/dorm $ sudo mkdir Documents
pi#raspberrypi:/home/dorm $ ls -l
total 4
drwxr-xr-x 2 root root 4096 Feb 8 18:15 Documents
pi#raspberrypi:/home/dorm $ sudo chown -R dorm:dorm Documents
pi#raspberrypi:/home/dorm $ ls -l
total 4
drwxr-xr-x 2 dorm dorm 4096 Feb 8 18:15 Documents
test the connection etc. using your IP address from your host computer (ssh should reply No route to host)
$ sftp dorm#<IP>
dorm#<IP>'s password:
Connected to dorm#<IP>.
sftp>
you can see the created Documents folder and the user number that owns it (dorm's number)
sftp> ls -ltr
drwxr-xr-x 2 1001 1001 4096 Feb 8 18:15 Documents
you can't move out of the base directory
sftp> pwd
Remote working directory: /
sftp> cd ..
sftp> pwd
Remote working directory: /
you can't put files in the base directory as dorm doesn't have permissions. (file path will need to be altered for your system)
sftp> put /Users/<USER>/tmp
Uploading /Users/<USER>/tmp to /tmp
remote open("/tmp"): Permission denied
if you move into Documents then you can then upload files
sftp> cd Documents
sftp> put /Users/<USER>/tmp
Uploading /Users/<USER>/tmp to /Documents/tmp
/Users/<USER>/tmp 100% 0 0.0KB/s 00:00